关键词: 静止断层, 油气垂向运移, 断裂带结构, 烃源岩层压力, 断裂带排替压力, 输导能力

Abstract: The vertically differential hydrocarbon enrichment in Pinghu slope in Xihu Sag was significantly controlled by faults. But there is a poor correlation between the timing of fault activities and the period of hydrocarbon accumulation, that is, faults were inactive (hereinafter referred to as “static faults”) in hydrocarbon accumulation periods. As a result, a clear understanding on the characteristics and main controlling factors for vertical hydrocarbon migration along static faults enables to provide a theoretical basis for petroleum exploration in Xihu Sag or similar areas. The comprehensive wireline logging, mud logging, seismic data, and core testing data such as homogenization temperature and salinity of inclusions, and rock pyrolysis are used to analyze the hydrocarbon supply formations and periods of hydrocarbon accumulation, and determine characteristics and main controlling factors for vertical hydrocarbon migration along statistic faults. The study results show that hydrocarbon was supplied by the good-superior mature source rocks in Pinghu Formation and Baoshi Formation, and vertically enriched in the middle-upper parts of Pinghu Formation, showing characteristics of lower source rock and upper reservoir. Two stages of hydrocarbon charging occurred during the deposition periods of Yuquan-Liulang Formation and Santan Formation-present. While faults were mainly active during the deposition period of Baoshi-Longjing Formation, which had poor matching relationship with hydrocarbon accumulation period, and hydrocarbon migrated vertically along static faults in the late stage. The influencing factors for the vertical hydrocarbon migration along static faults include the width of fault zone, source rock pressure, and displacement pressure in the fault zone. In the study area, the width of fault zone ranges in 138-288 m, which has a positive correlation with the distance of vertical hydrocarbon migration. The source rock pressure experienced a complex evolution process, with a slightly lower pressure in the hydrocarbon accumulation period than the present, but still weakly overpressure or overpressure. The higher the pressure coefficient at present and during the hydrocarbon accumulation periods, the longer distance of vertical hydrocarbon migration. The displacement pressure in the fault zone ranges in 0.2-3.5 MPa, and it shows a negative correlation with the distance of vertical hydrocarbon migration. Based on the relationship between three influencing factors and the distance of vertical hydrocarbon migration, a quantitative evaluation formula for the vertical transport capacity of faults is developed, and the evaluation results indicate a distinctly positive correlation with the maximum hydrocarbon migration distance, according to which the favorable exploration targets in Pinghu slope are determined, including Pinghu Formation and the lower member of Huagang Formation near F2 and F5 faults.