Structural attributes,evolution and petroleum geological significances of the Tongnan negative structure in the central Sichuan Basin,SW China

The Tongnan secondary negative structure in central Sichuan Basin has controls and influences on the structural framework and petroleum geological conditions in the Gaoshiti-Moxi area.To clarify the controls and influences,the deformation characteristics,structural attributes and evolution process of the Tongnan negative structure were investigated through a series of qualitative and quantitative methods such as balanced profile restoration,area-depth-strain(ADS)analysis,and structural geometric forward numerical simulation,after comprehensive structural interpretation of high-precision 3D seismic data.The results are obtained in three aspects.First,above and below the P/AnP(Permian/pre-Permian)unconformity,the Tongnan negative structure demonstrates vertical differential structural deformation.It experiences two stages of structural stacking and reworking:extensional depression(from the Sinian Dengying Formation to the Permian),and compressional syncline deformation(after the Jurassic).The multi-phase trishear deformation of the preexisting deep normal faults dominated the extensional depression.The primary depression episodes occurred in the periods from the end of Late Proterozoic to the deposition of the 1st–2nd members of the Dengying Formation,and from the deposition of Lower Cambrian Longwangmiao Formation–Middle–Upper Cambrian until the Ordovician.Second,the multi-stage evolution process of the Tongnan negative structure controlled the oil and gas migration and adjustment and present-day differential gas and water distribution between the Tongnan negative structure and the Gaoshiti and Moxi-Longnüsi structural highs.Third,the Ordovician,which is limitedly distributed in the Tongnan negative structure and is truncated by the P/AnP unconformity on the top,has basic geological conditions for the formation of weathering karst carbonate reservoirs.It is a new petroleum target deserving attention.

四川盆地中部潼南负向构造的构造属性、演化过程与油气地质意义

为揭示四川盆地中部潼南次级负向构造对高石梯—磨溪地区构造格局和油气地质条件的控制作用和影响方式,通过高精度三维地震资料综合构造解析,运用平衡剖面恢复、面积-深度应变(ADS)分析和构造几何学正演数值模拟等系列定性-定量方法,对潼南负向构造的变形特征、构造属性和形成演化过程进行研究。研究表明:①潼南负向构造以二叠系/前二叠系不整合面为界,上、下层系构造分层差异变形。其经历了震旦系灯影组沉积前后至二叠系沉积前伸展凹陷活动阶段和侏罗系沉积后挤压向斜变形阶段的构造叠加改造。伸展凹陷活动受控于深部先存正断层的多期三角剪切变形,主凹陷幕发生在晚元古代末—灯影组1-2段沉积期、下寒武统龙王庙组沉积期—中晚寒武世—奥陶系沉积后。②潼南负向构造的多阶段形成演化过程控制着该地区与高石梯、磨溪—龙女寺构造高带之间油气的运移、调整以及现今气、水的差异分布。③残存于潼南负向构造区,顶部被二叠系/前二叠系不整合面强烈削截的奥陶系具备碳酸盐岩风化壳岩溶储集层形成的基本条件,是值得关注的油气新领域。

基于高精度构造解释的滩相白云岩储层预测——以四川盆地龙女寺—合川地区茅口组为例

四川盆地龙女寺—合川地区中二叠统茅口组气藏获得重大勘探发现,是近期实现万亿立方米规模突破的最佳领域。该区中二叠统茅口组以台内滩相白云岩储层为主,沿古隆起边缘发育,规模、潜力较大,但该气藏埋藏深、受不同程度岩溶作用影响导致储层空间分布复杂、物性差,表现为内部小层难以精细解释、储层地震响应特征不清、储层预测难度大等难点。为支撑该区茅口组勘探开发需求,以白云岩储层预测为导向,结合精细描述白云岩储层主要参数为目标,采用“高精度构造解释+微古地貌刻画”技术,基于茅口组内部小层精细解释开展茅口组古地貌、有利相带预测研究,最后利用相控白云岩储层反演技术开展储层空间展布研究,解决茅口组台内滩发育有利区精细刻画难题。研究结果表明,基于相控的白云岩薄储层预测技术能够更好地反映储层空间分布,为成功预测白云岩储层发育带打下基础,有效支撑了勘探开发井位部署并取得丰硕成果,为下一步川中地区井位部署提供有力支撑。