Offshore CO2 Research Articles

Effects of Aqueous Solubility and Geochemistry on CO2 Storage in Offshore Basins

The increasing global focus on carbon capture and storage (CCS) has highlighted the potential for offshore CO2 sequestration, particularly following recent successes in onshore projects. This research investigates the qualitative analysis of carbon trapping efficiency in offshore basins, employing a GEM simulator to incorporate factors such as aqueous solubility and geochemistry. The findings reveal that anticlines represent ideal geological structures for carbon storage, effectively trapping a significant portion of injected CO2. For effective mineralization, it is crucial to dissolve CO2 into saline aquifers to generate H+, which facilitates the release of Ca2+ and Al3+ from anorthite. This process leads to the dissolution of anorthite and the precipitation of kaolinite, while calcite transitions from a dissolved state to a precipitated state over time. The analysis indicates that structural trapping provides the highest storage contribution during the injection phase, whereas residual gas trapping becomes dominant by the end of the simulation. Notably, it is observed that the storage contribution of structural trapping decreases from 28.39% to 19.05%, and the percentage increase in storage contributions of residual gas, solubility, ionic, and mineral trapping are 4.12%, 3.25%, 1.69%, and 0.28% for CO2 plus water injection, thereby improving the long-term security of CO2 storage in offshore basins. It is most beneficial to optimize the layout and design of the injection well to ensure a uniform distribution of carbon dioxide and to increase the injection rate.

Sensitivity of Marine Controllable Source Electromagnetic Soundings for Identifying Plume Migration in Offshore CO2 Storage

Sensitivity of Marine Controllable Source Electromagnetic Soundings for Identifying Plume Migration in Offshore CO2 Storage

Early Opportunities for Onshore and Offshore CCUS Deployment in the Chinese Cement Industry

The promotion of deep decarbonization in the cement industry is crucial for mitigating global climate change, a key component of which is carbon capture, utilization, and storage (CCUS) technology. Despite its importance, there is a lack of empirical assessments of early opportunities for CCUS implementation in the cement sector. In this study, a comprehensive onshore and offshore source–sink matching optimization assessment framework for CCUS retrofitting in the cement industry, called the SSM-Cement framework, is proposed. The framework comprises four main modules: the cement plant suitability screening module, the storage site assessment module, the source–sink matching optimization model module, and the economic assessment module. By applying this framework to China, 919 candidates are initially screened from 1132 existing cement plants. Further, 603 CCUS-ready cement plants are identified, and are found to achieve a cumulative emission reduction of 18.5 Gt CO2 from 2030 to 2060 by meeting the CCUS feasibility conditions for constructing both onshore and offshore CO2 transportation routes. The levelized cost of cement (LCOC) is found to range from 30 to 96 (mean 73) USD·(t cement)−1, while the levelized carbon avoidance cost (LCAC) ranges from −5 to 140 (mean 88) USD·(t CO2)−1. The northeastern and northwestern regions of China are considered priority areas for CCUS implementation, with the LCAC concentrated in the range of 35 to 70 USD·(t CO2)−1. In addition to onshore storage of 15.8 Gt CO2 from 2030 to 2060, offshore storage would contribute 2.7 Gt of decarbonization for coastal cement plants, with comparable LCACs around 90 USD·(t CO2)−1.

Application of Feature, Event, and Process Methods to Leakage Scenario Development for Offshore CO2 Geological Storage

Application of Feature, Event, and Process Methods to Leakage Scenario Development for Offshore CO2 Geological Storage

Sleipner 26 years: how well-established subsurface monitoring work processes have contributed to successful offshore CO 2 injection

In August 2022, the world's longest running offshore industrial CO 2 injection project celebrated its 26-year anniversary. During these years, the Sleipner CO 2 injection project has been invaluable in demonstrating that offshore CO 2 storage is feasible, safe, and efficient. We will here show how time-lapse seismic monitoring of the CO 2 plume development has revealed depositional architecture in the Utsira Formation, and how thin mudstone layers have contributed to distributing the CO 2 in a larger rock volume, promoting trapping by dissolution. The relatively shallow depth (800–1000 m) of Utsira Formation in the Sleipner area also makes the Sleipner CO 2 injection site a good proxy for understanding the effects of overburden stratigraphy for deeper injection sites, giving important knowledge of detectability of thin, shallow CO 2 accumulations. Finally, we will show how the experience from Sleipner CO 2 injection has built confidence when planning monitoring programmes for future CO 2 injection sites.

Sub-surface geospatial intelligence in carbon capture, utilization and storage: A machine learning approach for offshore storage site selection

This study introduces an innovative data-driven and machine-learning framework designed to accurately predict site scores in the site screening study for specific offshore CO2 storage sites. The framework seamlessly integrates diverse sub-surface geospatial data sources with human aided expert-weighted criteria, thereby providing a high-resolution screening tool. Tailored to accommodate varying data accessibility and the significance of criteria, this approach considers both technical and non-technical factors. Its purpose is to facilitate the identification of priority locations for projects associated with Carbon Capture, Utilization, and Storage (CCUS). Through aggregating and analyzing geospatial datasets, the study employs machine learning algorithms and an expert-weighted model to identify suitable geologic CCUS regions. This process adheres to stringent safety, risk control, and environmental guidelines, addressing situations where human analysis may fail to recognize patterns and provide detailed insights in suitable site screening techniques. The primary emphasis of this research is to bridge the gap between scientific inquiry and practical application, facilitating informed decision-making in the implementation of CCUS projects. Rigorous assessments encompassing geological, oceanographic, and eco-sensitivity metrics contribute valuable insights for policymakers and industry leaders. To ensure the accuracy, efficiency, and scalability of the established offshore CO2 storage facilities, the proposed machine learning approach undergoes benchmarking. This comprehensive evaluation includes the utilization of machine learning algorithms such as Extreme Gradient Boosting (XGBoost), Random Forest (RF), Multilayer Extreme Learning Machine (MLELM), and Deep Neural Network (DNN) for predicting more suitable site scores. Among these algorithms, the DNN algorithm emerges as the most effective in site score prediction. The strengths of the DNN algorithm encompass nonlinear modeling, feature learning, scale invariance, handling high-dimensional data, end-to-end learning, transfer learning, representation learning, and parallel processing. The evaluation results of the DNN algorithm demonstrate high accuracy in the testing subset, with values of AAPD (Average Absolute Percentage Difference) = 1.486 %, WAAPD (Weighted Average Absolute Percentage Difference) = 0.0149 %, VAF (Variance Accounted For) = 0.9937, RMSE (Root Mean Square Error) = 0.9279, RSR (Root Sum of Squares Residuals) = 0.0068, and R2 (Coefficient of Determination) = 0.9937.

Insights and Guidance for China’s Offshore CO2 Storage Development: Evidence from Global Experience

Through extensive data research and analysis, this paper comprehensively summarizes the status and key insights of global carbon dioxide capture and storage (CCS) development. It aims to gain a comprehensive understanding of the relevant policies, technologies, and security measures adopted by major countries in their CCS development processes. Furthermore, it explores the existing status and limitations of China’s offshore development efforts, while providing valuable recommendations for enhancing China’s offshore CCS initiatives, as well as serving as a reference for other nations worldwide. Offshore CCS plays a crucial role for China to achieve the development target of carbon peak and carbon neutrality, due to its energy structure and industrial distribution. While China possesses significant offshore CCS potential, achieving commercialization still requires substantial efforts. To facilitate the process and draw insights from successful experiences in other countries, this paper illustrates the characteristics and generalizes the experience of offshore CCS industry practices in America, Europe and Japan, respectively. Furthermore, it is recommended that a new round of investigation into offshore CCS potential be conducted, while promoting integrated collaboration between geological surveying and marine scientific research. Additionally, further research on industrial policies and green financial strategies should be undertaken.

Investigation of Pipeline CO2 Leakage and Diffusion on Offshore Platforms Based on Numerical Simulation.

Pipeline transportation of CO2 is the key link to realize carbon capture, utilization, and storage. CO2 pipeline transportation may face the risk of leakage, which poses a great threat to the production process and personnel safety. It is of great significance to study the leakage and diffusion characteristics of CO2 in pipeline transportation for the safety design and personnel protection of the offshore CO2 storage platform. In order to study the leakage and diffusion characteristics of CO2 in pipeline transportation on offshore platforms, a physical model of a target platform and several numerical models were built, and a series of pipeline CO2 leakage and diffusion simulations were carried out using the method of numerical simulation. Based on the simulation results, the temperature distribution and CO2 concentration distribution on the offshore platforms after leakage were measured and analyzed. The influence of leakage direction (horizontal and oblique 45° upward) was also studied. Dangerous areas on the platform and suggestions for staff evacuation were given according to the simulation results. The research results of this work can provide guidance for the safe operation of offshore CO2 storage platforms.

Numerical simulation study of natural gas hydrate extraction by depressurization combined with CO2 replacement

Utilizing depressurization combined with CO2 replacement for extracting natural gas hydrates (NGHs) is vital for sustainable energy and carbon sequestration. In this study, a NGH reservoir numerical model was developed to investigate the impacts of depressurization combined with CO2 replacement on hydrate extraction at a field scale. Findings reveal an increase in methane production with reduced bottom hole pressure. When the bottom hole pressure is 3.5 MPa, the methane production reaches its maximum at 1.71 × 106 m3. Methane hydrates near production and injection wells decompose first, with deeper hydrates decomposing more easily. Higher differential pressures between injection and production enhance methane extraction and CO2 hydrate formation. However, excessive pressure differential (1.5 MPa) can lead to CO2 breakthrough across reservoir barriers, adversely affecting the purity of methane. At 1800 d, the methane purity is only 36.2 %. Optimal methane extraction and CO2 sequestration occur at higher injection temperatures (9 °C) below the CO2 hydrate phase equilibrium temperature. Temperatures above this equilibrium adversely affect both processes. The study validates the feasibility of depressurization with CO2 replacement for extracting hydrates in the Shenhu area, offering theoretical guidance for synergistic offshore methane extraction and CO2 sequestration techniques.

Optimization method of water-quality observation positions in offshore CCS sites using the adjoint marginal sensitivity method

Carbon dioxide (CO2) Capture and Storge (CCS) is recognized as a promising method to mitigate the global warming. In Japan, sub-seabed CO2 storage is considered to be commercialized in a decade. However, offshore CO2 storage has a risk of leakage. Since CO2 seepage into seawater may affect the marine environment, CO2 concentration must be monitored in CO2 storage sea sites under a Japanese law. However, there is no scientifically logical base to determine observation positions. In this study, we therefore developed a method of determining optimal observation positions in CO2 storage sea sites. First, we defined optimal observation positions as those that can estimate seepage positions with high accuracy with the minimal number using the adjoint marginal sensitivity method, even if the seepage positions locate anywhere in a target sea site. Second, non-dimensional parameters were proposed to determine whether a datum at a candidate observation position can be successfully used to estimate a possible seepage position using the adjoint method. Then, we defined a coverage index that indicates how much of a target sea site is “covered” in total by observation points and proposed an algorithm to optimally place observation positions. Finally, we validated the developed method numerically and indicated that, to perform highly accurate estimation, it is desirable that a seepage position be covered by at least three observation points.

CO2 abatement feasibility for blast furnace CCUS retrofits in BF-BOF steel plants in China

As one of the energy and carbon intensive industries, the steel industry's low-carbon transition will contribute to the achievement of China's carbon neutrality goal. In this study, a comprehensive source-sink matching-trinomial tree real option evaluation model for China's steel industry was established by combining the database of carbon emissions from blast furnaces of BF-BOF process steel plants, and onshore and offshore CO2 storage potential and injection capacity rate database. By using this model, we investigate the CO2 abatement potential and investment decisions for blast furnace CCUS full-chain projects in China's BF-BOF process steel plants. The results show that a total of 420.07Mt/a of CO2 reductions can be achieved, attributed to 111 steel plants screened for source-sink matching. If no extra incentive policy was included, the current carbon market only supported immediate investment in 14 steel plant CCUS retrofit full-chain projects, which could achieve 36.47Mt/a of CO2 reductions, with a critical carbon price ranging from 6.96 to 202.98USD/t, averaged at 86.97 USD/t. Technological advances, rising carbon prices and government incentives would all contribute to the development of CCUS full-chain projects in the steel industry. The findings provide a strategy for the deployment of blast furnace CCUS retrofit in China's steel industry.

Toward Cleaner and More Sustainable Cement Production in Vietnam via Carbon Capture and Storage

Vietnam is the world’s largest cement exporter. In 2022, it produced 118 Mtpa cement while emitting 109 Mtpa cement-related CO2, equal to 33% of Vietnam’s total CO2 emission. As Vietnam has pledged to achieve net zero by 2050, unabated cement-related CO2 emission must be drastically reduced in the future. This paper investigates the contribution of carbon capture and storage (CCS) to decarbonizing Vietnam’s cement industry to make cement production cleaner and more sustainable. A first-of-a-kind CO2 source-sink mapping exercise was conducted to map 68 cement plants to subsurface sinks, including oil and gas reservoirs and saline aquifers, using four CCS field development concepts. The results have identified four first-mover CCS projects where CO2 emissions from 27 cement plants are mapped to nearby offshore subsurface CO2 sinks. Two of these projects are located in Vietnam-north, one in Vietnam-central, and one in Vietnam-south. In the Vietnam-south CCS project, CO2 emission from the Kien Giang province is transported and stored in the offshore Block B gas field. In the other three CCS projects, CO2 emission is transported to nearshore saline aquifers in the Song Hong Basin. At a CO2 capture rate of 90%, these four projects will mitigate 50 Mtpa CO2, which is 46% of cement-related CO2 emission or 15% of total CO2 emission from Vietnam, thus making Vietnam’s cement production cleaner and more sustainable. Future research should focus on subsurface characterization of saline aquifers in the Song Hong Basin. The methodology developed in this study is usable in other cement-producing countries with significant CO2 sinks in the nearshore continental shelf.

Constrained nonlinear amplitude-variation-with-offset inversion for reservoir dynamic changes estimation from time-lapse seismic data

We develop a novel elastic amplitude-variation-with-offset (AVO) inversion process to estimate the fluid saturation and effective pressure or variations in these properties from time-lapse seismic data sets. These changes occur in oil and gas reservoirs caused by fluid injection or hydrocarbon production that leads to changes in the elastic wave properties, reflectivity, and seismic response. Our method is based on a seismic forward model that consists of a linearized AVO equation and a rock-physics model. The AVO equation links the elastic wave properties to seismic reflection amplitudes, whereas the rock-physics model maps the saturation and pressure into seismic velocities and density. The inversion approach relies on the gradient descent technique to estimate the unknown variables by searching for the minimum of the least-squares misfit between the observed and modeled data. The first-order gradient equations of the least-squares data misfit function with respect to effective pressure and water saturation are derived by using the adjoint-state method and the chain rule. The optimization method used to minimize the misfit function and obtain the best optimal solution is a limited-memory quasi-Newton algorithm. This inversion process allows us to incorporate prior constraints by using the logistic function to map the model variables to a bounded range. To achieve a stable solution to ill-posed inversion problems, optimal regularization weights are applied. The application of the developed workflow on 1D synthetic and real well-log data from the Edvard Grieg oil field simulating various saturation-pressure conditions during production demonstrates the validity of the approach with different noise levels. The inversion is then applied to a 2D synthetic data set modeled from the reservoir model of the Smeaheia field, a potential site for a large-scale offshore CO2 storage field located in the North Sea. Our results illustrate that our inversion method efficiently and accurately estimates reservoir saturation and pressure variations.

Covering tour problem with varying coverage: Application to marine environmental monitoring

In this paper, we present a novel variant of the Covering Tour Problem (CTP), called the Covering Tour Problem with Varying Coverage (CTP-VC). We consider a simple graph G=(V,E), with a measure of importance assigned to each node in V. A vehicle with limited battery capacity visits the nodes of the graph and has the ability to stay in each node for a certain period of time, which determines the coverage radius at the node. We refer to this feature as stay-dependent varying coverage or, in short, varying coverage. The objective is to maximize a scalarization of the weighted coverage of the nodes and the negation of the cost of moving and staying at the nodes. This problem arises in the monitoring of marine environments, where pollutants can be measured at locations far from the source due to ocean currents. To solve the CTP-VC, we propose a mathematical formulation and a heuristic approach, given that the problem is NP-hard. Depending on the availability of solutions yielded by an exact solver, we evaluate our heuristic approach against the exact solver or a constructive heuristic on various instance sets and show how varying coverage improves performance. Additionally, we use an offshore CO2 storage site in the Gulf of Mexico as a case study to demonstrate the problem's applicability. Our results demonstrate that the proposed heuristic approach is an efficient and practical solution to the problem of stay-dependent varying coverage. We conduct numerous experiments and provide managerial insights.

Carbonic Anhydrase-Embedded Hydrogen-Bonded Organic Frameworks Coating for Facilitated Offshore CO2 Fixation.

Exhausted emission of carbon dioxide (CO2 ) from ships or offshore platforms has become one of the major contributors to global carbon emissions. Enzymes such as carbonic anhydrase (CA) have been widely used for CO2 mineralization because of their high catalytic rate. However, CA in seawater is easy to inactivate and difficult to reuse. Immobilization would be a feasible solution to address the stability issue, which, however, may cause an increase of internal diffusion resistance and reduced catalytic activity. In this regard, design of high-performance biocatalysts for acquiring high catalytic activity and stability of CA is highly desirable. Herein, a monolithic catalyst of Filler-CA@Lys-HOF-1 (FCLH) was prepared by chemical sorption of CA on the surface of the Filler followed by the coating of Lys-HOF-1. The highest catalytic activity of FCLH was obtained by regulating the amount of HOF-1 monomer added. Due to the protection of Lys-HOF-1, the FCLH showed good tolerance against acidity and salinity, which could retain about 80.2 % of the original activity after 9 h incubation in simulated seawater. The catalytic activity of FCLH could retain 85.4 % of the initial activity after 10 cycles. Hopefully, our study can provide a promising biocatalyst for CO2 mineralization, which may drive down carbon emissions when used for CO2 capture and conversion on offshore platforms.

Carbon Dioxide Storage Potential of Cenozoic Saline Aquifers in the South Yellow Sea Basin

Carbon dioxide (CO2) storage in underwater reservoirs is a valuable method of reducing carbon emissions. Saline aquifers such as those in the South Yellow Sea Basin (SYSB), China, have great potential for geological CO2 storage. Thus, we use the recommended calculation method of USDOE and a formation volume model to determine the geological conditions for CO2 storage and estimate the CO2 storage capacity of the Cenozoic saline aquifers in the SYSB (depth: 800–3200 m). Overall, the SYSB exhibits weak fault activity and seismicity, medium and low geothermal fields, four types of source sandstone reservoir, and four sets of carbon reservoir–caprock assemblages developed from the Cenozoic strata, providing relatively good geological conditions for CO2 storage. The estimated capacity of the Cenozoic strata ranges from 39.59 Gt to 426.94 Gt (average: 155.25 Gt), indicating an extensive storage capacity that can meet the carbon sequestration needs of Shandong and Jiangsu Provinces for approximately 89 years. The Yantai Depression has a lower geothermal gradient and terrestrial heat, weaker seismic activity, and double the storage capacity of the Qingdao Depression, indicating that it is the most suitable area for Cenozoic CO2 storage in the SYSB, whereas the Laoshan Uplift is not suitable for storage. This study provides a scientific basis for the selection of offshore CO2 storage sites.

Assessing a potential site for offshore CO2 storage in the Weixinan Sag in the northwestern Beibu Gulf Basin, northern South China Sea

AbstractGeologic carbon storage (GCS) activities, especially offshore, are still far insufficient worldwide. Sedimentary basins in the northern South China Sea (nSCS) are identified to be favorable to offshore GCS deployment. This study investigates by numerical reservoir simulations the performance of the Weixinan Sag in the northern depression of the Beibu Gulf Basin (BGB), which is considered the most promising area for CO2 offshore GCS in saline formations. Simulations of CO2 injection at a potential site with a normal fault indicate that the pressure buildup induced by CO2 horizontal injection could penetrate extremely low‐permeability faults or caprock formations. The CO2 plumes under higher injection pressures are more constrained in the horizontal direction and hence appear thicker while CO2 tends to spread out horizontally in conditions of low pressure. The impermeable fault renders the CO2 plume about 200 m smaller in size horizontally. Assuming the presence of a fault with a highly permeable core causes leakage to occur after about 30 years of injection, which accounts for only 0.04% the injected amount. For the vertical‐well injection case, the potential CO2 leakage only accounts for around 0.28% of the injection amount, which is far less than the criterion (i.e., 2%) required to make GCS worthwhile. The storage capacities of the formations are mainly controlled by the depths and thicknesses since both their porosities and permeabilities are comparable. The formation Jiaowei‐2 and Xiayang have the largest and second largest storage capacities, respectively, when using a fully perforated well for vertical injection. The average storage capacity of the studied site is 13.04 kg m−3, which is comparable to that of the formation Xiayang. Average injectivities of formations Jiaowei‐2, Xiayang, Weizhou‐1, and Weizhou‐3 are 8.29 × 10−5, 1.75 × 10−4, 6.58 × 10−5, and 2.99 × 10−3 kg s−1 Pa−1, respectively. © 2022 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Offshore CO2 Capture and Utilization Using Floating Wind/PV Systems: Site Assessment and Efficiency Analysis in the Mediterranean

A methanol island, powered by solar or wind energy, indirectly captures atmospheric CO2 through the ocean and combines it with hydrogen gas to produce a synthetic fuel. The island components include a carbon dioxide extractor, a desalinator, an electrolyzer, and a carbon dioxide-hydrogen reactor to complete this process. In this study, the optimal locations to place such a device in the Mediterranean Sea were determined, based on three main constraints: power availability, environmental risk, and methanol production capability. The island was numerically simulated with a purpose built python package pyseafuel. Data from 20 years of ocean and atmospheric simulation data were used to “force” the simulated methanol island. The optimal locations were found to strongly depend on the power availability constraint, with most optimal locations providing the most solar and/or wind power, due to the limited effect the ocean surface variability had on the power requirements of methanol island. Within this context, optimal locations were found to be the Alboran, Cretan, and Levantine Sea due to the availability of insolation for the Alboran and Levantine Sea and availability of wind power for the Cretan Sea. These locations were also not co-located with areas with larger maximum significant wave heights, thereby avoiding areas with higher environmental risk. When we simulate the production at these locations, a 10 L s−1 seawater inflow rate produced 494.21, 495.84, and 484.70 mL m−2 of methanol over the course of a year, respectively. Island communities in these regions could benefit from the energy resource diversification and independence these systems could provide. However, the environmental impact of such systems is poorly understood and requires further investigation.

Safety Aspects of Offshore CO2 Storage in Depleted Levels of Hydrocarbon Cultivation Fields

Safety Aspects of Offshore CO2 Storage in Depleted Levels of Hydrocarbon Cultivation Fields

Greensand project – transport and offshore storage of CO2 in Denmark – status, outlook and challenges

The Greensand project includes, beside from safe and efficient geological offshore CO2 storage, offshore transport by ship and/or pipeline of CO2 from key side onshore facilities established to capture, liquefy, onshore transport and temporarily store the CO2 before offloading to storage site. The Greensand project builds on the usage of the offshore Siri complex sandstone reservoirs no longer in use for oil and gas production. The storage sites, offloading and injection systems and transportation means are currently being technically matured. The target is to be able to offer customers safe and reliable transport and storage services from the start of 2026. Currently meanwhile maturing a technical concept, commercial and regulatory activities are ongoing in parallel. The Greensand partners INEOS Energy and Wintershall Dea have also decided to perform an offshore pilot test of injecting liquified CO2 into a particular reservoir serving as candidate for future long terms storage of CO2. Along the pilot testing offshore project, material testing and deployment of monitoring techniques are being matured. The Pilot testing offshore planned to take place late 2022 with a 3-months duration.