Dynamic Characteristics of Supercritical CO2 Injection in Depleted Carbonate Oil Reservoir for its Sequestration Potential: An Experimental Study

Abstract

To reduce the amount of CO2 in the atmosphere and mitigate the severe consequences of climate change, capturing, utilizing, and storing CO2 has become very important for human survival. For utilization of CO2 in reservoir engineering practice, CO2-enhanced oil recovery (CO2EOR) as a mature technology has been widely applied in several types of reservoirs such as sandstone, carbonate, and shale gas/oil reservoirs, and the focus of concern is to study oil recovery efficiency and its influencing factors over the past few decades. Recently, more and more researchers are paying great attention to the geological storage of carbon dioxide in depleted oil reservoirs where scCO2 is injected as a displacing agent for secondary and tertiary oil recovery. Unfortunately, there is a lack of laboratory research on scCO2 sequestration in such reservoirs in terms of capacity, two-phase flow (the mixture of scCO2 and residual oil and water), injectivity of scCO2, and permeability loss of rocks. In this study, we evaluate the dynamic characteristics mentioned above subjective is based on laboratory results. Several experiments, including different injection modes such as horizontal and vertical injections, and their effects on displacing residual oil and water by scCO2 after water flooding has been performed using reservoir carbonate rock, live crude oil, and seawater under reservoir conditions. As a result of this study, the experimental methodology to obtain the scCO2 storage capacity of the depleted oil reservoir was proposed for the first time, and the calculation of scCO2 storage capacity assumes that the scCO2 dissolves into residual water and oil after scCO2 injection. This study found that the main scCO2 storage mechanism is pore space storage (structural trapping) for depleted oil reservoirs. Based on experimental results, the storage efficiency is found to be closely related to the permeability of rocks. In addition, the scCO2 injectivity and permeability loss of the rock were evaluated for a depleted carbonate reservoir, which was displaced by scCO2 injection at the final stage of the oil recovery process. The experimental results show that the scCO2 injectivity is not strongly affected, although the relative permeability to scCO2 slightly decreased after the scCO2EOR process. The experimental results can be applied directly for the evaluation and strategy of scCO2 storage and can be used to simulate the performance of the injection process of scCO2 storage.

Experimental study on dual benefits of improvement of CO2 enhanced oil recovery and its storage capacity for depleted carbonate oil reservoirs

“…These include properties of the formation and caprock, residual phases (water and oil), and maximum CO 2 saturation. (Orlic, 2016;Cao et al, 2020); 3) The reservoir environmental requirements for CO 2 storage sites are similar to those for oil reservoirs under pore pressure and overburden pressure caused by overlying formation (Carroll et al, 2014;Orlic, 2016;Cao et al, 2020); 4) Because of the prolonged interaction between liquid phases (water and oil)/mineral/CO 2 during the CO 2 -EOR injection process, some dynamic parameters such as injectivity and relative permeability of CO 2 tend to be stable, which favors injecting CO 2 only into the formation for the CO 2 storage (Zhou et al, 2023).…”

“…Real-time monitoring of oil and water production allowed for the calculation of oil recovery through the initial sc-CO 2 miscible injection and measurement of residual water in the composite cores. The amount of residual water in the cores was utilized to estimate the capacity of sc-CO 2 solubility in residual water (Zhou et al, 2023).…”

“…The displacement efficiency achieved through sc-CO 2 miscible injection was directly influenced by pore space utilization, which determines the distribution of the sc-CO 2 saturation, residual oil saturation, and water saturation when the injection process was completed. Evaluating the total sc-CO 2 storage capacity relies primarily on parameters such as sc-CO 2 saturation (structure trapping), residual oil saturation (dissolution trapping of sc-CO 2 in residual oil), and residual water saturation (dissolution trapping of sc-CO 2 in the residual water), which are measured at the laboratory scale (Zhou et al, 2023). It's important to note that the mineral trapping resulting from the interaction between sc-CO 2 , seawater, and carbonate rock is negligible in this study, as it may not fully represent the conditions observed in an actual oil field practice (Benson et al, 2012).…”

“…Additionally, the research found that properties of natural fractures, such as porosity and permeability, changed over production time, unlike the molecular diffusion-driven CO 2 -EOR process seen in field shale oil reservoirs. CO 2 storage sites in oil or gas reservoirs can be categorized into depleted oil reservoirs, depleted gas reservoirs, operational oil reservoirs, and saline aquifers (Korbøl and Kaddour, 1995;Sengul, 2006;Wei et al, 2023;Zhou et al, 2023). The primary mechanisms contributing to the CO 2 storage capacity in operational or depleted oil formations are as follows: Structural and stratigraphic trapping of gaseous CO 2 and sc-CO 2 , solubility trapping in the formation water or remaining water after waterflooding and residual oil, and mineral trapping (Shaw and Bachu, 2002;Shen et al, 2009;Sun and Chen, 2012;Ding et al, 2019;AlRassas et al, 2021).…”

“…Comparatively, when comparing an oil reservoir to a saline aquifer as a CO 2 storage site, the oil reservoir contains a substantial amount of oil within its pore space, while the depleted oil reservoir predominantly contains remaining oil and residual water, in addition to the formation water and bottom water (Shaw and Bachu, 2002;Shen et al, 2009). Zhou et al (2023) reported that when water flooding is employed as the secondary production technique, followed by CO 2 injection as a tertiary method, some volumes of fluids, such as seawater and residual oil, occupy in the pore space of the formation.…”