Organic carbon content and thermal maturity are critical parameters controlling the hydrocarbon storage potential of source rocks. We have identified and developed modifications for source rock analytic techniques and workflows that enhance interpretation of basic geochemical data. Using identical samples from the Permian Basin in West Texas, we ran parallel TOC and pyrolysis experiments involving solvent extraction and normal preparation techniques on core and cuttings. It is observed that there are consistent reductions in TOC and S2 after solvent extraction in comparison with the unwashed data. These reductions were strongly correlated with Tmax, which enables the calculation of an alternative maturity proxy. Depending on thermal maturity, 20–65% of the S2 peak is soluble in common organic solvents (bitumen). Our collection of data includes at least thirty-two wells that have continuous coverage over the upper Wolfcamp Formation; twenty-two of which also cover the entire Wolfcamp section (N= {10, 50+} samples per well).
Pyrolysis is one of the most direct assessments of bitumen in hydrocarbon source beds presently available to industry. Attempts to directly convert S1 weight percent data into in situ bulk volume of hydrocarbons prove conservative when compared to other widely used core- and log-based methods. We show how the soluble fraction of the S2 can be combined with the S1 for total weight percent bitumen to reconcile the typical shortfall. Using the API gravity of the local historic vertical/horizontal well production this weight percent can be converted to volume percent liquids at surface conditions. Standard reservoir engineering parameters, including the gas-oil ratio and formation volume factor, can convert this volume from stock tank barrels to reservoir barrels.
