Joel S. Watkins¹, Jianyong Bai¹, Carrie L. Decker¹
(1) Texas A&M University, College Station, TX

Abstract: "Back doors" improve charge efficiency

Fault-bounded reservoirs fill more efficiently when displaced water exits the reservoir by a "back door"-a fault other than the charging fault-while hydrocarbons charge. We have conducted finite-difference computer simulations of inclined faults and reservoirs that show that if a finite reservoir has no back door, limited oil charge still occurs, but the process is slow and inefficient. Computer simulations indicate optimal conditions for charge of fault-bounded reservoirs with back doors.

Oil charges both updip and downdip reservoirs; however, during simultaneous migration of oil and gas, oil favors downdip reservoirs, while gas charges updip reservoirs. Gas is less sensitive to the presence of a back door than oil. To trap oil and gas, bounding faults must have sufficiently high capillary displacement pressures, but gas requires a higher capillary displacement pressure than does oil.

Recognition of back doors as an essential element in optimal charge of stacked, fault-bounded reservoirs is expected to enhance exploration efforts.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana