WANG Pingxia, GONG Lei, DU Yijing, GAO Shuai, WENG Jianqiao, SU Hui, HUANG Jianguo
The distribution of the natural fractures controls the distribution and the accumulation of the hydrocarbon reservoir in the Triassic of Wenmingzhai area, Dongpu depression. The formation time of the fractures and the relationship between the effective evolution law and the hydrocarbon generation peak determine the behavior of the hydrocarbon reservoir. Based on the data of outcrops, cores, thin sections, logs, sound emission experiments, fluid inclusion analyses, oil component analyses and carbon isotope analyses, the distribution characteristics of the fractures, the fracture sequence and the relationship between the fractures and the hydrocarbon accumulation are discussed. The results show that the structural fracture is the dominant fracture type in the reservoirs of Triassic tight sandstone in the north of Dongpu Depression. The average porosity of the fractures and the related dissolved pores is 2.25%, and the average permeability is about 40×10-3 μm2. The fractures and the related dissolved pores are important storage spaces and seepage channels. The fractures of the tight sandstone reservoir of Triassic are formed in two stages. The oil sources of Triassic are the source rocks of Sha3 and Sha4 Member of Palaeogene whose peak period of the hydrocarbon generation is the period when the Dongying-Guantao Formation is formed. But the diagenesis was completed before Cenozoic. The period of the hydrocarbon generation is well matched with the effective fractures, while it is poorly matched with the pores. It follows that the oil is contained in the fractures rather than in pores. The distribution of oil reservoirs is controlled by the development of fractures and high part of the structure.
