Geomechanical Characteristics of the DeSoto Canyon Salt Basin, Eastern Gulf of Mexico

Abstract

Subsurface geologic storage of CO₂ can play a critical role in offsetting greenhouse gas emissions in a manner that is safe, economical, and acceptable to the public. Due to legal advantages and apparently vast resource capacity, offshore CO₂ storage offers an attractive alternative to onshore storage. Seal integrity is a critical issue that must be addressed to ensure safe long-term storage. Performing geomechanical analysis of the potential storage unit can help reduce the risk of leakage caused by injection.

Recent studies indicate that vast storage capacity exists in Cretaceous and Miocene sandstone in the DeSoto Canyon Salt Basin (DCSB) offshore of Mississippi, Alabama, and Florida (i.e., the MAFLA shelf). The sandstone reservoirs are overlain by thick sections of shale and chalk, which form regionally extensive seals. Based on geophysical well log data, the thickness of individual reservoirs is on the order of (10-30 m) with porosity commonly exceeding 20%.

Borehole breakouts were identified in 11 wells with four-arm dipmeter logs. Elongation of the borehole breakouts is oriented northeast-southwest and is aligned with the minimum horizontal compressive stress. Variation of borehole breakout azimuth occurs regionally and is related to major structural features, such as the Destin Fault System and large salt pillows. Vertical reservoir stresses are influenced by rock and fluid density. The average gradient of overburden pressure is ~20.8 kPa/m. Hydrostatic pressure gradient increases with depth along with brine density to a maximum of 12.2 kPa/m. Future work will focus on geomechanical properties, reservoir integrity, and seal integrity in Cretaceous strata of the DeSoto Canyon Salt Basin.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018