Fuzzy evaluation of water injection development effect based on three-level hierarchical analysis

To accurately and quantitatively evaluate the water injection development effect of different types of low-permeability and ultra-low-permeability reservoirs at different development stages in the Yanchang Oilfield and guide subsequent adjustment and treatment, based on the oilfield’s development life cycle, 10 evaluation indexs were selected from three dimensions: technical policy, injection and production system, and development indexs. According to the characteristics of low-permeability and ultra-low-permeability reservoirs in the Yanchang Oilfield and the lagging and moderate water injection development mode, five-level evaluation standards for each index were formulated for the medium and high water cut stages, establishing an evaluation index system for water injection development effect suitable for the Yanchang Oilfield. By comprehensively applying the analytic hierarchy process and fuzzy evaluation method, the weights of the evaluation indexs were calculated, the evaluation matrix of water injection development effect was constructed, and fuzzy transformation operations were performed to conduct a comparative evaluation of the water injection development effect of six representative reservoirs in the Yanchang Oilfield. The results show that the weights of development indexs, injection-production system, and technical policy in the evaluation system decrease in sequence. The evaluation index system and fuzzy evaluation method established based on reservoir geological characteristics, water injection development mode, and development stage can objectively and comprehensively evaluate the water injection development effect of reservoirs. The evaluation results of five blocks, including Haojiaping and Zhenjiamao, are good, while that of Fengfuchuan block is poor, which is in line with the actual development of the oilfield. This evaluation method has good reference significance for the comparative evaluation of water injection development effect among different types and development stages of reservoirs.