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

Abstract

AbstractTo 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.