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Robert A. Morton1, William A. White2
(1) U.S. Geological Survey, St. Petersburg, FL
(2) Bureau of Economic Geology, Austin, TX

Abstract: Production-induced subsidence and fault reactivation in the western Gulf Coast Basin

In the western Gulf Coast Basin, uplands are being converted to wetlands and wetlands to open water around large, mature oil and gas fields. These land losses are attributed to subsidence and fault reactivation induced by prolonged, large-volume withdrawal of subsurface fluids. The potential for induced subsidence as a result of moderately deep hydrocarbon production generally has been disregarded because in many old sedimentary basins, the magnitude of compaction strain associated with hydrocarbon production was small. Preliminary data indicate that surficial expressions of reactivated faults are detectable only when production exceeds 5 million bbls of liquid or gas equivalent and a period of about 10 to 20 years. At the surface, fault planes are highly correlated with deep-seated ( 1.8 km) faults that serve as structural traps for the producing reservoirs. Depending on the angle of fault planes near the surface, land elevations commonly are reduced several kilometers away from the producing wells and not directly above the reservoirs. The coupling between reservoir compaction and slip along the faults controls the locus of subsidence. Fault reactivation may be caused by the simultaneous production at nearby fields from stacked reservoirs within the same stratigraphic intervals that are in communication through common aquifers below the hydrocarbon column (regional depressurization). Continued extraction of hydrocarbons and associated formation water, and anticipated future production of geopressured-geothermal fluids in the Gulf Coast region will only increase land losses unless techniques are developed to control the induced subsidence or to mitigate the loss of elevation.

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