Study On Diagenesis And Sedimentary Facies In Linxi Formation In Suolun-Linxi Area

Suolun-Linxi area is located in the middle of the Inner Mongolia Autonomous Region.The study area includes small and medium-sized basins such as the Tuquan Basin,the Zhalute Basin and the Wulagai Basin,with a total area of about 150,000 square kilometers.Linxi Formation is widely distributed in the study area,and the whole thickness of deposition is huge,which is a stratigraphy with great value in shale gas.However,the rock type characteristics,diagenesis and sedimentary facies of the Linxi Formation in this area are still weak.Based on extensive collection of previous research results and a large number of field profiles,a variety of analytical tests were performed using polarizing microscope,total rock analysis,clay mineral analysis,scanning electron microscopy,electron probe composition analysis,porosity permeability test,particle size analysis The petrological characteristics,diagenesis and its influence on the physical properties of the Late Permian Linxi Formation in the Suolun-Linxi area were studied.Based on the study of the sedimentary facies in the restoration area,and the influence of rock mass and hydrothermal fluid on petrophysical properties is briefly discussed.The distribution of the Linxi Formation in the area is controlled by the Hegen Mountain-Heihe River fault on the northwest side and the in the south.and at the western part of the Hegen Mountain-Heihe fault,southern part of the Xilamulun River fault have no distribution.The Linxi Formation in the study area is mainly distributed in areas such as Suolun,Zhalute and Linxi.The main rock types in Linxi Formation are mud shale,lithic feldspar sandstone,feldspar lithic sandstone,lithic quartz sandstone and a very small amount of limestone.The contents of quartz,feldspar and cuttings in sandstone are all about 30%.Only the top of the section of Linxi has higher maturity and the quartz content is 80%.The results of the whole rock analysis show that the quartz content in the shale of the Linxi Formation is not very different,which is 48% ±.The clay mineral content is higher in the spring and Zhalute areas,which is 34.9% and 39.9% respectively.,Suolun and Xiwuqi areas were 19.2%,26.7% and 28.0% respectively.Xray diffraction analysis showed that the clay minerals in Linxi area were mainly illite,with an average content of 76.1%,followed by chlorite,with an average content of 14.0%.The diagenesis of the clastic rocks in the Linxi Formation of the study area is mainly compaction,cementation,metasomatism and dissolution.The main results are as follows: the contact type of the mineral contact is the contact with the bumps and the grain orientation.The cementation is the clay mineral,the siliceous minerals and the carbonate minerals in the sandstone.The clay cements are the most.The silicate cement is mainly composed of quartz secondary enrichment and autotrophic microcrystalline quartz.The metasomatism mainly appears in Linxi area,which mainly represents calcite symplectite quartz;dissolution The role of the performance of mineral particles for the formation of mold holes and intra-granular pores.The diagenesis of carbonate rocks is mainly due to compaction,cementation,metasomatism,dissolution,compaction,grain orientation,limestone interglacial contact,cementite cements,Mainly for the crystallization of calcite;metasomatism for the calcite to explain the quartz,the particles produce dolomitization;dissolution of the performance of cement due to the phenomenon of dissolution pores.The test data of 67% of the vitrinite reflectance(Ro)of Linxi Formation were distributed in the range of 2 ~ 4%.The content of S(%)in the mudstone illite / smectite(I / S)% of the data <15%;quartz secondary increase level for the first;particle contact type to the main line contact;illite crystallinity data in 72% of the <0.2(?2?)interval.A number of data indicators show that the clastic rocks of Linxi Formation in Linxi area are in the late diagenetic stage.The porosity and permeability of the sandstone in the Linxi Formation in the study area are low,the average porosity is 2.64%,and 85% of the permeability data is <0.04 × 10-3?m2,indicating that the Suolun-Linxi area is a low pore low permeability reservoir.The physical properties of sandstone reservoirs are closely related to diagenesis,and the porosity and permeability of reservoirs are reduced by compaction and cementation.The porosity of reservoir is improved by dissolution.Geochemical microelement Sr / Ba are both <1 and 93% of B / Ga data <3.3;Drilling in the Zhalute Basin reveals that the lithology of the deep Linxi Formation is dominated by thick mudstone;the paleontological fossils are Siberian plant Group,freshwater bivalve fossils and three freshwater leaf limbs.The above evidence shows that the Linxi Formation in the Suolun-Linxi area is a continental sedimentary environment.The Linxi Formation in the Suolun area is the sedimentary facies of the fan delta leading facies and the transition to the semi-deep lake facies.The combination of the positive sequence sandstone and the massive mudstone occurs.The Zhalute region is the fan delta front facies and the confluence of the semi-deep lake facies,which is characterized by the combination of the granulated sandstone and the thick mudstone in the south of Zhalute,and the thick mudstone in the northern part of Zhalute.The main body of the Linxi area is fan delta front facies deposit,There are several small-scale transgressions in the Banlashan Village area,which is manifested as a combination of sand and shale rock,and the sandstone is a limestone body.The Xiwuqi area is a semi-deep lake facies and the thick mudstone is the main section.The comprehensive analysis shows that the study area is composed of the semi deep lake-fan delta sedimentary system with the north to south source supply as the main control area with the Xilamulun River and Hegang-Heihe fault as the main control area.