Comparison of Methods for Reconstructing the Erosion and Thermal History in the Maverick Basin, South Texas, Using Vitrinite Reflectance, Bottom-Hole Temperature, and Well Log Data

摘要

Observations of Cenozoic coal rank indicate anomalous, high thermal maturity near the surface in the Maverick Basin area in South Texas. Vitrinite reflectance values near the surface are about 0.5%, compared to normal, near-surface values of about 0.2% (Dow, 1977; Dow and O'Connor, 1982). The anomalous thermal maturity has been attributed to basin exhumation and/or a phase of heating, possibly related to nearby emplacement of Cretaceous-Paleocene magmatic rocks (Ewing and Barker, 1986; Hackley et aL, 2012, and references therein). The thermal history of the Maverick Basin is important to modern petroleum exploration. For example, it may have influenced the petroleum generation and charge history of natural gas accumulations in Campanian-Maastrichtian reservoirs and Cenomanian-Turonian Eagle Ford shale oil accumulations, both located tens of miles to the southeast of the area of maximum anomalous thermal maturity in Maverick County. To the extent that the anomalous thermal maturity reflects basin exhumation, the development of anomalous thermal maturity may have also helped to expose oil to near-surface groundwater and bacterial alteration and contributed to the evolution of the heavy oil deposits in Campanian-Maastrichtian strata in the Maverick Basin (Ewing, 2011). We compare methods for reconstructing the thermal and/or erosion history of the basin. For 17 wells in Maverick, La Salle, and McMullen counties, we constructed forward models of time-temperature history for the Aptian Bexar and Pine Island shales. Modeling was conducted with the software program HeFTy~1 (version 1.9.2) (Ehlers et aL, 2005; Ketcham, 2005), and employed the vitrinite reflectance kinetics of Sweney and Burnham (1990). The models incorporate several constraints on time-temperature history, including deposition at near surface temperatures and modern temperatures from a database of corrected bottom-hole temperature (BHT) measurements (Blackwell et aL, 2010). The BHT data were assembled by th