Characteristics of buried hill reservoir in Jizhong Depression

It is difficult to explore the buried hill reservoir in Jizhong Depression because of the strong heterogeneity of carbonate reservoirs and the complex hydrocarbon distribution. The theories and methods of petroleum geology, geophysics and organic geochemistry, combined with exploration practice, were applied to systematically study the charac-teristics of buried hill reservoir in Jizhong Depression. The result shows that the hydrocarbon in buried hill mainly came from the source rocks of Eogene and Permo-Carboniferous system. The reservoir is composed of Middle-Upper Praterozoic and Lower Paleozoic carbonate rocks, and pores, caves and fractures are the main reservoir spaces. The cap rocks are composed of argillaceous rocks of Eogene, coal measure strata of Permo-Carboniferous system and interlayers of inner buried hills, and there developed eight sets of reservoir-cap rocks assemblage. The faults and unconformities are the main hydrocarbon migration pathways of buried hills. The buried hill reservoirs can be divided into hilltop type, hillside type and inner buried hill type. The buried hill reservoirs are mainly located in eastern depressed areas, and distributed close to fractural belts near source rocks, forming the complex hydrocarbon accumulation belts. These research results will be helpful for the disclosure of hydrocarbon accumulation rules, and provide guidance for the target evaluation and favorable zone selection.