The Influence Of Structural Characteristics On The Shale Gas Preservation Conditions Of The Silurian Longmaxi Formation

In recent years,shale gas exploration and development has obtained increasing attentions.Sichuan,Chongqing and Guizhou regions become the main battlefield of shale gas exploration.Based on the study of six field profiles and the description of four wells,this thesis takesshale of the Upper Ordovician Wufeng Formation-the Lower Silurian Longmaxi Formation as an object to systematically discusses the structural characteristics of the shale formation in the Wufeng Formation-Longmaxi Formation,and analyzes the influencing factors of the shale gas preservation condition,Moreover,it predicts the preservation of favorable blocks,which provides the basis for further exploration of the Wufeng Formation-Longmaixi Formation.The southeastern part of Chongqing is subjected to multi-period tectonic actions of the Caledonian movement,the Indosinian movement,the Yanshan movement and the Himalayan movement.The tectonic deformation characteristics of this area are dominated by extrusion deformation,and both the folds and the fault structures are very developed.The folds are mainly eastward and northward,which is characterized by the progressive change of the comb folds and transitional folds from the south to the northwest.In the study area,the Gongtan diagonal,the Tongxi diagonal and the Zhuoheba diagonal which are located in the middle of the southeastern Chongqing are typical transitional folds.They are subdivided into three structural styles--gentle syncline,laterally lying syncline,and high and steep fault folds.The fold was generally NE-northward and later pointed southward as a result of pressure-torsional effect.There are 12 large-scale fault systems in the area,and the faults are concentrated in the Gongxi diagonal and western diagonal nuclei.The thrusts are mostly NW and NW-northward.The scale is relatively small.Shale gas preservation conditions are affected by factors such as their thickness,caprock,roof and floor conditions,tectonic movement,and structural styles.Three types of shale gas preservation and dissipation models are developed in the southeastern Chongqing area,including the preservation of the persistent type,the dissolution of the residual type and the loss of the damaged type.The thickness of the Wufeng Formation-Longmaxi Formation in the study area which is mainly between 60-80m is relatively large.The burial is moderate.The overlying area is more complete.The Silurian-Middle and Lower Permian mudstone,Middle and Lower Triassic mudstones and gypsum can be used as an effective regional cover for the study area.As a direct cover over the Longma River group,it is a good roof of the Longma River group.The lower pagoda group is a good floor.At Wufeng Formation-Longmashi Formation,the bottom of the organic-rich shale plasticity is strong,and prone to smooth sliding.The development of sliding slope of the shale is favorable for shale gas enrichment.but unfavorable for shale gas preservation.According to the structural characteristics of the study area and the evaluation index of the storage conditions,the favorable blocks of ?,? and ? preservation conditions are preferred in Zhanhe dam diagonal and Gongtan diagonal respectively.