Geochemical Characteristics And Favorable Reservoir Prediction Of Formation Of Chang7 And Chang9 In Yanchang Area

This paper is guided by sedimentary petrology,petroleum geology and geochemistry,Through the study of the characteristics of the organic geochemistry,isotope geochemistry,petrology,the space and structure of reservoir of Chang7 and Chang9 Formation in Yanchang Area,And tried to find out the technical method to predict the favorable reservoir.The main achievements and understandings are as follows:(1)The peak organic carbon content of chang7 shale is 2%-6%,the average is 4.78%.The peak organic carbon content of chang9 shale is 1.0%-7.0%,the average is 4.47%.The organic matter types of chang 7 and chang 9 shale are mainly type ? 1 and ?2 type,with a small amount of sum type ? and type ?.The Ro of Chang7 Shale ranged from 0.8%to 1%,with an average of 0.9%;The Ro of Chang9 Shale ranged from 0.9%to 1.1%,with an average of 1.04%.The carbon isotope characteristics indicate that the shale gas is thermogenic kerogen cracking gas in the study area.(2)The mineral composition of Chang 7 and Chang 9 shale have the same characteristics,the main mineral are quartz,clay,feldspar,in addition to a small amount of carbonate and pyrite et al.The average content of quartz is 30.8%,the average content of clay minerals is 48.7%,and the average content of feldspar is 13.5%.(3)Intergranular pores of shale with silty laminae are mainly composed of primary intergranular pores and intergranular dissolution and expansion of intergranular pores and intercrystalline pores;Intragranular pores are mainly intragranular dissolution pores,and there are also interlaminar slot,mold holes and pyrite aggregate Intergranular pore;There also contains a small amount of organic matter hydrocarbon-generating pores.The intergranular pores of pure shale are mainly clay mineral intergranular pores and contain a small number of pores under the pressure shadow of rigid particles;The intragranular pores are mainly composed of authigenic clay minerals intragranular pores,strawberry pyrite intergranular pores,intragranular dissolution pores,and mold holes et al.There also find many organic matter pores in pure shale.(4)Pore diameter distribution generally have two peaks in pure shale.The peaks were located at pore diameters of 0.4nm and 3.5nm;However,the pore size distribution of silty laminae is multi-peak,and the pore size range varies greatly,with pores diameter in the range of 0.3nm to 10um.The pore volume of pure shale is mainly composed of mesopore,followed by micropore and macropore;The pore volume of silty laminae is mainly composed of macropore,followed by mesopore,micropores contribute little.(5)Based on the study of the main factors affecting the pore structure and physical properties of shale reservoirs,a reservoir evaluation standard was established by selecting the six main parameters of shale thickness,the total thickness of silty laminae,TOC,porosity,brittle mineral composition and gas content;In the study area,four favorable areas were selected from Chang 7 and three from Chang 9 according to this evaluation standard.