Study On The Minimum Miscibility Pressure Of Mixed Gas Of CO₂-N₂

This paper is part of National Science and Technology Major Project in 13 th Five-Year,?2017ZX05009004?"low permeability and dense reservoir high efficiency improvement of recovery technology" the task "low permeability and ultra-low permeability reservoir compound gas improvement CO₂ gas drive feasibility study".In this paper,CMG has been used to predict the minimum miscibility pressure of pure carbon dioxide and crude oil,the minimum miscibility pressure of carbon dioxide nitrogen gas mixture and crude oil,and the displacement efficiency of the combination of carbon dioxide and nitrogen slug.The minimum miscibility pressure of carbon dioxide and crude oil is 25.9 MPa and 27.8MPa respectively at the temperature of 90 ? and 108 ? at the temperature of the oil layer at the oil layer and 108 ?,respectively,as the reference value.PVTI is used to fit the data in the reservoir numerical simulation software Eclipse.The CMG method is used to predict that the minimum miscibility pressure of carbon dioxide and crude oil is 25.66 MPa and 29.44 MPa,respectively,when the oil layer temperature is 90 ? and 108 ?,and the relative error between the measured values of the experimental method and the fine tube experiment method is 1.21% and 5.56%,respectively.All are 3.39%.The minimum miscibility pressure of carbon dioxide and crude oil in the 101 block of tree 101 area under the same conditions is calculated by the method of empirical formula with relatively good adaptability.The average relative error between the Silva method and the Emera-Sarma method is 3.30% and 4.68%,respectively.The error of the results is larger than the result of the CMG calculation,indicating the use of CMG calculation.The minimum miscible pressure between carbon dioxide and crude oil is accurate and reliable.Secondly,the homogeneous conceptual model was established by using the component model GEM in CMG.After calculation and fitting,the minimum miscibility pressure of carbon dioxide mixed with different nitrogen gas was simulated,and the relation curve of the minimum miscibility pressure and different nitrogen content mixed gas was drawn,and the exponential function curve was shown with the mixture gas.With the increase of nitrogen content,the miscibility pressure increases rapidly,the nitrogen content in the mixture increases by 1% and the miscibility pressure will increase by 1.15 MPa,which makes the adaptability of the mixed gas flooding worse,and the displacement efficiency of the mixed phase flooding is gradually reduced.Finally,the 0.3PV CO₂+ follow-up N2 slug oil displacement is simulated,and the recovery rate is 96.24%,not less than the recovery rate of 96.21% when the pure carbon dioxide is displaced.It shows that it is difficult to realize the nitrogen carbon dioxide miscible displacement,and the combination of carbon dioxide plus nitrogen slug displacement mode can also achieve the ideal improvement of recovery efficiency.