Evaluation Of Shale Gas Content Of Lower Jurassic Xiahuayuan Formation In Xuandong Area

The shale gas resources of medium and small continental coal-bearing basins have great potential,but the degree of research is low.The evaluation of shale gas content is a key content in evaluating the potential of shale gas resources,which is of great significance for shale gas exploration and development.The thesis takes Xiahuayuan Formation of Xuanhua Basin in the east of Xuanhua Basin,Zhangjiakou City,Hebei Province as the research object,and evaluates its gas content.The main understanding is as follows:Lake,fan delta,and alluvial fan deposits developed in the vertical direction of the Xiahuayuan Formation in the study area,which showed the process of shrinking the lake basin,and the water body gradually deepened from west to east,and the sedimentary center moved to the southeast.The content of shale clay minerals is relatively high,with an average value of 60.1%.It is mainly composed of montmorillonite.The type of organic matter is mainly type III,with a small amount of type II2;the average TOC is 5.47%,and the hydrocarbon generation potential is good;the average S₁+S₂ is 16.46mg/g,and the residual hydrocarbon generation potential is higher.The mean value of R_o is 1.5%,which is mainly in the stage of maturity to high maturity,and has strong anger.The reservoir space is dominated by inorganic pores with an average porosity of 0.93%and an average permeability of0.82mD.The mesopores are the main sources and the fractures are developed.The overall performance is low pores and high permeability.Compared with the marine shale gas in the United States,the shale gas formation geological conditions are unique in 10 aspects.The average gas content of shale adsorption is 2.21cm³/g,and the adsorption capacity is strong;the average gas content is 1.22cm³/g,and it increases with the increase of burial depth.The gas content of shale below?₃ coal seam is higher,V coal The shale has the highest gas content in the sedimentary period.The composition of shale gas is mainly methane and nitrogen,the average methane value is64.08%;the average nitrogen value is 33.06%,the overall nitrogen content is relatively high,it is speculated that it may be atmospheric,mantle source or biogenic gas.According to the analysis of gas carbon isotope values,shale gas is mainly coal-type gas.The theoretical recoverable gas content of shale is 1.10cm³/g,the Analytical recoverability is 86%,and the recoverability is generally good.From the perspective of gas composition,dry gas and other gas with good gas quality account for 65%,mainly distributed in the lower part of diabase.Through the optimization of favorable intervals of organic geochemical,mineral composition,storage properties and gas content,and through a comprehensive analysis of the multi-factor superposition method,3 favorable intervals of gas content were selected,and on this basis,the establishment of The optimal reference standard of shale favorable interval of Xiahuayuan Formation in Xuanhua Basin is introduced.Sedimentary environment and preservation conditions are the main influencing factors of the shale gas content of the Xiahuayuan Formation in the study area.Favorable sedimentary environments are mainly divergent bays and divergent channels in the Fan Delta Plain,and shallow lakes.The source and storage configurations are reasonable and the overall gas content is good.In terms of preservation conditions,it is mainly affected by faults,magma intrusion,and roof and floor conditions.From the perspective of source reservoir and roof and floor configuration,six shale gas enrichment types are divided.The diabase is used as the capping layer?roof?,and the purple mudstone of the lower Xiamaling Formation in the lower part is used as the floor,forming a"two-source and three-reservoir"accumulation pattern.