Saline fluid flow and hydrocarbon migration and maturation as related to geopressure, Frio Formation, Brazoria County, Texas
The Pleasant Bayou geopressured-geothermal test wells in Brazoria County, Texas, display a prominent thermal-maturity anomaly in the Oligocene Anahuac and Frio Formations. Highly geopressured, more-mature shales are interbedded with hydropressured to moderately geopressured sandstones in the upper Frio and Anahuac. In contrast, shales and sandstones in the lower Frio, including the Andrau geopressured-geothermal production zone, are highly geopressured but exhibit lower thermal maturities. Vitrinite-reflectance data, supported by hydrocarbon-maturation data and anomalous concentrations of C/sub 5/ to C/sub 7/ hydrocarbons at Pleasant Bayou, indicate that the upper Frio was subjected to an extended period of hot, extremely saline, basinal fluid flow which caused the above thermal anomaly. Regional salinity studies (Morton and others, 1983) suggest that regional growth faults were the conduits for vertical basinal brine movement at depth. At shallower levels the upwelling waters migrated laterally through permeable sandstone-rich sections such as the upper Frio. Anomalously mature gasoline-range (C/sub 5/-C/sub 7/) hydrocarbons were introduced into the upper Frio by this process. Fluid influx in the lower Frio was probably limited by high geopressure, consequently maturity in the deep Frio section (greater than 14,000 ft) remained consistent with the regional geothermal gradient.
- Research Organization:
- Texas Univ., Austin (USA). Bureau of Economic Geology
- DOE Contract Number:
- AC08-79ET27111
- OSTI ID:
- 5914243
- Report Number(s):
- CONF-850207-6; ON: DE85007900
- Resource Relation:
- Conference: Geopressured-geothermal energy conference, Austin, TX, USA, 4 Feb 1985; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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