Vaporization Development By Injecting Natural Gas In High Water Cut Oilfield

At present,most of the main old oilfields at home and abroad have entered the stage of high water cut.In the later stage of oilfield water injection,the oil recovery rate is low,the water consumption is relatively large,the remaining oil is particularly dispersed,and the development efficiency is reduced.There is still a large amount of remaining oil that cannot be extracted.Therefore,how to improve the recovery of high water cut oilfields is a problem that needs to be solved in the exploitation of high water cut oilfields in China.This paper puts forward the method of improving oil recovery by injecting natural gas into high water cut oilfield.Firstly,based on the Winprop module of CMG software,the phase state of formation fluid is fitted,and the feasibility and vaporization effect of natural gas injection in high water cut oilfield are preliminarily studied.Secondly,based on the geological parameters of the Ansai oilfield research block,the inverse nine-spot well pattern model is established using the GEM module of CMG.The model of different water cuts in the study block was established by water flooding,and then the natural gas vaporization mining was studied.At the same time,the development scheme of water flooding and continuous natural gas flooding was simulated and compared.The results show that for high water cut oilfields,natural gas injection can improve oil recovery and reduce the comprehensive water cut of the oilfield.When the water injection pressure is 20.0MPa and the bottom hole flow pressure of the production well is 1.0MPa,natural gas is injected when the comprehensive water cut reaches 70%after water flooding,and the bottom hole flow pressure of the production well is adjusted to 3.0MPa.The simulated 30-year recovery rate can reach 44.90%,which is 8.36%and 2.83%higher than that of water flooding and continuous natural gas flooding,respectively,and the comprehensive water cut of the oilfield is reduced to 14.02%compared with water flooding.By comparing the component distribution of each component in the oil phase,gas phase and reservoir system at the end of the simulation of natural gas injection in high water cut oilfield,it can be obtained that the molar content of CH₄ in the gas phase at the leading edge of gas drive decreases,the molar content of C₃ decreases slightly,the molar content of C₂and C₄-C₉ components increases,and there is a small amount of C₁₀～C₂₀₊components,which proves that as the gas continues to advance,the injected gas continues to contact with the formation crude oil,and the light components in the crude oil are vaporized and act on the heavy components.After optimizing the parameters of natural gas injection model in high water cut oilfield,it is found that the recovery rate can be improved when the injected gas is mixed with some oilfield associated gas.The timely closure of the side well after gas channeling in the side well can maintain the average formation pressure and improve the recovery rate,and the final recovery rate can reach 67.19%.Shortening the well spacing under the inverted nine-point well pattern can still further improve the recovery rate.The conversion of high water cut oilfield to natural gas injection can improve the recovery rate and reduce the comprehensive water cut of the oilfield,which provides theoretical support for improving the recovery rate of high water cut oilfield in China.