Optimization Of Injection Parameters For Gas-water Alternative Displacement Technology In Extra-low Permeability Reservoirs

Gas-water alternative displacement technology can give full play to the advantages of water drive and gas drive and improve oil displacement efficiency.At the same time,it can stabilize the displacement front and improve the sweep efficiency.It is an effective technical methods to improve the recovery rate of extra-low permeability reservoir.Because of the less application of gas-water alternative displacement technology in extra-low permeability reservoir,it is necessary to study the distribution and seepage mechanism of oil,gas and water in the process of gas-water alternative displacement for extra-low permeability reservoir,and optimize the corresponding injection parameters in the target block.Based on the tree-like network structure,this paper analyzes the fluid distribution and seepage mechanism of extra-low permeability reservoirs with different wettability in the initial stage,water flooding stage and gas-water alternative displacement stage respectively.Based on the reservoir geological characteristics,pore throat structure characteristics and reservoir physical properties of T80 block,the fluid distribution near injection wells,between injection wells and production wells and near production wells in the process of gas-water alternative displacement is quantitatively analyzed.The experiment of gas-water alternative displacement is carried out by using long core displacement device.Based on the ideal numerical model,the sensitivity of injection parameters is analyzed by single factor analysis.On this basis,the actual numerical model of C49 well cluster is established.The development plan is designed by orthogonal test.The best development plan is selected by range analysis.It is found that the gas phase occupies the large pore throat with r?600 nm in T80weak water wet reservoir during gas water alternate flooding.The pore throat with r<400 nm occupied by water phase.The oil phase is displaced into the pore throat of medium size with 400?r<600 nm.The long core experiment and the sensitive parameter analysis of the ideal numerical model show that there is an optimal range of gas water ratio,alternate period and injection rate.The best development plan is obtained by using the actual numerical model and the orthogonal test method:the injection is 12 m~3/d;the gas water ratio is 2:1;the alternative period is 60 d.The order of influence on development effect is:the injection rate is the highest;the gas water ratio is the middle;and the alternation period is the lowest.