中国中西部山前构造变形结构分带模式与油气

Deformation zoning model of piedmont thrust, western China, and its petroleum response

复合大陆内部的山前冲断特征及其结构分带研究是探索山前带油气富集分布规律的有效方法。通过对中国中西部地区主要山前带深部地质结构与沉积盖层构造变形特征的分析,认为陆内山前冲断变形受控于不同层次的滑脱层、复合陆块空间几何形态与位置。复合陆内山前冲断是在板块边缘构造挤压应力作用下,由造山楔向盆地方向沿不同深度的滑脱层发生阶梯式拆离冲断引起的构造形变。基于此认识,建立了以“主滑脱层深度为主、兼顾变形样式”为原则的复合陆内山前冲断变形4分带模式,即复合陆内山前冲断变形由古造山带向盆地依次划分出厚皮带、过渡带、薄皮带,其中过渡带又可划分为过渡Ⅰ带和Ⅱ带。变形带在变形构造层、构造样式、断层破裂机制、褶皱方式、断层相关褶皱原理与几何学模式等方面均具有各自独特的特征。陆内冲断变形带结构类型与油气聚集成藏有明显的关联响应:规模油气发现主要分布在过渡带;过渡Ⅰ带多为残留或调整型油气藏,成藏过程具有边聚集、边调整的特点,带内前缘油气相对富集;过渡Ⅱ带以晚期成藏为主,断裂形态及其与盖层的匹配样式是油气成藏富集的关键,带内中部是油气富集相对有利部位。中西部山前厚皮构造向薄皮构造转换的过渡部位是山前地震勘探技术攻关与勘探部署的重点。

The deformation structure and zonation model of piedmont thrust in an intra continental composite system is an effective method of studying hydrocarbon accumulation regularity.The conjoint analysis of the characteristics of deep geological structures and sedimentary cover in the main piedmont thrust belt,western China indicate that the deformation of the intra continental piedmont thrust belts is controlled by the different detachments and also by the geometric form and location of the compound land mass.The intra continental composite piedmont thrust belt is essentially a deformation system formed by an orogenic wedge step sliding along different levels of soft strata from the orogenic wedge to the basin.Four zonation models divide the intra continental piedmont thrust belt using the depth of main detachment as a key factor combined with deformation style.The models include a thick belt,a transition belt and a thin belt from the orogenic region to the basin,and a transition belt is further divided into transitionⅠbelt and transitionⅡbelt.Each belt has its unique characteristics with respect to deformation strata,deformation styles,fault rupture mechanism,folding styles,fault related fold principles and geometric theory.The deformation style of the in tracontinental thrust belt clearly influences hydrocarbon accumulation regularity.The industrial oil and gas is mainly distributed in the transition zone.During accumulation,oil and gas in transitionⅠbelt also adjusted,so the present petroleum reservoirs are mainly residual and always in the front part of the belt.Oil and gas in the transitionⅡbelt mainly accumulated at the late stage and in the center of the belt.Therefore,the key factor for accumulation is the matching style of fault shape and seal.The transition from thick belt to thin belt in the central and western piedmont thrust belt is the key area for seismic technology development and exploration deployment.