Sedimentology, geological modeling and prediction of the remaining oil distribution in a complicated fault-block reservoir in the Weicheng Oilfield, Dongpu Depression, China

Abstract

Reservoirs in the Weicheng Oilfield, which occur in Paleogene Shahejie Formation Member 4 (Es4), were formed during the initial and strongly rifting stage of the Dongpu Depression. The geometry and distribution of sands of different types have controlled the heterogeneity of the reservoirs and have resulted in exploration challenges and relatively low recoveries. Based on various static and dynamic geological data including drilling, logging, seismic and production data, the microfacies features and distribution of Es4 were analyzed. Geostatistical three-dimensional (3-D) models and an integrated numerical simulation were constructed to quantify the geometry, spatial distribution and continuity of the reservoir sands and to predict the remaining oil distribution rules. Two depositional systems were recognized in Es4: terminal fans deposits in the lower part and partial shallow-lake deposits in the upper part. The three-dimensional geological model provided insights into the external and internal geometries, distributions and physical properties of the reservoir units. A sedimentary and connectivity feature analysis suggested four types of flow units: Type I units, which are primary sands of distributary channels and bars; Type II units, which are primary sands of proximal overbank and beaches; Type III units, which are sands of distal overbank; and Type IV units, which are mud flats and inter-beach-bar. The numerical simulation reproduced the changing process of the remaining oil, and the areas that have both high remaining oil saturations and reserve abundance, which are controlled by micro-facies and influenced by the structural trend and injection-production relations, comprise the key potential reservoirs: the sand pinch-out area, the imperfect pattern area and structural highs in Type I units and most of the areas in Type II units.