Study On Feasibility Of Increasing Recovery Of CO In Sub - Condensate Gas Condensate Gas Reservoir

Nowadays, for the condensate gas reservoir with high condensate oil content, the research on the enhanced oil recovery with CO2injection are still in the stage of exploration, and field practice have not yet been reported. The past few decades have witnessed primary progress in the EOR of oil reservoir with CO2injection. Several filed test have been carried out some oil field in eastern, resulting in good economic and social benefits. However, few relevant research is conducted on the condensate reservoir. Especially for the condensate gas reservoir with high condensate oil content, many fields are in lack of in-depth study, such as the formation fluid phase behavior during the CO2injection, miscible flooding mechanism, the seepage flow characteristics and the microcosmic seepage flow mechanism considering the diffusion and adsorption effects, etc.With the combination of geological modeling, in-house experiment and numerical simulation, this paper aims to reveal there maining oil and gas system phase behavior, miscible flooding mechanism and the seepage flow characteristics in the condensate gas reservoir with CO2injection, thus providing theoretical and practical basis for the reasonable development strategy design. The main research results are as follows:(1) With the method of phase control modeling, the formation geological model is established for Hua-2Block condensate gas reservoir, which agrees with the practical reservoir description.(2) The PVT phase behavior experiment of the original formation indicates:the COndensate oil saturation increases as the formation pressure drops, and the formation fluid belongs to the condensate gas with high condensate oil content.(3) The expansion experiment with injection of different proportions of CO2shows:after the CO2injection, the bubble point pressure of the condensate oil-gas system displays an increasing trend; the growth amplitudeis gradually expanding, while the overall growth is relatively small; the larger the proportion of the injected CO2, the lighter the reservoir fluid would be.(4) The change of the liquid phase volume after the injection of different proportion CO2shows:when the injected gas amounts to a certain value, the phase behavior inversion could occurs to the condensate oil-gas system, which transforms into the condensate gas system; The p-X phase diagram shows:the first contact miscibility pressure of the present formation fluid is23.8MPa, much higher than the present formation pressure(15MPa); the pseudoternary phase diagram research indicates:the minimum miscibility pressure for the present remaining fluid is21.6MPa theoretically.(5) The slime tube experiment and modelings:under the present formation pressure, the minimum miscibility pressure of the CO2injection is20MPa, lower than the original formation pressure. Therefore, with the injection pressure kept at or higher than the minimum miscibility pressure, the injected CO2can be miscible with the remaining fluid system, thus enhancing the condensate oil recovery greatly.(6) The miscible phase mechanism research indicates: under the same injection volume, the higher of the injection pressure, the shorter the transition zone would be, and the CO2dissolution content in the remaining oil grows larger. Accordingly, heavier drop will be viewed in the oil viscosity, getting closer to that of the gas phase. Therefore, the oil-gas interfacial tension gets lower, and the miscible degree is higher, resulting in much higher displacement efficiency. Under the same injection pressure, the larger of the injection volume, the larger swept region would be.(7) A combination of the long core displacement experiment and numerical simulation reveal the CO2drive flow mechanism that different exploitation has different recovery and CO2drive flow is better than depletion and water drive. The pressure recovery is more high, the oil displacement more evidentConsidering the CO2diffusion and adsorption of condensate gas reservoir influence recovery degree, more attention should be paid to the process of gas reservoir development.(8) Numerical simulation of exploitation scheme take four factors into consideration, including injection-production pattern, inject rate, injection and production gas ratio, pressure maintain, compared with the basic scheme, the favor scheme show that the pressure above the MMP can improve the gas recovery much greatly which the condensate oil recovery has improved24.66%to49.56%and natural gas has improved24.66%to75.57%.