A comprehensive review of remediation strategies for mitigating salt precipitation and enhancing CO2 injectivity during CO2 injection into saline aquifers.

Geological CO2 sequestration is a proven method for mitigating climate change by reducing atmospheric CO2 levels. However, CO2 injection often induces salt precipitation, leading to decreased formation permeability, which in turn limits CO2 injectivity and storage capacity. Conventional approaches, such as freshwater and low-salinity water injection, have been employed to mitigate salt precipitation. Despite their widespread use, these methods provide only temporary improvement and can be ineffective in some scenarios, resulting in long-term issues such as salt recrystallization and clay swelling. Given the complexity and significance of this issue, a comprehensive review of salt precipitation mechanisms and remediation techniques is essential. This paper critically examines the processes of salt precipitation during CO2 injection in saline aquifers and evaluates various remediation techniques aimed at improving CO2 injectivity. The paper reviews the influence of CO2 flow dynamics, geochemical reactions, and fluid properties on salt precipitation and pore throat accumulation, assessing the efficacy and limitations of existing mitigation methods. Additionally, the paper explores alternative techniques with potential for long-term CO2 sequestration, analyzing their advantages and drawbacks. Based on insights from the reviewed sources, the paper recommends exploring alternative treatment measures and the integration of hybrid solutions to enhance CO2 injectivity. The findings presented serve as a valuable reference for advancing research and practice in this critical area, offering a deeper understanding of the challenges and potential solutions for effective CO2 sequestration in saline aquifers.

A modelling study to evaluate the effect of impure CO2 on reservoir performance in a sandstone saline aquifer.

Carbon capture and storage (CCS) is expected to play a key role in meeting greenhouse gas emissions reduction targets. In the UK Southern North Sea, the Bunter Sandstone formation (BSF) has been identified as a potential reservoir which can store very large amounts of CO2. The formation has fairly good porosity and permeability and is sealed with both effective caprock and base rock, making CO2 storage feasible at industrial scale. However, when CO2 is captured, it typically contains impurities, which may shift the boundaries of the CO2 phase diagram, implying that higher costs will be needed for storage operations. In this study, we modelled the effect of CO2 and impurities (NO2, SO2, H2S) on the reservoir performance of the BSF. The injection of CO2 at constant rate and pressure using a single horizontal well injection strategy was simulated for up to 30 years, as well as an additional 30 years of monitoring. The results suggest that impurities in the CO2 stream affect injectivity differently, but the effects are usually encountered during early stages of injection into the BSF and may not necessarily affect cumulative injection over an extended period. It was also found that porosity of the storage site is the most important factor controlling the limits on injection. The simulations also suggest that CO2 remains secured within the reservoir for 30 years after injection is completed, indicating that no post-injection leakage is anticipated.

Reactive transport modeling of produced water disposal into dolomite saline aquifers: Controls of barium transport.

Experimental results on barium transport in dolomite are used to formulate, calibrate, and validate a reactive transport model of produced water disposal into dolomite saline aquifers. The model accounts for sorption, dissolution/precipitation reactions of minerals (dolomite, calcite, barite, gypsum, and witherite) and complexation and acid-base reactions of most abundant ionic species (H+, HCO3-, SO42-, Ca2+, Mg2+, and Cl-) in produced waters including Ba2+ which is the most common and abundant heavy metal present in produced water from oil and gas reservoirs. The model is applied to determine the chemical controls of barium transport in Arbuckle dolomite aquifers. The simulated scenario corresponds to produced water disposal through a Class II injection well located near an abandoned well that can facilitate the transport of barium to underground sources of drinking water (USDW). Simulation results reveal that most suitable dolomite aquifers to prevent the contamination of USDW by barium are dolomite aquifers of high SO42- content (>1000 mg/L). The mobility of barium which is promoted by the formation of Ba(Cl)+ and competition of cations (Ca2+ and Mg2+) for hydration sites of dolomite can be suppressed by the precipitation of barium as barite in dolomite saline aquifers of high SO42- content. A sensitivity analysis conducted using a two-level factorial design of experiments indicates that barium transport can be controlled by the initial concentration of a single ionic specie (mostly SO42-) or the concentration of various ionic species (e.g., SO42-, Cl-, and Mg2+). This depends on the chemical composition of both the dolomite saline aquifer and injection produced water. This work highlights the potentiality of a reactive transport simulation approach to conduct compatibility analysis of dolomite saline aquifers and produced waters to select dolomite aquifers and/or decide on treatment methods to prevent the contamination of USDW by barium.

Measurement and estimation of CO2-brine interfacial tension and rock wettability under CO2 sub- and super-critical conditions.

Saline aquifer storage is considered to be a promising method of carbon dioxide (CO2) mitigation. The CO2-brine interfacial tension (IFT) and the caprock wettability under reservoir temperature and pressure conditions are essential for storage capacity estimation. In this study, the CO2-brine (NaCl + KCl) IFTs were obtained by using the pendant drop method under 298-373 K temperature, 3-15 MPa pressure, and 1.0-4.9 mol·kg-1 salinity. A detailed analysis of the relationship of IFT with temperature, pressure, and salinity was conducted. In addition, an empirical equation was developed to estimate the CO2-brine IFTs in a wide range of temperatures, pressures, and salt molality. The contact angles (CAs) of brine on quartz, Berea Sandstone, and limestone surfaces in the presence of supercritical, liquid, and gaseous CO2 were measured by using the sessile drop method, and the wettability alteration of the rock surfaces in the presence of supercritical CO2 was systematically investigated. According to the results, the CO2-brine IFTs increased with salinity and temperature and decreased with pressure until reaching a plateau. For a CO2-mixed brine system, a linear relationship between the IFT increase (Δγ) and molality was observed. The CAs of the different rock samples varied with temperature and pressure. However, all the three rock samples became less water-wet when the CO2 phase state changed from subcritical to supercritical.

Microbial community structure in deep natural gas-bearing aquifers subjected to sulfate-containing fluid injection.

In the natural gas field located in central Japan, high concentrations of natural gases and iodide ions are dissolved in formation water and commercially produced in deep aquifers. In the iodine recovery process, the produced formation water is amended with sulfate, and this fluid is injected into gas-bearing aquifers, which may lead to infrastructure corrosion by hydrogen sulfide. In this study, we examined the microbial community in aquifers subjected to sulfate-containing fluid injection. Formation water samples were collected from production wells located at different distances from the injection wells. The chemical analysis showed that the injection fluid contained oxygen, nitrate, nitrite and sulfate, in contrast to the formation water, which had previously been shown to be depleted in these components. Sulfur isotopic analysis indicated that sulfate derived from the injection fluid was present in the sample collected from near the injection wells. Quantitative and sequencing analysis of dissimilatory sulfite reductase and 16S rRNA genes revealed that sulfate-reducing bacteria (SRB), sulfur-oxidizing bacteria, and anaerobic methanotrophic archaea (ANME) in the wells located near injection wells were more abundant than those in wells located far from the injection wells, suggesting that fluid injection stimulated these microorganisms through the addition of oxygen, nitrate, nitrite and sulfate to the methane-rich aquifers. The predominant taxa were assigned to the ANME-2 group, its sulfate-reducing partner SEEP-SRB1 cluster and sulfur-oxidizing Epsilonproteobacteria. These results provide important insights for future studies to support the development of natural gas and iodine resources in Japan.

Identification of the microbes mediating Fe reduction in a deep saline aquifer and their influence during managed aquifer recharge.

In this study, indigenous microbes enabling Fe reduction under saline groundwater conditions were identified, and their potential contribution to Fe release from aquifer sediments during managed aquifer recharge (MAR) was evaluated. Sediment and groundwater samples were collected from a MAR feasibility test site in Korea, where adjacent river water will be injected into the confined aquifer. The residual groundwater had a high salinity over 26.0 psu, as well as strong reducing conditions (dissolved oxygen, DO<2.0mg/L; oxidation-reduction potential, ORP<-100 mV) with high Fe(2+) concentrations. The indigenous microbes that mediate the reduction of Fe-minerals in this deep saline aquifer were found to be Citrobacter sp. However, column experiments to simulate field operation scenarios indicated that additional Fe release would be limited during MAR, as the dominant microbial community in the sediment would shift from Citrobacter sp. to Pseudomonas sp. and Limnohabitans sp. as river water injection alters the pore water chemistry.