Analysis of Secondary and Tertiary High-Pressure Gas Injection at Different Miscibility Conditions: Mechanistic Study

Abstract

Summary In the current survey, the time required to rupture the water film shielding the oil as a result of oil swelling caused by the diffusion of dissolved gas in the water phase and trapped oil behind it has been investigated in porous medium at high pressure and temperature. To study the active mechanisms, the experiments have been conducted with two different types of injectants: carbon dioxide (CO2) and methane (with different solubility in water), under different miscibility conditions at equal reduced pressures. Experimental observations have been interpreted using theoretical studies. Furthermore, the time of water-film rupture has been identified in production data and matched by an analytical model. This time and its monitoring during various gas-injectant types and regimes under reservoir conditions have not been previously addressed. The results show that water film reduces the performance of oil recovery by limiting the interface of oil and gas phases. Under such a condition, the best scenario is miscible gas injection because the gas can effectively swell the oil and rupture the water shield. At miscible and near-miscible conditions, the time required to eliminate the water film increases as the injectant solubility in water decreases; however, there is a negligible difference at the immiscible regime. The trend of oil-recovery curves after rupture of the water film shows that oil swelling is one of the main mechanisms involved in water-trapped oil recovery. These results suggest practical guidelines to better understand the effect of the water-shielding phenomenon in the field of tertiary gas injection. The outcome of this integrated study could effectively increase the knowledge of shielded oil recovery using different gas-injectant types under various miscibility conditions and could prepare the required basis for compositional simulation of waterflooded oil production during tertiary gas injection.

Oil production performance and reservoir damage distribution of miscible CO2 soaking-alternating-gas (CO2-SAG) flooding in low permeability heterogeneous sandstone reservoirs

“…The larger oil volume and lower viscosity both allow the oil to enter the former CO2 flow pathways and CO2 breakthrough channels [11][12] . The soaking period provides the extra time the CO2 needs to interact fully with the residual oil, substantially increasing CO2 sweep and displacement efficiency in the subsequent secondary CO2 flooding, which is the third phase of the process.…”

“…Regrettably, only a few core-flooding experiments studying the technical benefits and significant potential of SAG injection have previously been carried out and reported in the literature [10][11][12][13][14] . The studies, however, are informative enough to allow us to target several important variable parameters and processes which would need to be studied.…”

A data analysis of immiscible carbon dioxide injection applications for enhanced oil recovery based on an updated database

“…The CO 2 injection pressure and the reservoir temperature are two extremely important factors that will impact the CO 2 dissolution in the oil, and also the oil swelling, and thus will impact the productivity of the immiscible CO 2 injection process. As the reservoir temperature increases, the CO 2 solubility in the oil will decrease due to the increase in the activity of the gas molecules which will result in a tendency of the molecules to liberate from solution rather than become soluble in the oil [29,30]. This decrease in solubility will result in a lower oil swelling, which in turn will result in a decrease in oil recovery due to the decrease in the interaction of the CO 2 with the oil.…”

A new approach for predicting oil recovery factor during immiscible CO2 flooding in sandstones using dimensionless numbers

“…As the aim of this paper is to develop a correlation for immiscible CO 2 flooding in sandstones, the lithology of the porous media and the state of injection, attempts were made to keep the parameters the same in all experiments. The range of the collected data is shown in Table 1 (Cao and Gu 2013;Kazemi et al 2015;Khosravi et al 2014Khosravi et al , 2015Nobakht et al 2007;Norouzi et al 2018;Shyeh-Yung 1991;Wang and Gu 2011).…”