Sedimentary Microfacies And Favorable Reservoir Sandbodies Distribution Of The Chang 6 Member In Yanchi Area,Jiyuan Oilfield

Based on core,logging,analytical data,etc.,by using some discipline theories,such as Sedimentary Petrology,Sequence Stratigraphy,Petroleum Reservoir Geology and so on,the microfacies types and distribution,diagenesis and diagenetic facies of the Chang 6 Member in Yanchi area,Jiyuan Oilfield are systematically analyzed.On this basis,the preferred criteria for the favorable reservoir sandbodies is established,and the plane distribution range of the favorable reservoir sandbodies is divided.According to the researching methods of regional marker beds,the Chang 6 Member is finely divided into six layers from bottom to top in Yanchi area,which are the Chang 632,Chang 631,Chang 622,Chang 621,Chang 612 and Chang 611 layers.The provenance of the Chang 6 Member is derived from the Alxa Block in the northwest of the Yanchi area,Jiyuan Oilfield,and the parent rock types are medium-high grade metamorphic rocks of the Lower Paleozoic.During the Chang 6 Age,the deltafront subfacies are developed in study area,that include subaqueous distributary channel,subaqueous natural levee and tributary bay microfacies.The sedimentary evolution law is further analyzed by the study of plane microfacies distribution.The result shows that during the Chang 6 Age,the sedimentary process of Lacustrine Regression-Sand Transgression took place in study area.During this process,the lake level gradually decreased and the lake basin area decreased correspondingly.Meanwhile,the delta began to develop,and underwater distributary channel sandbodies kept advancing toward the center of the lake basin.The sandbodies on the plane were distributed in pieces with an increasing scale and channel features of vertically overlapping and widening.The reservoir of the Chang 6 Member in Yanchi area,Jiyuan Oilfield is generally in the middle diagenetic A stage,having experienced diagenesis such as compaction,cementation,metasomatism,dissolution and fractur.According to the observation of thin sections and charactstics of diagenesis,the diagenetic facies of the Chang 6 Member are divided into five types.The feldspar dissolution facies,chlorite cementation-feldspar dissolution facies and micro-fracture facies which obviously improve reservoir quality are the main constructive diagenetic facies,while the strong compaction facies and carbonate-kaolinite cementation facies have destructive effect on the pore space,which belong to the destructive diagenetic facies.Based on the study of sedimentary microfacies,sandbody thickness,diagenesis,diagenetic facies and physical properties,the distribution characteristics of favorable reservoir sandbodies of the Chang 6 Member are analyzed in Yanchi area,Jiyuan Oilfield.The result shows that the favorable reservoir sandbodies are distributed in bands and branches with a tendency that upward sandbodies have better qualities,and feature that the main body are the underwater distributary channel sandbodies.The favorable reservoir sandbodies of the Chang 622,Chang 621,Chang 612 and Chang 611 layers have great thicknesses and better physical properties,and are widely distributed,well connected and develop the constructive diagenetic facies,therefore these layers can be regarded as the main potential layers as storage and production.