珠江口盆地开平凹陷构造单元划分与平面复原

Tectonic division and plane restoration of Kaiping Sag,Pearl River Mouth Basin

盆地构造单元划分与平面复原是构造地质研究的基础问题,也是盆地普查和区域详查阶段的主要任务,对揭示研究区构造演化过程及动力学机制、促进油气勘探具有重要意义。以开平凹陷最新2D/3D地震和钻井资料为基础,根据控凹断裂及地层尖灭线展布、断陷期各反射层T_(0)构造图和△T_(0)厚度图,重新厘定了开平凹陷构造单元分布,将其划分为西洼、北洼、西南洼、主洼、东洼和①号、②号、③号、④号、⑤号背斜带共10个三级构造单元。在此基础上,结合平衡剖面分析,将开平凹陷断陷期文昌组构造演化划分为断陷Ⅰ幕的下文昌组下段、中段和断陷Ⅱ幕的下文昌组上段,上文昌组下段、中段、上段共6个阶段。其中,断陷Ⅰ幕以“南断北超”为特征,断陷Ⅱ幕转变为“北断南超”,早期彼此孤立的洼陷开始逐渐扩张连片。边界断层周期性活动控制着地层发育和展布,凹陷构造活动具有向西南迁移的趋势,沉积中心由主洼逐渐向西南洼和西洼迁移。凹陷中部的主洼和北洼伸展率最大,西南洼、东洼次之,西洼最小。本研究的构造单元划分方案,可通过平面复原进行动态验证,合理性更强,为开平凹陷动力学演化研究、生烃中心和砂体展布刻画提供了新的科学依据。

The tectonic division and the analysis of their plane restoration are basic geological issues,and also main tasks during basin survey for regional scrutiny.Based on 2D/3D seismic and drilling data,according to the distribution of faults,the T_(0) structural maps of reflection layers,and theΔT_(0) and strata pinch-out line,the Kaiping Sag,Pearl River Mouth Basin could divided into five sub-sags(the west sub-sag,north sub-sag,southwest sub-sag,main sub-sag,and east sub-sag)and five tectonic zones(Nos.1–5).On this basis,combined with the balance profile analysis,the structural evolution of the Wenchang Formation during depression period of the Kaiping Sag could be divided into six developmental stages in two episodes,during which the sag evolved from the“north dip fault”to the“south dip fault”.The early isolated sags began to expand,and interconnected gradually.The periodic activity of boundary faults controlled the sedimentary development and distribution.The center of structural activity of the sag trended to shift southwestward,and so did the sedimentary center of the main sag body.The main sub-sag and the north sub-sag in the middle of the sag have the largest extension,followed by the southwest sub-sag and the east sub-sag,and the west sub-sag has the smallest extension.The tectonic division of the sag in this study could be verified dynamically by plane restoration and shall be more reasonable;and provides a new scientific basis for the study of dynamic evolution and the distribution of hydrocarbon generation center and sand body in the Kaiping Sag.