鄂尔多斯盆地西缘中部乌拉力克组页岩储层精细表征及评价OA

[Objective]In recent years,exploratory breakthroughs in the Wulalike Formation on the western margin of the Ordos Basin have opened up a new field of marine shale gas in the North China Plate.Systematically characterizing the microscopic pore structure of low-TOC marine shale gas reservoirs and clarifying the main factors that control pore development is crucial for the prediction and evaluation of shale gas in the Wulalike Formation.[Methods]Well R16 was selected as the key research object,and a series of experimental tests such as X-ray diffraction whole-rock mineral analysis,argon ion polishing– scanning electron microscopy,and low-temperature gas adsorption were carried out.The storage space and capacity of the shale gas in the Wulalike Formation were characterized in detail.[Results](1)The reservoir as a whole has low porosity and low permeability.The upper section is mainly composed of clay shale,the middle section of interbedded gley shale and mixed shale,but the lower section of siliceous shale.Porosity is highest in the upper section,intermediate in the middle section,and lowest in the lower section.Overall,organic pores are not developed,and inorganic pores and micro-cracks predominate.(2)The pore volume of shale ranges from 4.021×10-3 to 8.307×10-3 cm3/g,with an average of 6.031×10-3cm3/g.The main contributors are mesopores and macropores.The specific surface area ranges from 1.131 to 6.605 m2/g,with an average of 2.986 m2/g.Micropores are the main contributors,followed by mesopores;macropores are the least relevant.Shale gas primarily occurs in pores ranging from 0 to 10 nm,accounting for an average proportion of 86.7%.A large number of microfractures connected with nanoscale pores form a complex pore–fracture network system,which is the main channel for the seepage and diffusion of shale oil and gas.(3)The pore structure,physical properties,and gas-bearing capacity of the reservoir are mainly influenced by clay minerals,which results in more developed pore volumes and specific surface areas in the upper and middle sections compared to the lower section.The intergranular pores of illite,as the main mineral,provide a certain storage space for the reservoir and constitute the main carrier for natural gas.[Conclusions]Comprehensive analysis indicates that the siliceous shale in the lower member of the Wulalike Formation and the interval of interbedded argillaceous-mixed shale in the middle member are favorable exploration intervals.[Significance]This study provides an in-depth analysis of the gas storage characteristics and influencing factors of low-TOC shale reservoirs in the research area,which will contribute to advancing the exploration of marine"low-TOC"shale gas in northern China.