Reservoir Characters and Controlling Factors of Upper Urhe Formation in Shawan Sag
Upper Urhe Formation in Shawan Sag has the similar reservoir conditions with that in Mahu Sag,but basic characters and controlling factors of objective reservoirs in Shawan Sag have not been clarified clearly,which hinders further exploration.On the basis of observation of drilling cores,analysis of thin sections,SEM,pressure mercury and physical property,we analyze the petrological,reservoir characteristics and their controlling factors of the study area.The results show main rock type in the first member of Upper Urhe Formation is sandy conglomerates,and reservoir spaces are mainly primary inter-granular pore and flake curved throat type,which suggests extra-low porosity and extra-low permeability reservoir.Main rock type in second member of Upper Urhe Formation is conglomeratic sandstone,and reservoir spaces are mainly primary inter-granular and inter-granular dissolved pores,with flake throat,which suggests reservoir belong to low porosity and low permeability reservoir.Controlling factors of reservoir quality are mainly sedimentary factor and diagenesis factor.Sedimentary environment and tuffaceous content decide distribution of reservoirs of high quality and reservoir property,and compaction has the greatest effects on physical property of reservoirs,with cementation and dissolution causing further difference to physical property.Abnormal pressure improves reservoir quality in a certain degree.All controlling factors make pore structures more complex in second member of Upper Urhe Formation,and reservoir property better.
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