CO2 Geological Storage Research Articles

Sensing at the Nanoscale Using Nitrogen-Vacancy Centers in Diamond: A Model for a Quantum Pressure Sensor.

The sensing of stress under harsh environmental conditions with high resolution has critical importance for a range of applications including earth's subsurface scanning, geological CO2 storage monitoring, and mineral and resource recovery. Using a first-principles density functional theory (DFT) approach combined with the theoretical modelling of the low-energy Hamiltonian, here, we investigate a novel approach to detect unprecedented levels of pressure by taking advantage of the solid-state electronic spin of nitrogen-vacancy (NV) centers in diamond. We computationally explore the effect of strain on the defect band edges and band gaps by varying the lattice parameters of a diamond supercell hosting a single NV center. A low-energy Hamiltonian is developed that includes the effect of stress on the energy level of a ±1 spin manifold at the ground state. By quantifying the energy level shift and split, we predict pressure sensing of up to 0.3 MPa/Hz using the experimentally measured spin dephasing time. We show the superiority of the quantum sensing approach over traditional optical sensing techniques by discussing our results from DFT and theoretical modelling for the frequency shift per unit pressure. Importantly, we propose a quantum manometer that could be useful to measure earth's subsurface vibrations as well as for pressure detection and monitoring in high-temperature superconductivity studies and in material sciences. Our results open avenues for the development of a sensing technology with high sensitivity and resolution under extreme pressure limits that potentially has a wider applicability than the existing pressure sensing technologies.

Field tests of geological storage of CO 2 at the Otway International Test Centre, Australia: trapping and monitoring the migrating plumes

The capture and geological storage of CO 2 is essential for net zero. Large volumes of secure subsurface storage will be required, much in unexplored saline aquifers. At the Otway International Test Centre we have executed a series of storage tests, including geophysical surveys, geochemical and petrophysical characterization, drilling and instrumenting six deep wells and conducting two intensively monitored injections each of 15 Kt CO 2 . We summarize the execution and outcomes to draw out the implications for larger-scale storage and for migration trapping of CO 2 plumes. Immobilization of most of the plume is essential for long-term safety. Suitable saline aquifers should have sealing caprocks but need not have structural traps. Buoyant CO 2 could move kilometres beneath the seal, with immobilization occurring by capillary forces and dissolution. Predicting and monitoring plume behaviour with practical methods integrated with risk management will be necessary. We characterized and monitored migration trapping, demonstrated plume immobilization, and tested monitoring methods tailored to large saline aquifers. We developed pressure tomography and continuous seismic monitoring; these provide less detailed information than conventional methods but can be targeted at risks. Passive methods, such as the seismic response to earthquakes, can also act as sentinels for specific events. These methods can bridge the ‘monitoring gap’ between detailed but infrequent methods and more frequent but simpler methods and the results will enable better trade-offs between cost, complexity and risk for a technology crucial for controlling CO 2 levels in the atmosphere. Supplementary material : Detailed descriptions of unpublished modelling are available at https://doi.org/10.6084/m9.figshare.c.7148197

Effects of aquifer size and formation fracture pressure on CO2 geological storage capacity

Introduction: Carbon capture and storage (CCS) is important for achieving net-zero carbon emissions. However, although the current geological storage capacity stands at approximately 3,000 Gt-CO2, the formation pressure increases with CO2 injection, imposing severe constraints on capacity from a geomechanical perspective. This study numerically examined nine cases (combinations of three fracture pressures and three aquifer radius factors) through sensitivity analysis to quantify the effects of these parameters on CO2 injection mass and storage capacity.Methods: The CO2 injection mass was determined as the cumulative CO2 injected until the formation pressure reached a specified fracture pressure. Storage capacity was defined as the amount of CO2 enclosed within the reservoir based on a fill-and-spill analysis encompassing 200 years after the start of injection (2230).Results: Based on the sensitivity analysis, the aquifer radius had a greater impact on the CO2 injection mass and storage capacity than the fracture pressure. A sufficiently high aquifer radius factor can compensate for the capacity limitations imposed by a low fracture pressure. For the lowest fracture pressure (20.95 MPa), considering a safety factor of 0.8, the CO2 injection mass increased approximately 5.5 times, from 3.2 to 17.6 Mt-CO2, depending on the aquifer radius factor ranging from 2 to 7.Discussion: Therefore, geological sites with high aquifer radius factors and low fracture pressures were preferred over those with low aquifer radius factors and high fracture pressures. Nevertheless, when considering space-limited capacity, storage efficiency, defined as the ratio of injected to stored CO2, tends to be higher (approximately 80%) when both parameters are low. The scenario featuring the highest aquifer radius factor and fracture pressure reached an injection mass of 68.9 Mt-CO2. However, the storage efficiency was only 23% due to space constraints. This study provides key insights into two pivotal parameters from pressure- and space-limited perspectives, which must be collectively considered to reliably evaluate CCS projects.

Assimilation of Geophysics-Derived Spatial Data for Model Calibration in Geologic CO2 Sequestration

Summary Uncertainty in geological models usually leads to large uncertainty in the predictions of risk-related system properties and/or risk metrics (e.g., CO2 plumes and CO2/brine leakage rates) at a geologic CO2 storage site. Different types of data (e.g., point measurements from monitoring wells and spatial data from 4D seismic surveys) can be leveraged or assimilated to reduce the risk predictions. In this work, we develop a novel framework for spatial data assimilation and risk forecasting. Under the U.S. Department of Energy’s National Risk Assessment Partnership (NRAP), we have developed a framework using an ensemble-based data assimilation approach for spatial data assimilation and forecasting. In particular, we took CO2 saturation maps interpreted from 4D seismic surveys as inputs for spatial data assimilation. Three seismic surveys at Years 1, 3, and 5 were considered in this study. Accordingly, three saturation maps were generated for data assimilation. The impact from the level of data noise was also investigated in this work. Our results show increased similarity between the updated reservoir models and the “ground-truth” model with the increased number of seismic surveys. Predictive accuracy in CO2 saturation plume increases with the increased number of seismic surveys as well. We also observed that with the increase in the level of data noise from 1% to 10%, the difference between the updated models and the ground truth does not increase significantly. Similar observations were made for the prediction of CO2 plume distribution at the end of the CO2 injection period by increasing the data noise.

Transient H2O–CO2 wellbore leakage under evolving recharge conditions considering CO2 phase change

Abandoned wells are one of the dominant pathways of deep CO2 leakage, threatening the safety and effectiveness of CO2 geological storage. Although CO2 wellbore flow has been discussed in several studies, the analysis of the CO2 wellbore leakage under evolving recharge conditions based on the transient wellbore-reservoir fully coupled model, which can describe the CO2 gas-liquid phase change, has yet to be reported. Thus, a transient wellbore-reservoir fully coupled model is established in this study to investigate the interaction between CO2 injection and wellbore leakage. The results show that the fluid wellbore leakage may cause significant disturbance to the reservoir and injection well, and the fluid leakage process can be divided into different stages according to the leakage and recharge characteristics. Besides, the wellhead temperature of the abandoned well shows a different variation trend compared with previous studies, which is attributed to the evolving reservoir recharge. The parameter analysis indicates that the gap aperture in the plugs of the abandoned well, plug locations, CO2 injection rate, and reservoir permeability have apparent effects on the fluid leakage rates but have little impact on the leakage pattern. Finally, a dimensionless parameter, the ratio of leakage to injection mass, is proposed to generalize the leakage degree, and the empirical relationship of the ratio of leakage to injection mass with time is established to facilitate quick estimation. This study broadens the understanding of CO2 wellbore leakage and provides a simple method to predict similar leakage scenarios approximately.

Migration characteristics of constant elements in the process of coal dissolution by liquid CO2

The effect of liquid CO2 on coal dissolution plays a key role in improving coal bed methane (CBM) recovery and CO2 geological storage. In order to study the effect of liquid CO2–H2O reaction on the migration of mineral constant elements in coal, three kinds of coal samples (lignite, bituminous coal, and anthracite) with different degrees of metamorphism were selected as the research objects. The one-factor experiments of dissolution of liquid CO2 and water-bearing coal samples were carried out by simulating the temperature and pressure of the stratum. X-ray fluorescence spectroscopy (XRF) was used to test the changes in the relative content of constant elements in coal samples after liquid CO2 injection under different pressure conditions. Scanning electron microscopy (SEM) was utilized to observe the evolution pattern of the surface features of the coal before and after the dissolution of liquid CO2. A quantitative analysis of coal pore development characteristics was conducted based on low-temperature N2 adsorption/desorption experiments, and isothermal adsorption experiments were carried out before and after etching the coal samples to understand the adsorption characteristics of CH4 and CO2 by coal under different pressure conditions. The research results indicated that the migration ability of constant elements in coal showed a trend of first decreasing and then increasing with the increasing degree of coal metamorphism. Among the three selected coal samples, the migration ability of constant elements was found to be strongest in anthracite, followed by lignite and bituminous coal. Most of the element migration in coal was carried out through chemical reactions (hydrolysis, carbonation, redox), while some elements were primarily transported through physical means (such as the low-temperature impact of liquid CO2). The dissolution process expands the original pore space of coal and generates new pores, greatly increasing the coal's capacity for CO2 adsorption. These findings deepen our understanding of mineral dissolution in coal by liquid CO2 and provide important insights for achieving efficient and long-term coalbed CO2 geological storage and enhanced methane recovery techniques.

CCUS in India: bridging the gap between action and ambition

India has committed to reaching net-zero greenhouse gas emissions by 2070. While targets for CO2 capture, utilization and storage (CCUS) technologies are not explicitly set, the Government of India’s agencies and public-sector enterprises have mentioned CCUS approaches conditionally subject to availability of feasible technology and financing. This paper aims to examine the gap between the current status of CCUS in India and the levels of deployment as projected by modeling exercises. It takes a Talanoa dialogue approach to answer the following questions on CCUS perspective in India: where are we right now, where do we need to be, and how do we get there. The current status of CO2 capture in India is at the pilot/demonstration stage, with the chemicals and steel sectors, being the most advanced. Emergence of the methanol economy as a key avenue for CO2 utilization may be seen at a large-scale. Geologic CO2 storage is at an advanced planning stage via enhanced oil recovery, and will likely be targeted over this decade. From the current and planned stage, India would likely need 400–800 Mt-CO2/year by 2050 to meet its share of the 1.5 °C carbon budget. We suggest several priority research directions for technology development across the CCUS value chain.

Assessing the potential for CO2 storage in saline aquifers in Brazil: Challenges and Opportunities

AbstractThis study underscores the critical role of carbon capture and storage (CCS) in mitigating greenhouse gas emissions and addresses the potential for CCS projects in saline aquifers in Brazil, one of the world's largest carbon emitters. The country's ability to adopt CCS is significantly influenced by the availability of data related to regional CO2 storage potential and identifying suitable geological framework for CO2 injection. While oil and gas reservoirs have traditionally been prioritized, saline aquifers represent an underexplored and potentially higher capacity storage option. Despite Brazil's 31 sedimentary basins, the data quantity and availability for these contexts remain insufficient for advanced studies on the geological storage of CO2 considering saline aquifers. An initial study was conducted indicating five potential targets in the Paraná and Potiguar Basins for geological storage in saline aquifers based on available public data, mainly drilling data. This review reveals substantial challenges related to the evaluation of Brazil's CO2 storage capacity, such as the lack of modern seismic studies, the absence of a regulatory framework for CO2 storage, and insufficient investment in new well exploration. These challenges necessitate multistakeholder collaboration, the development of a supportive regulatory environment, and investment in extensive site characterization campaigns. Addressing these barriers is fundamental to realizing the country's CCS potential and contributing to global decarbonization efforts. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Using the Tidal Response of Groundwater to Assess and Monitor Caprock Confinement in CO2 Geological Sequestration

Carbon geological storage (CGS) is an important global practice implemented to mitigate the effects of CO2 emissions on temperature, climate, sea level, and biodiversity. The monitoring of CGS leakage and the impact of storage on hydrogeological properties is important for management and long-term planning. In this study, we show the value of passive monitoring methods based on measuring and modeling water-level responses to tides. We review how monitoring can be used to identify time-varying horizontal and vertical permeabilities as well as independently detect time-varying fracture distribution in aquifer–caprock systems. Methods based on water-level responses to Earth tides are minimally invasive, convenient, economic (since they use existing groundwater wells), and time-continuous. We show how measurements can be used to detect aquifer leakage (caprock confinement) and the distribution of surrounding faults and fractures, which are the two most important unsolved quantities in assessing geological CO2 storage strategies.

High-Pressure adsorption of supercritical methane and carbon dioxide on Coal: Analysis of adsorbed phase density

The occurrence of supercritical CH4 and CO2 in coal is significant for both coalbed methane recovery and CO2 storage. Adsorption isotherms of CH4 and CO2 on two coals have been measured at three temperatures up to pressures of 25 MPa. Three modified supercritical adsorption models (SL-V, SBET-V, and SDR-V) were used to describe the excess adsorption behavior, with the pressure-independent adsorbed phase volume being considered. The adsorbed phase density (APD) and absolute adsorption amount were calculated based on the modified models and compared with those estimated by previous models. The results indicate that SDR-V is the most suitable for CH4 adsorption due to the dominant role of filling of micropores by CH4, while SBET-V is the most appropriate model for CO2 adsorption because of multilayer adsorption of CO2 in both micropores and meso-macropores. The APD increases with pressure until reaching a maximum value but decreases as temperature increases following a Langmuir-style trend. The previous models, which use a fixed APD, seriously underestimate the absolute adsorption, the extent of which increases with increasing pressure and temperature, leading to significant errors in deep formations with high temperature and pressure conditions. Furthermore, as burial depth increases, the adsorption process can be divided into three stages based on changes in APD and free phase density (FPD). These findings contribute to a comprehensive understanding of the behavior and occurrence of CH4 and CO2 within deep coal seams, enhancing the applicability of CO2-ECBM (CO2 Geological Storage Enhanced Coalbed Methane Recovery).

Evaluation of the Potential for CO2 Storage and Saline Water Displacement in Huaiyin Sag, Subei Basin, East China

CO2 geological storage combined with deep saline water recovery technology (CO2-EWR) is one of the most effective ways to reduce carbon emissions. Due to the complex structural features, it is difficult to use CO2-EWR technology in Huaiyin Sag, Subei basin, East China. In this study, the multi-source information superposition evaluation technology of GIS was utilized for the selection of CO2 storage sites and water displacement potential target areas in this area, which mainly focused on the sandstone reservoirs of Cretaceous Pukou Formation. Based on the results, a three-dimensional injection–extraction model was established. Various scenarios with different production/injection well ratios (PIR) were simulated. Research has shown that the suitability of the surrounding site of Huaiyin Power Plant can be divided into two levels: relatively suitable and generally suitable; the area in the generally suitable level accounts for more than 80%. At a PIR of 1, CO2 is distributed asymmetrically, whereas at PIRs of 2 or 4, CO2 is distributed symmetrically. When the number of production wells is constant, a higher injection rate results in a faster expansion rate of the CO2 plume. This means that the time taken for the CO2 plume to reach the production wells is shorter. Reservoir pressure increases rapidly after more than 60 years of CO2 injection at lower PIR values, while at higher PIRs, reservoir pressure eventually stabilizes. Higher PIR values correspond to higher gas saturation, indicating a greater capacity for CO2 sequestration with more producing wells. When PIR = 4, the total CO2 injection increased by 55.73% compared to PIR = 1. However, the extraction of saline decreases with an increase in the number of producing wells, resulting in a decrease in replacement efficiency. This study provides a theoretical basis and technical support for the implementation of large-scale CO2-EWR engineering and technology demonstration in this region.

Experimental investigation of CO2 huff-n-puff in tight oil reservoirs: Effects of the fracture on the dynamic transport characteristics based on the nuclear magnetic resonance and fractal theory

CO2 huff-n-puff is a promising method for enhancing oil recovery in tight reservoirs while simultaneously contributing to CO2 geological storage. However, the performance of this method is significantly affected by fractures resulting from hydraulic fracturing and natural fractures. The impact of fracture on oil transport behavior in different pores remains unclear and warrants further investigation. In this study, CO2 huff-n-puff experiments were conducted under induced fracture conditions. A new method for quantifying the relationship between transverse relaxation time T2 and pore radius was proposed by fitting the slopes of the T2 spectrum and the pore size distribution (PSD) curve derived from Micro X-ray computed tomography (Micro-CT). The impact of the fracture on the effective utilization limit was explored, and the fractal dimensions of different cycles were evaluated during CO2 huff-n-puff. The results showed that the oil recoveries of the fracture-free and the fractured samples were 19.97% and 31.16%, corresponding to the effective utilization limits of 1.52 μm and 0.96 μm, respectively. Moreover, based on the fractal characteristics of the whole process of CO2 huff-n-puff, the pore system was divided into micropores (<0.20 μm), small pores (0.20–0.63 μm), intermediate pores (0.63–2.00 μm), and large pores (>2.00 μm). Furthermore, the incremental recovery for each cycle mainly comes from large pores and gradually decreases as the fractal dimension is less than 2.85. The fracture has a significant impact on the migration characteristics of crude oil. The incremental oil in the intermediate pores of the fractured sample, caused by negative convection, was 2.88 times greater than that of the fracture-free sample. Finally, it was found that the gravity effect was more prominent, significantly affecting the remaining oil distributions in fractured reservoirs.

Characterization of a marine mudstone confining unit at a proposed CO2 storage hub: Kemper county energy facility, Mississippi, USA

Cretaceous and Tertiary strata across Mississippi, Alabama, and the adjacent continental shelf constitute a widespread succession of sandstone, mudstone, and carbonate that have proven to be important objectives for deployment of geologic CO2 storage technology in saline formations. Analyses of stratigraphy, sedimentology, and reservoir properties indicate that the Cretaceous-age Paluxy Formation, Washita–Fredericksburg interval, and lower Tuscaloosa Group may provide a 1.4 gigatonne storage opportunity at the Kemper County Energy Facility in east-central Mississippi. The marine Tuscaloosa shale is a widespread reservoir seal in the deep subsurface of Mississippi and Alabama, and detailed geologic investigation of the shale includes integrated analysis of geophysical well logs and core that have yielded a multiscale analysis of the confining strata. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), quantitative X-ray diffraction (XRD), and permeability analyses from core were used to interpret microfabric, pore types, mineralogy and fluid properties within mudstone of the east-central Mississippi Embayment. This study has importance for identifying potential migration of fugitive CO2 into or across the shale. Results indicate that mudstone in the marine Tuscaloosa shale is an effective confining unit that is a key component of the storage complex in Kemper County. Water saturation in the marine Tuscaloosa shale units promotes rock ductility and contributes to low permeability, which is on the order of 10–100 nanodarcies (nD) as determined by pressure-decay permeametry. Accordingly, the marine Tuscaloosa shale is interpreted to prevent significant cross-stratal migration of injected CO2 from deeper sandstone reservoirs.

Denitrification induced calcium carbonate precipitation by indigenous microorganisms in coal seam and its application potential in CO2 geological storage

Carbon capture, utilization and storage (CCUS) is an effective means to achieve dual carbon goals. However, the leakage of CO2 is a considerable risk. In this work, a new method was proposed to reduce the leakage of CO2 in coal seam by denitrification induced carbonate precipitation (DICP) using indigenous microorganisms (IM). After enrichment and optimization, the mineralization efficiency of IM reached 90.47% and Pseudomonas was dominated. The degradation of negatively charged groups in extracellular polymeric substances (EPS), especially carboxyl, was essential to the formation of CaCO3. The mineralization efficiency even increased under the presence of coal while the pore development was significantly reduced by the formed bio-minerals. The microflora was proven to resist the negative effects of CO2 on bacterial growth and metabolism. Then, a conceptual model of industrial application was proposed. Our results demonstrated the good application potential of DICP technology in coal seam CO2 geological storage.

Study on the Wetting Mechanisms of Different Coal Ranks Based on Molecular Dynamics

The exploration of coal wettability is not only of paramount significance in the mitigation of coal dust and the development of coalbed methane, but it also provides crucial technical support for realizing the geological storage of CO2 within the ‘dual-carbon’ background. Molecular simulation serves as an effective means by which to investigate coal wettability at the microscopic level. This study employed a molecular dynamics simulation to investigate the wettability of coal across 13 distinct coal ranks. Through the analysis of trajectory files, and the incorporation of experimental data during the modeling process, the mechanisms governing the evolution of wettability were revealed. The results demonstrated that the contact angle on the surface of coal increases with the elevation of coal rank. The molecule relative concentration analysis revealed that, with increasing coal rank, the overlap range between water droplets and the coal slab decreases, the height increases, and the diffusion degree of water molecules decreases, which are outcomes consistent with the results of the contact angle measurement. The contact angle was strongly correlated with the number of hydrogen bonds and secondarily correlated with the numbers of carbonyls, hydroxyls, and ether oxygens. The formation of hydrogen bonds was notably correlated with the number of hydroxyls, followed by that of ether oxygens, while its correlations with carbonyls and carboxyls were comparatively weaker. The contact angle exhibited positive correlations with vitrinite reflectance and carbon content, while showing negative correlations with oxygen content, H/C, and O/C. Additionally, it demonstrated positive associations with total sp2 carbon (fa), aromatic carbon (fa′), and non-protonated aromatic carbon (faN), and negative associations with aliphatic carbon (fal) and methylene carbon (falH). Understanding the variations in wettability among different coal ranks can provide a foundational model and theoretical basis for further exploration of the complex interactions among coal, gas, and water across various coal ranks.

A Three-Stage Psychosocial Engineering-Based Method to Support Controversy and Promote Mutual Understanding between Stakeholders: The Case of CO2 Geological Storage

Subsurface engineering projects with high socio-environmental impacts raise strong controversies among stakeholders, which often affects the projects’ implementation. These controversies originate from a loss of public confidence in the decision-making process, lack of information about new technologies, and the desire of some promoters to avoid conflict. The lack of methodologies to structure each stage of the debate can, in this context, lead to the crystallization of the stakeholders’ positions and to the failure of the project. To promote mutual understanding and constructive exchanges, this article presents a combination of methods based on psychosocial engineering principles to support debate and encourage stakeholders to participate with an openness posture. The method is based on a set of studies conducted as part of the “Social Governance for Subsurface Engineering” project and includes three stages: (1) develop stakeholders’ knowledge so that they are able to participate in the debate with an informed viewpoint; (2) commit stakeholders to participate in the debate by adopting a posture conducive to constructive exchanges; and (3) structure exchanges between stakeholders through the use of cooperative methods facilitating the adoption of an openness posture.

Carbon storage units and carbon storage obligations: A review of policy approaches

Policies that incentivize the capture and geological storage of CO2 from large point sources (‘CCS’; and more recently, atmospheric removals), have so far tended to reward the resultant avoided CO2 emissions (or CO2 removals) achieved by operators at the point of capture. The expectation has been that geological CO2 storage sites, as well as the connecting infrastructure, will be developed and operated based upon the funding delivered from the single point of incentive (e.g. under an emissions trading system or a carbon tax, only CO2 capture installation operators are absolved of the obligation to acquire and surrender CO2 emission rights or to pay the tax). Project-based crediting mechanisms (e.g. in the voluntary carbon market) tend to treat the entire chain of operations as a single entity to be supplied with emission reduction or removal credits. Consequently, there has been minimal explicit financial incentive to store CO2. Yet a multiple gigaton-per-year scale capture and storage industry requires complex CO2 networks to evolve, with multiple sources connecting to multiple sinks, with installations owned by different operators with different technical expertise, climate mitigation goals and obligations. This multiplicity of goals and incentives can create agency problems and cross-chain risks, which impact negatively upon investment decisions. In this paper, we review the history, evolution and potential of geological net zero (GNZ) and carbon storage (or takeback) obligation concepts applied to fossil carbon producers and suppliers as a means to address these risks alongside policies aimed at atmospheric net zero (ANZ) and fossil carbon emitters.

A review on geological storage of marine carbon dioxide: Challenges and prospects

Carbon capture, utilization, and storage (CCUS) is believed to be the most promising technology to mitigate climate change and global temperature rise. As an effective method for reducing carbon emissions, carbon dioxide (CO2) storage on the seabed can be achieved by injecting captured CO2 from offshore platforms into subsea storage sites, such as the sediment layers, depleted oil and gas reservoirs and deep saline aquifers, thereby permanently removing it from the atmosphere. Additionally, hundreds to thousands of meters of seawater above seabed storage layers provide naturally high seawater pressure and abundant barrier settings that can reduce leakage risk. Consequently, this has become an ideal storage location for long-term CO2 storage. In order to thoroughly investigate the mechanism and potential of marine CO2 storage and promote further development of CCUS, this paper provides a comprehensive description of theoretical research of marine CO2 geological storage, including storage mechanisms, storage capacity, wellbore flow, CO2 migration, cap rocks integrity and CO2 leakage monitoring. The implementation status of global engineering projects is summarized. Currently, there are relatively few successful marine storage projects globally, with the majority of others still in the research and testing stages. Finally, the challenges and prospects of marine CO2 storage are also discussed. This review demonstrates the enormous potential and promising future of marine CO2 storage, but there are also leakage risks. It can be avoided through in-depth theoretical research to clarify the entire process of storage mechanisms and take corresponding technological measures. Ultimately, a new technology for large-scale efficient injection and enhanced storage of marine CO2 storage will be formed.

Buoyancy-Driven Dissolution Instability in a Horizontal Hele-Shaw Cell.

The dissolution of minerals within rock fractures is fundamental to many geological processes. Previous research on fracture dissolution has highlighted the significant role of buoyancy-driven convection leading to dissolution instability. Yet, the pore-scale mechanisms underlying this instability are poorly understood primarily due to the challenges in experimentally determining flow velocity and concentration fields. Here, we integrate pore-scale simulations with theoretical analysis to delve into the dissolution instability prompted by buoyancy-driven convection in a radial horizontal geometry. Initially, we develop a pore-scale modeling approach incorporating gravitational effects, subsequently validating it through experiments. We then employ pore-scale numerical simulations to elucidate the 3D intricacies of flow-dissolution dynamics. Our findings reveal that a simple criterion can delineate the condition for the onset of buoyancy-driven dissolution instability. If the characteristic length falls below a critical threshold, dissolution remains stable. Conversely, exceeding this threshold leads to two distinct regimes: the unstable regime of the confined domain affected by the initial aperture and the unstable regime of the semi-infinite domain independent of the initial aperture where the instability is no longer influenced by the lower boundary. We demonstrate that the pore-scale mechanism for this instability is due to the concentration boundary layer attaining a gravitationally unstable critical thickness. Through theoretical analysis of this layer and the time scales of diffusion and advection, we establish a theoretical model to predict where the dissolution instability occurs. This model aligns closely with our numerical simulations and experimental data across diverse conditions. Our work improves the understanding of buoyancy-driven dissolution instability in radial horizontal geometry. It is also of practical significance in understanding cavity formation in karst hydrology and preventing leaks in geological CO2 storage.

CO2 dynamic mass balance of low permeability reservoir based on “four regions”

AbstractIn order to limit the increase in global average temperature to 1.5°C, it is necessary to reduce carbon dioxide (CO2) emissions by 45% by 2030. CO2 capture, utilization and storage (CCUS) is one of the effective ways to reduce CO2 emissions. Geological storage of CO2 provides a solution with the lowest economic cost and the fastest effect for reducing CO2 emissions. This article proposes a CO2 storage regional division method based on the characteristics of low‐permeability reservoirs in the Yanchang W oilfield in China. The storage space is divided into four regions: gas phase region, two‐phase or near‐miscible region, diffusion region, and oil phase region. As the displacement progresses, the volume of the gas phase region and the two‐phase or near‐miscible region gradually increases; the volume of the diffusion region first increases and then decreases. By calculating the storage capacity of each region separately, the total storage capacity is finally calculated. The impact of different pressures and injection rates on dynamic CO2 storage capacity was evaluated. The results show that pressure and injection rate are positively correlated with total storage capacity. When CO2 miscible conditions are reached, the increase in total storage capacity will significantly decrease. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.