Field Evidence of Subsidence and Faulting Induced by Hydrocarbon Production in Coastal Southeast Texas
R. A. Morton, N. A. Purcell, and R. Peterson
U.S, Geological Survey, Center for Coastal and Regional Marine Geology, St. Petersburg, FL
Wetland losses and their progressive conversion to open water around producing fields in the Gulf Coast region have been attributed to a variety of natural and anthropogenic processes. Three large, mature hydrocarbon fields in coastal southeast Texas were examined to evaluate competing hypotheses of wetland losses and to characterize subaerial and submerged surfaces near reactivated faults and zones of subsidence. Detailed topographic and bathymetric profiles and shallow cores at the Port Neches, Clam Lake, and Caplen fields provide a basis for distinguishing between (1) extensive land-surface subsidence without significant subaqueous erosion, and (2) localized minor subsidence near faults accompanied by extensive erosion. The erosion results from submergence of wetlands, excavation of surface sediments and organic detritus, and exportation of the eroded sediments through water bodies with swift currents such as navigation channels.
Responses to induced subsidence and fault reactivation are different at each site. Detailed stratigraphic correlation of core pairs show that at Port Neches, nearly circular subsidence of about 65 cm created over 15 million m3 of accommodation space, but the marsh surface experienced little erosion. At Caplen the marsh surface subsided only about 4 cm, but the surficial sediments eroded 30 to 40 cm and created about 3.5 million m3 of accommodation space. The breakup of wetlands and their conversion to open water appears to be in an initial stage at the Clam Lake field. There minor subsidence along a fault is submerging the marsh plants that weaken and eventually die either as a result of water logging or salt-water intrusion.
AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana