西湖凹陷保俶斜坡带平北地区平湖组“多元控砂”机制分析

“Multi–factor control of sandboies distribution”in the Pinghu Formation, Pingbei region of Baochu slop, the Xihu Sag

  • 摘要: 随着勘探开发程度的不断升高,西湖凹陷保俶斜坡带平北地区中上始新统平湖组构造―岩性复合油气藏显示出较大的勘探潜力。然而,该区构造―岩性复合油气藏勘探基础薄弱,加之构造、沉积条件复杂,砂体展布规律不清,阻碍了该区的勘探进程。本文基于三维地震及钻井等资料,从构造、层序及沉积3个方面对砂体分布的控制因素进行分析,认为构造古地貌及可容纳空间控制地层厚度及沉积体规模;同沉积断裂坡折带控制砂体的展布;体系域类型控制砂体的时空配置,沉积微相类型控制砂体的储集物性。综合分析控砂因素认为:断陷期的平下下段和平下上段是构造―岩性圈闭发育的主要层段,勘探方向为低位体系域控沉积断层下降盘的地势低洼汇砂区,而平中上段有利的岩性圈闭勘探区为三角洲前缘砂地比低或三角洲前端发育的潮汐砂脊带。

     

    Abstract: With the progress of hydrocarbon exploration and development, structural-lithologic reservoirs have become more and more significant. However, the exploration of the structural-lithologic reservoirs is not so successful owing to the complexity of the tectonic evolution of the region and the changes in related sedimentary conditions. The sand bodies’distribution boundaries and patterns are difficult to define and have always become the difficult problems to exploration. Based on the newly acquired 3D seismic and drilling data, this article analyzed the controlling factors on sand bodies from the viewpoints of structure, stratigraphic sequence and sedimentation. It is found that there are four factors to be considered: The paleotectonics, paleogeomorphology and accommodation spaces, which control the thickness of the strata and the spatial distribution of sand bodies; the syn-depositional faulting slope break belt which restricted the lateral extension of sand bodies; the sequence patterns and system tracts, which control the spatial and temporal framework of sand bodies; and the types of sedimentary microfacies which determines the reservoir physical properties. The Lower Pinghu Formation was deposited in an intensive faulting period, in which there developed plenty of structural - lithologic traps, which are always been found in the low-lying areas of the downthrow block of syn-depositional fault. However the favorable structural-lithologic traps in the upper-middle Pinghu Formation may occur in the delta front deposits and tidal ridge sandbodies.

     

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