OPTIMIZATION OF GAS INJECTION PARAMETERS FOR CO2 FLOODING IN OFFSHORE LOW PERMEABILITY RESERVOIRS

In order to improve the development effect of CO2 flooding in low permeability and thick reservoir, this study takes cumulative oil production, daily oil production and dynamic parameters as evaluation indexes, and carries out the optimization process of CO2 flooding gas injection parameters by using the Eclipse numerical software. Considering the problems of large reservoir thickness, strong vertical heterogeneity and structural dip angle of about 20 degrees, we adopts the method of plugging high permeability layer for displacement development. Taking Bohai A oilfield as an example, the CO2 flooding parameters are optimized. The results show that the mixed flooding of 90% CO2 + 5% C-5 + 5% C-6 is more conducive to the balanced advance of underground crude oil, and the area with oil saturation of 0 is larger. Gas injection 3 months in advance can increase the formation pressure, delay the depletion of formation energy and improve the production effect. When the gas injection rate is 50 x 10(4)m(3)/d, it can not only promote the mixing of oil and gas, expand the gas swept area, but also inhibit the occurrence of gas channeling. The cumulative oil production in 30 years is 194.5 x 10(4)t, which is 22.7% higher than that of the original scheme. The recovery ratio is increased from 29.4% to 36.1%, increased by 6.7%, and the production gas oil ratio is decreased by 51.1%. This combination of gas injection can effectively improve the production efficiency of the low permeability reservoir.