The Sedimentary Facies Of The 8th Member Of The Lower Shihezi Formation In Yanchi Area And Its Relationship With The Reservoir

With the theory guidance of the Sedimentary Petrology,Petroleum Geology,Reservoir Geology,Logging Geology and so on,this paper give a research on field section and the core,and then,give a micro and macro research by conventional microscope,casting thin sections,SEM and so on.It make sure that the the stratigraphic characteristics,rock type,source direction,sedimentary facies,basic reservoir characteristics and the relationship between sedimentary facies and reservoir in P2x8 of Yanchi area.May this research can provide a certain theoretical basis for the natural gas exploration of P2x8 in this area.According to a large number of drilling core,field observation and laboratory research,,the P2x8 can be divided into two sub-members,including upper P2x8 and lower P2x8,which based on the lithology characteristics and combined with regional geological survey and previous research results.In the study area.P2x8 contact with underlying P1s1 in an erosion surface;the surface between P2x8 and the overlying P2x7 is also an erosion surface.In the lithology,the two sub-members are similar,they both have two cycles.From the bottom to the top of the P2x8 the debris content increases and the color is slightly deeper.The upper P2x8 even appears the oxidized color.In granularity,the sandstone are mainly the coarse and medium.In mineral composition,it mainly contains quartzose and lithic quartz sandstone.P2x8 has a relatively stable plane distribution,which is the characteristics of thick in north and east,thin in south and west.The crystalline basement and ancient formation of Ordos Basin is mainly composed of multiple sets of metamorphic rock series,including various types of archean and proterozoic meta-volcanics and meta-sedimentary rocks.According to the study of the wild paleocurrent's direction determination and the many kinds of provenance analysis method including single clastic,heavy minerals and so on.It can basicly determine that the provenance of the western study area came from the Alashan area in the northwestern basin;the provenance of eastern study area came from Yinshan Mountain area in the northern basin.In the study area,the sand body has a trend of NW-SE direction.The P2x8 inherited the sedimentary characteristics of P1s1,but as a result of the structure uplift in the northern basin,the provenance increased,and the study area developed braided delta facies,which contains bratded delta plain,delta front and prodelta subfacies and various microfacies from the north to the south.The sedimentary facies' continuity in N-W section is obviously better than the E-W section.The sedimentary facies has a NW-SE trend in the plane distribution,and it developed many braided channels.Because the climate of later period of P2x8 became dry and hot,the top of upper P2x8 appears oxidized color.The most favorable reservoir rocks in P2x8 are quartz sandstone.In granularity,they include coarse and medium sandstone;The reservoir space is mainly intragranular dissolved pores,intergranular pore,kaolinite intracrystalline pores and intergranular dissolved pores;the reservoirs have a characteristic of ultra-low porosity and low permeability.The sedimentary facies which are most favorable to the development of reservoirs distribute in distibutary channel,and the underwater distributary channel and mouth bar microfacies followed.The sedimentary facies is the foundation of the distribution and connectivity of the reserviors.