Carbonate Sedimentary Characteristic Of The Fourth Member Of Shahejie Formation In The South Of Chezhen Sag

Carbonate of the fourth member of Shahejie formation in Chezhen is divided into four stage.They are are named A,B,C,D from top to bottom.In the lower fouth member of Shahejie formation, the range of carbonate is small.Section D,carbonate sporadic developed in Southern gentle slope.It mainly sporadic developed limestone,dolomite and Plaster rock in Che28,Chegu10,Da101 and Da92;Section C,carbonate began to Contiguously develop in southern gentle slope.Micritic limestone is begin to develop in Guojuzi and development area is Gradually expanding.To nouth Dagu 64 is begin to develop micritic limestone.In the upper fourth member of Shahejie,carbonate is begin to develop largely.The sedimentary more thicker.Section B, carbonate in south gentle slope contiguously developed. In north steep slope limestone developed.Section A, the sedimentary range is larger than section B.Chegu 54 in south gentle sope developed bioclast limestone. limestone is mainly in littoral and shallow lacustrine.Micritic limestone is mainly in bathyal lacuatrine and deep lacustrine.In study area,there are limestone, dolomite and mixes sedimentary rocks developed. Limestone rocks include grain limestone,grain-bearing limestone and micritic limestone; Dolomite rocks include grain dolomite,grain-bearing dolomite and micritic dolomite. The types of grain inclue sand clast, chondruie,oolitic,algal-gobbet and bioclast. Overall,therer's mainly grain carbonate and grain-bearing carbonate in littoral and shallow lacustrine.There's micritic carbonate in bathyal lacuatrine and deep lacustrine.In the fourth member of Shahejie formation that is in the earlier rifting. Tectonic activity is stong.East and west are districted or south and north are districted are the feature of Chezhen.Clastic rocks are in west and carbonate rocks are in east.The development stage of section C,D in lower member of Shahejie.The climate is arid, The river level is low.Tectonic activity is stong in north steep slope,The supply of detrital material of terrigenous origin is adequate in south gentle slope,the supply of detrital material of terrigenous origin is unadequate.carbonate rocks develop only in the gentle slope in south.The development stage of section A,B in upper member of Shahejie,the climate is humid.The basin basement dropps rapidly.The lack level rises.The supply of detrital material of terrigenous origin is unadequate.Carbonate rocks develop largely.They extend into bathyal lacuatrine and deep lacustrine from littoral and shallow lacustrine in south gentle slope in lower fourth member of Shahejie.The diagenesis of the study area is divided into three types.The constructive diagenesis concludes dolomitization and solution; Destructive diagenesis concludes compaction, cementation and creaming;Double impact diagenesis concludes silicification, removel creaming and removel dolomatization.Reservoir space concludes pore and crack. The dissolved pore is the most important pore.Structure crack is common crack. The secondary dissolved pore is the leading role.Based on the standard of Luo Zhetan,the carbonate reservoir in the fourth member in Chezhen area is divided into four categories:Bio beach isâ… category reservoir; Limestone phase in littoral and shallow lacustrine isâ…¡category reservoir;Micritic beach in Guojuzi sag,in bathyal lacuatrine and deep lacustrine isâ…¢orâ…£category reservoir.