The Dongpu Depression is a secondary salt‐bearing tectonic unit in the Bohai Bay Basin, eastern China. The depositional environment of this depression regarding its Paleogene strata is clearly different in plane, including the saltwater environment (SE) in the north, the freshwater environment (FE) in the south and the brackish water environment (BE) in the middle. The result of oil and gas exploration in the Dongpu Depression shows that more than 90% of the proven oil reserves are distributed in the northern saltwater environment. Previous studies indicate that the organic geochemistry characteristics and the hydrocarbon generation capacity of the source rocks are very clearly diverse under different environments, which results in the significant differences in the proved reserves between the north and the south. In order to further explore the differences in the hydrocarbon generation capacity of the source rocks under distinct depositional environments and the mechanism of their occurrence, three samples from different depositional environments (W18‐5 for SE, H7‐18 for BE, CH9 for FE) were used for confined gold tube pyrolysis experiments. The results show that the CH4 yields of W18‐5, H7‐18 and CH9 increase with increasing temperature, the maximum yields being 405.62 mg/g TOC, 388.56 mg/g TOC and 367.89 mg/g TOC, respectively. The liquid hydrocarbon yields of W18‐5, H7‐18 and CH9 firstly increase with increasing temperature and then decrease after the critical temperatures. The maximum yields of C6–14 are 149.54 mg/g TOC, 140.18 mg/g TOC and 116.94 mg/g TOC, the maximum yields of C14+ being 852.4 mg/g TOC, 652.6 mg/g TOC and 596.41mg/g TOC, respectively for W18‐5, H7‐18 and CH9. To summarize, the order of hydrocarbon potential from high to low is W18‐5, H7‐18 and CH9. On this basis, through analyzing the influencing factors of hydrocarbon differences, this paper reveals that the saltwater environment is characterized by 4 factors: higher salinity, halophilic algae, high paleo‐productivity and a strongly reducing environment, which are beneficial to the enrichment of organic matter and lead to the formation of high levels of sapropelite and exinite. According to the variation of oil and gas components in the pyrolysis experiments, the hydrocarbon generation process is divided into three stages: kerogen cracking, oil cracking and C2–5 cracking. Combined with hydrocarbon generation characteristics and stages, the evolutionary model of hydrocarbon generation for source rocks under different environments is established.
In comparison to the continuous breakthrough in shale gas of marine basins, the pace of study of lacustrine basins is relatively slow. The latest studies have shown the saline lacustrine rifting basins (SLRBs) are one of the favorable exploration areas from the view of shale pore, mineral composition, and organic matter accumulation. However, the study on the gas generation potential and characteristics is still lacking because the traditional view is that lacustrine source rocks are oil-prone. Therefore, to identify gas generation potential and characteristics of oil-prone shale in SLRBs, the samples from the saline area (SA) and non-saline area (NA) of the Dongpu Depression are selected for the organic geochemical experiments and closed gold cube thermal simulation experiments. Geochemical results show that the SA samples are definitely oil-prone source rocks with high quality, and their main type is II kerogen. However, the results from thermal simulation experiments indicate that the gas generation potential of oil-prone shale in SLRBs is enough for the accumulation of shale gas with the peak gas yield of 469.11 mg/g of TOC at the heating rate of 20 °C/h TOC and 466.75 mg/g of TOC at the heating rate of 2 °C/h and TOC. Moreover, according to the dynamic hydrocarbon yields and carbon isotope (ln C2/C3, ln C1/C2, and δ13C1–δ13C2) during the increasing temperature, the gas generation process for SA and NA samples can be divided into three stages: kerogen cracking, oil cracking, and wet gas cracking. In comparison to other types of source rocks (marine shale, coal, and coal mudstone), the SA oil-prone shale can experience longer intervals in kerogen cracking and oil cracking, which may be the main stage of gas generation. The model based on kinetic parameters shows that the main gas generation period for SA and NA samples is the late Es1 (the first member of Shahejie Formation) to Ed (the Dongying Formation) of the Early Cenozoic, which can be consist of the depression stage with the deepest depth and the largest subsidence amplitude in the Dongpu Depression. Such information can be a reference for other SLRBs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.