ABSTRACT

Basic geological information on individual oil and gas fields are not commonly found in the geologic literature. This study is designed as part of a series of field studies being conducted at the Louisiana Geological Survey to fill this need. Deltaic depositional environments, often in conjunction with structural elements, have created significant oil and gas accumulations in South Louisiana, and the Breton Sound area (Fig. 1) is no exception. The three fields in this study, Breton Sound Blocks 37, 39 and 49 are shown in Figure 2. Data presented in this paper for each of these fields includes only a type log, a structure map and a production graph, due to space limitations.

The Breton Sound Block 37 field discovery well was drilled to a depth of 8,865 ft and completed in August, 1966. Since that time 23 wells have been permitted. The field is located on a west-northwest trending anticlinal structure bisected by an east-northeast striking south dipping normal fault. Twelve producing zones in this field range in depth from 2,650 ft to 7,802 ft and are of Middle-Upper Miocene age. Block 37 has produced (1966-1998) 15,209,364 mcf of gas, 1,905,981 bbls of oil, 105,202 bbls of condensate, and 3,087,911 mcf of casinghead gas (Fig. 3, 4, 5).

The discovery well in Block 39 field was completed in July 1966 and has a total depth of 13,100 ft. Ten wells have been permitted, and the two productive zones in this field range in depth from 6,270 ft to 7,538 ft (Middle-Upper Miocene). A type log for the Block 39 field is shown in Figure 6, and a structure map for the 6600 sand in this field is shown in Figure 7. The field has a northeast-striking down-to-the-basin fault with a small horst block upthrown to this fault which is joined from the west by an east-west striking and north dipping fault. This gas field has produced 1,629,465 mcf gas through the end of 1998 (Fig. 8).

The Breton Sound Block 49 field discovery well drilled to a depth of 10,082 ft was completed in March 1961 and nine wells have been permitted. The field has two productive zones ranging in depth from 8,836 ft to 11,344 ft (Middle Miocene) and a domal structure broken by an east-northeast and southeast-striking fault. Field production totals (1961-1998) are 54,613 mcf of gas, 202,147 bbls of oil, 1,692 bbls of condensate and 1,865,418 mcf of casinghead gas (Fig. 9, 10, 11).

The data compiled for Breton Sound Blocks 37, 39, and 49 in this study again shows that within the fluvio-deltaic deposits, the deltaic zone, especially the downdip region, forms an ideal fairway for hydrocarbon generation and entrapment. In such an environment, further field development could be successfully achieved if the vertical sequences of superposition of depositional events and depositional packages are examined. Different genetic types of sand bodies are characterized by different sizes, shapes, orientation, lithology, transmissibilities and lateral and vertical depositional associations. Hence a detailed mapping of reservoir geometry in fields presented in this compilation and other similar areas is likely to reveal more subtle unexploited stratigraphic traps and perhaps other combination traps. Studies of this type bring together all the necessary basic information for future exploitation of the existing oil and gas fields. The subsurface data so compiled enables the geologist and geophysicist to extract the necessary information and clues for recognition and understanding of the prospects and their regional settings.