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Because of the numerous surface indications of hydrocarbons at the outcrop of Tertiary and Mesozoic formations in the foothills of the Apennines throughout Italy and Sicily, the search for oil in both Italy and Sicily began shortly after the first oil fields were discovered in the United States nearly 100 years ago. Although the early explorations by the Italian Government and by private companies resulted in the discovery of small volumes of oil in shafts and shallow bores at several localities in northern and central Italy, only ten small oil fields with a total cumulative production of slightly more than 100,000 metric tons had been developed to 1925. Till then most drilling had been done in the vicinity of seeps where formations were highly disturbed and the oil-beari g formations had little cover. After 1925 attention was given to the search for oil and gas on geophysical structures in areas outside of seepage districts. Although this line of search during the next 15 years led to the discovery of a few minor oil and gas fields, it did not yield important results until near the close of World War II. Since then six large gas fields, one yielding oil, have been developed in the Po Basin of northern Italy on seismic structures, and others are likely to be discovered in the near future. As a consequence of these discoveries, several Italian and foreign companies are actively engaged in exploratory work. Although the Po Basin offers the best prospects, extensive areas in central and southern Italy and Sicily justify a thorough search for oil and gas./CJSABSTRACT>
The Republic of Italy comprises the Italian peninsula, Sicily, Sardinia, Elba, and numerous other smaller Mediterranean islands. The peninsula extends southeast into the Mediterranean for 725 miles and covers an area of 101,575 square miles (Fig. 1).
The Apennines form the backbone of the Italian peninsula and extend across the Messinian straits into northern Sicily. Consequently, most of the Italian peninsula and Sicily is either mountainous or hilly. The only extensive flat country is in the Po Basin in northern Italy.
According to Behrmann (1936) the main structural provinces of the Italian peninsula are the Apennine ranges, the young Tertiary foredeep, and the Adriatic
Fig. 1. Index map of Italy.
foreland (Fig. 2). Most of the Po Basin and the area surfaced by Upper Tertiary formations northeast of the Apennines belong to the foredeep province. The Adriatic foreland occupies parts of the east coast and southeast Sicily.
The structure of the northern Apennines is characterized by folded and faulted overthrusts of great complexity generally attributed to gravitational sliding of shale formation off highlands now submerged beneath the Tyrrhenian Sea. This type of structure is replaced in the central Apennines by parallel overthrust folds that expose Mesozoic limestone in high ranges separated by mountain valleys occupied by Tertiary marls and clays. In the southern Apennines the overthrust folds give way to ridges of granite and metamorphosed sediments, flanked on the east by cuesta ridges of Tertiary sandstones and conglomerates separated by valleys of Tertiary clays and marls. The geology of the other two structural provinces, which include most of the prospective oil and gas territory, are reviewed u der subsequent headings.
Fig. 2. Geological sketch map of Italy, after Behrmann.
OIL AND GAS PROVINCES
Five major oil and gas provinces are generally recognized, all of which are a part of a sedimentary basin that during the Upper Tertiary occupied the Po Basin, the east coast of the peninsula, and the south half of Sicily. Four basins of minor importance occur on the west coast of the peninsula (Fig. 1).
A. Po Basin
B. Marche-Abruzzi coastal plain
C. Lucanian Basin (Fossa Bradanica)
D. Campanian Basin
E. Southern Sicily
F. Four small basins on the west coast:
3. Val d'Arno
The first five of these provinces or basins are occupied by a thick series of Tertiary marine clays, sands, and marls, overlying Mesozoic limestone and shale formations. Tertiary formations in the central part of the Po Basin and the minor basins on the west coast (except F-4) are concealed by flat Quaternary deposits and require geophysical surveys for their exploration. Extensive areas in the provinces of eastern and central Italy are surfaced by nearly horizontal Pliocene strata which also require geophysical surveys to outline subsurface structures accurately. Surface mapping, however, is of value in parts of most of the provinces and especially in central Italy and Sicily. The oil and gas seeps that appear in many of these provinces indicate petroliferous strata beneath the surfa e, but in few places do they furnish reliable evidence of the presence of important underground accumulations of oil or gas in their vicinity.
LOCATION AND GEOGRAPHY
The Po Basin occupies the lowland in northern Italy drained by the Po River and its tributaries. These rivers rise in the Alps north of the basin and in the Apennines south of it (Fig. 3). The basin is a flat plain about 400 kilometers long and 100-200 kilometers wide. Although its west end is about 200 meters above sea-level, its central part has an elevation of less than 100 meters and extensive areas along the lower course of the Po are only 10-20 meters above the sea and are protected by dikes. When these give way during high water, large districts of rich agricultural land are flooded.
A belt of foothills lies between the Po River plain and the higher Apennine ranges on the southwest side of the basin. These foothills are a part of the Po Basin and are discussed under the heading of pre-Apennine foothills. Developments in the plain north of the foothills are considered under the headings of the central Po Plain and the eastern Po Plain; the latter is confined to the low land between the Adige and Reno rivers, the northern part of which is commonly known as the Polesine area.
Fig. 3. Po Basin oil and gas fields.
The Po Basin with its excellent agriculture land, fair climate, adequate rainfall, and abundance of hydroelectric power has for years been the most prosperous part of Italy. With the rapid development of its gas fields, it is now having a marked industrial growth.
The Po Basin is occupied by a thick sequence of Quaternary, Tertiary, and Mesozoic sedimentary formations that show a wide range in thickness and character throughout the basin. Flat Quaternary sediments occupy the surface throughout most of the Po Plain and overlie gently folded Pliocene sand and clay except over the crest of a few anticlines where the Pliocene may be sharply folded or eroded. Tertiary and Upper Mesozoic formations are exposed in the pre-Apennine foothills and are involved in overturned folds and overthrusts.
Data on the stratigraphy and structure of different parts of the basin are presented in the description of the geology of the oil and gas fields in the basin. For details of the stratigraphy consult papers by Greig (1937), Wiedenmayer (1950), Jaboli (1951), and Fois (1953).
SUMMARY OF EXPLORATIONS
Oil seeps, known since early Roman time at several localities in the pre-Apennine foothills, were exploited by hand-dug pits prior to 1866 and later by shallow bores. Important volumes of oil, however, were not developed until about 1892, when a French company, later acquired by the Italian firm of Societa Petroli d'Italia, brought in the Velleja field 50 km. west of Parma (Fig. 3). This development was soon followed by the discovery of the Montechino and Gratera fields in the same district and in 1909 by the Vallezza, Montechiaro-Rallio, and Ozzano-Vizzola fields in the same structural belt. In consequence of this development annual production in 1910 reached 6,000 or 7,000 tons. The next discovery of note was at Salsomaggiore in 1923.
In 1926 the Italian Government formed a company, the Azienda Generale Italiana Petroli (AGIP), to develop its domestic and colonial oil and gas resources. The following year the Standard Oil Company obtained possession of the majority interest in the old Italian firm of Societa Petrolifera Italiana (SPI). Since then AGIP and SPI have been the major operators in the Po Basin. Both companies made gravimetric and electric surveys of Quaternary-blanketed areas in the Po Plain. Although these surveys were accompanied by exploratory tests, they led to the discovery of only three small fields: Fontevivo in 1929, Podenzano in 1931, and Montalbano in 1943. Better results were obtained when AGIP employed Western Geophysical Company in 1940 to make seismic refraction surveys in the central part f the Po Plain. These surveys led to the discovery of the San Giorgio field in 1942 and the Caviaga field in 1944. Since then AGIP has brought in the following additional gas fields on seismic structures in the central part of the Po Plain: Ripalta (1947), Cortemaggiore (1949), Corneliano
(1950), Bordolano (1951), and Correggio (1952). AGIP's gas fields are now producing over 5,000,000 cubic meters daily and have a capacity greatly in excess of this. One of the fields--Cortemaggiore--is producing daily approximately 225 tons of oil and a considerable volume of condensate.
Immediately after its reorganization in 1927, SPI increased the oil production of the fields discovered by the original Italian company and was the chief oil-producer in Italy to 1950. During the Thirties it covered most of the Po Basin by gravimetric surveys and drilled thirty-four exploratory wells with an average depth of 580 meters, mostly in the foothills belt. During the war, SPI's properties were sequestered and administered by AGIP. The company, consequently, had little opportunity to do exploratory work during the early Forties. In 1946 it initiated seismic surveys in the area of its limited permits in the southeastern part of the Po Basin. Later when it was prepared to spend large sums in exploratory drilling, AGIP's successes had increased its prestige with the Italian Gove nment to such an extent that SPI's requests for further permits were not granted. Ever since, SPI has been limited to a few small permits in the southeastern part of the Po Basin and four producing properties, reduced in 1950 to three: Vallezza, Vizzola, and Montalbano.
In the Polesine area 82 small gas companies since 1934 have drilled about 2,500 shallow gas wells, most of which struck small flows of dry gas in shallow Quaternary sands. The production has increased yearly and is now approximately 800,000 cubic meters daily.(FOOTNOTE 3)
South of the Polesine area small production has been obtained in basal Quaternary sands in isolated districts surrounded by barren territory. The two largest fields are Montalbano and Consandolo, discovered by SPI and SIN, respectively; the latter field has been abandoned. AGIP during 1952 brought in gas wells near Ravenna and Imola.
PRE-APENNINE FOOTHILLS FIELDS
During the period of 1890-1927 eight small oil fields were discovered in the pre-Apennine foothills. Most of them were developed by the old Italian companies of Petroli and SPI and were the result of explorations in the vicinity of surface showings of oil and gas, where in some places earlier attempts had been made to find oil in shafts and shallow wells. The total cumulative production of these fields to the end of 1952 was 401,800 metric tons of oil. Before 1930 the gas produced had no market. Since then a total of 186,078,276 cu. m. has been produced, most of which has been compressed and marketed in containers. Present daily production from all of these fields is about 9 tons of oil, 17,000 cu. m. of gas and one ton of condensate. The largest fields in amount of oil produced are Vall zza, Salsomaggiore, and the group of three pools known as Velleja-Montechino-Gratera (Table 1).
FOOTNOTE 3. Unless otherwise noted, all statements of total or daily production are as of January 1, 1953.
Most of the oil and gas in these older fields has come from thin Miocene and Oligocene sands or conglomerates and fractured Cretaceous limestones in highly tilted or overthrust attitudes. Porosity has been the chief factor in accumulation.
The following notes summarize the more important facts pertaining to these fields. Data on their production are presented in Tables I, II, and III.
Rile del Olio:
This uncommercial pool situated in the edge of the foothills, 55 km. southwest of Piacenza, is the most westerly of the Po Basin fields. It was discovered by SPI in 1900 as the result of boring in the vicinity of surface seeps. About 18 wells were drilled which yielded only 21 tons of oil and around 30,000 cu. m. of gas from middle Miocene sands. Deep tests drilled to the Oligocene at 1,080 m. and 1,690 m. were unproductive. The field has been inactive for many years.
This is a minor field located 20 km. south-southwest of Piacenza. It was discovered by Petroli in 1909 as a result of explorations near seeps. Previous to 1930, about 17 wells were drilled which yielded 112 tons of oil and 150,000 cu. m. of gas. Following a period of inactivity during the Thirties, 12 additional wells were drilled which to the end of 1951 had produced about 1,712 tons of oil and 1,750,000 cu. m. of gas. Six wells are still producing a fraction of a ton of oil daily. Oil and gas are found in highly folded and fissured middle Eocene limestones at depths of 250-350 m.
These three oil pools are situated 25-30 km. south of Piacenza and within a few kilometers of each other. They were discovered by Petroli and an earlier company in 1890, 1892, and 1907, respectively. Drilling began in the area because of oil and gas seeps near which the Romans built a temple to worship the eternal fires.
The following table gives the production of these fields since 1906. In previous years Velleja and Montechino had produced approximately 37,500 tons of oil.
Velleja reached its maximum annual production of 4,000 tons in 1895. Since then its yield has gradually declined; it produced 388 tons in 1938 and 157 tons in 1952. Montechino and Gratera obtained maximum production of 13,000 tons in 1911. They produced 1,738 tons in 1938 and 316 tons in 1952. In January, 1952, the three fields were producing about one ton of oil and 2,000 cu. m. of gas daily from 134 wells, some of which have been producing for 50 years. No definite oil sands are recognized. Most of the oil comes from joints and fissures in Upper
Table I. CRUDE-OIL PRODUCTION BY YEARS (METRIC TONS)
Table II. ANNUAL GAS PRODUCTION BY YEARS (CUBIC METERS)
Cretaceous limestones. The Velleja pool obtains a little oil from fissured Eocene limestone.
The Vallezza field occupies hilly land about 25 km. southwest of Parma and 5 km. southeast of Farnovo Taro. Seeps in the locality were prospected in early times by hand-dug pits. Between 1868 and 1907 several shallow wells were drilled and a small volume of oil was obtained. In 1907 SPI began exploratory drilling, and by 1909 it had proved a commercial field and was granted a 50-year concession by the Government. The producing area was gradually extended westward and southward. The first wells were small producers, seldom exceeding ½ ton daily, and the maximum annual yield was only 819 tons in 1926. In the following year, the Standard Oil Company of New Jersey took over controlling interests in SPI. The new organization extended the field southwest and by deeper drilling brought in ells producing as high as 20 tons of oil daily with considerable wet gas. Production reached a maximum of 8,581 tons in 1932. Its 1952 yield was 2,376 tons of oil, 2,246,196 cu. m. of gas, and 300 tons of casinghead gasoline. Its cumulative total to the end of 1951 was 124,526 tons of oil, 72,238,356 cu. m. of gas, and 8,403 tons of casinghead gasoline.
The total number of producing wells drilled is 178, twenty of which have been abandoned. The wells have an exceptionally long life, and after a few years their decline curve is almost horizontal.
The Vallezza field has an exceptional structure the details of which have been determined by Greig (1937) and other SPI geologists. The surface is occupied by a syncline which overlies a recumbent fold of Eocene and Oligocene formations (Fig. 4). In the southwest half of the field wells, begin in the Tongrian (Oligocene),
Table III. CASINGHEAD GASOLINE OR CONDENSATE PRODUCTION (IN METRIC TONS)
Fig. 4. Vallezza field cross section, after Greig. Same vertical and horizontal scale.
pass through the Redbed series at the base of the Oligocene, then after penetrating the Eocene pass back into the Redbed series and then into the Tongrian. In the northeastern part of the field, wells start in the Redbed series and bottom in overturned nearly horizontal Tongrian.
The average specific gravity of Vallezza crudes was 52.8° in 1936 and 49° in 1951. They have a paraffine base, straw yellow color, and gasoline content of 60-70 per cent with an octane rating of 60.
Gas produced with the oil contains 100 grams of light spirit per cu. m., and casinghead gasoline has been an important product. Since 1932 more than 8,390 tons has been produced. Formerly 1,000 cu. m. of stripped gas was returned to the sands daily to maintain reservoir pressure and to keep the oil light. Gas is also used for drilling and for generating power.
Geologists who made the first studies of the Vallezza field thought that its crude oil was derived from deep sources, probably the Upper Triassic, and that its heavy constituents were filtered out during its upward migration. It is now generally agreed that the oil originates in the Oligocene and Cretaceous marls and limestones.
This small field, 20 km. southwest of Parma in the Taro River valley, was first drilled by SPI in 1909 but evidently produced only a few tons of oil before it was abandoned. Production was obtained from thin sands near the base of the Pliocene at shallow depths. In 1942 SPI discovered oil and gas in middle Miocene sands at 650-750 m. About ten wells have produced 3,588 tons of oil and about 10,000,000 cu. m. of gas. Five wells during 1952 yielded 426 tons of oil and 1,020,724 cu. m. of gas. Average daily production is 1.16 tons of oil and 2,788 cu. m. of gas. A well drilled in 1952 encountered oil in a Piacentian (lower Pliocene) sand at 461-456 m. The well is reported to have flowed considerable oil for a few days but is now producing less than a ton daily.
The Ozzano-Vizzola field lies along the strike of the Salsomaggiore structure. Pre-Pliocene formations are strongly folded and thrust-faulted, and Tongrian shales (Oligocene) overlie middle Miocene sands (Fig. 5).
The Salsomaggiore field occupies the hills northwest and southeast of Salsomaggiore, 30 km. west of Parma. There are three producing districts, about 2 km. apart, known as Salsominore, Centopozzi, and Rovacchia. Showings of oil in thermal wells in the resort town of Salsomaggiore induced the exploratory drilling that resulted in the discovery of oil in the Centopozzi district in 1923. During the next 15 years SPI completed 71 producing wells in the Centopozzi district and 11 oil and gas wells in the Salsominore district. About 1930 AGIP secured concessions covering the southern part of the Centopozzi district and the Rovacchia district, 2 km. southeast of Centopozzi. In the former district 32 small producers were drilled along SPI's concession boundary during 1931-1934. At about the same time 16 oil wells and four gas wells were completed in the Rovacchia district.
Oil production from the three districts reached its maximum of 12,792 tons in 1932, after which many of the wells became watered and production rapidly declined. AGIP wells, after producing 2,000 tons of oil, were abandoned in 1935. SPI production declined to 1,500 tons in 1940. By November, 1950, most of the wells had been invaded by water and the field was abandoned. Considerable gas has also been produced, the maximum being around 1,400,000 cu. m. in 1933. All three districts have produced a cumulative total of 66,833 tons of oil and 17,000,000 cu. m. of gas.
Oil and gas in the Centopozzi and Rovacchia districts were obtained from thin
Fig. 5. Ozzano-Vizzola field cross section.
sandy beds in Langhian (lower Miocene) marls at depths of 150-250 m. In the Salsominore district production came from lower beds, possibly Oligocene in age, encountered at 305-530 m.
The structure of the Salsomaggiore field, as interpreted by SPI geologists, is a folded overthrust with lower Miocene marls exposed in a fenster surrounded by Oligocene marls and redbeds (Fig. 6). According to this conception of the geology, the north flank of the structure consists of a down-folded and imbricated overthrust. Behrmann (1940) on the other hand attributed the complex structure on the northeast flank of the fold to an upward diapiric flowage of the Argille scagliose.
Salsomaggiore oil is a high-grade, bright-yellow, low-viscosity oil, which increases in specific gravity and decreases in gasoline content with depth. This reverses the rule observable in most oil fields that crudes become lighter and richer in gasoline with depth, and it has been interpreted as proof that the oils originated from older formations and had their heavier fractions filtered out during migration. However, there is little ground for the assumption that oil
Fig. 6. Salsomaggiore field cross section.
moving along fractures is fractionated as when it is filtered through fine dry Fullers earth in the laboratory. Moreover, there are many examples of the deterioration of crudes that have migrated along faults.
This small field is 40 km. south of Bologna in the heart of the Apennines. It was discovered by Societa Idrocarburi Nazionali (SIN) in 1938 following explorations induced by oil seeps described by Pliny in Roman time. Of 180 wells drilled in the district, only 20 yielded oil and gas. Total cumulative production to the end of 1952 was slightly more than 20,000 metric tons of oil and 71,500,000 cu. m. of gas. At present ten wells are producing about one ton of oil and 6,000 cu. m. of gas daily.
The Pietramala field is unique in that it lies near the crest of a mountain chain and produces from practically flat overthrust strata. The oil and gas are obtained from porous beds in the Argille scagliose which here overlies Helvetian (middle Miocene) sandy marls. According to Italian geologists, the Argille scagliose has overridden younger strata in the district by gravitational sliding. The porous beds in which oil and gas are encountered are claimed to be erratic blocks of Lower Tertiary limestone engulfed in the sliding mass. Prominent ranges, 2-3 kilometers long and 200 m. high, consisting of serpentine or Eocene limestone rising above the flat terrane of Argille scagliose, are also regarded as erratic masses.
Careful mapping of the surface geology of the region, combined with a detailed study of well data, may show that the structure at Pietramala is a thrust-faulted recumbent fold in which minor thrusts branch off the major sole fault.
CENTRAL PO PLAIN FIELDS
To date, eight oil and gas fields have been developed in the central Po Plain. These occupy flat agriculture land on both sides of the Po River between the cities of Reggio and Lodi. The area in which these fields are located is about 115 km. long and 15 km. wide, or about 1/10 of the total area of the Po Plain. All were discovered by AGIP as a result of exploratory drilling following geophysical surveys.
Two fields, Fontevivo and Podenzano, discovered in 1929 and 1931, were based on gravimetric surveys. The other fields, discovered between 1942 and 1952, occupy structures located by seismic reflection surveys. All are predominantly gas fields; only three--Podenzano-San Giorgio, Fontevivo, and Cortemaggiore--produce oil as well as gas. A condensate also is obtained at Caviaga and Cortemaggiore.
As Jaboli (1951) has shown, the central Po Plain fields occupy the crest of anticlines that are well defined in the Miocene, progressively less so in the overlying Pliocene and Quaternary, and not apparent at all in the surface topography (Fig. 7.) Most of the gas is obtained from porous sands in the Caviaga formation (Pliocene-upper Miocene). A few wells in the Ripalta and Corneliano fields obtain commercial volumes of gas in lenses of the Ripalta formation (lower Pliocene). Oil is obtained from the Caviaga and Tortonian formations in the Cortemaggiore
field. Structural control is obvious in the Caviaga sands. Porosity evidently has played the principal role in accumulation in the other sands.
The following is a brief description of individual fields presented in the order of their discovery.
The Fontevivo oil field is about 15 km. northwest of Parma and was the first discovery (1929) credited to gravity surveys. A small amount of oil was obtained from a conglomerate at the base of the Quaternary. The Pliocene is absent from the crest of the structure. About 40 shallow wells were drilled, which have yielded 14,050 tons of oil and 829,533 cu. m. of gas. In April, 1952, the field was producing daily about ½ ton of oil, 400 cu. m. of gas, and large volumes of salt water from which iodine is extracted.
The Bellena gas field occupies the northeast flank of the Fontevivo structure 1.5 km. east of the Fontevivo field. The first well completed in 1939 was a small gas-producer from Messinian sands (upper Miocene) at a depth of 800-900 m. Showings of gas were also obtained in Tortonian sands. Fifteen wells produced 4,433,335 cu. m. of gas before the field was abandoned in 1946.
A test drilled in 1936, to 2,430 m., near the crest of the Fontevivo structure stopped in the lower Miocene with showings of gas in the Tortonian and gas and water in the Langhian.
Podenzano is about 8 km. directly south of Piacenza. The first producer was completed in 1931 on a gravity anomaly. Flows of gas were encountered in sands in the upper, middle, and lower Miocene and a little oil was obtained from the Langhian (lower Miocene). Very little use was made of the gas until about 1935. In 1936 the field produced about 2,000 cu. m. daily. When compressed gas began to be utilized for the operation of motor vehicles in 1938, production was greatly increased. By 1940, 18 producers had been completed, proving an area of 130 hectares and with an annual production of 6,114,950 cu. m. of gas.
A seismic survey in the area resulted in eastward extension of the field in 1942. This part of the field known as San Giorgio was the first discovery credited to seismic surveys. To the end of 1951 fifteen wells had been completed, producing gas and some oil from the Miocene at depths of 550-1,400 m. The total cumulative yield to the end of 1951 is 8,032 tons of crude and 102,421,022 cu. m. of gas.
Production from the Podenzano-San Giorgio field reached a maximum of 15,441,066 cu. m. in 1942. The daily production in April, 1952, was 9,000 cu. m. of gas and 2 tons of oil.
Caviaga is about 8 km. southeast of Lodi and 35 km. southeast of Milano. The first well was completed in the early part of 1944 before the capture of northern Italy by the Allies. It was the first large field discovered on a seismic structure, but its importance was not widely apparent until 1947 when large volumes of gas began to be marketed from the field. Since then it has been the leading gas-producing field in the Po Basin. Last April, Caviaga had 24 producers, three abandoned wells, and five dry holes. In 1949, three wells--Nos.
Fig. 7. Structure of central Po Basin.
Fig. 7. Continued. See caption on page 618.
13, 14, and 18--blew out, cratered, and were lost because of faulty casing. The casing in No. 11, situated between wells 13 and 14, also parted above the cover rock and allowed gas to escape in shallow water sands. When this flow of gas occurred, fissures with escaping gas appeared at the surface throughout a belt 1,500 m. long and 500 m. wide. The largest were approximately one km. long and 1-10 cm. wide and showed a vertical displacement of 1-10 cm. Since May, 1949, no new cracks have been observed and little escaping gas can be noted. To decrease this flow into shallow sands, No. 11 and an adjacent well (No. 15) have been produced at their full capacities of nearly 600,000 cu. m. daily.
Caviaga's daily production in April, 1952, was 1,600,000 cu. m. of gas from 17 wells, seven wells being shut in. Four tons of condensate were also produced. The field is fully defined and is 7.5 km. long and 2 km. wide. Most of the wells are 600 m. apart and there are 15-20 undrilled locations.
Caviaga occupies the crest of a well defined anticline trending N. 70° W. The section across the west end of the field shows a gently arched structure with flanking dips of 15°-20° at the top of the Caviaga and 5°-10° at the top of the Ripalta (Fig. 8-A). Gas is obtained from sands separated by partings of shale in the top of the Caviaga formation, overlain by an effective cover rock of Pliocene shale 350-480 m. thick. Salt water occurs uniformly throughout the field at about 1,400 m. subsea-level, and, as the top of the producing sand lies at about 1,200 m. on the crest of the structure, the producing zone is approximately 200 m. thick in the center of the field and wedges out toward the outer edge of the field where the sand is entirely occupied by water. On y one deep test, Caviaga-6, has been drilled in the field. It bottomed in the Helvetian at 2,513 m. without shows below the Caviaga formation.
Caviaga is a water-drive field but original reservoir pressures of 148 atmospheres have decreased to 110-125 atmospheres.
An analysis of Caviaga gas from well 16 shows the following constituents.
Percentage Ethane 2.3 Methane 96.7 Nitrogen 1.0
Caviaga gas yields a condensate of ethane amounting to 2.4 tons per million cu. m. of gas.
Ripalta (FOOTNOTE 3a):
The Ripalta field is 12 km. east of Lodi and 8 km.northeast of the Caviaga field. The seismic survey of the structure was completed in July, 1942. The field was discovered in the latter part of 1947 and connected with the SNAM pipe-line system in 1949. Its 1951 gas production was 235,135,356 cu. m. Its daily yield in the early part of 1952 was 800,000 cu. m. from 11 wells with 13 wells shut in, one abandoned, and two dry holes. Wells are spaced 500-750 m. apart. The field is fully outlined and is about 5 km. long by 1.5 km. wide.
FOOTNOTE 3a. For a full description of this field see Fois' paper in this issue of the Bulletin (Bull. Amer. Assoc. Petrol. Geol., Vol. 37, No. 4, April, 1953, pp. 654-64).
Fig. 8. Cross sections of Caviaga and Ripalta field.
The Ripalta field occupies the crest of a small east-west elongate dome or anticline with a broadly arched crest and a sharply dipping south flank (Fig. 8B). On the crest of the fold there is about the same thickness of Quaternary sandy shale (925 m.) as at Caviaga but the Pliocene shales are 200 m. thicker (550-580 m.). The main gas comes from two sands at the top of the Caviaga formation which are separated by a thin parting of shale and have a combined thickness of about 60 m. Edge water (saline) in the upper sand is at 1,532 m. subsea-level and in the lower at 1,513 m. Consequently, the higher sand is productive over a larger area than the lower.
Small flows of low-pressure gas are also obtained in sand lenses in the Ripalta formation 120-200 m. above the Caviaga sands. Wells 1, 3, 6, and 20 produce from these sands. In well No. 20, 17 m. of sand with two clay partings yield 40,000 cu. m. of gas daily. The other wells show 0.5 m. of sand. AGIP plans to drill 25 locations to test the Ripalta sands which may extend some distance north of production in deeper sands. Three wells now drilling (April, 1952) will fully develop the Caviaga sands.
Ripalta is a water-drive field in the Caviaga sands. The large volume of gas withdrawn from the field during 1951 has caused no drop in pressure which is about 150 atmospheres.
The following are analyses of Ripalta gas.
The Cortemaggiore field is 20 km. southeast of Piacenza and 8 km. southeast of Lodi. AGIP brought in the first well on this structure in May, 1949. The well flowed gas with a condensate and a considerable volume of oil. The discovery was widely reported and aroused the interest of petroleum geologists throughout the world. The field has been actively developed and in September, 1952, had 31 gas wells, 15 oil wells, 5 dry holes, and 2 abandoned wells. The two abandoned wells, 18 and 21, blew out. No. 21 ignited and burned for 3 months with an enormous waste of gas and oil. A crater 100 m. in diameter and 35 m. deep engulfed the drilling equipment. The fire was not extinguished until a directional well starting 78 m. from the burning well penetrated it at around 1,200 m. and made it possib e to shut off the flow of gas by pouring cement into the hole. No. 18 also cratered and was lost.
In the early part of 1952 only 7 of the 31 gas wells were connected with the SNAM pipe-line system. The field was then producing 700,000 cu. m. of gas, 175 tons of oil, and 16 tons of condensate daily. Gas production has been held down in the past, pending the construction of a large condensation plant purchased in the United States in 1950. This plant has a reported daily capacity of nearly
3,000,000 cu. m. of gas and when completed in the latter part of 1952, gas and condensate production will be greatly increased.
The cross section of the Cortemaggiore field shows a gently arched fold (Fig. 9). In plan it has a sinuous east-west trend. The producing area is well defined except at the east end where drilling is still in progress and a subsidiary fold, separated from the main structure by a slight saddle, is indicated. The formations penetrated at Cortemaggiore have about the same thickness and character as those in the Caviaga field. The only noticeable difference is in the Caviaga beds which consist of thin sand lenses interbedded with shales. Gas is found in
Fig. 9. Cross section of Cortemaggiore field.
four or five Caviaga sands, occupying a zone 100 m. thick. The individual sands have a thickness of 5-15 m. and are separated by about the same thickness of clay or shale. The gas sands may lense out between adjacent wells. Edge water (saline) occupies different levels in each sand. Because of the discontinuity of the sands, Cortemaggiore is not a water-drive field. The first or main sand appears to be the best developed and together with the second sand yields most of the gas.
Oil is obtained in the east end of the Cortemaggiore field from the fourth upper Miocene gas sands and a Tortonian sand lying 330 m. lower. The upper Miocene sand yields commercial oil in five wells. The Tortonian sand yields oil in ten wells which occupy the subsidiary dome previously mentioned. Each of the 15 producing wells yielded 15 tons daily (average) during September, 1952.
Although 14 wells have been drilled to the Tortonian sand, so far only those drilled in the eastern end of the field have found oil. No. 29 was drilled to 4,083 m. (13,392 ft.) in 1951 and stopped in the Aquitanian (lower Miocene) without showings below the Tortonian sand at 1,950 m.
The following are analyses of Cortemaggiore gas and crude oil.
ANALYSES OF CORTEMAGGIORE GAS
ANALYSES OF CORTEMAGGIORE CRUDE OIL
This small gas field is 3.5 km. southwest of Lodi and 30 km. southeast of Milano. The first gas well was completed in 1950 and in April, 1952, 13 gas wells and one dry hole had been drilled. Five wells then were producing 300,000 cu. m. daily with 8 shut in. The field is about 5 km. long by 1.5 km. wide. Two locations only remain to be drilled.
Corneliano occupies the crest of a small elongate dome trending N. 80° E. and showing very gentle dips. The Caviaga beds lie at a subsea-level of 1,273 m. on the crest of the dome and at 1,385 m. on the outer margin of the field. The
upper part of the Caviaga beds consists of porous sand which contains gas above the 1,385 m. subsea-level and water at lower levels. The thickness of the pay zone, consequently, varies from 112 m. in the center of the field to zero at its outer margin. The Ripalta (Pliocene) cover is 550 m. thick. Well 8 which encountered water in the Caviaga gas zone obtained a flow of gas in a thin Ripalta sand about 300 m. above the Caviaga formation.
Corneliano is a water-drive field in the Caviaga sand. Rock pressures are about 150 atmospheres in the Caviaga sand and 136 atmospheres in the Ripalta sand.
The following are analyses of the gas from two Corneliano wells.
The Bordolano field is 15 km. east of Ripalta and 38 km. east of Lodi. AGIP's first test of this structure was completed in December, 1951. During the first half of 1952, four additional gas wells were brought in and a sixth well started.
The Bordolano structure as outlined by seismic surveys in an east-west anticline whose area of closure is 7-8 km. long and 2 km. wide. How much of this will be gas-bearing can not be determined until more wells are drilled.
The completed wells penetrated an extraordinary thickness of Quaternary strata; consequently, the Caviaga beds were reached at a greater depth (1,700 m.) than in the other fields of the district. Flows of gas were encountered in three sands separated by shales in the upper 75 m. of the Caviaga formation. Well 1 was drilled to 2,001 m. and stopped in the Helvetian without encountering rocks of sufficient porosity to yield either gas or water below the Caviaga.
The Correggio gas field is 12 km. northeast of Reggio and about 60 km. southeast of Cortemaggiore. The first well was completed on this seismic structure early in 1952 and tested 200,000 cu. m. of dry gas with a pressure of 117 atmospheres. The gas was encountered in the Pliocene at a depth of 1,122-1,161 m. By January 1, 1953, eight additional gas wells were completed.
EASTERN PO PLAIN
Quaternary gas is found widely in the eastern part of the Po Plain. A large area northeast of Ferrara, which yields gas and water wherever wells are drilled, is known as the Polesine gas-producing area. South of it, two small fields have produced water-free gas from sand lenses near the base of the Quaternary. Only Montalbano is still producing. During 1952, AGIP discovered gas in the Pliocene on seismic structures north of Ravenna and at Imola.
Polesine gas-producing area:
The Polesine gas-producing occupies a
triangular area of 2,000 sq. km. in the Po Delta (Fig. 3). Most of the wells are between the Adige and Po rivers east of Rovigo and occupy low agriculture land that lies only slightly above the normal level of the Po River and is protected by dikes and drained by canals.
The first gas well in this area was discovered about 1934. Development was not active until 1939, when gas began to replace gasoline as a motor fuel and coal for heating and industrial purposes. Thereafter a great many wells were drilled each year. At the end of 1951 about 2,500 had been completed, 1,400 of which were still producing, the others having been exhausted or abandoned. The cumulative production then was 753,149,952 cu. m., or 34 per cent of Italy's total of 2,162,446,257 cu. m.
The volume of gas has increased rapidly since 1939. In 1943 the area was producing more gas than all other fields in Italy and continued to do so until 1949, when the central Po Plain fields began marketing large volumes of gas (Table II). The daily production in October, 1951, before the area between the Po and Adige rivers was flooded by the Po River in November, was about 700,000 cu. m. Thereafter production fell off a few months as noted in the following figures for the period of October, 1951, to February, 1952. During the summer of 1952 production was back to normal. During the early part of 1953, it was at the rate of 24,000,000 cu. m. per month.
Cubic Meters October 21,262,000 November 13,861,000 December 10,026,000 January 13,991,000 February 15,380,000
During the flood 1,000 sq. km., or about half of the producing area, was covered by water. The principal damage was done to compressor plants, about 50 of which were submerged, but as the water receded these were repaired. At the end of March, 1951, a dozen plants still remained under water and only about 5 per cent of the wells were reported damaged permanently.
The depth of the first wells in the Polesine area rarely exceeded 300 m. but wells drilled since 1950 average 450 m. Few wells have been drilled deeper because the legal depth permitted until recently was 500 m. The production life of most wells is less than 5 years, chiefly because of pipe corrosion. Some, however, last twice as long. Wells usually flow 1-2 years and then must be pumped. The production of the individual wells varies but seldom exceeds 600 cu. m. daily during the first year, decreasing 20 per cent each succeeding year. The yield of a well depends on several factors, the most important of which are sand thickness, porosity, and well spacing. Calculations based on production data of 20 leases representing more than 600 wells, half of which are exhausted, give the follow ng figures for the ultimate yield of wells.
According to these calculations, the average ultimate yield per well is slightly more than 600,000 cu. m. Other sources place it at 800,000 cu. m.
The wells are drilled by rotary rigs and cased with 5-inch pipe, perforated opposite producing zones. Although gas without water has been encountered in several localities, most wells produce about as much salt water as gas. Where gas is produced without water, the pressure is equal to the hydrostatic head, and the flow continues for a long period. When the gas is associated with water, the pressure is only a few atmospheres and is reduced to zero in a short time; thereafter wells must be operated mechanically.
The salt water produced with the gas must be pumped into the nearest river or canal. As a consequence, development has proceeded along the Po and Adige rivers and intervening canals. Water-disposal costs and damage claims paid to surface owners contribute to operation costs and, where wells have a short life and small production, the profit if any is small.
The cost of drilling a well, including casing, is 10,000-12,000 lire per meter. A 400-m. well consequently costs around 4,500,000 lire. Producers in 1951 were paid from 12.6843 L to 14.7631 L per cu. m. A well producing 600,000 cu. m. will yield its owner around 8,000,000 L. Operation costs, taxes, and damage claims reduce and in some instances wipe out the difference between the cost of the well and the amount received for the gas. Operators formerly paid no royalty but under the new mining law will pay 12-20 per cent royalty.
The gas is produced by 82 small independent operators holding 226 permits. Most of the operators a short time ago formed a joint company known as the Consortio Italiano Metano (CIM) to operate their wells. Most of the other producing companies belong to a second Consortio known as SIRCI. About 80 per cent of the gas is transported through a network of pipe lines operated by Azienda Metandotti Padani (AMP), jointly owned by the principal gas-producing companies and Ente Nationale Metano (ENM). The network consists of more than 500 km. of lines with a daily capacity of 1,100,000 cu. m. These lines extend north to Verona, northeast to Venezia, and southwest to Ferrara. Recently a 7-inch line was laid to Bologna. The gas is forced into the line with booster pumps at a pressure of 80 atmos heres.
The Quaternary formation from which the gas is obtained consists of a series of alternating clays and sands. The producing sands are 10-50 m. thick. Those
most productive occur at depths of 150-200 m., 350-400 m., and 450-500 m. Although the legal depth permitted in the past was 500 m., the Government has allowed a few wells to be drilled deeper. In the locality of Bottrighe, south of Adria, four deep wells were drilled. The deepest (1,200 m.) was still in the Quaternary. All but the fourth reported gas and salt water at 700-900 m. but the wells were lost. Several wells more than 1,000 m. deep north of and south of the mouth of the Po stopped in the Quaternary. Southwest of Chioggia in the locality Ca Bianca, a well, drilled to 1,200 m., reached the base of the Quaternary at 800 m. A test, 12 km. southwest of Rovigo, did not reach the basal Quaternary formation (Calabrian) at 800 m. Another drilled by CIMA in 1951, 4 km. northeast of Ro igo, is reported to have encountered the Pliocene at 780 m.
As far as can be determined, the Quaternary is practically flat except for the minor warping common to a broad shallow basin. The fact that certain areas have yielded gas without water has suggested the possibility that they occupy the crests of minor domes, but this has not been substantiated. Wells in the coastal strip of the Po Delta, north of the mouth of the Adige River, are reported to have produced 50,000 cu. m. of gas daily without water.
The degree of deformation of pre-Quaternary formations is not known, but they may be appreciably folded. South and southwest of the area the Quaternary transgresses strata showing considerable deformation.
Analyses of Polesine gas in percentage are given in the following table.
The Montalbano gas field, formerly called Malabergo, is on the north side of the Reno River about 12 km. south of Ferrara. A gravimetric survey by SPI showed an anomaly in the locality. A test drilled in 1943 obtained gas at a shallow depth in a Quaternary sand and salt water in Messinian sands. From 1943 to 1949 five additional producing gas wells and two dry holes were completed. The field was connected with SIN's pipe line to Bologna and Florence in 1944 and has produced 65,712,500 cu. m. of gas to the end of 1952. Its present production is around 35,000 cu. m. daily.
The wells are spaced about one km. apart. The gas is obtained at depths of 320-350 m. and is found in a Calabrian sand with a thickness of about 10 m. and an average porosity of 30 per cent. The following sequence is encountered in the deeper tests.
Non-marine series consisting of yellowish gray clay with lenses of loose sand and traces of lignite
Sicilian--Marine fine-grained sand with thin streaks of fossiliferous sandy clay. Some gas
Calabrian--Marine plastic clay with sandy streaks. Main gas production
Piacentian--Globigerina zone consisting of sand and clay, encountered only in two wells. Overlies thick series of soft bluish gray shale with streaks of sand
Messinian--Thick series of gray micaceous laminated shale with sandy streaks and traces of lignite. Overlies more compact shale with thin streaks of hard sandstone
Tortonian--Homogenous series of hard light gray calcareous shale with fish teeth and other pelagic fauna
Helvetian--Hard yellowish brown arenaceous calcareous shale with Echinoids and a rich middle Miocene microfauna
Accumulation of gas in the Montalbano field is controlled more by porosity than structure. The field occupies the south flank of the Montalbano anticline which began to take shape at the end of the Miocene and continued to form during Pliocene and the Quaternary. No definite evidence of faulting has been recognized.
Gas in the Montalbano field formerly was produced without water. During 1951, however, salt water began to appear. Rock pressure which was originally 33 atmospheres is now around 30 atmospheres.
The gas shows the following constituents and qualities.
CH4 96.7 - 99.% N 1. - 2.7% Calorific value 1056 - 1065 Specific gravity 0.55 - .56° (Air=1)
LOCATION AND TOPOGRAPHY
This province, which extends along the east coast 300 km. southeast of the Po Basin, has an average width of 40 km. (Fig. 10). Most of it is hilly country that owes its relief to the erosion of small rivers that rise in the Apennine ranges west of the province. In the western margin of the basin there are low ridges that parallel the bordering mountain ranges. Structural relief is also evident along the coast south of Ancona and near Ascoli in the central part of the basin. At the former locality a high ridge known as Mt. Conero rises abruptly 572 m. above the sea. South of Ascoli a mountain range 15 km. long culminates in Mt. dei Fiori which has a maximum elevation of 1,815 m. above sea-level. The ranges west of the province--Sibillini, Gran Sasso, Morrone, and Majella--rise to eleva ions of 2,500-3,000 m. and comprise the highest ranges in the Apennines.
Fig. 10. Oil provinces of central and southern Italy.
Fig. 10. Continued. See caption on page 630.
The same succession of strata is present in the Marche-Abruzzi province as in the Po Basin with the exceptions that there is practically no Quaternary cover, the Oligocene is missing or very slightly developed, and the thick shale series, present in the foothills west of Bologna and known as the Argille scagliose, is replaced by limestone and dolomite.
SECTION IN NORTHERN PART OF PROVINCE (FOOTNOTE *)
Terrace deposits limited chiefly to river valleys, 25-50 m.
Marine marls and clays with sands in lower part, 1,500-2,000 m.
Messinian, 300-400 m. Brackish sands and marly clays with lenses of gypsum
Tortonian, 100-200 m. Marl
Helvetian-Langhian, 400-600 m. Dark marine marly shales at top grading downward into well bedded marls and grayish limestone. Outcrop usually occupied by vineyards
Eocene, 100-150 m.
Dense reddish well bedded limestones with nummulites and orbitoids grading upward into marly shales
Dove-colored to pink and gray well bedded dense crystalline limestone with a few pelagic fossil forms, 400-500 m.
Variegated shales with fucoids, 100 m.
Limestone with Rupestri, 400 m.
Sandy shales with Aptici, 150 m.
Reddish marls and limestone with ammonites, 100-150 m.
Massive limestone, 1,000-1,500 m.
SECTION NEAR SAN VALENTINO IN SOUTHERN PART OF PROVINCE (FOOTNOTE ^dagger)
Sand and gravel, 10-50 m.
Astian sands and conglomerate, 50-100 m.
Piacenzian marine clays, 100 m.
Messinian--Calcareous marls and sandy shales, 20-30 m.
Sandstone with lenses of gypsum and shell-bearing calcareous sandstone, 80-100 m. Sandstones, alternating with marl and gypsum
Lithothamnium limestone with fish remains and pectens, 50-100 m.
Asphalt bearing at several localities
Alternating beds of sandy shale and calcareous marls, 150-200 m.
Bryozoan limestones, 50 m. Important asphalt-bearing beds
Granular massive-bedded nummulitic limestone, 150-300 m.
Asphalt bearing at several localities
Cretaceous limestones exposed south and west of San Valentino
Jurassic dolomites and limestones exposed in the Ascoli anticline, 600 m.
FOOTNOTE *. Based on sections prepared by Sacco and Bonarelli (1936), and well logs and field observations by the writer.
FOOTNOTE ^dagger. Based in part on reports by Lotti (1926) and Beneo (1939).
The province is bordered on the west by high mountain folds of Mesozoic limestone that show marked thrust faulting and overturning on their east flank and normal faulting on their west flank. East of these ranges are long parallel anticlines that commonly expose Miocene formations. The eastern half of the province is surfaced generally by nearly flat Pliocene strata. A major fold, however, comes in form the sea south of Ancona, exposing Cretaceous and Eocene limestones in Mt. Conero. It plunges northwest and disappears as a recognizable feature southwest of Ancona. However, upper Miocene strata are sharply folded and faulted along the same trend in the vicinity of Pesaro.
The other folds that expose pre-Miocene strata are present west and south of the Mt. Conero fold. The smaller, situated 40 km. southwest of Ancona, is about 16 km. long and 4 km. wide. The principal exposures along its crest are Upper Cretaceous limestones showing a broad arch with a fault along its east flank. Jurassic limestones appear in stream channels crossing the axis of the fold.
A major fold, the largest in the province, lies south of Ascoli near the center of the province. It is about 20 km. long and 4 km. wide and exposes Mesozoic limestones which form Mt. dei Fiori. The west flank of the anticline is displaced by a normal fault on the upthrown side of which Jurassic and Cretaceous limestones show moderate northeast dips.
SURFACE INDICATIONS AND EXPLORATIONS
Surface showings of oil and gas, though not as numerous as in the southern part of the Po Basin, are present in several districts. The most notable are the asphalt deposits in the vicinity of San Valentino and the oil and gas seeps at Tocco di Casuaria. Surface showings of oil or gas also occur near Fontespina, Amandola, Ascoli, and Biscenti. Other surface indications such as mud volcanoes and sulphur springs are described by Lotti (1924). A brief account of the principal surface showings and exploratory wells drilled in their vicinity follows.
San Valentino asphalt deposits:
The San Valentino asphalt deposits occur at the northern end of a major fold that exposes Eocene and Cretaceous limestones in its crest. These limestones form Mt. Majella, which rises to altitudes of more than 2,500 m., a few km. southeast of San Valentino. The asphalt occurs as an impregnation of fractured porous Miocene and upper Eocene limestones that are exposed at several places at the north base of this mountain. The impregnated beds have a thickness of 6-20 m. in which the asphalt content is 10-15 per cent.
The deposits were first prospected in 1818 by a company backed by English and German capital. They are extensively worked at the present time by an Italian firm which manufactures cement and tar at Scarfe, 10 km. northwest of the main workings. The reserves are estimated to be many million metric tons.
The origin of the asphalt is not definitely known. Some Italian geologists assume that it is a weathered oil derived from source material in the formations in which it is found. Others credit it to Mesozoic source beds for which there is also some evidence.
Two exploratory wells, drilled 15-20 years ago by AGIP in the district, are reported to have struck a little gas and oil in the asphalt-bearing beds. The one drilled near Abbateggio is reported to have showed the presence of asphalt and heavy oil down to and including the Lower Cretaceous. A test farther north at Allano, completed in 1937, encountered the asphalt-bearing Helvetian limestone at 678 m. The well ended in dense Cretaceous limestone at 1,185 m.
Tocco di Casuaria:
Seeps of light oil and gas in springs issuing from an overturned fold of Helvetian limestones, 10 km. west of the asphalt deposits and 2 km. south of Tocco di Casuaria, were prospected by shafts and hand-drilled bores as early as 1860. These encountered heavy sulphur oil, and a few hundred tons annually were produced for several years. Production was raised to 2,000 tons in 1899 when the wells were deepened but soon declined and was less than 50 tons for several years. The total production in the field to 1934 is reported to be 7,000 tons.
In 1934 AGIP obtained control over the area and by 1942 it had drilled 21 wells. Nineteen of these obtained heavy oil (0.95 gravity) amounting to 2-3 tons daily. From 1936 to the end of 1951 about 7,252 metric tons were produced. A year ago II wells were in operation, yielding a total of one ton daily.
The wells occupy a belt of highly tilted upper Miocene sandy shale that crops out along the eastward base of an overturned and thrust-faulted fold of Helvetian reef limestones, forming a high ridge known as Colle de Oro. Most of the oil is obtained at depths of 100-200 m. in porous Helvetian limestones. Three wells also produce from sands in the Messinian and four wells at the contact of the two formations. The deepest well reached 1,100 m. and encountered the Messinian beneath overthrust middle Miocene limestone.
While developing Tocco di Casuaria, AGIP drilled exploratory wells at Tremonti and Popoli in a mountain valley a few kilometers west of the oil field. They were located in a highly folded terrane in the vicinity of oily impregnations of fractured Eocene limestone. Only slight showings of gas were obtained, and the wells were abandoned at depths of 1,287 and 778 m., respectively.
Oil is observable on the surface of the Adriatic Sea, 2 km. east of Fontespina and 30 km. southeast of Ancona. In 1934 AGIP drilled a test ½ km. west of Fontespina on what appeared to be a slight surface structure exposing Quaternary strata. The well started in Quaternary sands and ended in Pliocene clays at 1,950 m. without showings. In recent years AGIP has made seismic surveys in the district and reports that the well was located on the southwest flank of a fold which the company plans to test in 1953.
In September, 1951, AGIP started a deep test on the south bank of the Chienti River 6 km. south-southeast of Morrovalle and 11 km. southwest of Fontespina. The well is located on a seismic structure surveyed in 1951 by Compagnie Generale de Geophysique (CGG). The well was drilled to 2,494.5 m. without showings except for evidence of porosity and gas at 439-453 m.
The log of the well follows.
Gas seepages along a slight surface fold of upper Miocene strata northeast of Amandola have resulted in the drilling of several wells. The first was put down by AGIP in 1934 near San Ruffino, 5 km. northeast of Amandola. The well reached the total depth of 1,400 m. and was still in the Messinian. No showings were encountered, but a large flow of sulphur water with hydrogen sulphide gas was struck in sands at the bottom of the well.
In 1942 ENM and the Macerata Chamber of Commerce developed a small gas field near a light surface showing of gas 8 km. northeast of Amandola. Seven wells were drilled, six of which produce about 20,000 cu. m. of gas per month from Messinian sands at a depth of 100-200 m. The gas is piped to Magli, 3 km. west of the field, where it is bottled and marketed. Another well drilled in 1949 in the same locality was abandoned at 950 m. without showings.
Upper Miocene sands and marls, according to Porro (1921), are impregnated with oil in the vicinity of Ascoli. The impregnations are associated with sulphur water and occur in steeply dipping and possibly faulted strata exposed at low levels on the plunging end of the major anticline that forms the range south of Ascoli. No wells have been drilled in the locality.
A slight showing of bitumen near Biscenti induced AGIP to put down a test in its locality in 1932-1935. The well reached the depth of 1,319.5 m. without showings. It is reported that the log was lost with other AGIP records during World War II; consequently, it is not certain what formations were penetrated, but it is probable that the well did not reach the base of the Messinian.
LOCATION AND TOPOGRAPHY
The Lucanian province extends from near Termoli southeastward to the Gulf of Taranto (Fig. 10). A narrow belt of tilted Tertiary strata that extends farther southward along the Calabrian coast is also included in the province. The main part of the province is about 250 km. long and 30-50 km. wide. It is a part of the Tertiary sedimentary basin of which the Po Basin and Marche-Abruzzi province are subdivisions. Unlike the latter province it is for the most part separated from the Adriatic Sea by limestone ranges which form the Murge hills and the Gargano promontory. The western boundary of the province north of Taranto Bay is arbitrarily placed at the western margin of the Upper Tertiary exposures.
The surface of the province varies from hilly to plain country across which several rivers and their tributaries have formed a system of branching valleys. The Bradano River drains part of the basin north of the Taranto Gulf, and as a consequence the province is sometimes referred to as the Bradanica trough.
The surface throughout most of the province is occupied by marine Pliocene clays which in places are overlain by Quaternary sands and conglomerates. Along its eastern margin Pliocene sandy clays overlap Cretaceous limestones. At the west the Pliocene transgresses Eocene and older formations. The Eocene occupies a wide belt of mountainous land west of the province and is represented by possibly more than 1,000 m. of marine sandy shales with intercalations of sand, conglomerate, marl, and limestones. This area is not included in the oil province, as Cretaceous formations are exposed in the crest of most of its folds, and there is hence little possibility of oil accumulation. Farther west, Mesozoic limestones form more rugged ranges, but none of them reach the heights of those west of th Marche-Abruzzi province.
An exploratory well, Genzano No. 2, in the central part of the basin shows the following section.
Calabrian and Piacentian, 654 m.
Clay with lenses of sand. Thin coarse-grained sandstone at base
Eocene, 787 m.
Compact Nummulitic limestone with brecciated zones containing basaltic boulders
Evidently the Eocene flysch facies in the mountains west of the basin is replaced by limestone. Tertiary sands and boulder beds west and south of Crotone are overlapped and cut out by the transgressive Pliocene.
FORMATIONS EXPOSED SOUTH OF TARANTO GULF
Sicilian--Terrace deposits of sands and gravel
Calabrian--Buff friable sand
Upper and Middle, 1,000 m.--Gray and white clays containing marls and thin limestones that weather into badland topography. These clays overlie cross-bedded sands with thin lenses of hard calcareous shell-bearing sandstone at their base
Lower, 700 m.--Well bedded coarse sand with pebbles and shells
Upper, 200 m.--Gypsum and sulphur-bearing clays overlying sands and ash beds
Middle, 100-400 m.--Sandy clay with Clipeastri, lenses of sand, and bryozoan limestone. Boulder conglomerate at base which transgresses older strata westward
Upper, 200 m.--Thin-bedded coarse-grained sand with large boulder conglomerate at base
Middle and Lower, 1,250 m.--Marine shale series with beds of coarse-grained conglomeratic sandstones in lower part
Turonian, 100-150 m.--Nummulitic limestone
Upper and Middle, 250 m.--Hard dolomitic limestone
Metamorphic schists and granite
Pliocene beds are practically flat in the eastern part of the province. They overlap the slightly folded Cretaceous limestones that are exposed in the highlands east of the basin. In the western part of the basin the Pliocene is gently folded and overlies sharply folded Eocene formations. South of the Gulf of Taranto, Tertiary and Mesozoic formations show a continuous seaward dip away from highlands of granite and metamorphic rocks, the Mesozoic strata being inclined at 60°-70°, Lower Tertiary at 20°-40°, and the Upper Tertiary at 10°-20°. Normal faulting also occurs in some localities.
SURFACE INDICATIONS AND EXPLORATIONS
No surface indications are reported in the confines of the basin, but oil and gas seeps, impregnations of bitumen, and sulphur springs occur at numerous localities in the mountain district west of the basin. Most of them are confined to the folded belt in which Eocene formations form the principal exposures, and most of them clearly issue from fractured Eocene sandy marls and limestones. The most important are near Castelfranco, San Angelo dei Lombardi, Caposele, San Angelo le Fratte, Tramutola, and Cersosimo (Cortese, 1926, and Crema, 1926). Some of these seepage districts were prospected in the latter part of the last century.
Systematic investigations of oil prospects in the Lucanian province were begun by Migliorini (1937) and other AGIP geologists in 1934. These were followed in 1936 by seismic refraction surveys. In 1937 AGIP began a drilling program during which it put down three tests near Genzano in the central part of the province and several shallow wells in the vicinity of seepages in the mountains along its western border.
The Genzano wells encountered Calabrian and Piacentian clays with sandy intercalations and a basal coarse sand overlying Eocene limestones and basaltic breccias. Traces of oil and gas were reported at several horizons in two of the wells. The following summarizes the principal facts pertaining to these tests.
GENZANO NO. 1
Location--5 km. southeast of Genzano
Date of drilling--1937-1939
Depth to top of Eocene--959.1 m.
Total depth--1,072.3 m.
Showings of gas at 604.7, 620.5, 702.5, 939, and 960 m.
Showings of gas and oil at 806.1 and 972.8 m.
GENZANO NO. 2
Location--12 km. S. 20° E. of Genzano
Date of drilling--1939-1941
Depth to top of Eocene--654 m.
Total depth--1,441 m.
Showings of gas--960.5 m.
Showings of oil and gas--654.5 and 746.6-747.6 m.
GENZANO NO. 3
Location--11 km. S. 15° E. of Genzano
Date of drilling--1941-1943
Depth to top of Eocene--1,325 m.
Total depth--1,770 m.
Shallow wells drilled near the seeps in the vicinity of San Angelo dei Lombardi and San Angelo le Fratte during 1937-1938 obtained good showings but no commercial volume of oil.
At the Tramutola seeps 3 km. northwest of Tramutola village, AGIP succeeded in producing small volumes of oil in 1937, which was increased in the early Forties to about 2 tons daily from 20-40 shallow wells. The total yield till the end of 1951 was 6,198 tons. The oil is obtained at depths of 50-100 m. and comes from thin beds of sandstone and limestones in the flysch facies of the Eocene. The Eocene in this locality occupies a narrow syncline between ranges of Triassic and Cretaceous limestones.
In the last 3 years Italian companies have obtained prospecting permits and made exploratory surveys of areas in the Lucanian province and on the Calabrian coast. Soc. Richerche Petrolifere Meridionali (RPM), which holds a 120,000 hectare permit between Tramutola and the Gulf of Taranto, engaged the Western Geophysical Company in 1949 to make a seismic survey of its holdings and may start drilling in 1953, if a drilling rig can be obtained.
During 1950 and 1951 surface geological surveys were made by Montecatini of their drilling permit along the west coast of Taranto Bay. Following these investigations and a seismic survey by the Western Geophysical Company in 1949-1950, the company engaged Dunlap and Graham, drilling contractors of Los Angeles, California, to put down a test on a surface structure near Scandale, 14 km. northwest of Crotone. The well was started on December 15, 1951, and abandoned at 2,651 m. in 1952. Formations penetrated to 2,035 m. are as follows.
0-122 m.--Porous sand
112-500 m.--Bentonitic clays
500-700 m.--Sandy clays
700-1,150 m.--Alternating beds of sand, clay and marl with a slight amount of anhydrite in lower part
Miocene [Formazione Gessoso Solfifera]
1,150-1,450 m.--Alternating clays, sands, and marls with anhydrite concretions and rock salt
1,450-1,680 m.--Dense shale with clay and thin beds of rock salt and sand
1,680--1,800 m.--Shale with beds of rock salt and thin beds of anhydrite and gypsum
1,800-2,035 m.--Compact shale with intercalations of clay. Cores taken between 1,550 and 1,610 m. gave traces of oil
A second well now drilling on a geophysical structure at Capo Cimitri, 15 km. south of Crotone, encountered gas in the middle Pliocene at 560 m. Other wells will be drilled in this locality in 1953.
LOCATION AND TOPOGRAPHY
This small oil province, 15 km. wide by 130 km. long, is east and southeast of Rome in the drainage basins of the Liri and Tiber rivers and their tributaries. Most of the province occupies two intermontane valleys, known as the Latina and Roveto valleys, which are separated by high limestone ranges (Fig. 10). Latina valley, the larger, is drained by the Sacco River and is separated from the Tyrrhenian Sea by a range which rises 1,000-1,500 m. above sea-level. The Roveto valley, 30 km. northeast of the Latina valley, is drained by the Liri River, which joins the Sacco southeast of Frosinone.
The Campanian province contains two grabens surfaced by Miocene and Quaternary formations lying between Mesozoic limestone ranges. The following is a typical section according to Beneo.
Alluvial fans, recent terrace deposits, volcanic tuff and lava, old stream terraces, travertine, moraines, and basal conglomerate
Upper Miocene--Gypsum-bearing clays, marls, and sands, 300-500 m.(FOOTNOTE *)
Middle and Lower Miocene--Bryozoan and foraminiferal limestone, 200 m.±
Compact semicrystalline Nummulitic limestones, 0-500 m.
Upper--Granular limestone with lenses of dolomite. Rudistids and other Upper Cretaceous fossils, 300-500 m.
Lower--Thick series of limestones and dolomites, 500-700 m.
Upper and Middle--Dense fossiliferous limestones and dolomites with Middle and Upper Jurassic fossils, 500-800 m.
Lower--Gray dolomite, compact yellowish limestones, sandy shales, and cherty gray and black limestones, 400-600 m.
Dense crystalline dolomite and granular limestones with abundant Triassic marine fossils, 500 m.±
The region occupied by the Campanian province was subjected to epeirogenic movements during the Mesozoic and tectonic deformation during the early
FOOTNOTE *. Thicknesses are rough estimates only.
and late Tertiary. The main crustal deformation occurred during the early Pliocene when pre-Pliocene formations were folded and massive calcareous Mesozoic formations were overthrust on the Tertiary. Normal faulting has produced the graben structures represented by the Latina and Roveto valleys. In the former the Miocene formations are broadly arched and overthrust by Mesozoic limestones along its southwest border; in the latter they show a general westward tilt towards a normal fault. Differential erosion coupled with volcanic activity and faulting in Quaternary time has produced the present rugged topography of the region.
SURFACE SHOWINGS AND EXPLORATIONS
Numerous surface indications of oil occur in the Campanian province. They consist of liquid seepages and asphaltic impregnations, most of which appear in the vicinity of faults. Some of the surface showings were prospected by shafts and hand-dug wells 70-80 years ago. More recently, shallow bores have been drilled in several localities in the Latina valley in two of which a total of approximately 11,000 tons of oil has been produced. The following is a description of the principal surface showings and an account of the explorations in their vicinity.
A small oil seepage in Quaternary tuffs, 2 km. southeast of Ripi and 8 km. southeast of Frosinone, was prospected by a tunnel in 1871. In 1917 the Italian Government began drilling in the district and in the period of 1918-1923 put down 12 shallow wells, most of which obtained small volumes of heavy oil at depths of 75-260 m. Approximately 400 tons was produced before the company abandoned the field in 1933. In 1924 Societa Petroli d'Italia drilled two tests, Ripi-1 and Ripi-2, northeast of the producing wells. They reached depths of 751 and 712 m., respectively, encountered salt water in porous Miocene formations and may have stopped in Cretaceous limestone.
In 1939 AGIP took over the Ripi concession and during the period of 1939-1943 drilled 28 wells in the locality north of the old wells. About 15 of these were productive and produced 6,589 metric tons of oil to the end of 1951. Maximum production was attained in November, 1941, when the daily yield from eight wells was about 10 tons daily. Since then the production has declined. At the end of 1951, 12 wells were still in production, yielding about 2 tons daily. Three of these were also producing 800-900 cu. m. of gas. Most of the wells also produced considerable salt water.
The productive wells evidently occupy a low dome with the edge wells encountering salt water. The main producing formation is porous Helvetian limestone 10 m. thick, encountered at depths of 150-200 m.
The oil is a heavy (0.935 sp. gr.) sulphur-bearing crude yielding 22 per cent gasoline and 10 per cent asphalt. The gas is compressed in containers and is marketed locally.
San Giovanni Incarico:
An oil seep in the vicinity of San Giovanni Incarico, 14 km. southeast of Ripi, was prospected by shafts between 1867 and 1883 from
which a little oil was obtained. In 1915 Societa Petroli d'Italia (SPd'I) started to explore the area and drilled a total of 23 wells, 14 of which were productive. By 1943 when the field was abandoned it had produced around 3,500 tons of oil. The producing area occupied 4 hectares on a small strongly folded anticline near the boundary fault on the southwestern margin of Latina valley. Oil was obtained in a lower Miocene Globigerina limestone around 3 m. thick encountered at depths of 460-470 m. The oil was a heavy (0.88-1.02 sp. gr.) gas-free sulphur-bearing oil and was produced with considerable salt water.
Other surface showings and explorations:
At Pico, 6 km. south of San Giovanni Incarico, oil formerly seeped from lower Miocene strata within a few meters of the border fault where Mesozoic limestones are overthrust on the Tertiary. A well drilled near this seep by SPd'I in the Nineties reached the depth of 858 m. without penetrating Mesozoic strata. A little oil was encountered in conglomeratic sands in the lower Miocene.
At Castro dei Volsci, 15 km. northwest of Pico, brecciated Helvetian limestones and overlying Quaternary conglomerates are impregnated with bitumen. The locality was prospected by hand bores for a number of years and was finally tested by SPd'I in two shallow bores without encouraging results.
Near a sulphur spring in the vicinity of Posi, 6 km. south of Ripi, SPd'I drilled a 521-m. test without showings.
At Ceccano, 10 km. southwest of Ripi, the same company drilled a 1,100-m. test and encountered compact non-fossiliferous limestone possibly Cretaceous in age.
On the north side of Latina valley near Monte S. Giovanni, 7 km. northeast of Ripi, where Pliocene strata occupy a small downfaulted block between Helvetian limestone, porous limestone and sand in the Pliocene are impregnated with asphalt in a belt several hundred meters long. A shallow bore in the locality encountered asphalt and heavy tar in the basal 200 m. of the Pliocene.
In addition to the foregoing surface showings, most of which are in areas underlain by Miocene or younger strata, a number of asphaltic occurrences are reported in exposures of Mesozoic limestones outside the basin, near the following villages northeast of Latina valley: Guarcino, Collepardo-Trisulti, Colle San Magno, and Filletino. All of these asphaltic showings occur in Cretaceous limestones except the one at Filletino, which is in Triassic dolomite. An important deposit of asphalt also occurs near Capistrello in the Roveto valley where both upper Miocene and Jurassic limestones on opposite sides of the boundary fault are impregnated.
SICILIAN OIL PROVINCE
LOCATION AND TOPOGRAPHY
The southern half of Sicily is prospective oil territory. A curving line drawn through Catania, Nicosia, Bivona, and Sciacca may be considered as the approximate northern limit of the more promising parts (Fig. 11). The area so defined is 120 km. long and its maximum width is 80 km.
Most of the southern part of the island is rolling upland country which in places is fairly rugged. The most prominent features are ridges, mesas, badland forms, and well defined stream valleys. This type of topography merges northward into the mountain ranges that extend across the northern part of the island. These ranges have an abundant rainfall and are forested. The rest of Sicily has considerably less rainfall and little forest growth; the summers are hot and dry, the winters wet and cold. The southern half of the island is thickly populated, most of the inhabitants living in small walled towns or villages situated on ridges or high mesas. A large part of the population of northern Sicily is confined to coastal towns, some of which are important winter resorts.
Fig. 11. Sicilian oil province.
The principal geological provinces of the Italian peninsula--the Apennines, the young Tertiary foredeep, and the foreland--are recognizable in Sicilian geology (Fig. 2).
The Sicilian Apennines comprise the north coastal ranges and a group of mountains in the west-central part of the island. The young Tertiary foredeep occupies central Sicily. The foreland is represented by the so-called Ragusa plateau of southeastern Sicily. The circular area of volcanic rocks culminating in Mt. Etna and rising 3,774 m. above the east coast, is a Quaternary-Recent volcano.
The granitic and metamorphic rocks which form the core of the Southern Apennines in Calabria reappear across the Messina Straits in the Peloritani Mountains of northeastern Sicily. From there westward to Palermo, the formations consist chiefly of sharply folded and faulted Lower Tertiary strata which form the Caronie Mountains with maximum elevations of 1,500-1,800 m. At Palermo, Mesozoic limestone ranges dominate the north coast. Isolated ranges extend inland south of Palermo and form the Sicani Mountains which rise more than 1,000 m. above the foothills of Lower Tertiary shales that surround them. The Mesozoic section exposed in these limestone ranges is in general as follows.
Cretaceous, 200-1,000 m.
Turonian variegated shales with thin bands of fossiliferous limestone and small boulders (bioherm masses) of Rudistid limestones.
Marly limestones, 250-500 m.
Dolomites, 1,000-1,500 m.
The structure of the Sicilian Apennines is complex. East of Palermo the general trend is east-west and the folding and thrusting appear to have been directed from north to south. The ranges south and west of Palermo consist of fault blocks of limestone and dolomite in which structural trends are obscure. However, accurate mapping of the geology of these mountain districts will doubtless show that they are due to tectonic forces and are not erratic blocks that have reached their present position by gravitational sliding off a landmass that formerly lay north of the present island.
Young Tertiary foredeep:
The young Tertiary foredeep occupies that part of central Sicily that lies between the Apennine ranges and the Ragusa plateau. Actually there is no sharp boundary between it and the mountains on the north. The following formations are present in the area.(FOOTNOTE 4)
Upper and Middle--Calcarenites and shelly limestone, 10-50 m. Bluish gray marine clays, 100-350 m.
FOOTNOTE 4. Section furnished by Carlo Marchetti, geologist in charge of Gulf's field investigations in Sicily.
Messinian (Formazione Gessoso-Solfifera)
"Trubi" Globigerina marls, 80 m.
Gypsum with thin beds of sulphur, 0-150 m.
Limestones, 0-80 m.
"Tripoli" siliceous shales, 0-40 m.
Clays with Globigerinae, 150 m.
Brown and gray clays with thick sandstone intercalations, 150 m.
Gray clays and gypsiferous shales, 200 m.?
Variegated clays with thick intercalations of sandstones, 200-300 m.
Nummulitic limestones and thinly bedded calcareous shale, 100-200 m.
Variegated calcareous shales and Rudistid limestones
Folding in the young Tertiary foredeep is fairly pronounced, especially in its northern and western parts. North of Caltanissetta closely folded and overthrusted anticlines are common features and have structural trends parallel with the mountain folds on the north. The crests are occupied by highly inclined Lower Tertiary variegated clays with Cretaceous calcareous shales appearing in the cores of some of them.
In the area west and south of Caltanissetta, irregular elongate domes defined by ridges of upper Miocene gypsiferous sandstones, enclose basins of middle Miocene clays and in some places Oligocene and Eocene variegated calcareous shales.
The irregularity of these structures, because of the great variation in the thickness of the upper Miocene gypsum beds and also because of local land slides combined with close folding, faulting, and the absence of easily recognizable horizon markers in the thick series of Miocene and lower Tertiary argillaceous formations, has led some geologists to regard these structures as diapirs. In late years the hypothesis that the deformation is due to gravitational sliding of a shallow part of the crust off highlands in northern Sicily has been also widely held. The clay-shale formations, ranging in age from middle Miocene to upper Cretaceous and known as the Argille scagliose, are regarded as a jumbled mass, and exposures of Eocene or Cretaceous limestones are supposed to be erratic blocks hat have been carried along by the sliding mass. Even the Mesozoic limestone ranges in the Sicani Mountains are claimed to have no structural roots.
Field studies in central and southern Sicily by Marchetti have demonstrated that the clay formations are not a jumbled mass but a series of recognizable and mappable units that have been deformed in definite tectonic patterns. The writer is inclined to believe that accurate mapping in northern Sicily also will
show that the geological structure is due to tectonic forces and not to gravitational sliding.
With the exception of a narrow coastal plain the peninsular area of southeast Sicily is occupied by the Ragusa plateau. It covers an area about 70 km. long by 40 km. wide. The surface rises gently inland and attains its maximum elevation of 985 m. in Mt. Lauro, 25 km. northeast of Ragusa. The rivers that flow outward from this central area occupy deep valleys.
Most of the Ragusa plateau is surfaced by middle and lower Miocene limestones and marls overlain by Quaternary sands and calcarenites along the east coast and by Quaternary to Recent basaltic flows in its northern part. Senonian (Upper Cretaceous) limestones are the oldest formations exposed in the plateau. They crop out at the western margin of the basin, north and northwest of Monterroso and near Pachino in the southeast extremity of the island. All the formations are more calcareous than equivalent units in the young Tertiary foredeep and were doubtless deposited on a foreland that received little detrital material and where conditions were suitable for the growth of reef-building organisms during the Lower Tertiary and middle Miocene.
The following is a generalized stratigraphic section of the Ragusa plateau.(FOOTNOTE 5)
Tortonian (middle Miocene)
Lithothamnium reef limestone, 100 m.
Siracusa limestone (calcarenites and shelly limestone), 100 m.
Palazzola limestones, fine-grained calcarenites (Gaetani limestones at base), 400 m.
Helvetian (middle Miocene)
Upper Tellaro marls and claystones, 280 m.
Lower Tellaro calcarenites with asphalt, 130 m.
Ragusa limestone and calcarenites with asphalt, with basal conglomerate locally developed, 150 m.
Middle cherty limestones of Boschetello near Licodia and coral reef limestones of Pachino, 80 m.
Basal conglomerate of Boschetello, 2 m.
Senonian well bedded cherty buff-colored limestone exposed near Boschetello and Pachino, 100 m.±
The Ragusa plateau is bounded on its northwest margin by a series of normal faults with downthrow on the west. At Comiso west of Ragusa the displacement is about 400 m. Here the lower Miocene Teilaro limestone forms a high scarp on the east side of the fault, and Quaternary sands occupy lowlands on the west side. Twenty-five km. northeast of Comiso, Cretaceous and Eocene formations dipping 5°-10° southeast are exposed on the upthrown side of the marginal fault. Overlying Oligocene and Miocene formations dip slightly eastward for a few kilometers
FOOTNOTE 5. Courtesy of Carlo Marchetti.
and then show minor northeast-trending faulted folds. One such fold is evident at Ragusa, showing southeast dips of 5°-10° toward a fault. Minor folds with possible faulting appear farther eastward along the highway between Giarratana and Palazzolo. Structural control of southwesterly flowing streams is also evident. In the eastern half of the plateau the Palazzolo limestone is inclined generally southeastward toward the edge of the plateau where it is downfaulted beneath Quaternary formations that occupy the narrow coastal plain. Eocene and Cretaceous limestones are again brought to the surface in a minor faulted structure at the southeast tip of the island.
SURFACE INDICATIONS OF OIL AND GAS
Surface indications of oil and gas appear at widely separated localities throughout Sicily. They consist of asphaltic deposits, seeps of oil and gas in sedimentary formations, traces of oil in volcanic rocks, and emissions of methane and volcanic gases in mud volcanoes and elsewhere (Fig. 11).
The most important surface indications of oil in Sicily are the asphalt deposits north and south of Ragusa. They have been worked for more than half a century at Ragusa and Castelluccio, 8 km. south of Ragusa, and prospected at Licodia, 24 km. north of Ragusa, and at Vizzini, 3 km. northeast of Licodia.
The deposits at Ragusa and Castelluccio consist of tarry impregnations of a granular limestone (calcarenite) of lower Miocene age. Only the porous facies, about 50 km. thick, is impregnated and it is reported that the deposits are restricted to a fractured zone on the crest of a northeast-southwest anticline. Both the Ragusa and Castelluccio deposits are reported to occupy the same anticline, but it appears more than likely that they are situated on separate folds.
The deposits at Licodia and Vizzini occur in fractured lower Miocene and Oligocene calcarenites southeast of a major fault that forms the northwest margin of the Ragusa plateau and exposes Eocene and Upper Cretaceous limestones. At Licodia the Cretaceous is also impregnated with asphalt.
It is probable that the asphalt in the Ragusa plateau is a weathered product of oil that has migrated along fissures from source beds or possibly from a lower oil reservoir.
The deposits at Ragusa and Castelluccio were first prospected in 1838 but were not worked on a very large scale until 1890 when 4,000 tons were mined. Production was increased in a few years to 100,000 tons, most of which was exported to foreign countries for street and highway construction. Four Italian and foreign companies now own concessions in the two localities. One or two of these are operating open-cuts and tunnels near Ragusa and are producing cement, tar, and diesel oil. The average asphalt content of the limestones at Ragusa and Castelluccio is 6-9 per cent. The proved reserves are placed at 250,000,000 cu. m. The potential reserves are probably many times this but can not be estimated as there has been little exploratory drilling beyond the boundary of the limited
concessions which cover only a few hundred hectares and are confined to a narrow belt only 200-300 m. wide in which the asphalt-bearing beds are exposed or lie at shallow depths.
Asphalt occurs also in fissures and joints of Mesozoic limestones at several localities south of Palermo.
Oil seeps in sedimentary rocks:
Seeps of oil in sedimentary formations are reported at several localities. Most of them issue from Eocene flysch beds or from Miocene formations as indicated by the following list.
Seeps in volcanic rocks:
Oil seeps associated with volcanic rocks occur in eastern Sicily. Traces of oil are found in Cretaceous dolerites near Pachino and in Quaternary tuffs 2 km. northwest of Palagonia. Light kerosene oil is found in the cavities of Quaternary to Recent basalts near Paterno at the southwest base of Mt. Etna and also at its northern base near Francavilla. These occurrences may represent distillation products of carbonaceous shales or other organic deposits in the vicinity of volcanic centers.
Gas seeps are located as follows.
In addition to these gas seeps, emissions of CH4, CO2, and H2S occur in mud volcanoes at several localities in southern Sicily. Especially well known is the huge mud volcano 4 km. south of Aragona. Actually it comprises a group of 12 situated along an assumed fault in Lower Tertiary clays that occupy the eastern part of the Aragona dome. Gas issues as bubbles in salt water in these volcanoes. In 1940 a big eruption occurred and the gas caught fire. A chemical analysis of the gas shows carbon dioxide 1.3 per cent, methane 95.6 per cent, and nitrogen 3.1 per cent. Another important gas seep is reported 4 km. west of Palagonia where methane and carbon dioxide erupt from Lake Naftia. Small mud volcanoes 3 km. northeast of Caltanissetta in Pliocene clays sh w some gas.
The search for oil and gas in Sicily has had a long history which is briefly
summarized under the headings of early explorations, AGIP exploratory wells, and recent explorations.
For longer than a century, local inhabitants prospected for oil near seeps in Sicily. Shafts and galleries in the vicinity of Lercara Friddi, Cerami, Troina, Bivona, Petralia, and Nicosia yielded a little oil for domestic use. The Sindacato Idrocarburi, about 1900, drilled three shallow bores near Nicosia in which slight showings of oil and gas were encountered. Other shallow bores were drilled elsewhere, near seeps, by English and French concerns without success. The Sinclair group made a general survey of the island in 1920. During 1936 and 1938 extensive geological surveys were made throughout the island by the Socony Vacuum Oil Company, but no exploratory drilling was done (Beneo, 1952).
AGIP exploratory wells:
Shortly after it was organized in 1926, AGIP began drilling in Sicily and during the next 15 years put down several wells, most of which were drilled in the vicinity of seeps. None produced commercially, but few if any were geologically well located. The following is a summary of these tests.
1. Bivona--1.104-m. test, drilled in 1928-1931 near oil seep in Eocene formations south of Bivona, is reported to have found showings of oil and gas at 200 m.
2. Lercara Friddi--
No. 1--Northeast of Lercara, was drilled in 1939-1940. Reported to have ended in Permo-Carboniferous sandstones and shales at 1,483 m. Numerous showings of gas down to 660 m.
No. 2--Southwest of town of Val Riena, was drilled in 1937 to 653 m. Reported to have penetrated Permo-Carboniferous strata but no showings of oil or gas
3. Gangi--Well drilled 5 km. south of Gangi in 1928-1931 to depth of 1,148 m. penetrated Eocene flysch, in basal beds of which traces of oil and slight showings of gas were found
4. Nicosia--Well drilled in 1939, 3 km. west of Nicosia reached depth of 2,016 m. without showings. Penetrated steeply dipping Tertiary clays with thin beds of limestone
5. Gioitto--In 1939 AGIP struck a little gas in test drilled near Gioitto 22 km. east of Nicosia. In following 4 years seven additional wells were drilled, five of which encountered small volumes of gas at shallow depths in Eocene flysch. Field yielded yearly production of 30,000 cu. m. before abandoned
6. Bronte--Three wells were drilled 2-5 km. west of Bronte in 1940-1941. No. 2 reached depth of 608 m.; other two less than 300 m. All penetrated Eocene flysch beds. No. 2 reported traces of oil and gas at 220 and 280 m.
7. Nicastro--Test drilled in 1935 at location 30 km. E.-NE. of Ragusa and 10 km. north of Noto stopped in Eocene at 1,320 m. Penetrated almost continuous series of limestones from top to bottom and obtained only slight showings of gas at 600-700 m., 860-910 m., and 1,220-1,140 m. Following is skeleton log of well:
0-130 m. Helvetian granular limestone
130-605 m. Langhian
130-225 m. Gray limestone and marl
225-310 m. Clay
310-360 m. Limestone and marl
360-460 m. Clay
460-605 m. Granular marly limestone
605-905 m. Aquitanian. Grayish white limestone with intercalations of marl
905-1,060 m. Oligocene? Limestone with nodules of chert and sandy limestone
1,060-1,320 m. Middle Eocene. White limestone and some sandstone wiht intercalations of marl and nodules of chert
8. Pachino--During 1936-1939 three wells were drilled a few km. west and northwest of Pachino. They reached depths of 538,327, and 407 m. All three wells are reported to have stopped in Cretaceous basalts. No. 1 encountered impregnations of oil and gas at several places down to 440 m.
In 1947 Macmillan Petroleum Corporation became interested in Sicily and later employed Enzo Beneo, now director of the Geological Survey of Italy, to investigate the oil prospects of the island. As the result of his investigations and recommendations the company took several permits.
Early in 1950 the Sicilian Government enacted petroleum laws permitting the leasing of large areas by private companies. Shortly thereafter several foreign and domestic companies applied for prospecting permits and began exploratory work. Among the most active are the Mediterranean Oil Company, composed of 35 per cent Macmillan and 65 per cent American International Fuel (Gulf), Anglo Iranian Oil Company, and Ente Nazionale Metano. These three companies have been occupied in surface geological studies, followed in some places by scout boring and gravimetric surveys. Test wells will be drilled by the Mediterranean Oil Company and other permit holders in 1953 and 1954.
The Sicilian Government has withdrawn three large areas, which are being surveyed by geological parties and two Schlumberger crews employed by the Sicilian Government and under Beneo's direction. The Schlumberger crews are making telluric electric surveys which will be followed by seismic explorations. It is claimed that after these surveys are completed the reserved areas will be leased to competent companies for development.
WEST COAST BASINS
All but the most northerly of the west coast basins are small embayments of Quaternary sediments overlying older formations in the lower course of major rivers. In the Albenga Basin highly disturbed Upper and Lower Tertiary strata are exposed between mountain ranges of Mesozoic limestones. ARDOR, a subsidiary of the Italian insurance company--Riunione Adriatica di Sicurta--took four permits in this area in 1950.
Permits on the Volturno and Sele basins are held by Soc. Meridionale Metano (SME). The Western Geophysical Company made seismic surveys of these permits in 1951. SME plans to drill two exploratory tests in 1953 if drilling rigs can be obtained. Soc. Dalmine holds a permit on the Val d'Arno Basin.
Italian proved petroleum reserves are estimated at one million metric tons of oil and 75 billion cubic meters of gas.
The Po Basin undoubtedly will yield additional gas reserves from Upper Tertiary and Quaternary formations in central and eastern parts of the basin. Two deep tests in the western end of the basin in 1952 were disappointing. Recent exploratory wells in the eastern part of the basin struck large flows of gas in the Pliocene at Corregio, Ravenna, and Imola. The first two discoveries have been sufficiently exploited to prove the presence of large accumulations of gas.
Exploratory drilling to date has furnished little information on the potentiality
of Lower Tertiary and Mesozoic formations in the Po Plain. The Oligocene has been penetrated in only two or three wells and the Eocene and Upper Cretaceous possibly in only one. It is apparent, therefore, that the chief oil-bearing formations in the pre-Apennine foothill fields remain unexplored in the Po Plain. Although these formations lie at depths greater than 4,000 m. in the central Po Plain gas fields, there are structures such as Colombano, Casalpusterlango, and and Ferrara in which they can be reached at 1,200-2,500 m. However, the area offering the best oil and gas prospects in pre-Upper Tertiary formations lies along the southern margin of the Po Plain where Lower Tertiary and Cretaceous formations obviously contain source material. In that area the more calcareous members p obably are sufficiently fractured to serve as reservoir rocks and are definitely sealed in by a thick cover of Upper Tertiary clays and shales. The complicated folds involving the plastic Upper Tertiary formations there may be replaced by simpler folds in the more massive underlying formations.
Pliocene and Miocene formations beneath well defined seismic structures in the eastern half of the Marche-Abruzzi province offer fair oil and gas prospects. Mesozoic formations also warrant testing on major folds, such as the Mt. Conero anticline and those in the western and southern parts of the basin.
In the Lucanian province Eocene and Cretaceous formations should be tested throughout the central and eastern parts of the basin wherever stratigraphic or structural traps occur. The recent discovery of Pliocene gas in the Montecatini test south of Crotone is an encouraging development.
The Campanian basin looks promising for minor accumulations of oil and gas in Miocene and older strata on seismic structures in central and southern parts of Latina Valley.
Accumulations of oil and gas will probably be discovered in southern Sicily. Tertiary formations occupying surface and seismic structures south and southeast of Caltanissetta and Lower Tertiary and Mesozoic reef limestone underlying the Ragusa plateau offer the best prospects.
The three southern of the west coast basins may yield gas, but probably no oil. The Albenga basin offers little promise for the discovery of either oil or gas.
Undiscovered oil and gas reserves in Italy's principal basins may exceed all expectations or they may be of no great importance outside of the Po Basin. At any rate, there are few if any geological provinces in Europe that offer as promising prospects, and full exploration is warranted at least in the five major basins.
Initial stages of exploration are well advanced. Geological studies and reconnaissance geophysical surveys by magnetometer, gravimeter, and telluric current outfits have been made of most of the basins. Seismic surveys have been carried out or are in progress in all the basins except possibly Sicily and Albenga. AGIP has had eight to ten seismic crews working in the Po Basin and eastern Italy for several years. Private companies also have had their holdings investigated by American and other foreign geophysical companies.
The next step--exploratory drilling--has been delayed because of uncertainty about petroleum laws and the scarcity of drilling rigs. As these handicaps are removed exploratory drilling in all parts of Italy and Sicily will be increased.
The preparation of the report on which this paper is based was made possible by the assistance of many persons. Official and technical staffs of oil and gas companies operating in Italy and the heads of Italian Government and provincial bureaus related to the oil and gas industry have been very cooperative. Consulting geologists and engineers in charge of geophysical and drilling crews and business men interested in the development of Italy's natural resources have all contributed much information.
To all these individuals the writer here expresses his thanks for their assistance and courtesies, also for permission to use information that less cooperative persons and organizations would hold confidential.
Among the geologists, engineers, and administrative officials of oil and gas companies who have made the chief contribution to the investigation are the following.
Azienda Generale Italiana Petroli (AGIP), Milan
Carlo Zanmatti, general manager
Tiziano Rocco, chief of Division of Geophysical and Geological Surveys
G. Facca, chief geologist
Societa Petrolifera Italiana (SPI), Farnovo Taro
A. L. Owens, general manager
Siro Bronzini, engineer
D. A. Greig, former resident geologist, now on the geological staff of Standard Oil Company
American International Fuel and Petroleum Company (Gulf subsidiary), Rome
Hollis D. Hedberg, Gulf Corporation's chief geologist, New York
Niccolo Pignatelli Aragona, general manager, Rome
Carlo Marchetti, geologist in charge of field explorations in Sicily
The writer is greatly indebted also to the following Italian geologists and engineers who are either directors of Government surveys and mining bureaus or professors of geology in Italian universities.
Enzo Beneo, director, Geological Survey of Italy, Rome
Dino Rossi, director, Government Hydrocarbon Office, Bologna
Giovanni Bulgarelli, director, Department of Mines, Padova
Mario Anelli, professor, Parma University
G. Merla, professor, University of Florence
Roberto Signorini, professor, Rome University
The following also contributed important information.
Carlo I. Migliorini, consulting geologist, Florence
Italo Veneziani, consulting engineer, Bologna
Gino Minucci, director, Societa Idrocarburi Nazionali, Florence
Alberto Stefano of Societa Montecatini, Milan
J. V. Brennan, petroleum attache, U. S. Embassy, Rome
Felix Gillieron, consultant, Mutual Security Agency, Rome
Professor Piero Sacerdoti, director general, and Gustavo Volterra, secretary, Riunione Adriatica di Sicurta, Milan and Rome
Renzo Piga of Societa Richerche Petrolifere Meridionali, Rome
Mario Osella, director, Azienda Metandotti Padani, Padova
Alfred Giarranda, director, Consortia Italiana Metano, Padova
Alfredo Mazzoni, director, Larderello Sp. A., Florence
Michael A. Boccalery, vice-president, Western Geophysical Company International, Milan
Fred Nelson and Donald O. Nichols, in charge of Dunlap and Graham Drilling Company crews at Crotone, Calabria
Walter Elliot, general superintendent of Santa Fe Drilling Company at Cortemaggiore
Franco F. Fenzi of Macmillan Petroleum Company, Rome
E. D. Hardison, petroleum engineer, Bureau of Mines, Washington, D. C.
C. E. Anderson, petroleum engineer, Bureau of Mines, Washington, D.C.
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