Study On The Mechanism And Controlling Factors Of Shale Gas Enrichment In Shanxi Formation

The shanxi formation,as a coal-bearing formation in the transcontinental facies of the ordos basin,is one of the key reservoirs for the exploitation of shale gas and has great potential for gas exploration.In this paper,the maturity and organic matter types of source rocks of shanxi formation are studied by analyzing comprehensive geological data,combining with drilling data,using experimental methods such as organic geochemistry and elemental analysis.The pore and permeability characteristics of mineral components and reservoirs in shanxi formation were analyzed by means of scanning electron microscope analysis,sample thin section observation and physical characteristics analysis.Moreover,the hydrocarbon evolution history of shanxi formation in the study area was simulated and analyzed by basin simulation software,so as to establish the hydr70 ocarbon accumulation pattern of source rock and the main controlling factors affecting shale gas enrichment.According to the comprehensive experimental results and geological data analysis,the main hydrocarbon generation and expulsion periods of the source rocks of shanxi formation in the study area are from the early Jurassic,middle Jurassic to early cretaceous,and the cumulative exhaust intensity of the source rocks in the early cretaceous period is 146×103m3 /km2,which is the highest in history.In terms of influencing the main control factors of shale gas,the type of organic matter is type III,which is conducive to the enrichment of shale gas.The values of TOC in the study area were positively correlated with gas content,with the values of0.51%~3.54% in the first segment and 0.58%~5.15% in the second segment.The Ro of mud shale in shan-1 segment is basically 1.76-3.38%,and the Ro in shan-2 segment is 2.0%-3.34%.The average of shan-1 segment is 2.39%,and the average of shan-2 segment is 2.51%.Both have reached the high-over-mature stage and entered the gas stage,indicating that the maturity of organic matter directly controls the production of shale gas.The content of clay mineral in shan 1 and shan 2 is 57.87% and 60.3% respectively.The content of clay mineral is too high to generate adsorbed gas easily,which is not conducive to mining.The content of brittle minerals in the two reached 42.12% and 42.27% respectively.The high content of brittle minerals is conducive to the fracturing of the reservoir and the generation of micro-fractures,whichincreases the content of free gas and improves the mining efficiency.Therefore,mineral fragility is also one of the main controlling factors.