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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 25 (1941)

Issue: 10. (October)

First Page: 1880

Last Page: 1897

Title: High-Pressure Yates Sand Gas Problem, East Wasson Field, Yoakum County, West Texas

Author(s): Alden S. Donnelly (2)

Abstract:

High-pressure Yates sand and "Brown lime" gas or "Previous HitairNext Hit" has caused casing with ample collapse safety factors to collapse in drilling and completed wells in the Wasson field. Data are presented on: the history and geologic occurrence of the gas; structural and areal location of the part of the field where the gas is encountered; theories about the cause of the collapsed casing with geologic and other supporting evidence; and various methods used to counteract this hazard, including equipment, calculations, and procedures developed in squeeze cementing with salt-water cement, setting of "stub" strings of casing for permanent control of the gas. Operations are given in such detail as to be applicable, with minor changes, to other fields confronted with similar problems.

JSABSTRACT>

Text:

INTRODUCTION

The high-pressure lean or non-inflammable gas at shallow depths in the Permian Yates sand of the Wasson field has caused formations to cave, resulting in collapsed casing in both drilling and completed wells. Under present low allowables and long well pay-outs, drilling costs were one of the important factors to be considered in combating this hazard. To develop a safe, sure drilling program and casing pattern at minimum cost required a study of the geologic section, the manner in which it drilled, and a use of the drilling engineering principles that were particularly applicable to the subsurface conditions encountered.

This article gives the calculations and the different methods employed. It has been the intention to compile a record containing sufficient detail that the experience gained on these leases in the Wasson field would be available for similar problems in other localities.

OCCURRENCE

The Yates sand gas occurs near the top of the Yates sand (Whitehorse, Permian) at an average depth of 3,120 feet. Not all wells in the Wasson field (Fig. 1) encounter this gas. The geological section shown in Figure 2 indicates the relationship between the gas and the formations penetrated.

The gas is lean but inflammable in the central and west parts of the Wasson field. In the east and northeast part the gas is non-inflammable, 97 per cent nitrogen and is called "Previous HitairNext Hit" by the field men. It has a

End_Page 1880------------------------------

Fig. 1. TOP OF YATES SAND WASSON FIELD YOAKUM COUNTY, TEXAS

End_Page 1881------------------------------

Fig. 2. GEOLOGICAL SECTION Honolulu-Cascade No. 5-741 Willard

Fig. 3. TIME RATE OF DRILLING No. 5-741 Willard

Fig. 4. CASING PROGRAM FOR SQUEEZE CEMENTING No. 7-741 Willard

Fig. 5. Honolulu - Cascade No. 5-741 Willard

End_Page 1882------------------------------

suffocating effect on men. Pressures reach a maximum of 2,800
psi., averaging 1,800-psi. in most of the wells that have given trouble. Volumes that have been gauged by spot tests with a manometer range from 2 million to 15 million cubic feet per day.

HISTORY

Development came south from the Honolulu Oil Corporation and Cascade Petroleum Company's Bennett No. 1-678 discovery well in NE. ¼ of Sec. 678, completed in 1935 (Fig. 1). The Previous HitairNext Hit was not present in the few cable-tool wells on the north edge of the field. As drilling progressed south, the Previous HitairNext Hit, if present, was under too low a pressure to unload the holes of 10-lb./gal. salt-water mud; consequently, it did not present a serious drilling problem. The casing program in use was 200+ feet of surface casing and 4,800± feet of 5½-inch (15-lb. or 17-lb.), or 7-inch (24-lb. or 26-lb.) oil string. As the oil "pay" is porous Permian dolomite with very little sand, it is usually left open.

Crump and Black's Bennett wells, Section 695, in the northeast part of the field, were the first to encounter the Yates sand Previous HitairNext Hit. The pressure was not sufficient to unload the holes but did blow out some of the mud after trips when the Previous HitairNext Hit bubble came around out of the drill pipe. It was not necessary to run an intermediate string of casing through the redbeds to the top of the anhydrite at 2,400± feet. Crump and Black drilled 11-inch holes to 3,200 feet in their last two of four wells, thereby increasing the volume of the hole and decreasing the velocity of the mud column should the Previous HitairNext Hit start to unload the hole. The procedure was successful; the wells did not unload, principally because of the low pressure in the Yates Previous HitairNext Hit.

During December, 1938, the Devonian Oil Company's Hodges No. 1, S. ½ of Sec. 696, encountered the Previous HitairNext Hit at 3,140-3,160 feet in large volume under a pressure of approximately 2,800-psi. as shown by the amount of weighted mud necessary to kill the Previous HitairNext Hit. Neither the Devonian nor any of the other operators in this part of the field expected the volume and pressure of Previous HitairNext Hit encountered. The only casing in the hole was 200+ feet of 10 3/4-inch surface casing to protect the upper domestic water. The hole unloaded and the mud cake was blown off the redbeds above the salt section releasing the intermediate redbed waters that occur at the following average depths: 350 feet, 975 feet, 1,875 feet, and 2,050 feet. These waters assisted the Previous HitairNext Hit in cutting and blowing out the redbeds. Approximately carloads of redbeds and mud were blown out, the flow often going over the crown blocks. The Devonian well was killed with 176 tons of Baroid, and 50 sacks of cement were spotted from 2,350 feet to 2,440 feet before reaming to

End_Page 1883------------------------------

Fig. 6. HONOLULU "B" 12-804 WILDER WASSON FIELD YOAKUM COUNTY, TEXAS

End_Page 1884------------------------------

run the intermediate string of 7 5/8-inch casing cemented with 500 sacks at 2,370 feet in the top of the anhydrite. At the total depth of 4,870 feet, that is, 230 feet in the limestone, the 5½-inch 17-lb. oil string was cemented at 4,860 feet with 250 sacks of cement. Prior to drilling plug the casing was tested with 600-lb. pump pressure which showed a leak at about 3,240 feet. The casing was Previous HitgunNext Hit-perforated just below this depth and 1,000 sacks of cement squeezed behind it through a cement retainer. The squeeze cement job was successful. At this time it was believed that faulty 5½-inch casing caused the leak and not the formations as was proved later.

During the same month the Texas Pacific's Bennett No. 16, SW. ¼ of Sec. 695, blew out at 3,150 feet with only the usual 220 feet of surface casing. It acted in the same manner as the Devonian well had acted. No attempt was made to plug or complete this T. P. well, which continues to flow Previous HitairNext Hit and water after a year and a half, indicating the large volume of Previous HitairNext Hit present in the Yates sand.

The E. ½ of Sec. 741, which adjoins the Devonian lease on the south, had a larger volume of Previous HitairNext Hit under higher pressures, yet the Previous HitairNext Hit ended abruptly along the center line of this section. The Honolulu-Cascade wells in the NE. ¼ of Sec. 741 unloaded over the derrick, but the offset wells 880 feet west on the Mabee lease missed the Previous HitairNext Hit, though it reappeared in the first Mabee well on the east, which is due south of the Honolulu-Cascade wells. This Mabee well was lost and plugged in the Yates sand, because it did not have an intermediate string of casing to hold back the caving redbeds.

The Honolulu-Cascade's Willard wells in the NE. ¼ of Sec. 741 (Fig. 1) were some of the largest gas wells in this part of the field. The problems encountered on this lease are representative of all wells in this part of the Previous HitairNext Hit belt. Because of the completeness and availability of the records, they shall be referred to in this article.

USUAL CASING PATTERN IN YATES Previous HitAIRNext Hit AREA

If there is a possibility of Previous HitairNext Hit in the Yates, the standard practice is to set either 13-inch or 10 3/4-inch surface casing at 200± feet, and 9 5/8-inch or 7 5/8-inch casing in the top of the anhydrite, or in the anhydrite at the base of the main salt (base of Salado) and an oil string of 4,800 feet of Grade H-40 of 7-inch or 5½-inch. The 7-inch being 24-pound or 26-pound and the 5½-inch 15-pound or 17-pound. Occasionally, 300 feet of heavier casing with a higher carbon-content steel, such as Grade N-80, were put in the string so as to be opposite the zone of collapse. As usual, when running a mixed string of casing, the top joint should be the same as the heaviest casing in the string since the increase in weight decreases the I.D. of the casing.

End_Page 1885------------------------------

Fig. 7. CASING HEAD

End_Page 1886------------------------------

CASING SEAT INTERMEDIATE STRING

Care is taken not to drill into the salt before setting and cementing the 9 5/8-inch or 7 5/8-inch casing in the 40± feet of anhydrite cap over the salt. This casing seat is determined from a study of the well cuttings and the time rate of drilling. There have been wells in the Texas-New Mexico Permian basin with casing cemented in the salt section in which the cement and salt behind the shoe joint were cut out by lower gas, and the shoe joint whipped off to fall over into salt cavities and junk the hole. The primary cause of this seems to be that the salt leaches a thin layer of water from the cement and thus destroys the bond at the cement salt contact. The main salt section (Salado) from 2,300 feet to approximately 3,100 feet stands up well in uncased cable-tool holes. Experie ce has shown that large cavities are washed out by the rotary drilling mud until the drilling fluid becomes a saturated salt solution which weighs about 11 lb./gal. and contains very little mud.

BRIDGING

In all the Previous HitairNext Hit wells the holes bridged from 100 feet to 150 feet below the top of the Previous HitairNext Hit. When going back into the hole, it was necessary to drill or wash out one or more redbed and salt bridges from 3,200 feet to 3,250 feet. In several wells the oil string had to be circulated and occasionally rotated through these bridges. The shoe used was a Baker rotary saw-tooth shoe with the teeth cut down to 3/4-inch in length, beveled for ¼-inch at a 45° angle, and hard-surfaced in a machine shop. This shoe was effective for drilling out bridges whereas before the bevel was used there was a tendency to start off in a new hole in one of the many large cavities. A few wells had to pull the casing, drill the bridges with the rotary, and re-run the casing. Had the present down-whirler t pe shoes been known at that time, they might have been effective for washing out the bridges.

In Section 804 on the south, the water-hammer, after a bridge went out, had sufficient force to raise 3,100 feet of 3-inch drill pipe and a Hydril rotary table one foot, bursting a previously tested 3,000-psi. drilling head.

MUD

Because of the salt section drilled and the resultant almost saturated salt brine, mud weight could be kept at a maximum weight of 11 lb./gal. Previous HitAirNext Hit pressure was often more than 2,800-psi. so 18-lb./gal. weighted mud would have been needed to hold the Previous HitairNext Hit. As often happened, a bridge would probably form while changing the bit, the pressure build up below it, then break through with a terrific water-hammer and blow the weighted mud over the country-side. In the

End_Page 1887------------------------------

lower-pressure Previous HitairNext Hit wells it was found that the Previous HitairNext Hit would bubble through 10½- to 11-lb./gal. salt water without unloading, whereas it would build up sufficient pressure and volume under mud to unload the hole. Drilling fluids were not always watched as closely as they should have been. Later developments showed the most desirable drilling fluid to be a saturated salt solution. Ground salt was dissolved in the mud before any of the salt section was drilled, thus preventing the fluid from dissolving the large cavities in the salt section. Zeogel, or bentonite with 1 to 5 per cent of lime, was used where the Previous HitairNext Hit pressures were sufficiently low that the Previous HitairNext Hit could be partly or completely mudded off.

COLLAPSED CASING

Collapsed oil strings of casing became a regular occurrence in this part of the field after the Devonian casing collapsed in December, 1938. In most of the wells the casing collapsed either while the cement was setting or after the plugs had been drilled and 30-50 feet of new hole made. During March and April, 1940, the oil strings collapsed in several wells that had been completed for more than a year. In all such wells the tight place or dent in the casing was at the same stratigraphic point in the section, at a depth of 3,240± feet, or approximately 120 feet below the top of the Yates Previous HitairNext Hit. It has been possible to predict the depth of the tight place in the casing within a few feet from the well cuttings and the time rate of drilling. Figures 2 and 3 show the anhydrite shell th t acts as a buttress against which the casing is bent or dented as a result of caving beds sloughing off in the large washed out salt and sand cavities. Another explanation is that the salt beds and salt cement in the sands and shales above and below this anhydrite shell are washed out, permitting the shell itself to break off and move against the casing. Surveys and casing recovered show a sharp kink rather than a long dog-leg as would result from loose unconsolidated cavings settling on all sides of the casing.

DETAILS OF REMEDIAL PROCEDURE WHEN CASING COLLAPSED

The Honolulu-Cascade's Willard No. 5-741 (Figs. 1, 2, and 3) in the northeast corner of Sec. 741 is typical of wells with collapsed casing. The 9 5/8-inch casing was cemented with 250 sacks at 2,375 feet, 30 feet below the top of the anhydrite. Previous HitAirNext Hit encountered at 3,115 feet unloaded the hole of 10-lb./gal. salt-water drilling fluid. No foreign salt had been added to the mud; the salt came from the drilling of the salt section. After each trip the well bridged from 3,210 feet to 3,300 feet. The bridges were 10-60 feet thick. While running the 7-inch casing it was impossible to circulate through a bridge at 3,220 feet;

End_Page 1888------------------------------

the casing was pulled out of the hole, the bridges drilled with the rotary, and the casing re-run with a guide shoe. As the original rotary saw-tooth shoe had not been beveled, it had probably started to drill a new hole in one of the cavities when the casing was rotated and circulated in an attempt to drill through the bridge. The second attempt to run the casing was successful after pumping through bridges from 3,142 feet to 3,309 feet. The hole unloaded constantly through the annular space. The 7-inch 24-lb. seamless casing was cemented at 4,844 feet. The first 100 sacks of the 300 sacks of cement used were mixed with 2 per cent aquagel on the rare chance that some of it would go into the Previous HitairNext Hit formation. Cement slurry was kept at 16 lb./gal. Previous temperature surveys showed that he top of the cement is at about 4,150 feet, the middle of the Yoakum "Brown lime," whether 200 or 600 sacks of 16-lb./gal. cement slurry are used.

Cement set for 84 hours. Casing was tested for 30 minutes under 600-psi. pressure; there was no drop. Plugs were drilled and 37 feet of new hole drilled to 4,881 feet. While coming out of the hole the bit hung up at 3,242 feet. A new 6¼-inch bit would not go down through this tight place. The naked 4 5/8-inch O.D. drill collar went 3 feet, slacking off a maximum of 6 points of weight. The total tight place was from 3,230 feet to 3,245 feet. After 30 hours the same drill collar would go only 18 inches, slacking off 6-8 points of weight. The drill collar was turned 6 turns, it backed up 1½ turns, and carried marks for 10 inches, indicating a sharp dent rather than a dog-leg. Casing had been carefully tallied in feet and hundreds of feet; from this, the tight place was found to be in the center of a joint and not in a coupling.

The survey shown in Figure 5 was run. It verified the theory of a sharp dent or kink in the casing. The 3-inch O.D. instrument in the 7-inch casing gave a modified and straighter picture of the hole than existed.

Casing was Previous HitgunNext Hit-perforated with 5 holes from 3,264 feet to 3,265 feet. Cement retainer was run on tubing to 3,229 feet and circulation established through the holes. Cement was mixed with a 5 per cent by weight saturated salt solution. Pressure on the casinghead between the 9 5/8-inch and 7-inch was maintained at 600-psi., the cement went in at a surface pump pressure of 400-psi. for the first 1,250 sacks when it began to increase steadily and the gas volume from the bleeder on the casinghead began to decrease, indicating that the cement was going into the "Previous HitairNext Hit" bed. The casinghead was then shut in. An additional 473 sacks of cement were squeezed through the tubing, reaching a maximum pump pressure of 1,600-psi. Pumps were slowed while

End_Page 1889------------------------------

flushing the cement out of the drill pipe, thus keeping the pump pressure on the tubing at 1,600-psi. Excess cement was circulated out of circulating joint from casing and tubing; circulating joint closed and retainer tested. Gas or "Previous HitairNext Hit" pressure on the 9 5/8-inch × 7-inch casinghead had decreased to 590-psi. Cement slurries and salt mixtures were recommended and maintained by Harry Sessums, cementing engineer of the Trinity Cement Company.

Cement set 72 hours, the cement retainer was drilled with 6¼-inch bit, and as the bit started to stick at 3,240 feet, 5 3/8-inch bits were used to complete the hole. The smaller bits drilled out the cement without any trouble indicating that the pressures and cement had partly straightened the bent place in the casing, since the 4 5/8-inch drill collar had hung up prior to the squeeze job. Casing was tested for 30 minutes before and after drilling cement with 600-psi. pump pressure. The cement job was successful as there was no pressure drop in either test.

DEEPER Previous HitAIRNext Hit

To complicate an already bad drilling situation, later wells at the south in the vicinity of Sections 804 and 825 began to have Previous HitairNext Hit blowouts in the porous dolomite and sand beds at the top of and in the Yoakum "Brown lime," an upper member of the Queen sand (average depth to top of Yoakum brown limestone 4,100 feet).

This became known as the "4,100-foot Previous HitairNext Hit" (Fig. 2). Pressures and volumes were about the same as the pressures and volumes of the Yates Previous HitairNext Hit. If the shallower Yates Previous HitairNext Hit did not occur or had been shut off, this lower Previous HitairNext Hit, because of its greater depth, could be controlled in most wells by the weight of the mud column.

The early rotary wells drilled in the Previous HitairNext Hit area east of the center line of Section 804 did not have Previous HitairNext Hit in the 4,100-feet or "Brown lime" as have later wells. The porosity may or may not be connected over the entire field. Cuttings from the few cable-tool wells in the northeast part of the field appear to have the same porosity in this bed but it is dry, containing no oil, gas, Previous HitairNext Hit, or water. The theory has been advanced that the lower Previous HitairNext Hit has migrated from the upper Yates section since it did not appear until after the Yates Previous HitairNext Hit had been penetrated in several wells completed with only two strings of casing. This theory can be supported by the following evidence: the redbeds from 1,500 feet to 2,000 feet are known to cave and effectively freeze casing a short time after it is cemented, leaving the lower porous beds as the only avenue of escape for the Yates Previous HitairNext Hit, thus permitting the downward movement. Most of the wells with the upper redbeds cased off had

End_Page 1890------------------------------

closed 3,000-psi. to 6,000-psi. test casingheads that would also permit the downward migration. The Yates sand itself appears to be porous throughout the field but contains Previous HitairNext Hit or gas in only a part of the field, not necessarily in those areas that are the highest structurally. Rather, it is limited to the crest of the north-northeast Yates axis near the east edge of the field, indicating that the porosity may be sealed locally, thereby trapping the Previous HitairNext Hit. The seal could be accomplished by the varying amount of shale in the sand and the salt cement seen in the few cores of the Yates. This salt cement is washed out of the cuttings in both rotary and cable-tool samples leaving what appears to be a porous sand throughout the field.

On the southeast edge of the field in the vicinity of Section 824 the lower or 4,100-foot Previous HitairNext Hit is present with sufficient volume and pressure to unload the hole if a trip is made immediately after the Previous HitairNext Hit is penetrated and before enough additional hole has been drilled to thoroughly mud off the Previous HitairNext Hit. This unloading was avoided by keeping the mud in good condition and putting on a new bit just before the Previous HitairNext Hit zone was to be drilled. The bit was not changed until the bottom of the hole was at least 50 feet below the Previous HitairNext Hit. Had the bit worn out before then, the hole would have been circulated near bottom for two hours or more before coming out. The Yates Previous HitairNext Hit is either absent in this area or its pressure and volume are so low that it is not noticed. It is the writer's belief that the lower Previous HitairNext Hit is in place, is separate and distinct from the Yates Previous HitairNext Hit and has not migrated downward from the Yates sand. The somewhat spotted occurrence of the lower Previous HitairNext Hit is caused by disconnected porosity. Unfortunately, there is no record of coring through this part of the section. Cores would possibly show disconnected porosity in the wells that have no Previous HitairNext Hit. Analyses of the two gases would probably establish their relationship, as the Permian gases above the "top of the lime" (San Andreas in this field) ordinarily have a decreasing nitrogen content with depth. Below are two analyses of the upper Previous HitairNext Hit.

PODBIELNIAK ANALYSIS, YATES GAS

SECTION 696, BLOCK D

                              Percentage
Methane                            6½
Ethane                              3/10
Propane                             2/10
Butane                              3/10
Pentane                             1/10
Nitrogen and inert gases          92½
No helium from spectroscope
analysis

GAS IN SECTION 894, BLOCK D

Nitrogen   97
End_Page 1891------------------------------

DRILLING PROCEDURES USED TO PREVENT COLLAPSE OF CASING

With the appearance of the lower Previous HitairNext Hit it became necessary to develop new methods of drilling the wells in the "Previous HitairNext Hit belt." The collapsed casing was not caused by using casing with too low a collapse safety factor. Naturally, it was realized that the use of additional strings of casing and the resulting larger-size holes as are used in cable-tool holes would be the simplest and surest insurance against collapsed oil strings. Unfortunately, the additional casing seemed to be by far the most expensive cure.

The most conservative drilling procedure at all times is to take care of each troublesome zone as it occurs rather than to try to take care of several together at the same time. In at least one well it was impossible to run casing with both Previous HitairNext Hit bodies unloading the hole.

It was decided that the least expensive method would be to cement the intermediate string of casing in the anhydrite at the base of the salt and squeeze-cement the Previous HitairNext Hit. To select the casing seat for this intermediate string required an exact correlation of the time rate of drilling and sample logs of offset and near-by wells. This work has been done by a geological engineer thoroughly familiar with the changing geological section, the drilling personnel, sampling and drilling equipment. The importance of the correct selection of this casing seat becomes very evident when one realizes that to drill too deep and penetrate the Previous HitairNext Hit horizon with the redbeds open means a lost hole or at best an expenditure of $7,000 to $10,000 for weighted mud to regain control of the well. To set the casin too high would result in the shoe joint being in salt instead of the competent anhydrite shell at the base of the main salt. The geologist's personal reaction can be compared with smoking a cigarette on a keg of powder.

After cementing and testing the intermediate string of 9 5/8-inch or 7 5/8-inch casing at 3,070± feet, the wells were drilled to 60± feet below the top of the Previous HitairNext Hit into an anhydrite shell. A cement retainer was set in the bottom of the intermediate string (Fig. 4). It was found that the retainers could be consistently set in the bottom joint without damage, if a float shoe were used on the casing, instead of a guide shoe with a float collar on top of the first joint. The retainer occasionally hung up in the float collar thereby breaking off the brittle slips. This was caused by the smaller size of the hole drilled through the float collar by a bit whose O.D. was necessarily smaller than the I.D. of the casing.

The Previous HitairNext Hit bed was squeezed in stages with 16+-lb./gal. cement slurry mixed with a 5 per cent by weight saturated salt brine to enable the

End_Page 1892------------------------------

cement to form a bond with the salt section and also to secure the jelling effect with the resulting high angle of recline in the larger cavities. The drill pipe was connected to the retainer through a circulating joint. Pressures of 1,700-psi. to 3,200-psi. were usually needed to break down the formation. The first batch of cement circulated varied from 150 sacks to 200 sacks, the drill pipe and casing were flushed, and the cement allowed to set for 6 hours. Additional small batches of cement of about 25 sacks each were squeezed into the formation until the resulting pressure was in excess of the formation break-down pressure, indicating the formation was sealed. The seal was usually accomplished with a total of 350 sacks of cement in three batches. One well required four squeeze job of three batches each and a total of 2,200 sacks of cement before the caving formations and Previous HitairNext Hit were shut off. Including day work, cementing service, cement, cement retainer, and rental on the circulating joint, the average cost of a squeeze job was found to be $1,000. In a few wells the drill pipe whipped the cement squeezed into the formation until it fractured and allowed some of the Previous HitairNext Hit to come into the hole before the oil string of casing was run and cemented. Where sufficient Previous HitairNext Hit was liberated to unload the hole additional squeeze jobs were used until the Previous HitairNext Hit was again sealed off. A single squeeze job of three stages was successful on three wells but on the fourth it was necessary to perform three different squeeze jobs. The cost of three squeeze jobs approached the cost of an add tional string of casing. As already mentioned, additional casing would be far more desirable, dependable, and a much simpler procedure, free of the danger present in a squeeze job of cementing a string of drill pipe in the hole.

TWO-STAGE CASING CEMENT JOBS

Two-stage cement jobs were about 50 per cent successful in the areas of lower pressure and volume where it was possible to run casing with the Yates and Yoakum brown limestone airs occasionally accompanied by gas from the gas cap unloading the hole. Many operators object to stage cement jobs except as a remedy for damaged casing, because of the holes that are either shot into or left in the casing with only cement to close them. On one Wasson well it was necessary to cement the ports twice for the second stage. A stage cementing collar now on the market has check valves in the ports which would remove this objection if the ports are not held open or fouled by cement. The ports are run 50 feet below the anhydrite shell at 3,240 feet (top of Seven Rivers formation) where the casing usua ly collapses. The

End_Page 1893------------------------------

further objection to stage cementing in this field has been that no tension can be slacked off the casing after the cement around the shoe has set and before the upper stage job is performed unless 24 hours are allowed to elapse between the stages; this is enough time to permit the casing to collapse. Too much tension in the casing between two stages of cement would increase the possibility of collapse after the heat of reaction of the cement has been dissipated in the formation and the casing has contracted. Caving beds against a taut string of casing would probably part the casing.

INTERMEDIATE LINER

Owing to the partial success and potential cost of formation squeeze jobs, it was decided to run another string of casing if the cost of the casing could be decreased. In the Seminole field, Gaines County, Texas, the Amerada set 9 5/8-inch casing at the base of the salt as for a formation squeeze; drilled through the Previous HitairNext Hit and the caving zone below; then ran a string of 7 5/8-inch casing to bottom with a left-hand back-off nipple 200 feet above the shoe on the 9 5/8-inch casing. The 7 5/8-inch was cemented with 50 sacks of cement by the usual pump and plug method. This procedure was successful on the one well where it was used. With this casing and cement program, it is necessary to leave all the 7 5/8-inch casing in the hole until the oil string of 5½-inch is run and cemented in o der to prevent the lower 4,100-foot Previous HitairNext Hit from combining with the Yates Previous HitairNext Hit at 3,100± feet and unloading, bridging, and tearing up the hole. After the 5½-inch casing is cemented, it is necessary to turn loose of it to strip out the 7 5/8-inch casing above the left-hand back-off nipple. When a slender flexible string of casing such as 5½-inch is allowed to rest on the cement around the shoe with all tension from the casinghead released there is danger of its falling into a salt cavity and kinking. This has happened so often in the Wasson field that nearly all company field men have instructions not to turn loose of any string of casing. If the 7 5/8-inch casing does not part at the nipple, it is impossible to run a casing cutter.

To overcome these objections and pull the 7 5/8-inch above the back-off nipple before running the 5½-inch casing it was decided to squeeze cement between the 9 5/8-inch and the 7 5/8-inch casing with 200 sacks of cement and rid the annular space of the Previous HitairNext Hit. This was accomplished by carefully checking the volumes, displacements, and pressures of casing, hole, and pumps. A graphical representation is shown in Figure 6, with the Amerada bomb temperature survey for location of cement as a check on the following tabulated calculations and instructions:

End_Page 1894------------------------------

INSTRUCTIONS FOR WILDER "B" NO. 12-804:

SQUEEZE JOB BETWEEN 7 5/8-INCH CASING AND 9 5/8-INCH CASING WITH LEFT-HAND NIPPLE 583 FEET ABOVE SHOE, TO PERMIT PULLING OF 7 5/8-INCH CASING BEFORE RUNNING 5½-INCH OIL STRING

After the first joint of the 7 5/8-inch is out of 9 5/8-inch casing start circulating ahead of each joint of 7 5/8-inch, do NOT wait until casing freezes before circulating.

DEPTH OF 7 5/8-INCH SHOE 3,318 feet.

Start cement in hole after circulating completely around the casing.

TOP OF LEFT-HAND COLLAR, 2,735 feet. TOP OF FLOAT COLLAR, 3,283 feet. TOP OF HYDRIL CASING, 3,014 feet.

1 sack fills 4.12 feet inside 7 5/8-inch casing. 200 sacks fill 824 feet inside 7 5/8-inch casing. Cement STARTS AROUND SHOE when plug is at depth of 2,494 feet. (Bottom of 7 5/8-inch casing minus 824 feet.) START BLEEDING 9 5/8-inch × 7 5/8-inch casinghead.

1 sack fills 10.9 feet in annular space between 7 5/8-inch and 8 3/4-inch hole.

SHUT IN 9 5/8-inch × 7 5/8-inch casinghead when cement is up 400 feet in annular space or when plug is at a depth of 2,642 feet. (Bottom of 7 5/8-inch casing, 3,318 minus 676 = 2,642 feet.)

Pressure on cementing pump on 7 5/8-inch should rise about 400-psi.

MAINTAIN EQUAL PRESSURES ON 9 5/8-inch casing head and on 7 5/8-inch casing with TWO cementing pumps, pressures will equalize at from 1,500-psi to 2,000-psi.

Calculation for plug depth:

400 feet annular space ÷ 10.9 feet/sack equals 36 sacks; 36 sacks × 4.12 feet/sack equals 148 feet; 824 feet minus 148 feet = 676 feet.

BLEED OFF: When plug is about 300 feet above float collar, bleed off 1 barrel of water or fluid from 9 5/8-inch × 7 5/8-inch casinghead which will bring cement up an additional 60 feet in the annular space. After bleed-off, annular pressure will drop to about 1,200-psi. if formation below continues to take cement. Pressure on 7 5/8-inch will increase to 2,000-psi. or more and remain there.

Bleed-off calculations:

[EQUATION]

To raise cement 60 feet in the annular space between casings: 60 × 0.017 = 1.02 barrels to bleed from annular space.

End_Page 1895------------------------------

TEMPERATURE SURVEY: Shut in for 8 hours and run temperature survey to locate top of cement.

The cement is mixed with 5 per cent salt brine. The left-hand collar is on the top of a joint so as to act as an adapter for the 5½-inch oil string (Fig. 6). Experience proved that the left-hand thread should be 10 "V" thread on 8 round thread casing. The 10 "V" thread, though requiring more rotations to break, does not make up as tightly as the 8 round thread, therefore will unscrew more easily, or if necessary the threads will strip before any of the regular 8 round threads on the rest of the string of casing. The 300 feet of 7 5/8-inch O.D. casing in the open 8 3/4-inch hole must have hydril joints, be extreme line casing, or external flush to have sufficient clearance (Fig. 6). The 7 5/8-inch casing on the first well froze at the stratigraphic horizon where the caving occurs 3,150-3,200 feet), but was pumped free in 2 hours. On all later wells the swage was attached and the hole washed ahead of the 7 5/8-inch casing from the time the shoe entered the open hole until the casing seat was reached rather than waiting for the pipe to freeze and then attempting to free it. As in all other upper-hole casing jobs it is desirable to have the shoe joint in a thick competent non-soluble anhydrite shell. This shell can be located by samples and time rate of drilling (Figs. 2, 3, 4, and 6). The 7 5/8-inch casing is run and cemented, suspended from the mandrel set in the bowl in order to squeeze cement. There is no tension available to slack off after the initial set of the cement. Temperature survey is run 8-12 hours after the plug is pumped down. Cement is allowed to se 36-48 hours when plugs are drilled and drilling continued to 20 feet below the gas oil contact or to the selected casing seat. The 7 5/8-inch casing is then backed off and pulled prior to running the 5½-inch oil string. The latter is run in the usual manner and cemented by the pump-and-plug method.

To remove the necessity of replacing the 9 5/8-inch × 7 5/8-inch casing head with a 9 5/8-inch × 5½-inch head after the upper 2,800 feet of the 7 5/8-inch casing was salvaged, a repackable head with Santa Fe coupling and mandrel suspension was used. The only change necessary was to replace the 9 5/8-inch × 7 5/8-inch mandrel and Santa Fe coupling suspension with a 9 5/8-inch × 5½-inch suspension that would fit in the same body or bowl. The 9 5/8-inch × 7 5/8-inch mandrel was used on many wells. The 6,000-psi. forged steel head with Santa Fe coupling as shown in Figure 7 is the type of head used and previously mentioned.

The oil string of 5½-inch was cemented with the usual tension of 3 inches or 1/3 the calculated stretch. This was released after the cement had set.

End_Page 1896------------------------------

There were not as many collapsed oil strings of casing in the wells that used 7-inch, 24-lb. or 26-lb. casing as in the wells completed with 5½-inch, 14-lb., 15-lb., or 17-lb. casing. This indicates that the larger 8 3/4-inch hole does not allow the mud to be blown out with as great velocity. The rapidly moving mud tears up the walls of the hole and causes caving. However, enough wells with both sizes of casing have collapsed to justify the liner in the areas of large Previous HitairNext Hit volume and pressure.

CONCLUSION

The drilling and casing method here described has been found very satisfactory for the following reasons: the trouble is taken care of as it occurs; the dangerous part of the hole is held back by a concrete and steel conduit; should the cement rise above the back-off nipple as would be shown in a temperature survey (Fig. 6), the casing can be cut with an expanding mill for about $200 and the major part of the 2,800 feet, or approximately $4,000 worth, of 7 5/8-inch salvaged; it is not necessary to turn loose of the slender oil string to strip the 7 5/8-inch casing; the well is protected for its long life of sour-crude production, as is indicated by the present low allowables. The Previous HitairTop, or gas, a potentially valuable source of energy, is conserved and confined to the zones in which it o curs, ready to be tapped for future use.

ACKNOWLEDGMENTS

The writer is indebted to R. K. DeFord for helpful criticism of the manuscript, Harry Sessums, cement engineer for the Trinity Cement Company, S. C. Scheuber, petroleum engineer, Amerada Petroleum Corporation, D. M. Evans, district geological engineer, and W. L. Morrison, field superintendent of the Honolulu Oil Corporation, for technical and practical assistance, and to the Honolulu Oil Corporation for permission to publish this article.

End_of_Article - Last_Page 1897------------

Acknowledgments:

(2) Texas division geological engineer, Honolulu Oil Corporation.

Copyright 1997 American Association of Petroleum Geologists

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