Abstract: Wufeng-Longmaxi formations in Yichang exploration area of western Hubei Province exhibit favorable geological conditions for shale gas accumulation, with exploration breakthroughs achieved locally. However, the Yichang exploration area has undergone multi-phase tectonic superposition and reworking, resulting in complex structural deformation characterized by pronounced differential deformation, enrichment and preservation. Based on field measurements of bedding joints and striations, acoustic emission experiments, fluid inclusion analysis, detailed seismic interpretation, and balanced cross-section restoration, this study systematically investigates the mechanisms of differential structural deformation and the shale gas accumulation model in the Yichang area. The results indicate that the Yichang exploration area is controlled by dual compressional stresses from Dabie Orogen to the east and Qinling Orogen to the north. The paleostress field exhibits a south-to-north transition from near-EW to near-NS orientation, resulting in the development of the eastward-convex Baokang-Yuan’an arcuate structural belt during the Middle Yanshanian. The Yichang area underwent five phases of differential structural deformation, with the early and late stages of the Middle Yanshanian representing critical periods of tectonic transformation. The arcuate structural belt controlled the differential structural deformation across the Yichang exploration area, with the Yuan’an-Hualin triangle zone in the central part experiencing the weakest tectonic modification and exhibiting the greatest structural stability. Fluid inclusion analysis reveals that the fractures formed during the Middle Yanshanian were well preserved, while reconstruction of the hydrocarbon accumulation history indicates that the Middle Yanshanian to Himalayan periods were critical for shale gas enrichment in Yichang exploration area. Based on the evaluation criteria for shale gas preservation conditions in complex structural areas, the Xunjian slope belt, Yichang slope belt, and the footwall of the Banqiao overthrust belt exhibit the most favorable preservation conditions. Among the four shale gas accumulation models identified in Yichang exploration area, the low-angle fault-transformed slope type and the exposed slope type are relatively favorable. Based on exploration practices and geological engineering conditions, it is recommended that exploration and evaluation of shallow shale gas in the Hualinsi slope area be advanced.

Key words: Yichang exploration area of western Hubei Province, Wufeng-Longmaxi formations, arcuate structural belt, differential structural deformation, shale gas accumulation model

摘要： 鄂西宜昌探区五峰组—龙马溪组页岩气的成藏地质条件优越，页岩气勘探已实现点上突破。宜昌探区受多期构造叠加改造影响，构造变形复杂，差异变形与差异富集、保存特征显著。基于野外地层节理和擦痕测定、声发射实验、流体包裹体分析、地震精细解释及平衡剖面恢复等手段，系统研究了宜昌探区的差异构造变形机制及页岩气成藏模式。研究结果表明：宜昌探区受其东部大别造山带和北部秦岭造山带双重挤压控制，其古应力场从南到北由近EW向转向近SN向，在燕山中期形成了向东凸出的保康—远安弧形构造带；宜昌探区经历了5期差异构造变形演化，其中，燕山中期早幕和晚幕为关键构造变革期；弧形构造带控制了宜昌探区的差异构造变形，构造改造以其中部的远安、花林构造三角带最弱，构造最稳定；流体包裹体分析揭示，宜昌探区的裂缝形成于燕山中期且保存条件良好；成藏演化史重建结果表明，燕山中期—喜马拉雅期为宜昌探区五峰组—龙马溪组页岩气富集的关键时期。基于复杂构造区页岩气保存条件评价标准，宜昌探区以巡检斜坡带、宜昌斜坡带和板桥叠覆带下盘的保存条件最好。在宜昌探区的4种页岩气成藏模式中，以低角度断层遮挡斜坡型和暴露斜坡型相对有利。基于勘探实践和地质工程条件，建议推进花林寺斜坡浅层页岩气勘探评价。

关键词: 鄂西宜昌探区, 五峰组—龙马溪组, 弧形构造带, 差异构造变形, 页岩气成藏模式