走滑断裂作用对油气成藏的控制——以歧口凹陷新生代断裂为例

Control action of strike-slip faulting on hydrocarbon accumulation:A case study from Cenozioc fault in Qikou Sag

大港油田的歧口富油气凹陷形成于新生代右旋张扭应力背景下,发育北北东—北东向和北北西—东西向为主的2组断裂带,并伴生有雁行模式的帚状断裂。走滑断裂作用引起断块走滑位移量变化,使得拉张断陷作用和挤压抬升作用并存,导致沉积中心由凹陷外区向凹陷内区迁移,且与凹陷外区抬升、侵蚀作用同时发生,形成"凹中隆"的模式,易于形成自生自储油气藏。由走滑断裂作用形成的断裂坡折带,构成古构造单元和沉积相域的分界,并控制着沉积体系的总体展布。该文应用层序地层学的沉积体系域概念,将走滑断裂控制的沉积相类型,归为一个体系域进行分析,论述了歧口凹陷陡坡带、缓坡带、洼陷带具有良好的生、储、盖组合。结果表明,走滑断裂控制着岩性-构造圈闭的形成。

Qikou Sag in Dagang Oilfield formed at the right lateral tensor shear background in Cenozoic,and developed two groups of fault（NNE-NE and NNW-EW trending）,accompanying echelon brush structure fault.The changes of strike-slip displacement caused by strike-slip faulting make the extension rift faulting coexist with the compression uplift and result in that the depocenter moved from outside to inside of the sag,and uplift and erosion outside of the sag occur simultaneously,which forms the model of ＂uplift in sag＂ that is easy to form self-generation and self-accumulation reservoir.The faulted slope break belts formed by strike-slip faulting constitutes the palaeostructure units and sedimen-tary facies boundary,and dominates the general depositional system distribution.Based on the concept of depositional system tract in sequence stratigraphy,the sedimentary facies controlled by strike-slip fault is analyzed under one system tract.The favorable source-reservoir-cap assemblages in actic region,gentle slope and sub-depression of Qikou Sag are discussed.The result shows that strike-slip fault controls the forming of lithologic-structural traps.