Research On Calculation Method Of Water Diversion Of Fracture-cave Water Injection Unit In Carbonate Reservoir

Carbonate reservoirs are different from conventional sandstone reservoirs.The reservoir space of carbonate reservoirs is mainly consists of karst caves and fractures.Karst caves are the main storage space,and fractures are the main flow channels and paths.The heterogeneity of carbonate reservoirs in Tahe Oilfield is extremely strong,mainly due to the diversity of reservoir space distribution and the complexity of fracture-cavity combinations.At present,in carbonate reservoirs mining,water injection is often used to supplement formation energy and improve fluid production capacity.Although the scale of water injection has expanded in the past two years,the current overall degree of water flooding is relatively low.The effective injection rate is only about 40%.The injected water is inefficient due to the injected water that cannot be displaced in the direction of the planned water flooding and the gravity infiltration.For a multi-injection well group,accurate calculation of the amount of water injected from the injection well to each effected well is the key to achieving balanced injection and production of the well group and improving the efficiency of water flooding.In this paper,based on the production of Tahe Oilfield,a conceptual model of the calculation of the water diversion of carbonate fracture-cavity units is established based on the fracture-cavity structure and water distribution.The material balance method was used to derive the water diversion formula of closed pure oil fracture-cavity unit and storage water-containing fracture-cavity unit,and the corresponding calculation formula of water diversion under the near-well karst cave and near-well fracture model was established.For the fractured-cavity units with bottom water,the bottom water intrusion has a great influence on the water diversion.Due to the difficulty of calculating the water intrusion,the material balance method is no longer applicable to the calculation of the water diversion of the unit with bottom water.In this paper,the calculation of water distribution takes into account the effect of bottom water on water diversion for the first time.Therefore,the fracture-cavity unit with bottom water is divided into injection water to supplement only the reservoir,injection water supplements both bottom water and reservoir,and injected water supplements the bottom water only.According to the different performance of the strong and weak bottom water reservoirs,the production data is used to establish the calculation formula of the water diversion amount under the corresponding bottom water conditions.Because the strong and weak bottom water plays an important role in determining the water distribution of carbonate reservoirs and formulating water injection schemes,this study explored the limit of the strong and weak bottom water through the Eclipse model.Use the actual well group injection and production data to calculate the water distribution,and use the Eclipse model to verify the water division results.Finally,according to the comparison of the optimal flow rate ratio and the actual flow rate of each round,the on-site injection and production parameters are adjusted.Therefore,it provides guidance suggestions for the quantitative water injection development of carbonate reservoirs.