Predicting seal efficiency and trapped hydrocarbon type in Gulf Coast hydrocarbon systems: Lessons learned from West Fulton Beach field, Mid-Texas Gulf Coast
Journal Article
·
· AAPG Bulletin
OSTI ID:411895
- Univ. of Texas, Austin, TX (United States)
Many Gulf Coast fields consist of multiple vertically stacked sandstones in which oil and gas are seemingly randomly distributed stratigraphically. Hydrocarbon entrapment is strongly affected by seal competency and possibly by formation pressure, and these factors are in turn controlled by the characteristics of the interbedded shales. In West Fulton Beach field, Arkansas County, Texas, the Oligocene Frio Formation shales were deposited as shelf mudstones and represent flooding events id a barrier bar/standplain and inner shelf setting. Reservoirs were placed into a high-frequency genetic stratigraphic framework to test the theory that hydrocarbon entrapment is controlled by a hierarchy of maximum flooding surfaces. Cumulative oil and gas production and gas-to-oil ratios were tabulated for individual reservoirs, as well as for all reservoirs in each 5th-, 4th-, and 3rd-order genetic unit, as measures of entrapment. Total producible hydrocarbons (oil plus gas, in barrels of oil equivalent) increase in volume in successively shallower 3rd-order Frio units (each 800 to 1,000 ft thick), capped by the 600 ft-thick Miocene Anahuac Shale. Likewise, successively shallower 4th-order units (120 to 200 ft thick) within each 3rd-order unit contain greater volumes of total hydrocarbons, as well as greater percentages of gas. This pattern exists independent of shale thickness or reservoir porosity, and it is repeated at the 5th- and 6th-order levels, when viewed on a per-gross-ft-of-sandstone basis. Thus, although appearing random, when evaluated carefully within a stratigraphic framework, total hydrocarbon volumes and oil-versus-gas distributions follow a systematic pattern tied to their position within a stratigraphic hierarchy. This finding can be used to more accurately constrain seal risk in exploration or deeper-pool drilling and to evaluate hydrocarbon type ahead of the drill bit.
- OSTI ID:
- 411895
- Report Number(s):
- CONF-9610180--
- Journal Information:
- AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 9 Vol. 80; ISSN 0149-1423; ISSN AABUD2
- Country of Publication:
- United States
- Language:
- English
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