Effect of Carbon Dioxide Dissolving in Formation Water on the Mechanism of Oil Displacement

Abstract

In order to study the effect of CO2 dissolving in formation water on the process of CO2 injection, a thermodynamic model of CO2-hydrocarbon-formation water has been used to study the dissolving law of CO2 in formation water and oil-gas-water phase behavior considering the CO2 dissolution in formation water. Based on compositional model considering the dissolution of CO2 in formation water, a dimensional model for long core CO2 displacement is presented to simulate the oil displacement efficiency, gas/oil ratio, oil or gas saturation profile, the solubility of CO2 in in-place oil or formation water with grid distance in the process of long core displacement of CO2 injection. The results show that the solubility of CO2 in formation water increases with increasing pressure and decreases with increasing temperature, and that the solubility of CO2 in formation water is usually about 5.5 wt% at the condition of reservoir pressure and temperature. In addition, oil saturation and gas phase saturation with the consideration of CO2 dissolving in formation water lag behind those without consideration of CO2 dissolution, which results in later breakthrough time for CO2 injection. Moreover, residual oil saturation with considering CO2 dissolving in formation water is higher than that without considering CO2 dissolution at the condition of the same hydrocarbon pore volume for CO2 injection, and the ultimate recovery for the former is lower than that for the latter when pouring into 0.3 hydrocarbon pore volume of CO2.

Review on Oil Displacement Technologies of Enhanced Oil Recovery: State-of-the-Art and Outlook

“…CO 2 flooding can greatly increase the production of crude oil. CO 2 diffuses the molecules in the crude oil, reducing its tension and increasing its flow. , CO 2 also improves the permeability of crude oil. Carbonic acid is produced in the process of carbon dioxide injection so that the blockage in the pore throat is dissolved by carbonic acid to dredge the pores, which promotes the flow of crude oil and enhances the exploitation capacity and production of crude oil.…”

Application and Research Progress of CO2 Stimulation Technology in Unconventional Oil and Gas Reservoirs: A Review and Prospect

“…Meanwhile, the volume expands. Eventually, it reaches saturation and no longer absorbs. − In addition, water can also absorb CO 2 . Its viscosity increases when CO 2 is continuously absorbed.…”

“…The water-plugging effect is overcome by crude oil expansion. , In addition, crude oil will also expand because of the absorption of CO 2 in small fractures and pores. This causes crude oil to be squeezed out of pores and fractures, thereby increasing crude oil recovery. , CO 2 is released to provide energy with continuous exploitation. In addition, continuously injected CO 2 can directly provide energy by expansion after the amount of absorption reaches the limit .…”

“…Meanwhile, the properties of the two phases will become more and more similar when CO 2 is absorbed. This reduces the interfacial tension between the two. ,, Eventually, the two are mixed to form a miscible phase when their interfacial tension is equal to zero, as shown in Figure . ,, In addition, CO 2 is easier to enter pores when their interfacial tension is reduced, thereby improving recovery …”

“…This causes crude oil to be squeezed out of pores and fractures, thereby increasing crude oil recovery. 58,68 CO 2 is released to provide energy with continuous exploitation. In addition, continuously injected CO 2 can directly provide energy by expansion after the amount of absorption reaches the limit.…”