CO2-enhanced Water Recovery Research Articles

Water availability may not restrict the implementation of carbon capture utilization and storage technology: Evidence from China's electric power sector

Carbon capture, utilization and storage (CCUS), a water resource-intensive technology, has been projected to be restricted by water resources in the future. However, the water-saving effects resulting from technology progress and CO2-Enhanced water recovery (CO2-EWR) process are not been fully considered. Based on the learning curve theory, this study proposes a new water accounting system for CCUS retrofitting of coal-fired power plants (CFPPs) from a dynamic perspective considering power generation, carbon capture, and CO2-EWR technology. The results show that the total water withdrawal per unit of CCUS retrofitting with the first-generation capture technology will decrease by 66.89 %, and the total water consumption per unit of that will decrease by 74.70 % from 2021 to 2050. By contrast, the water withdrawal and consumption per unit with the second-generation capture technology will decrease by 74.12 % and 82.51 %, with the overall unit water consumption below 0.5 m3/MWh. Moreover, the water usage caused by CCUS retrofitting will be greatly relieved through the progress of geological sequestration technology (especially the CO2-EWR). In addition, the water usage during the capture process for circulation cooling and air-cooling would present an “inverted U” shaped trend affected by the capture scale and technology progress. Remarkably, the water withdrawal and consumption intensity of CFPPs with air-cooling technology is significantly lower than those of the circulation cooling technology for power generation, while the opposite happens if the capture technology is applied. Even so, CCUS retrofitting for the CFPPs with air-cooling technology can save 60 × 104 m3 of water resource after 2040, which is positive for the CCUS deployment in the arid areas of China.

CO2-enhanced oil recovery with CO2 utilization and storage: Progress and practical applications in China

CO2 capture, utilization, and storage (CCUS) is a strategic emerging technology that has undergone rapid development in recent years. CO2-Enhanced oil recovery with CO2 utilization and storage (CCUS-EOR) is currently the most practicable large-scale carbon reduction technology and has become a key tool for large-scale applications of CCUS. In the inceptive period, CCUS-EOR was targeted towards flooding, but has since been extensively adopted for industrialization. At present, CCUS-EOR is being developed for synergistic flooding and storage, and is expected to gradually transition to utilization in geological storage for supporting large-scale carbon reduction to achieve the goal of carbon neutrality. The primary mechanisms controlling CCUS-EOR differ for high-permeability, high-water-cut oil reservoirs; low-permeability oil reservoirs; extra-low permeability oil reservoirs; and tight and shale oil reservoirs. Therefore, identifying the main constraints in the CO2 flooding process and formulating effective development strategies are necessary for maximizing both oil recovery and storage. In the geological storage of CO2, attention must be paid to key factors such as the storage capacity, injectivity, and safety. The storage performance can be enhanced through methods such as synergistic CO2-enhanced water recovery and CO2 storage (CCS-EWR), as well as rapid carbon mineralization in basalt. Globally, CCUS projects have undergone rapid growth, with more than 90 % of operational projects led by or involving oil and gas companies. In China, CCUS-EOR is currently in the early stage of industrial application. The first million-ton CCUS project has recently been completed. China has great potential for CCUS-EOR. An advantage of CCUS-EOR is the early adoption to large-scale applications, while CO2 storage in saline aquifers provides a foundation for promoting large-scale development. In the future, multiple CCUS-EOR clusters are expected to be established in the Bohai Bay Basin, Songliao Basin, Ordos Basin, Yangtze River Delta, and Pearl River Delta regions, which will drive high-quality development of CCUS applications in China. ChineseLibrary Classification Number TE341. Document CodeA.

Experimental and numerical investigation of supercritical CO2 migration in sandstone with multiple clay interlayers

CO2 enhanced water recovery (CO2-EWR) is one of the most promising technologies for geologic carbon sequestration. The migration characteristics and displacement efficiency of supercritical CO2 (SC-CO2) after injection into a saline aquifer directly affect the feasibility and economy of a CO2-EWR project. Multiple clay interlayers often develop in the target sandstone reservoir and combine in different expansive ways, which could influence the SC-CO2 migration. In this study, core flooding experiments were conducted using a special sandstone with multiple thin clay interlayers and the fluid behavior was monitored by an X-ray computed tomography (X-CT) scanner. Based on the porosity matrix obtained from X-CT images, a two-dimension model based on Darcy flow was developed to simulate the fluid behavior under the experiment conditions. The experimental results show that SC-CO2 pathways were developed in the sand part of the sample, while the clay interlayers were fluid-proof. Comparing the experimental and simulation results, it is evident that the porosity distribution, clay interlayers directionality/extent and flooding direction were the main factors that affected the fluid behavior in the sample. There were positive correlations between porosity and SC-CO2 saturation after drainage processes. Flooding directions and clay interlayers were combined to affect the fluid migration. The clay interlayers had functions of barrier and collection when the flooding direction pointed towards the opening of a wedge-shaped semi-open area formed by clay interlayers. While this area was almost free of SC-CO2 when the injection direction reversed, resulting a smaller SC-CO2 saturation in sample during the backward drainage process.

Coupled chemo-mechanical behavior of CO2 mineral trapping in the reservoir sandstones during CO2–EWR

Carbon dioxide (CO2) sequestration in deep saline aquifers is regarded as a potentially useful method of storing CO2 due to their large storage capacity. CO2-trapping mechanisms in such aquifers include solubility trapping, hydrodynamic trapping, structural trapping, and mineral trapping. CO2–water–rock interactions occurring in saline aquifers injected with CO2 are known to play a vital role in these trapping mechanisms. Stress is known to have a significant and positive effect on mineral dissolution, and therefore, pressure solution as a coupled chemo-mechanical behavior could make an important contribution to mineral trapping. Geological storage of CO2 can also be combined with enhanced water recovery (EWR) from deep saline aquifers, a process referred to as CO2–EWR. By exploiting the fluid during CO2–EWR, the pore pressure in the reservoir is altered, which could enhance pressure solution between the mineral grains in the reservoir. In this work, the role played by pore pressure in CO2 mineral trapping from the perspective of pressure solution as a chemo-mechanical coupling process is investigated. To achieve this, seepage–creep tests were performed on sandstone specimens by passing CO2–NaCl solutions through them at different pore pressures. Experimental results show that the lower the pore pressure a specimen is subjected to, the greater the amount of carbon trapped in the sandstone. On the basis of this result, a geometrical model is established for pressure solution in the materials used that quantitatively describes the mechanism responsible for pressure solution. Geometrical model is then used to analyze the effects of the various factors affecting the role played by pressure solution in CO2 mineralization sequestration (mineral type, pore pressure, porosity, and particle size). The results of the analysis are particularly instructive for the evaluation of long-term CO2 storage in terms of pressure solution. As for CO2–EWR, apart from relieving pressure buildup, increasing CO2 injection, regulating CO2 migration, and restricting CO2 leakage, it also enjoys the advantage of enhancing mineral trapping.

The evolution of water chemical characteristics and their indicative function in CO2-enhanced water recovery

A monitoring method that uses the variation in water chemical characteristics of the deep storage layer was studied by a three-dimensional numerical model under the background of a CO2-enhanced water recovery (CO2-EWR) site in the Junggar Basin. The effect of water chemical characteristics on the migration of CO2 in different phases and the transformations of major sequestered carbon minerals were determined from the resulting mechanism. The results show that the evolution of water chemical characteristics, such as pH, Ca2+ and dissolved inorganic carbon (DIC), can effectively indicate the migration distance and time of dissolved CO2 and supercritical CO2. The times corresponding to the turning points of the pH and DIC change curves at the monitoring points can plot the isochronal maps of dissolved and supercritical CO2 migration, which can be used to quantitatively evaluate CO2 migration in the reservoir. The changes of DIC and Ca2+ can be used to infer the main carbon sequestration minerals: at the rapidly falling stage of Ca2+ concentrate over time and the low concentrate of DIC, the main carbon sequestration mineral is calcite, and in other conditions is ankerite. Water chemical characteristics can identify the extent of injected CO2 impact in the corresponding region. This paper provides an alternative method for monitoring CO2 migration and conversion in different phases and determining the extent of injected CO2 impact in a region by the type of sequestered carbon minerals.

A Study on the CO2-Enhanced Water Recovery Efficiency and Reservoir Pressure Control Strategies

CO2 geological storage (CGS) proved to be an effective way to mitigate greenhouse gas emissions, and CO2-enhanced water recovery (CO2-EWR) technology may improve the efficiency of CO2 injection and saline water production with potential economic value as a means of storing CO2 and supplying cooling water to power plants. Moreover, the continuous injection of CO2 may cause a sharp increase for pressure in the reservoir system, so it is important to determine reasonable reservoir pressure control strategies to ensure the safety of the CGS project. Based upon the typical formation parameters of the China Geological Survey CO2-EWR test site in the eastern Junggar Basin, a series of three-dimensional (3D) injection-extraction models with fully coupled wellbores and reservoirs were established to evaluate the effect of the number of production wells and the well spacing on the enhanced efficiency of CO2 storage and saline production. The optimal key parameters that control reservoir pressure evolution over time are determined. The numerical results show that a smaller spacing between injection and production wells and a larger number of production wells can enhance not only the CO2 injection capacity but also the saline water production capacity. The effect of the number of production wells on the injection capacity and production capacity is more significant than that of well spacing, and the simulation scenario with 2 production wells, one injection well, and a well spacing of 2 km is more reasonable in the demonstration project of Junggar Basin. CO2-EWR technology can effectively control the evolution of the reservoir pressure and offset the sharp increase in reservoir pressure caused by CO2 injection and the sharp decrease of reservoir pressure caused by saline production. The main controlling factors of pressure evolution at a certain spatial point in a reservoir change with time. The monitoring pressure drops at the beginning and is controlled by the extraction of water. Subsequently, the injection of CO2 plays a dominant role in the increase of reservoir pressure. Overall, the results of analysis provide a guide and reference for the CO2-EWR site selection, as well as the practical placement of wells.

Cost curve of large-scale deployment of CO2-enhanced water recovery technology in modern coal chemical industries in China

China has emerged as a world leader in the coal chemical industry, which requires large amount of water and results in considerable CO2 emissions. This situation has led to the challenge of the CO2-Water nexus for China and particularly for the sustainable development of its coal chemical industry. CO2-enhanced water recovery (CO2-EWR) technology can provide large-scale CO2 mitigation and additional water supply in an integrated manner, especially in arid areas. Meanwhile, CO2 streams from industrial separation processes in the coal chemical industries are amenable to separation and can dramatically simplify or even dispense with the capture process. This study presents the first systematic assessment of a cost curve for onshore CO2-EWR potential using CO2 streams from industrial separation processes by an evaluation framework encompassing CO2 emission inventory, site suitability evaluation, and source–sink matching with techno-economic models. Preliminary results focused on the full capacity of several coal chemical processes as of 2015 suggest that CO2-EWR technology can mitigate 269 million tons of CO2 from industrial separation processes at relatively low cost ranging from 12 to 30 USD/t CO2 in China. Furthermore, 404 million tons of underground water could be produced for further desalination and utilization. When additional capacity under development could become fully operational, the emissions of 878 million tons of CO2 could be mitigated and provide 1318 million tons of vital water resources. Therefore, CO2-EWR technology can be essential to clean and sustainable development of the coal chemical industry and may provide low-cost opportunities to accelerate the deployment of large-scale CCUS projects in China.

Study on Field-scale of CO2 Geological Storage Combined with Saline Water Recovery: A Case Study of East Junggar Basin of Xinjiang

Xinjiang is the major energy production area, and one of the regions with the most serious water resources scarcity issues in China. In particular, the coal-fired power and coal chemical industry base in East Junggar Basin has faced severe carbon emissions and water shortages. Based on the 3D heterogeneous geologic model of the East Junggar Basin, the research of field-scale CO2 enhanced water recovery (CO2-EWR) was carried out to provide technical reference for the future field-scale CO2-EWR engineering practice in Xinjiang to solve the carbon emission and water shortage issues. The CO2-EWR technology can greatly relieve the reservoir pressure buildup, with a maximum cumulative CO2 injection and storage of 100 Mt (3 times more than CO2 Geological Storage only) and a maximum saline water production of 129.4 Mt (100 times more than saline water production only).

Numerical simulation of enhancement in CO2 sequestration with various water production schemes under multiple well scenarios

To determine the best CO2 injection and brine production strategy for achieving both the optimal water production and the optimal CO2 storage capacity while maintaining operational safety in CO2 enhanced brine production, three injection scenarios based on the typical geological parameters of the Junggar Basin in China are compared. They are the sole CO2 injection, sole water production and combined CO2 enhanced water recovery, and for the combined CO2 enhanced water recovery scenario, both the co-production of brine and pre-production of brine are considered. It is found that compared to the pre-production of brine, the combination of pre- and co-production of brine can be more effective in controlling the pressure perturbation and in increasing the CO2 storage capacity. However the volume of co-produced brine plays a smaller role in the pressure build-up. The influence of number of pumping wells is also analyzed. Although increasing the number of wells can enhance the CO2 storage, the economic analysis reveals that the revenue in water production and CO2 storage cannot compensate the expensive investment required in well drilling. The injection strategy is essential to the efficiency of CO2 enhanced water recovery; this paper compares the strategies for pre-production and co-production of brine on CO2 enhanced shale gas recovery. The conclusions given in this paper can serve as a reference for the design engineers interested in CO2 storage with co-production of brine.

Mesoscale Assessment of CO2 Storage Potential and Geological Suitability for Target Area Selection in the Sichuan Basin

In China, south of the Yangtze River, there are a large number of carbon sources, while the Sichuan Basin is the largest sedimentary basin; it makes sense to select the targets for CO2 geological storage (CGUS) early demonstration. For CO2 enhanced oil and gas, coal bed methane recovery (CO2-EOR, EGR, and ECBM), or storage in these depleted fields, the existing oil, gas fields, or coal seams could be the target areas in the mesoscale. This paper proposed a methodology of GIS superimposed multisource information assessment of geological suitability for CO2 enhanced water recovery (CO2-EWR) or only storage in deep saline aquifers. The potential per unit area of deep saline aquifers CO2 storage in Central Sichuan is generally greater than 50 × 104 t/km2 at P50 probability level, with Xujiahe group being the main reservoir. CO2 storage potential of depleted gas fields is 53.73 × 108 t, while it is 33.85 × 108 t by using CO2-EGR technology. This paper recommended that early implementation of CGUS could be carried out in the deep saline aquifers and depleted gas fields in the Sichuan Basin, especially that of the latter because of excellent traps, rich geological data, and well-run infrastructures.

Numerical simulation and optimization of CO2-enhanced water recovery by employing a genetic algorithm

Carbon dioxide geological sequestration simultaneously combined with water production from deep saline aquifer can effectively address the challenge faced by modern energy systems of reducing carbon dioxide emissions and water intensity while providing reliable, affordable, and secure energy. However, little attention has been paid to date in the literature on determining the carbon dioxide injection strategy for achieving both the optimal water production and the optimal carbon dioxide storage capacity while maintaining operational safety. This paper first establishes three injection–extraction scenarios based on the typical geological parameters of the Junggar Basin in China to analyze the effect of carbon dioxide injection on water extraction and the effect of water extraction on the carbon dioxide storage. The three injection scenarios considered are sole carbon dioxide injection, sole water production and combined carbon dioxide enhanced water recovery. The carbon dioxide enhanced water recovery scenario is then optimized using a genetic algorithm to determine the trade-off between the maximum possible water recovery and the safe carbon dioxide storage for both the constant mass injection and the variable time-dependent mass injection (for achieving constant pressure injection). The influence of number of pumping wells is also analyzed. It can be concluded from this work that the carbon dioxide enhanced water recovery technology can effectively manage the pressure perturbation caused by the carbon dioxide injection as well as the water production while significantly enhancing the carbon dioxide storage capacity, security and water production efficiency. Injection strategy is essential to the efficiency of carbon dioxide enhanced water recovery; the genetic algorithm based optimizer combined with the well-known multi-phase flow solver TOUGH2, designated as GA-TOUGH2 is used for the optimization of injection scenarios. It is found that in the allowable range of pressure perturbations, a higher carbon dioxide injection rate is more beneficial for carbon dioxide storage as well as for water production. Constant pressure injection operation is superior to the constant rate injection and leads to higher carbon dioxide storage capacity and stability, and water production efficiency. Adding pumping wells can somewhat enhance the carbon dioxide storage capacity especially for the constant pressure injection operation compared to the constant rate injection operation as well as the water production efficiency; however, the enhancement in water production is very small compared to the single well and cannot be regarded as economical considering the additional capital cost of well drilling. This paper addresses the method of combined numerical simulation and optimization for carbon dioxide enhanced water recovery from saline aquifers that can be employed in the implementation of enhanced water recovery at industrial scale.