| The Kaiping Depression is an oil and gas-bearing depression in the Zhu II sag of the Pearl River Mouth Basin,where significant breakthroughs have been made in recent years.However,the understanding of hydrocarbon accumulation is still unclear,and only 15 wells have been drilled so far,which seriously restricts the selection of future exploration directions and the understanding of resource potential.This study investigates the hydrocarbon accumulation process and periods,establishes a geological model of hydrocarbon accumulation,divides the hydrocarbon accumulation systems in the Kaiping Depression,and conducts comparative analysis on the hydrocarbon resource potential of different accumulation systems.Four conclusions are drawn from this study,（1）Under the influence of detachment faults,the distribution of source rocks around the main depression is lumpy.The main source rocks are lacustrine mudstones in the Wenchang Formation of the main depression,with thicknesses reaching 1600m in the lower section and 2400m in the upper section;TOC ranges from 0.5%to 3.0%,with an average of 1.5%,overall reaching the level of medium-good source rocks;the organic matter type is mainly humic-sapropel（Type Ⅱ1）kerogen;the average vitrinite reflectance of the source rocks is 0.67%,which is in the mature stage.（2）According to the study of fluid inclusion homogenization temperature and hydrocarbon generation and expulsion period of source rocks,there are mainly two accumulation periods in the Kaiping Depression,corresponding to 36 Ma and 19 Ma,with the accumulation period in the northern and western regions being slightly earlier than that in the southern part.（3）Hydrocarbon migration channels are mainly faults,among which Type I oil source faults have the best matching relationship with hydrocarbon accumulation periods and the best conduction capability.They are mainly distributed in the S block in the south of the main depression and sparsely in the N block in the north.Faults serve as hydrocarbon migration channels,connecting deep oil sources and allowing hydrocarbons to migrate to shallow levels,forming an accumulation in the Enping Formation reservoir,resulting in a geological model of hydrocarbon accumulation characterized by"lower generation-upper storage,vertical fault conduction,and fault-sandstone controlled reservoirs".（4）Based on the understanding of accumulation,the Kaiping Depression is divided into two sets of accumulation combinations using the regional cap rock as a boundary.Using the normalized fluid potential division method,the upper and lower sets of accumulation combinations are divided into three and four accumulation systems,respectively,and quantitative evaluation is carried out for each accumulation system.The No.1 accumulation system of the lower accumulation combination has the most oil and gas resources and is a first-class exploration zone for the future. |
