The article describes the solution and the results of practical application of the developed numerical and analytical model NAMGC which is based on a GORM numerical model and a CRM analytical model. On the basis of the developed model, a computer program has been created which allows to simulate the operation of a horizontal well in the conditions of gas coning and reservoir pressure maintenance. The data on Verkhnechonskoe field were used to perform the model runs. New functional features of the NAMGC model are associated with the account of the probability laws for the control parameters to solve the optimization task of automatic model matching. The studies of the influence of the type of distribution function - uniform and normal – have been carried out. The results of the model runs showed that only by using a uniform distribution one can achieve an acceptable quality of model matching. It was demonstrated that if the residual is only used for oil production, that leads to acceptable quality of the simulated bottomhole pressure profile and vice versa. The numerical assessment of the impact on the GOR of different geological and technological parameters of the Vc target shows that during well operation, the average GOR is characterized by an exponential dependence of the average BHP; therefore, reducing the bottomhole pressure or increasing the well rate will lead to a rapid increase in GOR. The wells of the under-gas-cap zone will produce the highest quantities of oil if a horizontal borehole is drilled just near the bottom of the reservoir. In this case, the wells can be operated with a maximum drawdown, providing acceptable GOR. Maintaining the reservoir pressure has a positive but non-uniform impact on the GOR - a decrease in BHP in a production well makes the GOR less sensitive to the volume of injected water.
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