西湖凹陷平北斜坡带平湖组层序构型差异及控砂模式

Sequence stratigraphic architectures and sand-body distribution models of the Pinghu Formation in the Pingbei slope belt of the Xihu Depression

平北斜坡带是西湖凹陷岩性油气藏勘探的重点区带之一,但实际勘探过程中存在岩性砂体厚度小、横向变化大等问题,亟需开展不同构造单元内地层发育样式、沉积中心变迁、砂体发育机制等构造-沉积响应研究。基于最新钻井、测井及覆盖全区的高精度三维地震资料,开展了平北斜坡带平湖组三级层序-体系域高精度层序地层研究。基于古地貌、断裂体系的差异,划分了平北斜坡带构造-沉积单元,分析了不同单元内层序构型下断裂组合样式、地层接触关系、沉积充填样式的差异,探讨了不同层序构型差异的控制因素和控砂模式。研究表明,平北斜坡带可以划分为断裂陡坡型、对向断阶型、反向断阶型、顺向断阶型4种层序构型,层序构型差异受物源供给强弱变化、断裂体系活动差异、微古地貌转换调节、基准旋回迁移变化等控制,形成了4种砂体发育模式。通过不同构造单元层序构型差异和控砂机制研究,对于推动西湖凹陷平北斜坡带岩性油气藏领域勘探进程意义重大。

[Objective]The Pingbei slope belt is one of the key zones for the exploration of lithologic reservoirs in the Xihu Depression.However,the exploration process was inhibited by issues of small thickness and significant lateral variation of sand-bodies.Therefore,research on the tectonic-sedimentary response,including the stratigraphic development patterns,deposition center evolution,and sand-body distribution mechanisms in different tectonic units,is urgently needed.[Methods]Integrating the newly obtained well drilling,well logging,and highresolution 3D seismic data,a high-precision sequence stratigraphic framework was established and the third-order sequences and systems tracts were analysed in the Pinghu Formation of the Pingbei slope belt.[Results]Based on differences in palaeogeomorphology and fault systems,the tectonic-sedimentary units of the Pingbei slope zone were classified.Differences in fault styles,stratigraphic contact relationships,and sedimentary filling patterns under different sequence stratigraphic architectures were analysed in various tectonic units.Additionally,the controlling factors and models of sand-body distribution in various sequence stratigraphic architectures were discussed.[Conclusion]This study revealed that the Pingbei slope zone can be divided into four types of sequence stratigraphic architectures:steep fault slope,opposite fault step,reversal step fault,and forward step fault.The sequence stratigraphic architectures that were controlled by factors of sediment supply,fault activity,palaeogeomorphic,and baselevel cycles generated four sand-body distribution models.Research on the differences in sequence configurations and sand-body distribution models in different tectonic units is important for promoting the exploration of lithological reservoirs in the Pingbei slope belt of the Xihu Depression.