Fine Characterization Of Shale Reservoir Of Taiyuan And Shanxi Formations In Yulin Area,Ordos Basin

The Taiyuan and Shanxi Formations shale of Permian in the Ordos Basin is an important marine-continent transitional facies-continental shale gas exploration horizon,with a wide range of distribution,a huge overall scale,and promising resource prospects.Takes the Taiyuan and Shanxi Formations shale in the Yulin area of the Ordos Basin as the research object,a variety of experimental methods was used to study the development characteristics of the shale,the sedimentary paleoenvironment,the qualitative identification and quantitative characterization of whole-aperture pore structure and its heterogeneity.Comprehensively compare and evaluate the two formations shale in the study area,to achieve a multi-angle and omni-directional fine characterization of the marine-continent transitional facies-continental shale reservoir.Following conclusions were achieved:(1)The Taiyuan and Shanxi Formations shale in the Yulin area of the Ordos Basin were deposited in a moderate-strong reduction environment,warm and humid paleo-climate.The Taiyuan Formation was a transitional facies deposition of brackish water,and the Shanxi Formation was a freshwater partial continental deposition.The ancient water depth of the Shanxi Formation was greater than that of the Taiyuan Formation when it was deposited,but the water body was relatively turbulent and experienced periodic water inflow and retreat.Sedimentary paleoenvironment has an important impact on organic matter enrichment.Generally speaking,the shale deposited in the reducing environment of warm and humid paleoclimate and relatively stable offshore salty water is most conducive to the preservation and final enrichment of organic matter.(2)The pores of the Taiyuan and Shanxi Formations shale in the study area can be divided into three types: organic pores,inorganic mineral pores and micro-cracks according to the shape and development position.On the whole,the organic pores of the two formations are relatively less developed.Pore types are dominated by inorganic mineral pores and microcracks,especially the most developed interlayer pores of clay minerals.Quantitatively speaking,the pores of the two formations shale are mainly developed in the four intervals of 0.4-1nm,2-6nm,10-30 nm and greater than 10?m.The pore volume is mainly contributed by macropores and mesopores,and the specific surface area is mainly come from mesopores and micropores.The pore development of different lithofacies is quite different.Among them,the pores of organic-rich siliceous shale are relatively developed,followed by organic-rich clay shale.(3)The heterogeneity of shale pores in the Taiyuan and Shanxi Formations mainly comes from macropores and mesopores,and the heterogeneity of micropores is relatively low;the development of pores at various scales and the heterogeneity of their structure controlled by mineral composition,abundance of organic matter,and Ro.(4)A comprehensive comparative study of the hydrocarbon-generating material basis,sedimentary paleoenvironment,pore development,and reservoir performance of the Taiyuan and Shanxi Formations shale shows that the hydrocarbon generation material basis of shale in the Taiyuan Formation is better than that of the Shanxi Formation,but its storage performance is worse than that of the Shanxi Formation;the disadvantages of thin single layer thickness and frequent interbeds limit their resource potential.