Gradient Based Method For Injection And Production Optimzation Of Waterflood Reservoir

For waterflood reservoirs, water is generally injected into the reservoirs to maintain the reservoir pressure and to displace the oil towards the production wells.Ideally,while the injected water moves into the production wells, all the oil between the injection wells and the production wells can be sweeped . However ,because of the areal, intrastratal and interstratal heterogeneities of the reservoirs,the displacement is non-uniform.Most of the injected water move into the production wells along the preferential flow paths ,such as the high permeability layers or the high permeability zones, much oil in the low permeability layers or the low permeability zones can not be produced as unsweeped by the injected water,and cause the low water flooding recovery.Injection and production optimal control of water flooding uses the system theory.The reservoir is seen as a complex dynamic system.The system uses the ground data of the oil and the water wells as the basic data .The water injection rate or the injection pressure of the injection well is seen as the input of the system and the oil prodution rate,or the liquid production rate or the bottom hole flowing pressure is seen as the output of the system.By optimizing the injection and the production working system of the well ,the injected water can be sweeped into the production well as uniform as possible,and thus increase the recovery and the economic efficiency of the reservoir.In this paper,the reservoir production system is first analysised,then optimization techniques and the reservoir simulation technology are combined organicly.This paper uses NPV(Net Present Value) as the objective function,injection and production parameters of the well as the decision variables,and reservoir flow differential equations as the constraints,then established the optimization mathematical model of injection and production control.According to the characteristics of solving method for adjoint equation, the fully implicit solving method of reservoir flow equations and the adjoint method of calculating the gradient are combined ,and modified the adjoint method of calculating the gradient.This modified adjoint method can increase the efficiency of calculating the gradient.Then use the steepest descent method to solve the optimizaiton mathematical model with the gradient calculated by the modified adjoint method, and program the optimization procedure for injection and production controling.Use the optimization procedure to optimize the injection and the production on a multi-layer heterogeneous conceptual model and analysis the result,which confirms the theoretical prediction.The injection and production optimizaion of a real block of LD5-2 oil field is studied,which is performed under four different constraints.The results of the four cases indicate that all the results under different constraints can improve the efficiency of the oilfield development contrast to the base case.