The Microscopic Characteristics Of Authigenic Chlorite And Influences Of Its On Sandstone Reservoir Quality In Chang-9 Member Of The Yanchang Formation,northwest Of Ordos Basin

Funded by the major and special project of national science and technology in the Twelfth Five Year Plan-“Ordos basin Yanchang Formation low porosity and low permeability reservoir characteristics and relatively high permeability reservoirs controlling factors”relying on selected in Triassic,Ordos Basin northwest Chang 9 Formation of authigenic chlorite as the research object,Through the physical property analysis, thin section analysis, whole rock and clay mineral X ray diffraction and scanning electron microscopy analysis on the occurrence and distribution of authigenic chlorite, formation mechanism, and its influence on reservoir is discussed, And some conclusions are as follows:(1)The main rock types is feldspar sandstone and lithic feldspar sandstone in Ordos Basin of northwestern Yanchang 9 reservoir sandstone,a lot of content of feldspar and lithic, so the debris content unstable, sandstone dissolution diagenesis of authigenic minerals and precipitation phenomenon is very common;(2)There are three main types of occurrence of authigenic chlorite in Ordos Basin of northwestern Yanchang 9 reservoir sandstone:(a)Chlorite particle film:thin,pooridiomorphic crystal degree,widely distributed, in hydrodynamics and low-energy depositional environment can development;(b)Pore-lining chlorite:the crystal is large, thickness greater than chloriteparticle film, has great influence on the preservation of the sandstone pore, mainly developed in the hydrodynamics of sedimentary environment;(c)Rosette chlorite:the crystal particles are large, euhedral degree is very good, need larger pore space to grow, mainly developed in the hydrodynamics of sedimentary environment;(3)According to authigenic chlorite output mode and the occurrence state,the formation process in Ordos Basin of northwestern Yanchang 9 reservoir sandstone is summarized as follows:(a) Chang 9 Formation sandstone burial form has a lot of volcanic material, including medium lava and pyroclastic material, which provides important material source to authigenic chlorite development in the northwest of the Ordos Basin;(b)The formation period of authigenic chlorite is began in the early diagenetic stage, there is no terrigenous origin of authigenic chlorite,the time of chlorite film precipitation as early as the time of majority of feldspar dissolution,and in the later buried diagenetic process, the diagenetic stage is continued until after the complete dissolution of feldspar or after the formation of authigenic quartz crystal precipitation;(c)There are two kinds of causes of authigenic chlorite in northwest 9 reservoir of Yanchang Formation sandstone:1, the cause of formation of the over- saturation of pore fluid;2,the dissolution and crystallization of the material;(4)Through to the northwest of Ordos Basin Chang 9 reservoir group thin section of 70 sandstone samples analysis, physical property analysis, studied the relationship between the content of chlorite and various cements in the sandstone, shows that when the sandstone in siliceous cementation, carbonate cementation development, authigenic chlorite on reservoir physical properties have a positive impact, when sandstone in the laumonite development, authigenic chlorite has a negative effect on sandstone reservoir.