渝东南地区南川区块膝折构造模式解析

Analysis of knee fold structure model in Nanchuan Block of southeastern Chongqing

近年来,南川区块逆冲推覆构造带下志留统龙马溪组页岩气勘探开发取得重大突破。截至2022年底,南川区块已完钻170口井,累计产气量51.6×10^(8) m^(3)。随着滚动开发的逐步推进,开发区域也由主体构造简单区向两翼构造复杂区过渡,前期的构造解释方案将南川区块各构造单元解释为大断距逆断层夹持的断背斜,并没有深入分析整个构造带的构造变形特征,因此,近年部署的几口扩边评价井存在较大的井震矛盾,造成了多口井的钻探失利,限制了页岩气开发产建的进程。综合前期钻探认识及正演模拟分析,认为南川区块龙马溪组地震剖面上显示的大断距高角度逆冲断层多为构造假象,断裂区多为高陡膝折构造,断距小、地层陡。通过高陡构造假象分析与识别,结合断层相关褶皱理论完善解释成果,井震联合构造建模逐步落实了南川区块龙马溪组气藏的构造特征,进而提出了高陡膝折带是龙马溪组页岩气勘探开发的潜在有利目标,在此基础上部署的5口评价井,均取得了较好的测试效果。

Significant progress has been made in the exploration and development of shale gas within the Lower Silurian Longmaxi formation of the thrust-nappe tectonic belt in the Nanchuan block.By the end of 2022,this area saw the drilling of 170 wells,achieving a cumulative gas production of 51.6 billion cubic meters.As development has progressed,the focus has shifted from the structurally simpler main area to the more complex peripheral regions.Previously,the structural interpretation of the Nanchuan block primarily identified faulted anticlines constrained by major reverse faults,without adequately addressing the structural deformation across the entire belt.Recent evaluations have revealed significant discrepancies between well data and seismic interpretations,leading to numerous drilling failures and hindering further shale gas development.This study revisits these challenges using advanced drilling insights and forward modeling analysis.It suggests that the apparent thrust faults with large displacements and high angles in the seismic profiles of the Longmaxi formation are likely structural misinterpretations,rather than true geological features.Instead,the fault areas are characterized by high-steep knee-fold structures with smaller fault distances and steeply inclined strata.By integrating high and steep structural illusion analysis with fault-related fold theory,the well-seismic joint structural modeling has been refined to better represent the structural characteristics of the Longmaxi formation gas reservoir in the Nanchuan block.This improved understanding has identified the high-steep knee fold zone as a potentially favorable target for further exploration and development,supported by positive results from five recently deployed evaluation well groups.