Study On Development Laws And Technical And Economic Limits In CO₂ Flooding For Low Permeability Reservoir

The paper reviews full history on CO2 flooding and draws conclusions on the present situation in the world, as well as open questions. The paper describes the physical and chemical properties of CO2 and sums up the mechanism of CO2 enhanced oil recovery, as well as displacement patterns and injection modes. In the chapter of the minimum miscibility pressure, it firstly introduces the factors influencing the minimum miscibility pressure. And then it detailedly depicts the different methods to determine the minimum miscibility pressure, including the experimental method, the empirical formula method and the numerical simulation method.In the chapter of the development laws in CO2 flooding, it firstly compares the difference between the depletion, water flooding, continuous gas flooding and gas alternating water flooding. Compared with the other displacement patterns, gas alternating water flooding can significantly enhance oil recovery. And it intimately presents the development laws in gas alternating water flooding, as well as optimizes plug number, single slug size, gas injection rate and gas-water slug ratio. If the bottom hole control pressure is constant, the best gas-water slug ratio is various, which is influenced by permeability, gas injection rate and bottom hole control pressure and other factors. The best ratio is more sensitive with permeability, followed by gas injection rate and bottom hole pressure. As we all know, permeability plays an important role in gas alternating water flooding. And it makes comparisons considered permeability size, permeability anisotropy in horizontal plane, permeability ratio of horizontal plane and vertical plane, rhythmic reservoirs, and composite reservoirs, concluding their development laws. The development indexs in homogeneous reservoir are better than the other reservoirs, followed by positive rhythmic and positive composite reservoirs, and then inverted rhythmic and inverted composite reservoirs. Moreover, it also presents study on different injection time in the alternate displacement process after depletion and water flooding, summing up their development laws.Genarally, the earlier injected CO2, the more favorable for enhanced oil recovery. The paper compares the difference between gas alternating water flooding and water alternating gas flooding. The former is superior to the latter.In the chapter of the economic evaluation, the recovery probability and risk factor are introduced. By calculation, the recovery probability in water flooding is greater than alternate flooding, while the recovery risk factor in the former is less. Therefore, compared with water flooding, there is a greater risk in CO2 flooding. According to certain block of Jilin Oilfield, based on the recovery changes in law and economic evaluation, it makes analysis different factors influencing the economic evaluation in alternate flooding and water flooding, which includes reservoir thickness, reservoir permeability, oil viscosity, reservoir porosity, oil saturation and permeability ratio of horizontal plane and vertical plane, and identifies an optimization standard on blocks.