--> Sedimentology, Geological Modeling and Prediction of Residual Oil Distribution for Complicated Fault-Block Reservoir in Weicheng Oilfield, Dongpu Depression, China
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Sedimentology, Geological Modeling and Prediction of Residual Oil Distribution for Complicated Fault-Block Reservoir in Weicheng Oilfield, Dongpu Depression, China

Abstract

Reservoirs in the Weicheng Oilfield, which were provided by Palaeogene Shahejie Formation Member 4 (Es4), formed during the initial and strongly chasmic stage of Dongpu Depression. Tectonic movement and the abrupt change of palaeogeomorphology generated greatest accommodation and resulted in development of faults and sudden changes of depositional facies, which controlled the physical properties. The prominent characteristics of strong heterogeneity made relatively low exploitation. Fine reservoir characterization were suggested to solve the layer and interlayer contradictions by geostatistical three-dimensional (3-D) modeling, which is on the basis of sedimentary analysis, and further prediction of residual oil distribution. Seismic and logging data were used to rearrange the fault; moreover, high-resolution stratigraphic theory was applied to construct the stratigraphic framework instead of classic. Two major depositional systems were recognized here: during lower submember sedimentary period, when Dongpu Depression began to rift, the flat paleotopography, shallow water of lake basin, deficient moisture, decreasing sediment-laden streams and vanish as a result of evaporation and transmission losses all led to rapid accumulation of sediments and contributed to the development of terminal fans; during upper submember period, when it came to the strong chasmic stage, lake basin expanded rapidly and water deepened, as a result, cones formed in underwater uplift, and thus bar and beach sands developed. The main reservoir sands are distributary channel in terminal fans and bars in shore and shallow lake facies, then the sheetflood and beach deposits. Three-dimensional (3-D) models provide insights into the distribution, the integrated external and internal structure, and the quantitative spatial orientation of oil sand body. Based on the depositional system analysis and structural modeling, the facies model guided by truncated Gaussian simulation and property models under the idea of facies-control was established in succession; by numerical simulation, the residual oil distribution was predicted and it was suggested that the movable oil mainly exists in sand pinchout area, the imperfect pattern area and structural highs, and mostly appears as dispergated, lamellate, and continuous distribution; the areas with both high remaining oil saturation and reserve abundance will constitute the additional potential reservoirs.