Comprehensive Evaluation Of Water Injection Effect Of The Fracture-cavern Reservoirs In The 4 District Of Tahe Oil Field

Since 2005,water flooding has been applied to enhance the recovery of the fracture-cavern carbonate reservoirs in Tahe Oilfield,which covers more than 45%of production units.It is of complexity and difficulties to accurately evaluate the oilfield because of the difference in injection-production balance,water utilization level and injection effect between different injection-production well groups resulting from the fracture-cavern reservoir space diversity,strong reservoir heterogeneity,complicated connectivity in the well groups.Therefore,it is necessary to comprehensively analyze the well pattern perfecting level,injection-production balance,water flooding application and injection effect of different injection-production well groups,and to conduct the evaluation study of water injection impacts on the fracture-cavern carbonate reservoirs in Tahe Oilfield.Based on the analysis of geologic conditions and development features of the fracture-cavern reservoirs in Tahe Oilfield,the injection effect evaluation index system suitable for reservoirs in Tahe Oilfield was studied by starting with well pattern perfecting level,injection-production balance,flooding application and comprehensive effect of different well groups in this paper.The evaluation limit of the injection effect evaluation index was delicately studied based on the unsupervised clustering analysis by analyzing the injection effect evaluation index relevance;the weight analysis of effect evaluation index was studied based on the optimized analytic hierarchy process by analyzing the key purpose of flooding effect and relationship between each indice;the injection-production indices of 97 water flooding well groups in Tahe Oilfield were collected,and the effect evaluation of water injection to 97 injection well groups was studied by fuzzy comprehensive evaluation and artificial neural network.It can be concluded that the well pattern perfecting level,injection-production balance,water utilization and comprehensive effect of injection well groups with fracture-cavern reservoirs in Tahe Oilfield could be comprehensively evaluated by nine indices,including water flooding reserves control level,water flooding reserves producing degree,energy maintaining degree,enhanced oil recovery,etc.Meanwhile,the index evaluation limit and weight of injection well group could be achieved by K-means cluster analysis method and Delphi analytic hierarchy process.The water flooding impacts on different injection well groups could be comprehensively evaluated nu fuzzy comprehensive evaluation and artificial neural network.The neural network method had strong non-linear fitting ability and fault tolerance,and its results owns a satisfactory reliability.In addition,this study provided reliable theoretical basis and complete technical process for comprehensive evaluation of injection effect of the fracture-cavern reservoirs in Tahe Oilfield as well as similar reservoirs.