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

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.