Objective The Chang 6 reservoir at the Ansai oilfield of the Ordos Basin is one dense type, and the role of various types of diagenesis in the formation of high−quality reservoirs is not clear, However, there has been limited research on the diagenetic and its evolution history of this reservoir, which hampers the accurate prediction of the distribution of residual oil in the area.
Methods To address this problem, the data of core, casting sheet, scanning electron microscope, cathode luminescence, X−ray diffraction and high pressure mercury pressure were comprehensively studied on the microscopic pore development type, pore structure characteristic and diagenesis type of Chang 6 reservoir.
Results The research results show that the rock types are mainly fine−grained feldspar sandstone, containing a small amount of extremely fine−grained lithic feldspar sandstone. The reservoir space types include primary pores, secondary pores and micro−fractures, and the pore structure is mainly meso−fine pores and micro−fine pipes. In general, the reservoir belongs to the type of low porosity−ultra−low porosity, low permeability−ultra−low permeability.
Conclusions The diagenetic evolution stage is in the middle diagenetic stage A, which is formed by strong compaction and siliceous cementationand carbonate cementation, which is the main reason for low porosity and low permeability of the reservoir. To some extent, the corrosion and chlorite cementation improve the physical properties of the reservoir. The crude oil of the Chang 6 section has significant geological correlation with the dark mudstone and mud shale of the regional Chang 7 section, but the hydrocarbon potential is limited, and the development potential is constrained by the reservoir conditions as it mainly relies on the supply of hydrocarbons from its hydrocarbon source rock.
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