Water Drive Gas Reservoir Recovery Forecast

With the development of the world oil industry,the exploitation of gas reservoirs are increasing speedily.The gas reservoirs are classified as constant-volume gas reservoirs and water drive ones according to water flooding.A large proportion of developed gas field are water drive gas reservoirs so that making a deeply study of it will contribute to exploiting a gas reservoir more rationally and more efficiently.The material balance equation was the first choice means when petroleum reservoirs engineers research how to develop the water drive gas reservoirs,because it takes no account of complicated underground seepage and demands less data,the water influx is the primacy puzzle utilizing the material balance equation to study the water flooding gas reservoirs because of the invasion of water that-makes the difficulties in calculating geological reserves and dynamic analysis.The paper is on the background of the actual problem to be solved. It is based on many literature investigations and analysis researches,by sorting the water-drive reservoirs and analyzing the conventional research methods,utilizing equation of motion, equation of state and equation of continuity for both the gas and water,get the non-linear partial differential equation.Because the coefficient items have the unknown functions K_rg(S_g),K_rw(S_w),S_g, S_w,to solve the PDA is actually to solve a counter-problem -the non-linear PDA with the unknown parameter.The paper adopts the numerical solution of differential equations,then the counter-problem has been converted to be a nonlinear objective function:(?)For the optimal problem,this paper has presented the numerical solution method and programmed to calculate.That is to say, giving a series of initialized iteration dispersed values for K_rg(S_g)_,K_rw(S_w),S_g,S_w on the difference points,by iterating to get the optimal solutions.,this paper has got the optimal theoretical pressure solutions P(r_w,t_k),which is compared with the actual pressures f(t)has the minimal errors.The variation trends for the optimal solutions P(r_w,t_k)is inosculated with the actual development of the water-drive gas reservoirs,the results indicates that the calculation method in this paper is reliable. Finally,to calculate the recovery of the water drive gas reservoirs, by utilizing the numerical simulation software and the optimal solutions P(r_w,t_k),and has predicted the final cumulative gas production.Utilizing the optimal principle and the material balance equation, with the inheritance arithmetic,this paper has programmed to solve the geological reserves.