平面走滑层内微幅构造对页岩气保存条件的影响——以川南地区宝藏向斜Y3井为例

THE INFLUENCE OF INTRA-LAYER STRUCTURE IN PLANE STRIKE-SLIP LAYER ON THE PRESERVATION CONDITIONS OF SHALE GAS:NEW INSIGHTS FROM THE Y3 WELL IN BAOZANG SYNCLINE,SOUTHERN AREA IN SICHUANBASIN

四川盆地南部是目前中国海相页岩气勘探开发最为成功的地区,随着川南页岩气的勘探开发迈向深层,在实际生产过程中,却常因深部构造地质复杂、页岩气“甜点”认识不清、目的层追踪导向困难等问题而导致钻井施工失利。针对上述问题,前人常从沉积相变化、页岩孔隙度、区域宏观构造、地层压力、地应力等因素去分析,鲜见从影响钻头钻进尺度的层内微幅构造去剖析原因。实际上,层内微幅构造对页岩气富集、“甜点”分布及钻井施工等影响非常大。本次研究以川南地区宝藏向斜Y3井为研究对象,利用三维地震资料对其进行了构造精细解释与微幅构造、微小断层识别,并在此基础上探讨了平面走滑体系下页岩层层内微幅构造对页岩气保存条件的影响。研究结果表明,Y3井用液强度(主体段为30m^(3)/m,风险段为21m^(3)/m)、加砂强度(2t/m)等与其周缘高产井差异较小,施工参数对其产量的影响较小。三维地震水平切片结果显示,Y3井位于左行平面走滑体系内,若走滑体系所伴生的次级构造仅在目的层中形成断距极小的局部断层,其在地震剖面上表现不清,但在地震水平切片上反映明显。Y3井水平井段上顶板因受小断层突破,对页岩气保存条件不利,从而降低了该井页岩气产能。该发现对川南地区页岩气相似构造区域的下步勘探开发工作有重要借鉴价值。

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 m^(3)/m in the main section and 21 m^(3)/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 smal 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.