Bobby L. Jones

Regional Chronostratigraphic and Depositional Hydrocarbon Trends in Offshore Louisiana State Waters

ABSTRACT Successful exploration for hydrocarbons in the Northern Gulf of Mexico basin requires a systematic understanding of hydrocarbon producing trends, sand body geometries and the geologic, engineering and reservoir parameters of the producing sands. This study forms part of the Offshore Atlas project in progress at the University of Texas at Austin, Bureau of Economic Geology, Texas, in cooperation with the U.S. Department of Interior, Minerals Management Service, and the Geological Survey of Alabama, and is aimed at achieving this goal. In this study, 26 chronozones were grouped into 12 sub-groups. The chronozones were defined on the basis of the benthic foraminiferal biostratigraphic zones and were correlated across the Gulf using well and seismic data and were projected from the Federal offshore into the State waters. The chronozones on each well log in the 22 cross sections constructed from West Cameron area eastward to the Chandeleur Sound, Breton Sound and Main Pass areas, were subdivided as applicable into four depositional groups consisting of aggradational, progradational, transgressive and submarine fan facies based primarily on SP log shapes. In the Louisiana State waters there are 92 fields containing 685 reservoirs. This includes 214 oil, 347 gas, 33 condensate and 91 combination type reservoirs. Total combined cumulative production is 1,44l,091,263 barrels of oil, 117,641,457 barrels of condensate and 11,802,821,997 thousand cubic feet of gas. Total assigned production (1977-1995) shows the progradational facies to be most productive yielding 51.69% oil, 93.84% condensate, and 77.47% gas. The aggradational facies sands produced 46.98% oil, 1.70% condensate and 15.76% gas. The submarine fan facies yielded 1.21% oil, 4.45% condensate, and 6.74% gas. Production from the transgressive facies sands was less than 0.2% of the total assigned production of oil, gas and condensate.

Field Studies of Breton Sound Blocks 37, 39 and 49, Offshore Louisiana

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.