Geochemical characteristics of lower cretaceous lacustrine organic matter in the southern sag of the Wuliyasitai depression, Erlian Basin, China

Characterization of Crude Oil, Formation Water, and Fluid Inclusions of Hydrocarbon-Bearing Strata and Their Hydrocarbon Geological Significance in the Wuliyasitai Southern Sub-sag of the Erlian Basin, China

“…The desulfurization effects are not strong in the southern sub-sag as discussed before. Despite making up the majority of the cement in rocks, carbonate minerals have limited solubility in the study area . The gas fraction test results from the PetroChina Huabei Oilfield Company indicate that the average volume quantity of CO 2 is only 0.5%.…”

“…Organic acids and CO 2 tend to appear during the thermal evolution of OM, which benefits the birth of HCO 3 – and Na + . , The Wuliyasitai oilfield appears to be favorable for the accumulation of HCO 3 – , especially for K1bt (Figure ). Furthermore, at the hydrocarbon generation threshold of 1500 m, the HCO 3 – concentration rises sharply (Figure g).…”

“…The distribution curves of n -alkanes in the oil samples are divided into three parts: the deviation from the linear curve in the low-carbon-number part (<C 19 ), the original linear distribution relationship in the middle curve (C 19 –C 28 ), and the linear relationship with a significantly smaller gradient in the latter part (>C 28 ) (Figure ). It is acknowledged that the loss caused by gas or water washing leads to the deviation of low-carbon-number curves, whereas the anomalous high-carbon-number curves are related to the crystallization and wax precipitation during hydrocarbon migration. , However, no large-scale gas reservoir has been discovered in the Wuliyasitai southern sag, and the source rocks (Ro < 1.2%) have not reached the geological conditions for significant gas generation …”

“…The hydrocarbon source rocks are mudstones of the K1ba and lower Tengger Member (K1bt 1 ), and a total of four sets of hydrocarbon-bearing strata are encountered during the drilling process (Figure ). The research area’s OM is in the immature to mature stage, and it generates hydrocarbons when vitrinite reflectance (Ro) values are >0.6%, with the characteristics of unimodal hydrocarbon generation . The hydrocarbon generation threshold is approximately 1500 m deep.…”

“…The lower limit of the TOC value for the K1ba source rocks (1.5 wt %) is lower than that for the K1bt 1 source rocks (2.5 wt %). The source rocks are sourced from a mixed input of terrestrial higher plants and lower aquatic organisms. , …”