An Improved Method for Evaluating Hydrocarbon Generation of Shale: A Case Study of the Lower Cretaceous Qingshankou Formation Shale in Songliao Basin

Abstract

Because of the influence of hydrocarbons, especially adsorbed hydrocarbons, on the detection of cracked hydrocarbon (S2) and total organic carbon (TOC), the hydrogen index (HI) based hydrocarbon generation model deviates from actual practice. In this study, the shale in the first member of the Qingshankou Formation in the central depression of the Songliao Basin was taken as the research object and a correction method for S2 and TOC was established. By correcting the experiment results of different maturity samples, the actual hydrocarbon generation model was revealed, the differences before and after correction were compared, and the evolution characteristics of the adsorbed hydrocarbon content were clarified. The results showed that the organic matter enters the hydrocarbon generation threshold at Ro–0.5% and reaches the hydrocarbon generation peak at Ro–1.0% and that the hydrocarbon generation process ends at Ro–1.3%. The hydrocarbon generation model established based on the measured values has a “lag effect” compared to actual values, which extends the hydrocarbon generation window of organic matter and delays the hydrocarbon generation peak. With the increase of maturity, adsorbed hydrocarbon content shows the characteristics of “first increasing, then stabilizing, and then decreasing”, and reaches the most abundant stage at Ro of 0.9%–1.3%.