THE INFLUENCE OF INTRA-LAYER STRUCTURE IN PLANE STRIKE-SLIP LAYER ON THE PRESERVATION CONDITIONS OF SHALE GAS:NEW IN-SIGHTS FROM THE Y3 WELL IN BAOZANG SYNCLINE,SOUTHERN AREA IN SICHUAN BASIN
The southern area of the Sichuan Basin is currently the most successful region for marine shale gas exploration and development in China.As exploration and development progress into deeper layers,drilling operations often face challenges due to complex deep structural geology,unclear understanding of shale gas"sweet spots,"and difficulties in tracking and guiding the target layers.Previous research has primarily focused on sedimentary facies changes,shale porosity,regional macro structures,formation pressure,ground stress,and other factors.However,the micro-structure within the layers,which signifi-cantly affects the drilling efficiency of the bit,has been less frequently studied.In reality,micro-struc-tures greatly influence shale gas enrichment,"sweet spot"distribution,and drilling operations.Using Well Y3 in the Baozang syncline of southern Sichuan as the research object,this study interprets its struc-ture using 3D seismic data to identify micro-structures and micro-faults.The influence of micro-structures in the shale layer on shale gas preservation conditions within a plane strike-slip system is then analyzed.The research findings indicate that the fluid strength(30 m3/m in the main section and 21 m3/m in the risk section)and sand addition strength(2 t/m)of Well Y3 differ little from those of nearby high-produc-tion wells,suggesting that construction parameters have minimal impact on its production.The 3D seis-mic horizontal sectioning results show that Well Y3 is situated in a left-lateral plane strike-slip system.If the secondary structures associated with the strike-slip system create only local faults with very small fault spacing in the target layer,they may not be visible in the seismic section but can be detected in seismic horizontal sections.The study reveals that the upper roof of the horizontal section of Well Y3 is disrupted by a small fault,which negatively affects the shale gas preservation condition,leading to reduced produc-tivity.The results of this study provide important insights for the future exploration and development of shale gas in regions with similar structures in southern Sichuan.
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