Study On Heterogeneity Of Shanxi Formation Shale In Yanchang Exploration

The Shanxi Formation shale is developed in the Yanchang Exploration Area of the Ordos Basin,with high organic matter content and high maturity.It has a good prospect for shale gas exploration.However,the Shanxi Formation shale has strong heterogeneity.In-depth analysis of the shale Heterogeneity is the basic work for predicting shale gas reservoirs.Based on core,well logging,mud logging and other data,using geophysical methods and logging interpretation methods,starting from the geological characteristics of shale,this article analyzes the sedimentary characteristics,geochemical characteristics(organic matter abundance,organic matter type),and geochemical characteristics of the Shanxi Formation in the study area.Reservoir geological characteristics(lithological characteristics,shale thickness,mineral composition)and other geological elements are studied,and on this basis,the organic carbon vertical and plane,lithology in the vertical direction,shale plane,and mineral composition are explained.The heterogeneity in several aspects above the meter scale and microscopic(mainly millimeter to micron level),and the correlation analysis with the gas content of shale is done to determine the influence of heterogeneity on shale gas.The organic matter abundance of the Shanxi Formation is relatively high,and the TOC content of shale in Shan 2 Member(average 2.55%)is significantly higher than that of Shan 1Member(average 1.36%).The lithology is black and gray-black mudstone,dark gray silty mudstone,light gray-gray argillaceous siltstone and fine sandstone,and thin coal seams.The gray-black mudstone of Shan 2 Member is thicker than Shan 1,and the mudstone is intercalated with thin coal seams.The lithological combination types(mud-packed sand,sand-shale interbedded,sand-packed mud)are mainly mud-packed sand types,of which the TOC content in the mud-packed sand combination type and the sand-mud interbed combination type is between 3%-4%,Belongs to high source rock.Lithological heterogeneity is mainly reflected in the variation of the color,structure and composition of the rock in different depth ranges.The mineral types are mainly clay minerals(average 58.58%)and quartz(average 34.86%).The heterogeneity of mineral composition is mainly manifested as:the difference of mineral composition type and content above the meter scale;The above is mainly the heterogeneity of pores and cracks inside mineral particles.Through research on the correlation between shale heterogeneity and shale gas,it is found that TOC content and gas content are positively correlated.The thickness of mudstone not only affects the generation and accumulation of shale gas,but also directly affects the occurrence and development cost of shale gas.The content of brittle minerals affects the difficulty of fracturing in the later stage,and clay minerals mainly affect the adsorption performance of shale gas.