| Block A of Tuha oilfield is a low permeability reservoir whose porosity is15.3%, permeability is0.25■21.5mD, and viscosity is160■600mPa-s. Because the natural energy is insufficient, and early development and water flood’s result is poor, selection of the appropriate development approach is the primary problem restricting benefits of Tuha heavy oil reservoir.As gas flooding enhanced oil recovery (EOR) technology has been wildly used in domestic and foreign reservoir development, feasibility evaluation of this technology in low-permeability heavy oil reservoir has great significance.This paper studied Tuha Oilfield two heavy blocks with the means of laboratory experiments study, and carried out gas injection EOR laboratory research including crude oil PVT tests, gas injection swelling experiments, thin tube experiments, solid-phase deposition experiments, long core flooding physical simulation experiments, quantitative evaluation of effects of the different media of gas injection, gas injection methods on gas and oil displacement and the feasibility of gas injection.And the following conclusions and understandings are obtained:(1) The CO2and flue gas injection swelling experiments for the same formation fluid showed that effect of CO2injection on viscosity deduction is more obvious. For flue gas injection, the higher the viscosity of the formation fluid viscosity is, the stronger the effect is.(2) The thin tube experiments showed that when the injection pressure is up to46.3MPa (formation fracture pressure is35MPa), recovery is52.7percent, which is far below the standard gas miscible flooding recovery. So the block can only use non-miscible flooding.(3) Flue gas displacement solid phase deposition multiple contact experiment results show that with the increasing volume of injection gas, solid phase deposition content increases, but deposit amount is less than0.1%. So formation damage of gas injection solid phase deposition process can be neglected.(4) When viscosity of formation fluid is159mPa-s, different injection methods experiment results show that the recovery of flue gas-water alternating injection is71%and the injected amount is the least (2.07HCPV), average displacement pressure is low (7.14MPa), which is considered the preferred injection method.(5) When viscosity is555.8mPa-s, different injection fluid experiment results show that the effect of gas displacing oil is up to61%, which is significantly higher than the direct water flooding(37%); CO2-water alternately displacement breakthrough time is late (0.6■0.7HCPV), injection volume is little (2.01HCPV), and flooding effect is the best (61%), which is selected as the best injection method.(6) When viscosities are159.5mPa·s and555.8mPa·s, ultimate recovery of flue gas-water alternating flooding are70.88%and56.92%,respectively, indicating that the lower the viscosity is, the higher the recovery is. For the two blocks with permeability of21mD and2.1mD, the average displacement pressure of CO2flooding are8.31MPa and8.52MPa respectively, indicating that the lower reservoir permeability is, the greater the required injection pressure is. |
