Search Results (95)

This study develops an integrated environmental–economic assessment framework to evaluate the life cycle environmental impacts and economic costs of CO₂ geological storage and produced water treatment in saline formations in China. Using a case study of a saline aquifer carbon storage project in the Ordos Basin, eight full-chain carbon capture, utilization, and storage (CCUS) scenarios were analyzed. The results indicate that environmental and cost performance are primarily influenced by technology choices across carbon capture, transport, and storage stages. The scenario employing potassium carbonate-based capture, pipeline transport, and brine reinjection after a reverse osmosis treatment (S5) achieved the most balanced outcome. Breakeven analyses under three carbon price projection models revealed that carbon price trajectories critically affect project viability, with a steadily rising carbon price enabling earlier profitability. By decoupling CCUS from power systems and focusing on unit CO₂ removal, this study provides a transparent and transferable framework to support cross-sectoral deployment. The findings offer valuable insights for policymakers aiming to design effective CCUS support mechanisms under future carbon neutrality targets. Full article

This study investigates ground deformations in the southeastern Po Plain (northern Italy), focusing on the Bologna area—a densely populated region affected by natural and anthropogenic subsidence. Ground deformations in the area result from geological processes (e.g., sediment compaction and tectonic activity) and human activities (e.g., ground water production and underground gas storage—UGS). We apply a multidisciplinary approach integrating subsurface geology, ground water production, advanced differential interferometry synthetic aperture radar—DInSAR, gas storage data, and land use information to characterize and analyze the spatial and temporal variations in vertical ground deformations. Seasonal and trend decomposition using loess (STL) and cluster analysis techniques are applied to historical DInSAR vertical time series, targeting three representatives areas close to the city of Bologna. The main contribution of the study is the attempt to correlate the lateral extension of ground water bodies with seasonal ground deformations and water production data; the results are validated via knowledge of the geological characteristics of the uppermost part of the Po Plain area. Distinct seasonal patterns are identified and correlated with ground water production withdrawal and UGS operations. The results highlight the influence of superficial aquifer characteristics—particularly the geometry, lateral extent, and hydraulic properties of sedimentary bodies—on the ground movements behavior. This case study outlines an effective multidisciplinary approach for subsidence characterization providing critical insights for risk assessment and mitigation strategies, relevant for the future development of CO₂ and hydrogen storage in depleted reservoirs and saline aquifers. Full article

Deep saline aquifers in the eastern part of Drava Basin were screened for potential storage sites. The input dataset included three seismic volumes, a rather extensive set of old seismic sections and 71 wells. Out of all identified potential storage objects, only two sites were found to be situated in the favorable geological settings, meaning that the inspected wells drilled through structural traps had a seal at least 20 m thick which was intersected by only a few faults with rather limited displacement. Many more closed structures in the area were tested by exploration wells, but in all other wells, various problems were encountered, including inadequate reservoir properties, inadequate seal or inadequate depth of the identified trap. Analysis was highly affected by the insufficient quality and spatial distribution of the seismic input data, as well as in places with insufficient quality of input well datasets. An initial characterization of identified storage sites was performed, and their attributes were compared, with potential storage object B recognized as the one that should be further developed. However, given the depth and increased geothermal gradient of the potential storage object B, it is possible that it will be developed as a geothermal reservoir, and this brings forward the problem of concurrent subsurface use. Full article

Geological storage of CO₂ in offshore deep saline aquifers is widely recognized as an effective strategy for large-scale carbon emission reduction. This study aims to assess the mechanical integrity and storage efficiency of reservoirs using a multi-layer CO₂ injection method in the Enping 15-1 Oilfield CO₂ storage project which is the China’s first offshore carbon capture, utilization, and storage (CCUS) demonstration. A coupled Hydro–Mechanical (H–M) model is constructed using the TOUGH-FLAC simulator to simulate a 10-year CO₂ injection scenario, incorporating six vertically distributed reservoir layers. A sensitivity analysis of 14 key geological and geomechanical parameters is performed to identify the dominant factors influencing injection safety and storage capacity. The results show that a total injection rate of 30 kg/s can be sustained over a 10-year period without exceeding mechanical failure thresholds. Reservoirs 3 and 4 exhibit the greatest lateral CO₂ migration distances over the 10-year injection period, indicating that they are the most suitable target layers for CO₂ storage. The sensitivity analysis further reveals that the permeability of the reservoirs and the friction angle of the reservoirs and caprocks are the most critical parameters governing injection performance and mechanical stability. Full article

CO₂ geo-storage is a promising approach in reducing greenhouse gas emissions and controlling global temperature rise. Although numerous studies have reported that offshore saline aquifers have greater storage potential and safety, current suitability evaluation models for CO₂ geo-storage primarily focus on onshore saline aquifers, and site-level evaluations for offshore CO₂ geo-storage remain unreported. In this study, we propose a framework to evaluate the site-level offshore CO₂ geo-storage suitability with a multi-tiered indicator system, which considers three types of factors: engineering geology, storage potential, and socio-economy. Compared to the onshore CO₂ geo-storage suitability evaluation models, the proposed indicator system considers the unique conditions of offshore CO₂ geo-storage, including water depth, offshore distance, and distance from drilling platforms. The Analytic Hierarchy Process (AHP) and Fuzzy Comprehensive Evaluation (FCE) methods were integrated and applied to the analysis of the Ying–Qiong Basin, South China Sea. The results indicated that the average suitability score in the Yinggehai Basin (0.762) was higher than that in the Qiongdongnan Basin (0.691). This difference was attributed to more extensive fault development in the Qiongdongnan Basin, suggesting that the Yinggehai Basin is more suitable for CO₂ geo-storage. In addition, the DF-I reservoir in the Yinggehai Basin and the BD-A reservoir in the Qiongdongnan Basin were selected as the optimal CO₂ geo-storage targets for the two sub-basins, with storage potentials of 1.09 × 10⁸ t and 2.40 × 10⁷ t, respectively. This study advances the methodology for assessing site-level potential of CO₂ geo-storage in offshore saline aquifers and provides valuable insights for engineering applications and decision-making in future CO₂ geo-storage projects in the Ying–Qiong Basin. Full article

Under the dual-carbon policy framework, geological CO₂ storage, particularly in saline aquifers, is pivotal to achieving national emission reduction targets. However, selecting geologically favorable storage sites demands quantitative assessment of complex geological factors—a task hindered by subjective traditional methods. To address this, the study employs an integrated approach combining multi-criteria decision analysis (Analytic Hierarchy Process and Fuzzy Comprehensive Evaluation) with multiphase flow simulations to investigate the Dezhou Subdepression in Shandong Province. The results indicate that the Dezhou Subdepression is moderately favorable for CO₂ geological storage, characterized by geologically optimal burial depth and favorable reservoir conditions. When the injection pressure increases from 1.1 times the original Group pressure (1.1P) to 1.5 times the original Group pressure (1.5P), the lateral migration distance of CO₂ expands by 240%, and the total storage capacity increases by approximately 275%. However, under 1.5P conditions, the CO₂ plume reaches the model boundary within 6.3 years, underscoring the increased risk of CO₂ leakage under high-pressure injection scenarios. This study provides strategic insights for policymakers and supports strategic planning for a CO₂ storage pilot project in the Dezhou Subdepression. It also serves as a reference framework for future assessments of CO₂ geological storage potential. Full article

Carbon Capture and Storage (CCS) is a critical strategy for reducing CO₂ emissions from hard-to-abate sectors. Reliable and efficient reservoir simulation tools are essential for supporting the safe and effective deployment of CCS projects. This study presents a twofold contribution to CCS modeling in saline aquifers: (1) the validation of the Black Oil Model (BoM) as a computationally efficient alternative to compositional simulators, and (2) a systematic assessment of the impact of grid resolution on plume prediction accuracy. The BoM was benchmarked against three commercial compositional simulators—Eclipse E300, CMG-GEM, and TNavigator. The comparison focused on key aspects of CO₂ storage operations, including plume evolution to assess containment and storage security, as well as injection safety and efficiency through pressure and saturation profile analysis, evaluated across both the injection and the post-closure monitoring phases. The BoM successfully reproduced plume extent and CO₂ saturation distributions, with mean deviations of 3% during injection, 5% during post-closure, and an overall average of 4% across the entire project duration. Additionally, simulation times were reduced by a factor of four compared to compositional models. These results confirm the BoM’s practical utility as a robust and efficient tool for CO₂ storage simulation. In parallel, the study investigated the influence of vertical and lateral grid resolutions/coarsening on the accuracy of CO₂ modeling. Seven models were developed and evaluated using a hybrid qualitative–quantitative framework, consistent with the BoM validation methodology. Vertical resolution was found to be particularly critical during the monitoring phase. While a 5 m resolution proved adequate during injection, deviations in plume shape and magnitude during post-injection increased to an average of 15% compared to a fine 2 m vertical resolution model, highlighting the necessity of fine vertical discretization (≤2 m) to capture gravity-driven plume dynamics during the monitoring phase. Conversely, lateral grid resolution had a stronger effect during the injection phase. A lateral cell size of 150 m was required for accurate plume prediction, with 200 m remaining moderately acceptable for early-phase assessment and prospect ranking, whereas coarser lateral grids led to significant underestimation of plume spread and dissolution extent. These findings demonstrate that the BoM, when combined with informed grid resolution strategies, enables accurate and computationally efficient simulation of CO₂ storage in saline aquifers. The study provides practical guidelines for fluid model selection and spatial discretization, offering critical input to subsurface experts involved in CCS project development, monitoring design, and regulatory compliance. Full article

The study represents an innovative method to utilize the strong computational power of CMG-GEM, a numerical reservoir simulator coupled with artificial neural networks (ANNs) to predict carbon storage capacity in saline aquifers. The key parameters in geological storage formations are identified by generating a diverse dataset from CMG-GEM simulation runs by varying the different geological and operational parameters. Robust data analysis was performed to understand the effects of these parameters and access the different CO₂ trapping mechanisms. One of the significant novelties of this model is its ability to incorporate additional inputs not previously considered in similar studies. This enhancement allows the model to predict all CO₂ trapping mechanisms, rather than being limited to just one or two, providing a more holistic and accurate assessment of carbon sequestration potential. The generated dataset was used in MATLAB to develop an ANN model for CO₂ storage prediction across various trapping mechanisms. Rigorous testing and validation are performed to optimize the model, resulting in an accuracy of 98% using the best algorithm, which reflects the model’s reliability in evaluating the CO₂ storage. Therefore, the number of simulation runs was significantly reduced, which saves great amounts of computational power and simulation running time. The integration of machine learning and numerical simulations in this study represents a significant advancement in sustainable CO₂ storage assessment, providing a reliable tool for long-term carbon sequestration strategies. Full article

This study investigates the impact of injection depth on CO₂ plume migration dynamics in saline aquifers, a critical aspect of secure and efficient carbon capture, utilization, and storage (CCUS). While CCUS offers a vital pathway for mitigating greenhouse gas emissions, challenges such as buoyancy-driven flow, salinity effects, and potential leakage threaten long-term CO₂ containment. Using compositional reservoir simulation (CMG GEM 2021.10, Calgary, Canada) and Illinois Basin Decatur Project (IBDP) data, we modeled CO₂ injection into a 10,000 ppm salinity aquifer, evaluating the effects of single- and multi-depth injection (5370 to 5385 ft). The results demonstrate that multi-depth injection significantly enhances CO₂–brine contact area, promoting dissolution trapping and mitigating buoyancy-driven migration. This enhanced dissolution and residual trapping improves horizontal containment and overall storage security in the modeled salinity environment. The work provides valuable insights for optimizing injection strategies to maximize CO₂ storage efficiency and minimize leakage risks. Full article

Longitudinal dispersion coefficient is a key parameter governing solute transport in porous media, with significant implications for various industrial processes. However, the impact of microfractures on the longitudinal dispersion coefficient remains insufficiently understood. In this study, pore-scale direct numerical simulations are performed to analyze solute transport in microfractured porous media during unstable miscible displacement. Spatiotemporal concentration profiles were fitted to the analytical solution of the convection–dispersion equation to quantify the longitudinal dispersion coefficient across different microfracture configurations. The results indicate that the longitudinal dispersion coefficient is highly sensitive to microfracture characteristics. Specifically, an increased projection length of microfractures in the flow direction and a reduced lateral projection length enhance longitudinal dispersion at the outlet. When Peclet number ≥1, the longitudinal dispersion coefficient follows a three-stage variation pattern along the flow direction, with microfracture connectivity and orientation dominating its scale sensitivity. Furthermore, both diffusion-dominated and mixed advective-diffusion regimes are observed. In diffusion-dominated regimes, significant channeling alters the applicability of traditional scaling laws, with the relationship between longitudinal dispersion coefficient and porosity holding only when the Peclet number is below 0.07. These results provide a comprehensive scale-up framework for CO₂ miscible flooding in unconventional reservoirs and CO₂ storage in saline aquifers, offering valuable insights for the numerical modeling of heterogeneous reservoir development. Full article

Climate change has become one of the most pressing global challenges, with greenhouse gas emissions, particularly carbon dioxide (CO₂), being the primary drivers of global warming. To effectively address climate change, reducing carbon emissions has become an urgent task for countries worldwide. Carbon capture, utilization, and storage (CCUS) technologies are regarded as crucial measures to combat climate change, among which ocean CO₂ sequestration has emerged as a promising approach. Recent reports from the International Energy Agency (IEA) indicate that by 2060, CCUS technologies could contribute up to 14% of global cumulative carbon reductions, highlighting their significant potential in mitigating climate change. This review discusses the main technological pathways for ocean CO₂ sequestration, including oceanic water column sequestration, CO₂ oil and gas/coal seam geological sequestration, saline aquifer sequestration, and seabed methane hydrate sequestration. The current research status and challenges of these technologies are reviewed, with a particular focus on the potential of seabed methane hydrate sequestration, which offers a storage density of approximately 0.5 to 1.0 Gt per cubic kilometer of hydrate. This article delves into the formation mechanisms, stability conditions, and storage advantages of CO₂ hydrates. CO₂ sequestration via hydrates not only offers high storage density but also ensures long-term stability in the low-temperature, high-pressure conditions of the seabed, minimizing leakage risks. This makes it one of the most promising ocean CO₂ sequestration technologies. This paper also analyzes the difficulties faced by ocean CO₂ sequestration technologies, such as the kinetic limitations of hydrate formation and leakage monitoring during the sequestration process. Finally, this paper looks ahead to the future development of ocean CO₂ sequestration technologies, providing theoretical support and practical guidance for optimizing their application and promoting a low-carbon economy. Full article

Deep saline aquifers provide significant potential for CO₂ storage and are crucial in carbon capture, utilization, and storage (CCUS). However, ensuring the long-term safe storage of CO₂ remains challenging due to the complexity of coupled thermal, hydrological, mechanical, and chemical (THMC) processes. This study is one of a few to incorporate fault-controlled reservoir structures in the Enping 15-1 oilfield to simulate the performance of CO₂ geological storage. A systematic analysis of factors influencing CO₂ storage safety, such as the trap area, aquifer layer thickness, caprock thickness, reservoir permeability, and reservoir porosity, was conducted. We identified the parameters with the most significant impact on storage performance and provided suitable values to enhance storage safety. The results show that a large trap area and aquifer thickness are critical for site selection. Low permeability and large caprock thickness prevent CO₂ from escaping, which is important for long-term and stable storage. These findings contribute to developing site-specific guidelines for CO₂ storage in faulted reservoirs. Full article

The growing impacts of global warming demand urgent climate-change mitigation strategies, with carbon storage in saline aquifers emerging as a promising solution. These aquifers, for their high porosity and permeability, offer significant potential for CO₂ sequestration. Among the trapping mechanisms, solubility trapping—where CO₂ dissolves into brine—stands out for its long-term effectiveness. However, CO₂ dissolution alters brine density, initiating density-driven convection that enhances CO₂ migration. Accurate modelling of these density changes is essential for optimising CO₂ storage strategies and improving long-term sequestration outcomes. This study presents a two-step explainable artificial intelligence (XAI) framework for predicting the density of CO₂-dissolved brine in geological formations. A dataset comprising 3393 samples from 14 different studies was utilised, capturing a wide range of brine compositions and salinities. Given the complexity of brine–CO₂ interactions, a two-step modelling approach was adopted. First, a random forest (RF) model predicted the brine volume (as the proxy for the density) without dissolved CO₂, and then, a second RF model predicted the impact of CO₂ dissolution on the brine’s volume. Feature importance analysis and SHapley Additive exPlanations (SHAP) values provided interpretability, revealing the dominant role of temperature and ion mass in the absence of CO₂ and the significant influence of dissolved CO₂ in more complex systems. The model showed excellent predictive performance, with R² values of 0.997 and 0.926 for brine-only and CO₂-dissolved solutions, respectively. Future studies are recommended to expand the dataset, explore more complex systems, and investigate alternative modelling techniques to further enhance the predictive capabilities. Full article

CO₂ sequestration is considered one of the main pillars in achieving the ongoing decarbonization efforts. A myriad of CO₂ sequestration projects targeted sandstone reservoirs since carbonate reservoirs appeared to be unpropitious due to their geological complexity and unfavorable mineralogy and properties. This study investigates CO₂ sequestration potential in a carbonate saline aquifer while considering various geological complexities by capitalizing on numerical simulation. A synthetic anticline reservoir model examined the optimum well location and landing zone for CO₂ sequestration. Additionally, the model evaluated the role of natural fractures in the migration path of CO₂ plume and geochemical reactions throughout the storage process. The study demonstrates that placing the injection well away from the top of the structure in a low-dip region while injecting in the bottom interval would yield the optimum design. After applying a plethora of analyses, geological complexity could impede the migration path of CO₂ but eventually produce a similar path when injected in a similar region. The geochemical interactions between the injected CO₂ and reservoir fluids and minerals reduce the free and trapped CO₂ quantities by dissolving calcite and precipitating dolomite. Furthermore, natural fractures impact the CO₂ quantities during early times only when the fractures cross the top layers. Similarly, the CO₂ migration differs due to the higher permeability within the fractures, resulting in slightly different CO₂ plumes. Consequently, the role of natural fractures should be limited in carbon storage projects, specifically if they do not cross the top of the reservoir. This study reflects a unique perspective on sequestering CO₂ while capturing the roles of natural fractures and well placement in depicting the migration path of the CO₂ plume. A similar systematic workflow and holistic approach can be utilized to optimize the subsurface storage process for potential formations. Full article

The safety and long-term storage capacity of CO₂ geological storage are necessary factors for project design and engineering development. Evaluating the influencing factors of CO₂ storage and quantitatively analyzing the sensitivity of each parameter have an important guiding role in the design and development of storage projects. In this paper, the Liujiagou Formation in the northeast of the Ordos Basin is taken as an example. Based on the TOUGH/Petrasim simulation tool, the RZ2D geological storage model is established. Seven influencing factors, namely salinity, temperature, horizontal and vertical permeability ratio, pore geometry factor, residual gas saturation, liquid saturation and pore compression coefficient, were compared and analyzed to control the plume migration behavior, interlayer pressure accumulation and storage capacity of low porosity and low permeability heterogeneous reservoirs, and the sensitivity of each parameter to interlayer pressure and storage capacity was quantitatively analyzed. The simulation results show that the uncertain factors affect the safety of CO₂ geological storage to a certain extent by affecting the speed of the residual storage and dissolution storage mechanism. High residual gas saturation and salinity will make CO₂ mostly exist in the form of free state, which will adversely affect the safety and storage capacity of CO₂ saline aquifer storage. High temperature and high vertical permeability ratio will lead to higher interlayer pressure accumulation, which is not conducive to the safety of the storage project but is beneficial to the storage capacity. Temperature, transverse and longitudinal permeability ratio and pore geometry factor control the propagation velocity of plume. The larger these factors are, the faster the plume velocity is. Higher liquid phase saturation is not better; higher liquid phase saturation leads to a large build-up of pressure in the reservoir and can have an adverse effect on the storage volume. The sensitivity analysis of all factors shows that the liquid saturation and temperature have the greatest influence on CO₂ geological storage, and the pore compression coefficient has the least influence. The conclusions of this paper can provide a theoretical reference for the design and development of a CO₂ saline aquifer storage project in a low porosity and low permeability reservoir area. Full article