Shallow stratigraphic evidence of subsidence and faulting induced by hydrocarbon production in coastal Southeast Texas

Abstract

Wetland losses and their progressive conversion to open water around producing oil and gas 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 Topographic and bathymetric profiles at the Port Neches, Clam Lake, and Caplen Fields and shallow cores at the Port Neches 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 subaqueous erosion. Subaqueous erosion results from submergence of wetlands, current and wave excavation of surface sediments and organic detritus, and exportation of the eroded sediments through adjacent water bodies with swift currents such as navigation channels. Geologic settings and responses to induced subsidence and fault reactivation are different at each field site. Detailed stratigraphic correlations of sediment cores show that at Port Neches, subsidence of 35 to 90 cm and minor marsh erosion (20 to 35 cm) created more than 15 million m3 of accommodation space in a nearly circular pattern over the field. At Caplen the marsh surface subsided only about 4 cm, but the surface eroded 30 to 40 cm vertically, creating 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. At Clam Lake, minor subsidence along a fault is submerging the marsh plants that will weaken and eventually die either as a result of water logging or saltwater intrusion. The different surficial responses and wetland losses at each field are also related to the primary type and rate of hydrocarbon production. The greatest land-surface subsidence occurred at the Port Neches Field where a large volume of gas was produced rapidly. At the Caplen Field, both oil and gas were produced in significant quantities and there was a period of accelerated gas production. The wetland loss, which coincided with the rapid production phase, was controlled by fault reactivation and subsequent marsh erosion. Oil was the primary hydrocarbon produced at the Clam Lake Field where a reactivated fault is responsible for the observed wetland loss. Results from this study show that although the absolute magnitude of induced subsidence may be less than 1 m, even a minor reduction in land elevation is sufficient to initiate marsh degradation that quickly results in major wetland losses.

Avulsion regimes in southeast Texas rivers

“…The tectonic map of Ewing et al (1991) shows at least 19 mapped faults crossing the lower Neches valley, and White and Morton (1997) documented wetland losses related to reactivation of faults by hydrocarbon production along the southeast Texas coast, including the Port Neches oil field in the lower Neches valley. Morton et al (2001) and Sharp and Hill (1995) had earlier documented land subsidence and fault movement associated with hydrocarbon production in the lower Neches area in conjunction with oil fields tapping the Frio Formation. This formation as mapped by Ewing et al (1991) roughly corresponds with the 57-km high-avulsiondensity reach of the Neches.…”

Inelastic Deformation of the Slochteren Sandstone: Stress‐Strain Relations and Implications for Induced Seismicity in the Groningen Gas Field

“…Both effects are caused by compaction of the reservoir, resulting from the increase in effective stress accompanying pore pressure reduction. Subsidence typically constitutes several tens of centimeters (Ketelaar, ; Mallman & Zoback, ; Morton et al, ), corresponding to vertical reservoir strains generally <1% (Cannon & Kole, ; Kole, ). The densely populated Groningen gas field located in the Netherlands (Figure ) has attracted much attention in recent years, particularly since the occurrence of a damaging M w 3.6 earthquake in 2012 (Dost & Kraaijpoel, ).…”

Deformation Behavior of Sandstones From the Seismogenic Groningen Gas Field: Role of Inelastic Versus Elastic Mechanisms

“…Fluid extraction from subsurface sandstone reservoirs, in the context of oil, gas, and geothermal energy production, frequently results in surface subsidence (Fialko & Simons, ; Morton et al, ; Pratt & Johnson, ; Sharp & Hill, ; van Wees et al, ) and sometimes in induced seismicity (Davies et al, ; Grasso, ; Segall & Fitzgerald, ; Suckale, ; van Eijs et al, ). Both effects are caused by the stress changes due to depletion of pore fluid pressure and the associated reservoir compaction.…”

“…The magnitude of subsidence is typically several centimeters to several tens of centimeters. Examples include the Port Neches, Clam Lake, and Caplen oil fields in Texas (4–63 cm; Morton et al, ), the giant Groningen gas field in the Netherlands (NAM, ), and the Geysers geothermal field, California (40–80 cm; Mossop & Segall, ). In fields showing tens of centimeters of subsidence, induced seismicity is often widespread, as seen in the Groningen field, (van Eijs et al, ), the Geysers geothermal field in California (Eberhart‐Phillips & Oppenheimer, ), and the War‐Wink gas field in Texas (Doser et al, ).…”