IN-SITU STRESS IN THE DESOTO CANYON SALT BASIN, EASTERN GULF OF MEXICO

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, such as uniform ownership, and apparently vast capacity, offshore CO₂ storage offers an attractive alternative to onshore storage.

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%. Seal integrity is a critical issue that must be addressed to ensure safe long-term storage. Understanding the geomechanical parameters of the potential reservoir, such as in-situ stress and rock strength, helps minimize the risk of leakage during and after injection.

Borehole breakouts were identified in 11 wells with four-arm dipmeter logs of the MAFLA Shelf. The elongation of the borehole breakouts strike northeast-southwest and are 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, and deep geopressure in which pressure-depth quotient is as high as 12.2 kPa/m and is related to elevated brine density. Future work will focus on stress magnitude and rock strength of the reservoirs and seals.