Shiyou shiyan dizhi (Jul 2023)
Hydrocarbon charging stage and accumulation mode of forward fault step zone in fault basin: taking the Chengbei fault step zone in Qikou Sag, Bohai Bay Basin as an example
Abstract
Fault step zones are well developed in faulted lake basins in the eastern part of China, among which, forward fault step zones account for a large proportion, and their spatiotemporal configuration relationship, oil and gas accumulation periods and accumulation conditions, which play a key role in the geological evaluation of regional oil and gas exploration, are difficult to study. In order to further clarify its hydrocarbon accumulation mode and filling period, the authors, by taking the Paleogene Dongying and Shahejie formations in the study area as the main target layers, and selecting wells Qidong 3-1, Zhang 10 and Chenghai 16 to represent the low, medium and high fault levels of the fault area, respectively, conducted in-depth research on the oil and gas properties and distribution laws of different charging stages in various districts of Chengbei through reservoir microlithography observation, fluid inclusion identification, salt water inclusion homogenization temperature and salinity test, GOI statistical analysis and other technologies; applied laser Raman test to effectively identify the gas composition of single inclusions in wells Zhang-10 and Qidong 3-1, determined the specific oil and gas accumulation time in Chengbei fault step zone in combination with the single well burial history, paleogeothermal history and autoclastic illite K-Ar isotopic dating technology of well Qidong 3-1, and summarized the four accumulation elements of source rocks, reservoirs, preservation and transportation in Chengbei area. There are two charging stages in the reservoir, the specific accumulation time of the first stage is from the end of Dongying to the early stage of Guantao, about 16 Ma ±, while that of the second stage is in the early stage of Minghua Town, starting from 6 Ma ± and continuing to the present. Multiple sets of reservoir layers are developed in the study area, and the special fault step structure plays a controlling role in channeling the source rocks and reservoirs, the sealing and preservation of oil and gas, and the transportation and accumulation of reservoirs. The regional accumulation conditions are relatively mature, and the lateral migration-accumulation mode of dual-source hydrocarbon supply and multi-stage accumulation and the longitudinal migration-accumulation mode of fault-sand coupling and relay climbing are reflected in the process of oil and gas accumulation.
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