Key technologies and field practice of large-scale gas injection development in offshore low-permeability reservoirs
It is difficult to characterize the degree of gas channeling during gas injection development in offshore low-permeability reservoirs because the composition of injected gas differs greatly,and the coupling calculation of wellbore temperature and pressure is complicated.The phase change law and mixing mechanism of mixed gas injection from different gas sources were studied through laboratory experiments.The results show that the oil recovery of gas injection flooding is about 30 percentage points higher than that of water injection flooding,and the miscible pressure of the reservoir increases gradually during the injection of mixed gas sources.The wellbore fluid temperature and pressure coupling model and reservoir suction capacity equation are established.Through the further coupling of the model and the equation,the real-time dynamic monitoring chart of gas injection wells is obtained.A method to quantitatively characterize the degree of gas channeling by using the underground volume proportion of invalid circulating gas is proposed,which realizes the quantitative characterization of the degree of gas channeling in the process of gas injection development.The research results have guided the production optimization of WZ12-1 Oilfield,the first offshore gas injection project,and the development plan of WC9-7 Oilfield,the largest offshore miscible flooding project,with good application effect in low-permeability reservoirs in the western South China Sea.
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