THERMAL RECONSTRUCTION OF THE DELAWARE BASIN, WEST TEXAS, USING CARBONATE CLUMPED ISOTOPE GEOTHERMOMETRY

We utilized carbonate clumped isotope thermometry to explore the thermal history of the Delaware Basin, West Texas, USA. Carbonate wellbore cuttings from five oil/gas wells across the basin yielded apparent clumped isotope temperatures (T(Δ₄₇)) ranging from 26°C to 305°C, interpreted to reflect a combination of initial precipitation/recrystallization temperatures and solid-state C-O bond reordering during burial. Using calcite and dolomite samples within a wellbore provided a more robust, two-phase system for analyzing the thermal history of the basin. Dolomite samples yielded lower apparent T(Δ₄₇)s than calcite, interpreted to reflect greater resistance to reordering in dolomite. Using burial curves provided by the Chevron Center of Research Excellence, we created unique time-temperature histories for each sample by linearly applying a geothermal gradient. Using two different Thermal History Reordering Models, we iteratively modeled the extent of solid-state C-O bond reordering to find the time-averaged best-fit geothermal gradients for each of the five wells. Results of this modeling suggest that the shallower, southwestern portion of the study area experienced roughly 40% higher geothermal gradients throughout the sediment history (40-45 °C/km) than did the deeper, southeastern portion (30-35 °C/km), with the northern portion experiencing intermediate geothermal gradients (35-40 °C/km). This trend agrees with the observed gas/oil ratios of the Delaware Basin, increasing from east to west. We furthermore compared our modeled maximum burial temperatures to previously published vitrinite reflectance data in two of the wells and observed a good agreement in the maximum burial temperatures between the two methodologies. The results of this study demonstrate the value of carbonate clumped isotopes as an additional analytical tool for basin studies.