Reservoir Study Of Chlorite Cement Facies In The Xujiahe Formation In Upper Triassic In Middle Sichuan Province

Chlorite exist widely in all kinds of rocks and geological environment,and it belongs to low metamorphic rock and hydrothermal alteration of main minerals in the rock,and found in sedimentary rocks,it is widely distributed in sandstone reservoir of the meso-cenozoic continental basins in China.For a long time,the characteristics of chlorite,composition,origin,effect on reservoir gradually got the attention of geologists and scholars.In this paper,the Sichuan basin upper Triassic xujiahe on the regional group siltstones of authigenic chlorite in reservoir sandstone as a research object,to explore the overall occurrence of authigenic chlorite state in detail,formation and evolution mechanism,the spatial distribution and the relationship between the porosity and permeability,further explore sandstone reservoir of authigenic chlorite on the whole to the preservation of porosity and other physical properties on the relationship and influence.The study area reservoir belongs to low porosity,low permeability reservoir,type is given priority to with pore type and fracture pore type.The main type of sandstone is lithic quartz sandstone,the proportion is more than half.Elastic characteristics is given priority to with moderate granularity of sand grade,sorting and roundness are medium above,the mixed base content is low,only about 5.4%.Compaction and cementation is the main factor that affect the ability of the sandstone reservoir in the study area,cement average is only 4.09%,however,and given priority to with carbonate cementation,the damage to the reservoir is limited,cementation and compaction are both the main factors of reservoir physical property variation in this area.Authigenic chlorite is one of the main clay minerals content in the study area,the average content of about 3.2%,the form of more embodied in pore lining or particles such as thick rim,the existence of authigenic chlorite can make particles contact strength is generally low——the point contact-line contact Usually,in the particle contact gap of chlorite does not see more.Chlorite with generation structure,precipitation will continue to grow,we saw authigenic chlorite restrictions on authigenic quartz growth even erosion.Dissolved in skeleton particles,chlorite surrounded from forming on the boundary shape,to protect this kind of secondary porosity.In short,the chlorite lining rim cementation in the sandstone pore is the upper region,siltstones river group of important mechanism of sandstone pore is preserved,mainly from the following two aspects to save the pore in the deep strata: On the physical properties,chlorite cementation increase in porosity of rock mechanical strength and ability to resist the compaction,it makes primary intergranular pore and secondary dissolution pores,preserved in the geological process;Chemical properties,due to the late stage because of the existence of chlorite rim in a certain extent inhibitory effect of the quartz overgrowth,protecting the pore space.