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Deep saline aquifers are promising locations for carbon sequestration, but the impact of the CO2injection on rock properties requires careful investigation. This study will examine the effects of CO2-saturated brine injection on limestone, specifically analyzing how pore pressure influences wormhole formation and subsequent changes in the petrophysical and geomechanical properties. Four Indiana limestone samples, each with dimensions of 1.5 in. in diameter and 3 in. in length, were utilized. These samples exhibited an average porosity of 15.7% and an average permeability of 2.6 mD. During the experiments, the samples were subjected to one of selected pore pressure values (4000, 3000, 2000, and 1500 psi) and a temperature of 60 °C, with a brine concentration of 120,000 ppm mixed with CO2at a ratio of 70:30. Notice that the pressure was kept in the accumulator at 1200 psi initially before compressing it to the desired pressure to maintain the same mass of CO2in all experiments. An injection rate of 1 cm3/min was employed for the coreflooding experiments. Before and after coreflooding, Young’s modulus (YM) and Poisson’s ratio of the samples were measured at various confining pressures. Additionally, the porosity, permeability, and surface hardness of the treated samples were assessed. A micro-CT scan was employed to visualize the generated wormholes and quantify their volumes. Our study demonstrated that among the four tested injection pressures, 2000 psi yielded the lowest pore volume to breakthrough (PVBT). No clear trend was observed between PVBT and pore pressure. However, a strong correlation emerged between the mechanical properties of the treated samples and pore pressure values. The investigation established that increasing injection pressure results in greater damage to the core, as evidenced by reductions in both surface hardness and dynamic YM.

Excessive water production in the oil industry is a persistent challenge, impacting operational costs and environmental concerns related to water disposal. Fractures and channels are widely recognized as significant sources of water production in reservoirs produced under a water drive mechanism. Recent investigations have shown the efficiency of nanosilica gel in mitigating water production in high-permeability formations. However, these studies have not thoroughly evaluated its performance in addressing fractures as potential pathways for water migration. Therefore, this study investigates the performance of nanosilica gel in fractures and channels, which are major sources of water production. Four carbonate core samples of 1.5-inch diameter and 3-inch length were utilized: two containing an induced fracture and the other featuring an open channel. Core samples underwent core flooding experiments, computed tomography (CT) scans, and nuclear magnetic resonance (NMR) T2measurements. The coreflooding system was utilized to treat carbonate samples with two gels: a nanosilica gel solution comprising 75 (wt %) nanosilica and 25 (wt %) activator, and polyacrylamide/polyethylenimine (PAM/PEI) gel of (9/1) wt %. The injection of a sufficient volume of the gel ensured successful placement and curing at a high temperature of 200 °F. The nanosilica demonstrated exceptional plugging efficiency, with a remarkable 100% reduction in permeability and enduring durability under varying differential pressures, reaching up to 1000 psi. This performance was at the same level of plugging efficiency obtained with PAM/PEI gel with 9/1 (wt %) concentration. CT scans and NMR analysis further confirm the uniform distribution of both gels and the successful displacement of brine from the fractures and channels.

Global climate change is one of the most pressing environmental challenges facing the world, and numerous efforts are currently being undertaken to mitigate and reverse the effects. Carbon dioxide (CO2) is a major contributor to greenhouse gas emissions, totaling 76% of emissions. Hence, numerous methods have been proposed and utilized to convert, utilize, or permanently store CO2. A typical example is the dual application of CO2for enhanced oil recovery (EOR) and subsequent storage, which is highly required in the oil and gas industry due to the widespread availability of marginal fields and depleted oil reservoirs. Nonetheless, the injection of pure CO2into underground geologic formations faces some challenges owing to its high mobility, which can cause early breakthrough of the injected gas. As a result of these challenges, a significant amount of hydrocarbon is bypassed during the EOR process, which leads to poor sweep efficiency. To address these challenges, the utilization of CO2foam for EOR and subsequent storage is being examined. Foam enhances storage capacity by increasing a reservoir’s sweep efficiency and minimizing early breakthrough, which allows more CO2to fill the empty pore spaces. In this paper, the application of CO2foam for EOR and CO2geological storage (geo-storage) is reviewed. First, an overview of the CO2foam flooding process is provided. Moreover, the trapping mechanism of CO2geo-storage by foam is discussed. Besides, existing experimental studies on improving the storage capacity of CO2are analyzed. Finally, the technical challenges facing the application of CO2foam are identified, and recommendations for future research are offered.