A Study Of Reservoir Geological Features And Remaining Oil Analysis On Chang 2 Section In Huyaoxian Area, Ordos Basin

In the study, which is based on "wearing shoes and hat" sand and mudstone assemblage directly selected from the interval of interest, the thought of "starting from oil layer followed by oil reservoir and then oil field" is applied throughout the entire process. With the example of Chang 2 shallow water delta reservoir Zhidan area, the paper analyzes the influence on reservoir macroscopic occurrence process of hidden fractures caused by foundational faulting and dissects the oil and gas charging in the research area. And then, the paper gives an analysis of the types of remaining oils in the shallow water delta reservoir in the research area from two perspectives of technology and geology and provides corresponding suggestions in exploration. Following conclusions are reached:(1) According to the study, each single layer in the Chang 2 oil layer is subject to different degree of denudation, among which, the Chang 21is reduced to the most serious denudation but Chang 23almost remains intact. Chang 2 oil layer group is a large nose- shaped uplift in general with the amplitude of 15m or so, in which, many nearly East-west secondary lower nose-shaped folds with the amplitude of less than 10m. There is some hidden fractures developing nearly in the whole research area, in which, there are mainly low-angle fractures and parallel planes fractures in Chang 2 section and high-angle fractures in Chang 6 section.(2) The research shows that the research area belongs to the delta front of shallow water meandering river, with main sedimentary microfacies of underwater distributary channels, underwater interdistributary bays and underwater distributary channel flanks, among which, underwater distributary channels are the most widely distributed and account for about 80% of the entire research area.(3) Chang 2 reservoir porosity firstly decreases and then increases from top to bottom but the permeability increases in the beginning and then decreases with a large decentralized span in interval distribution. In general, it is of high heterogeneity longitudinally. And the hydrocarbon accumulation process in Chang 2 section in the research area goes in the following sequence:the area with the biggest power source serves as its main source ofdirection, and positive pressure difference in sedimentation period, negative pressure difference in uplifting period and buoyancy force in the stabilization period as the main driving force of movement respectively, and then, the fractures and fracture zones caused by "recessive activities" of permeable sandstone and foundational fault serve as the dredging medium, finally, the lithologic oil-gas reservoir is formed by movement, accumulation and occurrence.(4) The three factors:disordered well pattern, defective injection-production system and water channeling from oil well lead to enrichment of underground remaining oil; in the research area, the main geological factor influencing the remaining oil are micro-amplitude structures, denudated ancient landform and foundational activity hidden fracture zones. The remaining oil formed due to geological factor includes the four types:remaining oil in horizontal phase transformation, barrier-like interlayers and displacing agent (water add proppant) turbulence due to micro-amplitude structures and fracture development zones. In subsequent exploitation development, distribution and development of hidden fracture zones, characteristics of micro-amplitude structures and differences from ancient landform shall be taken into consideration.