The Influence Of Authigenic Kaolinite On The Reserivor Development In Chang 8 Oil-bearing Formation Sandstone Of Jiyuan Area

Based on the scientific research task of"The research on Clay minerals of Chang 8 oil-bearing Formation in Jiyuan-Huaqing area",and by analyzing the characteristics of rock in chang 8 oil-bearing formation sandstone of Jiyuan area,combining the optical microscopy,XRD,SEM analyses on core samples and other research methods. This thesis mainly discusses the characteristics of authigenic kaolinite,such as its content,occurrence,distribution,formation and the influence of authigenic kaolinite on the reserivor development in chang 8 oil-bearing formation sandstone of Jiyuan area. this thesis gives some conclusions in the following:Based on the description of well cores,the identification of the thin section and the grain size analysis,it shows that the reservoir rock type are dominantly the lithic arkose and feldspathic lithic sandstone in Jiyuan area,34.71% of the average content of feldspar is a significant feature in the rock matrix,which is characterized by low composition maturity and high textural maturity. Carbonate is the most major authigenic minerals in the study area,the authigenic chlorite and authigenic kaolinite only can be found in some area .The average content of authigenic kaolinite is 1.59% in chang 8 oil-bearing formation sandstone of Jiyuan area,it mainly distributes in chang-81 sub-oil-bearing formation of the western region in the study area,in which its average content is 2.60%;Authigenic kaolinite often occurs in the original intergranular pore and secondary porosity(such as feldspar dissolution porosity),at the same time,intergranular pore of authigenic kaolinite appears.The particularity of the various features of authigenic kaolinite is caused by its formation mechanism.Because the western of Jiyuan area is closer to the centre of hydrocarbon source rocks of chang 7 oil bearing formation,then the downward movement of organic acids causes the dissolution of many feldspars and the precipitation of authigenic kaolinite,moreover,it also causes all the kinds of characteristics of authigenic kaolinite.In the composition of pore of chang 8 oil-bearing formation sandstone in Jiyuan area,the original intergranular pore is the main part of the reservoir space,secondary porosity(feldspar dissolution porosity,debris dissolved pore and intergranular dissolution pores,etc)also accounts for part of the reservoir space. On the other hand,it also finds that the secondary porosity in chang-81 sub-oil-bearing formation of the western region in the study area is more than other area,and the content of the original pore in chang-82 sub-oil-bearing formation of the western region is the most one;Research in reservoir properties,the average porosity of sandstone is 11.66% and the average permeability is 0.38×10^-3μm²,in which we can see that it is ultra-low porosity and low permeability reservoir in chang 8 oil-bearing formation sandstone of Jiyuan area.On one hand,authigenic kaolinite occupies the reservoir space in its formation process. On the other hand,intergranular pore of authigenic kaolinite can expand part of the reservoir space. Therefore,quantitative research required in the study of authigenic kaolinite,it is harm to the development of primary porosity,and their correlation coefficient is -0.27,at the same time,authigenic kaolinite conducives to the development of secondary porosity,the correlation coefficient is +0.2. All in all,authigenic kaolinite takes the retention diagenesis in the the development of pore of the study area;Authigenic kaolinite in the study area on the impact of reservoir properties is not obvious,the decrease of porosity and permeability caused by authigenic kaolinite is very limited.