Sedimentary Microfacies of Chang 6 Oil-Bearing Formation and Its Control on Reservoir in Wuqi Oilfield, Ordos Basin

It is of great significance to re-recognize the characteristics of the sedimentary microfacies and sand body distribution in the middle and late stage of waterflood development for accurately locating remaining oil, adjusting development well pattern and improving water drive recovery. The authors studied in details the sedimentary microfacies of Chang 6 reservoir in Wuqi oilfield based on the core observation, thin section identification and well logging analysis. It is made clear that Chang 6 oil-bearing formation in the study area belongs to delta front subfacies and three sedimentary microfacies, namely underwater distributary channel, distributary Bay and channel flank. The authors classified the reservoir in the study area using 10 selected influencing parameters and drew out the plan of sedimentary microfacies and the map of reservoir classification, thus quantitatively evaluated the controlling effect of sedimentary microfacies on the reservoir. The results show that the Chang 6¹ and Chang 6² have good inheritance, and the underwater distributary channel of sand body is well developed. The oil and gas are mainly concentrated in the sand body of Chang 6¹ and Chang 6² underwater distributary channel and the combined sand body of underwater distributary channel and channel flank. The pore structure types of Chang 6 reservoir can be divided into three types. Type I and Ⅱ are mainly developed in the microfacies of underwater distributary channel, the pore structure parameters being preferable to developing in the future. Type Ⅲ is the most compact with poor structure parameters and low development value. The above three types in Chang 6¹ and Chang 6²are well-developed, among which type I and type Ⅱ reservoirs are the largest in distribution quantity and scale. The reservoir classification and evaluation map of each small layer provide a basis for accurate positioning of remaining oil and the adjustment of potential exploration plan.