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Over the years, Carbon Capture and Sequestration (CCS) has been recognized as a crucial element in the toolkit of measures to combat climate change. At the European Union (EU) level, CCS plays a vital role in climate policy, particularly in reducing CO2 emissions from hard-to-abate industries. However, no comprehensive legal framework covers all stages of CCS. These stages include carbon capture techniques, transportation by ships or pipelines, injection, site closure, and post-closure management. Each of these stages is regulated by different legal frameworks that address various topics such as geoengineering, climate change, industrial activities, property, transportation, port operations, waste management, dumping, health, and the environment. Critical legal questions remain unanswered, such as who is liable for discharges in the marine environment during the transportation of CO2 by ships and for the long-term management of sub-seabed storage sites. As the transportation of CO2 by ships will likely have transboundary implications, we explore the legal possibilities, limitations and risks associated with exporting CO2 streams for sequestration under the sub-seabed. [ABSTRACT FROM AUTHOR]

Geological disposal of CO2 after capturing the gas from large emitting sources is one of the safest and most prominent methods to eliminate CO2 from the atmosphere and mitigate climate change. The heterogeneities in porosity, permeability and capillary pressure in various underground formations impact gas distribution, affecting their storage capacity. Therefore, a numerical model is developed to study the plume migration under various physical heterogeneities by upscaling the variation in capillary pressure. Accordingly, homogeneous, heterogeneous and layered formations have been considered. The influence of capillary pressure and field-scale heterogeneities, such as porosity and permeability, is incorporated using the Leverett J function. The impact of variations in capillary pressure on gas migration is calibrated in different formations for ten years of injection. The analysis project that plume evolution in different formations highly deviates and a plume length of 3410 m is obtained for layered formation. A sensitivity analysis was conducted to understand the influence of interfacial tension in formations with differing heterogeneity. The change in interfacial tension impacts the average saturation of CO2, ranging from 0.287 to 0.155 in heterogeneous aquifers. The plume migration decreases in layered and increases in homogenous and heterogeneous media with decreased interfacial tension. [ABSTRACT FROM AUTHOR]

The injection of CO2 into deep, unmineable coal seams is an effective strategy for reducing greenhouse gas emissions. At depths greater than 800 m, the carbon dioxide transitions to the supercritical state (Sc-CO2). This study investigated the complex interactions between Sc-CO2 and coal, which substantially affected the pore structure, mineralogy, and permeability of the coal. We used low-pressure nitrogen gas adsorption (LP-N2GA) to assess the impact of Sc-CO2 on the pore characteristics of the coal. X-ray diffraction (XRD) was also used to determine the causal factors. We performed comparative triaxial permeability tests before and after Sc-CO2 exposure to evaluate the changes in permeability for various coal types. Our findings suggested that Sc-CO2 exposure markedly increased the complexity of the coal pore structure, which in turn affects coal-rock permeability. Specifically, a 10-day exposure period resulted in considerable increases of 43.5% and 50.9% in the pore volume and the specific surface area, respectively, along with a slight increase of 0.01 nm in the average pore diameter. Furthermore, there were notable decreases in the contents of minerals such as kaolinite, calcite, and pyrite, with decreases of 1.5%, 2.8%, and 2.2%, respectively, whereas the quartz content increased by 3%, indicating that significant mineral dissolution influenced the pore structure. A significant positive correlation was observed between the loss of coal mass and the increase in permeability. The effects of Sc-CO2 were most pronounced in coals with low permeabilities, particularly during the initial phase of saturation. Subsequent saturation cycles and prolonged exposure resulted in a reduced rate for permeability enhancement, which eventually reached a plateau. This study underscores the critical role of Sc-CO2 in long-term geological CO2 storage and improved efficiency for coalbed methane production. [ABSTRACT FROM AUTHOR]

Addressing critical environmental challenges such as greenhouse gas emissions, global warming, and eutrophication demands urgent and innovative solutions. In recent years, microalgae have emerged as a promising avenue for addressing these pressing issues. In this study, the combination of dairy and municipal wastewater is proposed as a culture medium for cultivating microalgae strains capable of sequestering atmospheric CO2. Specifically, the growth of Chlorella vulgaris was investigated using Bold's basal medium, along with varying concentrations of municipal and dairy wastewater, both with and without CO2 supplementation, to assess their CO2 capture potential. Concurrently, the efficiency of chemical oxygen demand (COD), total nitrogen, potassium, and phosphate removal from the wastewater was evaluated. Additionally, the combination of wastewater media with CO2 supplementation yielded the highest CO2 uptake rates, indicating the feasibility of simultaneous CO2 capture during microalgae cultivation. Media composition with 25% municipal wastewater: 75% dairy wastewater supplemented with CO2 demonstrated superior COD elimination with a higher percentage of nutrient removal from wastewater compared to other wastewater proportions. The nutrient removal capacity of aforementioned media also comes in line with high CO2 sequestration rate (13.57 mg L−1 h−1). These findings underscore the potential of utilizing wastewater from diverse sources as a viable culture medium for microalgae cultivation, facilitating concurrent CO2 capture and wastewater treatment. [ABSTRACT FROM AUTHOR]

Learning operators with deep neural networks is an emerging paradigm for scientific computing. Deep Operator Network (DeepONet) is a modular operator learning framework that allows for flexibility in choosing the kind of neural network to be used in the trunk and/or branch of the DeepONet. This is beneficial as it has been shown many times that different types of problems require different kinds of network architectures for effective learning. In this work, we design an efficient neural operator based on the DeepONet architecture. We introduce U-Net enhanced DeepONet (U-DeepONet) for learning the solution operator of highly complex CO2-water two-phase flow in heterogeneous porous media. The U-DeepONet is more accurate in predicting gas saturation and pressure buildup than the state-of-the-art U-Net based Fourier Neural Operator (U-FNO) and the Fourier-enhanced Multiple-Input Operator (Fourier-MIONet) trained on the same dataset. Moreover, our U-DeepONet is significantly more efficient in training times than both the U-FNO (more than 18 times faster) and the Fourier-MIONet (more than 5 times faster), while consuming less computational resources. We also show that the U-DeepONet is more data efficient and better at generalization than both the U-FNO and the Fourier-MIONet. [ABSTRACT FROM AUTHOR]

The fast developing world is in search of measures to control the accumulation of unused by‐products and waste materials generated during the production of useful commodities. Accordingly, wastes from agro‐industrial sectors can form raw materials for the production of various resources that are extensively used in many areas such as gas sorption and energy production. In the present work, cashew nut shell liquid (CNSL), the vesicant liquid present in the outer shell of cashew seed, forms the source material for the synthesis of porous organic polymers for carbon dioxide capture. Herein, novel types of hypercrosslinked polymers (HCPs) are synthesized via a simple Friedel–Crafts reaction with CNSL as the starting material. Polymerization of natural CNSL with dimethoxymethane/bis‐(chloromethyl)‐biphenyl as external crosslinker provides products in quantitative yield. One of the synthesized HCP is tuned to attain the required high porosity by carbonization at elevated temperatures using an activator. Thus, activated carbon material prepared at 700°C is found to have a high surface area of 880 m2/g with a good carbon dioxide adsorption capacity of 14.72 wt%. These porous materials had moderate isosteric heat of adsorption (23–31 kJ/mol) with excellent recycling capability. [ABSTRACT FROM AUTHOR]

This study characterized the AA-01 depleted hydrocarbon reservoir in the KOKA field, Niger Delta, using a multidimensional approach. This investigation involved data validation analysis, evaluation of site suitability for CO2 storage, and compositional simulation of hydrocarbon components. The primary objective was to determine the initial components and behavior of the hydrocarbon system required to optimize the injection of CO2 and accompanying impurities, establishing a robust basis for subsequent sequestration efforts in the six wells in the depleted KOKA AA-01 reservoir. The process, simulated using industry software such as ECLIPSE, PVTi, SCAL, and Petrel, included a compositional fluid analysis to confirm the pressure volume temperature (PVT) hydrocarbon phases and components. This involved performing a material balance on the quality of the measured data and matching the initial reservoir pressure with the supplied data source. The compositional PVT analysis adopted the Peng–Robinson equation of state to model fluid flow in porous media and estimate the necessary number of phases and components to describe the system accurately. Results from this investigation indicate that the KOKA AA-01 reservoir is suitable for CO2 sequestration. This conclusion is based on the reservoir's good quality, evidenced by an average porosity of 0.21 and permeability of 1 111.0 mD, a measured lithological depth of 9 300 ft, and characteristic reservoir – seal properties correlated from well logs. The study confirmed that volumetric behavior predictions are directly linked to compositional behavior predictions, which are essential during reservoir initialization and data quality checks. Additionally, it highlighted that a safe design for CO2 storage relies on accurately representing multiphase behaviour across wide-ranging pressure–temperature–composition conditions. [ABSTRACT FROM AUTHOR]

Abstract Addressing critical environmental challenges such as greenhouse gas emissions, global warming, and eutrophication demands urgent and innovative solutions. In recent years, microalgae have emerged as a promising avenue for addressing these pressing issues. In this study, the combination of dairy and municipal wastewater is proposed as a culture medium for cultivating microalgae strains capable of sequestering atmospheric CO2. Specifically, the growth of Chlorella vulgaris was investigated using Bold's basal medium, along with varying concentrations of municipal and dairy wastewater, both with and without CO2 supplementation, to assess their CO2 capture potential. Concurrently, the efficiency of chemical oxygen demand (COD), total nitrogen, potassium, and phosphate removal from the wastewater was evaluated. Additionally, the combination of wastewater media with CO2 supplementation yielded the highest CO2 uptake rates, indicating the feasibility of simultaneous CO2 capture during microalgae cultivation. Media composition with 25% municipal wastewater: 75% dairy wastewater supplemented with CO2 demonstrated superior COD elimination with a higher percentage of nutrient removal from wastewater compared to other wastewater proportions. The nutrient removal capacity of aforementioned media also comes in line with high CO2 sequestration rate (13.57 mg L−1 h−1). These findings underscore the potential of utilizing wastewater from diverse sources as a viable culture medium for microalgae cultivation, facilitating concurrent CO2 capture and wastewater treatment.

Abstract Learning operators with deep neural networks is an emerging paradigm for scientific computing. Deep Operator Network (DeepONet) is a modular operator learning framework that allows for flexibility in choosing the kind of neural network to be used in the trunk and/or branch of the DeepONet. This is beneficial as it has been shown many times that different types of problems require different kinds of network architectures for effective learning. In this work, we design an efficient neural operator based on the DeepONet architecture. We introduce U-Net enhanced DeepONet (U-DeepONet) for learning the solution operator of highly complex CO2-water two-phase flow in heterogeneous porous media. The U-DeepONet is more accurate in predicting gas saturation and pressure buildup than the state-of-the-art U-Net based Fourier Neural Operator (U-FNO) and the Fourier-enhanced Multiple-Input Operator (Fourier-MIONet) trained on the same dataset. Moreover, our U-DeepONet is significantly more efficient in training times than both the U-FNO (more than 18 times faster) and the Fourier-MIONet (more than 5 times faster), while consuming less computational resources. We also show that the U-DeepONet is more data efficient and better at generalization than both the U-FNO and the Fourier-MIONet.

Carbonating metallurgical slags plays a pivotal role in achieving efficient mineral CO2 sequestration and waste valorization. This research introduces a novel integrated approach that combines the carbonation of Ladle Furnace Slag (LFS) with the simultaneous degradation of Methyl Orange (MO) in synthetic water. The comprehensive characterization of LFS was conducted using X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Brunauer-Emmett-Teller (BET) analysis, and Scanning Electron Microscopy (SEM). The adsorption experiments reveal the high LSF capacity for MO degradation (149.25 mg/g) following pseudo-second-order kinetics (R2 = 0.99) and Langmuir isotherm (R2 = 0.98). The adsorption process was primarily governed by chemical and electrostatic interactions. Analysis of LFS-loaded MO indicated a reduction in Ca(OH)2 phases, responsible for CO2 mineralization and the formation of calcite (CaCO3). Furthermore, the study explored the reusability of LFS-MO composites through chemical and thermal modifications. Pyrolysis of carbonated LFS with KOH impregnation exhibited potential for regenerating Ca(OH)2 phases, while thermal modification induced significant mineral and microstructural changes, creating new active sites at various temperatures. Additionally, the Fenton-like reaction followed by thermal modification resulted in a highly organized and microporous LFS structure with enhanced surface area and porosity. Moreover, modification with ZnSO4 followed by thermal activation promoted the formation of ZnO nanoxides on the LFS surface. This research proposes an innovative carbonating approach for metallurgical slags and wastewater treatment, extending their utility and enhancing industrial sustainability. Carbonated LFS-MO composites hold promise for applications in construction, CO2 capture, and wastewater treatment, thereby fostering sustainable industrial practices with ongoing research and development efforts.

In the process of CO2-enhanced coalbed methane recovery, the behaviours of coal seam fractures significantly affect sequestration and extraction. To address the unclear impact of fracture roughness evolution on engineering efficiency under multi-physical field coupling effects, we developed an innovative interdisciplinary mathematical model. This model introduces a parameter to quantitatively describe coal seam fracture roughness and couples it with the gas flow control equations under multi-field effects in the coal seam. We investigated the thermo-hydro-mechanical (THM) coupling effects and fracture network characteristics in the coal seam gas extraction process. Results show that the mathematical model aligns well with field data and effectively characterizes coal seam fracture roughness. Fracture roughness significantly influences the residual gas pressure in the coal seam and the injection pressure of CO2. When the roughness parameter decreases from 0.24 to 0.18, the maximum methane content decreases by 32.5% and the maximum CO2 pressure increases by 26.7%, the maximum gas adsorption capacity of coal seam decreased by 31.7%, and the maximum CO2 adsorption capacity increased by 12.1%.

When the CO2 in a supercritical state (SCCO2) is released from deep coal seams, it reacts with minerals in coal, changing the porosity of coal, which in turn affects the effect of CO2 sequestration in coal seams and the effect of increasing methane production. In order to discover the influence characteristics of SCCO2-H2O-coal rock interaction on the porosity in coal, the experiments on the supercritical CO2 reforming coal under different water content conditions were carried out with coking coal as the research object. Based on the results of mineral composition and porosity measurements, the differences between the main minerals and the changes in pore cleavage at various scales in coal were compared, and the action mechanism of the SCCO2 fluid on the pore cleavage properties under various water content states was explored. The results show that: ① After the SCCO2 treatment, the surface of the coal body is rough and loose, some fissures are penetrated as a result of mineral dissolution, and the connectivity of micro fissure is improved. ② The SCCO2 fluid has a “pore-expanding”effect on coal, which is manifested by a decrease of the content of micro- and small pores, and an increase of the proportion of medium- and large pores, i.e., the conversion of micro- and small-sized pores to large pores, as well as the improvement of pore connectivity. Furthermore, it is discovered that the fractal dimension of the adsorption pores of the coal samples increases slightly in size and roughness, while the fractal dimension of the seepage pores decreases significantly, and the complexity and non-homogeneity are reduced. ③ The SCCO2 fluid has the best solubility on the carbonate minerals in coal, followed by clay minerals, and with the increase of water content, the proportion of carbonate minerals in the extracted coal first increases and then decreases. The SCCO2 fluid makes the carbonate minerals in the coal samples of the dry basal state and saturated water state dissolve significantly, which effectively improves the pore structure, and the effect on the coal samples of the saturated water state is better. After the air-dry basal coal samples were subjected to the SCCO2, the newly formed dolomite minerals gathered in the pore throats to cause the plugging effect, reducing the original large pore size, which is the main cause of the differential changes in the pore space of coals with different water content states.

The current review presents a discussion on the utility of neutron scattering, with emphasis on neutron total scattering and small‐angle neutron scattering (SANS), to explore the structural properties and the phase behaviour of fluids confined in nanopores. The effectiveness of contrast matching SANS on the evaluation of accessibility of porous materials to invading fluids is highlighted too. This review provides also an overview regarding the neutron scattering studies on the structure and the accessibility of greenhouse gases in the complex pore network of geomaterials, with applications to CO2 geological sequestration and enhanced oil and gas recovery. [ABSTRACT FROM AUTHOR]

CO2–slickwater hybrid fracturing technology is an essential part of shale gas recovery and CO2 geo-storage. However, the exposure to supercritical CO2 (ScCO2) and slickwater can result in potential changes of the pore structures and surface wetting behavior, which affect the gas transportation and CO2 sequestration security in shale reservoirs. Therefore, in this paper, X-ray diffraction (XRD), low-pressure nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP), and fractal analysis were used to describe the pore characteristics of shale before and after ScCO2–slickwater coupling treatments. Shale's surface wettability was confirmed by contact angle measurements. After the ScCO2–slickwater treatments, the number of micropores (<3.5 nm) and mesopores (3.5–50 nm) increased, while that of macropores (>50 nm) declined based on the N2GA and MIP experiments. Combined with fractal analysis, we argue that the pore connectivity diminished and the pore structure became more complicated. By analyzing the results of XRD, shale pore changes occurring after the ScCO2–slickwater treatment can be explained by the adsorption of polyacrylamide (PAM). Contact angle measurement results showed that the shale's surface treated by ScCO2 and slickwater was more hydrophilic than that treated by ScCO2 and water, and indirectly prove our argument above. Hence, the coupling using effect of ScCO2 and slickwater can impair the negative effect of CO2 on the shale capillary force to improve shale gas productivity, but it can negatively affect the security of CO2 sequestration in shale reservoirs. [ABSTRACT FROM AUTHOR]

It is acknowledged that injecting CO2 into oil reservoirs and saline aquifers for storage is a practical and affordable method for CO2 sequestration. Most CO2 produced from industrial exhaust contains impurity gases such as H2S that might impact CO2 sequestration due to competitive adsorption. This study makes a commendable effort to explore the adsorption behavior of CO2/H2S mixtures in calcite slit nanopores. Grand Canonical Monte Carlo (GCMC) simulation is employed to reveal the adsorption of CO2, H2S as well as their binary mixtures in calcite nanopores. Results show that the increase in pressure and temperature can promote and inhibit the adsorption capacity of CO2 and H2S in calcite nanopores, respectively. CO2 exhibits stronger adsorption on calcite surface than H2S. Electrostatic energy plays the dominating role in the adsorption behavior. Electrostatic energy accounts for 97.11% of the CO2-calcite interaction energy and 56.33% of the H2S-calcite interaction energy at 10 MPa and 323.15K. The presence of H2S inhibits the CO2 adsorption in calcite nanopores due to competitive adsorption, and a higher mole fraction of H2S leads to less CO2 adsorption. The quantity of CO2 adsorbed is lessened by approximately 33% when the mole fraction of H2S reaches 0.25. CO2 molecules preferentially occupy the regions near the pore wall and H2S molecules tend to reside at the center of nanopore even when the molar ratio of CO2 is low, indicating that CO2 has an adsorption priority on the calcite surface over H2S. In addition, moisture can weaken the adsorption of both CO2 and H2S, while CO2 is more affected. More interestingly, we find that pure CO2 is more suitable to be sequestrated in the shallower formations, i.e., 500–1500m, whereas CO2 with H2S impurity should be settled in the deeper reservoirs. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage supply chain is recently acknowledged as a crucial method to limit global warming. There is a notable desire to optimize supply chains simultaneously with respect to economic and environmental factors, and the development of a mathematical model integrating the life cycle assessment into source-sink matching is missing in the existing literature. The present work means to fill this gap by using a bi-objective mixed-integer linear programming problem. The case study for this research focuses on a real-life scenario in Germany where carbon dioxide is captured from flue gas and transported to be stored or/and used. The total profit and life cycle GHG reduction are maximized. The results show that the profit per unit of sequestered CO2 decreases from 2014 to −€332 as the rate of life cycle GHG reduction increases from −873 to 52 MtCO2eq/year. The findings from the model can provide valuable knowledge that can be utilized in various countries at different levels, such as at regional, state, and national levels. This knowledge can also assist decision-makers in selecting more sustainable solutions when designing carbon capture, utilization, and storage systems. [ABSTRACT FROM AUTHOR]

Depleted gas reservoirs with bottom water show significant potential for long-term CO2 storage. The residual gas influences mass-transfer dynamics, further affecting CO2 dissolution and convection in porous media. In this study, we conducted a series of numerical simulations to explore how residual-gas mixtures impact CO2 dissolution trapping. Moreover, we analyzed the CO2 dissolution rate at various stages and delineated the initiation and decline of convection in relation to gas composition, thereby quantifying the influence of residual-gas mixtures. The findings elucidate that the temporal evolution of the Sherwood number observed in the synthetic model incorporating CTZ closely parallels that of the single-phase model, but the order of magnitude is markedly higher. The introduction of CTZ serves to augment gravity-induced convection and expedites the dissolution of CO2, whereas the presence of residual-gas mixtures exerts a deleterious impact on mass transfer. The escalation of residual gas content concomitantly diminishes the partial pressure and solubility of CO2. Consequently, there is an alleviation of the concentration and density differentials between saturated water and fresh water, resulting in the attenuation of the driving force governing CO2 diffusion and convection. This leads to a substantial reduction in the rate of CO2 dissolution, primarily governed by gravity-induced fingering, thereby manifesting as a delay in the onset and decay time of convection, accompanied by a pronounced decrement in the maximum Sherwood number. In the field-scale simulation, the injected CO2 improves the reservoir pressure, further pushing more gas to the producers. However, due to the presence of CH4 in the post-injection process, the capacity for CO2 dissolution is reduced. [ABSTRACT FROM AUTHOR]

The urgent need to find mitigating pathways for limiting world CO2 emissions to net zero by 2050 has led to intense research on CO2 sequestration in deep saline reservoirs. This paper reviews key advancements in lab- and simulation-scale research on petrophysical, geochemical, and mineralogical changes during CO2–brine–rock interactions performed in the last 25 years. It delves into CO2 MPD (mineralization, precipitation, and dissolution) and explores alterations in petrophysical properties during core flooding and in static batch reactors. These properties include changes in wettability, CO2 and brine interfacial tension, diffusion, dispersion, CO2 storage capacity, and CO2 leakage in caprock and sedimentary rocks under reservoir conditions. The injection of supercritical CO2 into deep saline aquifers can lead to unforeseen geochemical and mineralogical changes, possibly jeopardizing the CCS (carbon capture and storage) process. There is a general lack of understanding of the reservoir's interaction with the CO2 phase at the pore/grain scale. This research addresses the gap in predicting the long-term changes of the CO2–brine–rock interaction using various geochemical reactive transport simulators. Péclet and Damköhler numbers can contribute to a better understanding of geochemical interactions and reactive transport processes. Additionally, the dielectric constant requires further investigation, particularly for pre- and post-CO2–brine–rock interactions. For comprehensive modeling of CO2 storage over various timescales, the geochemical modeling software called the Geochemist's Workbench was found to outperform others. Wettability alteration is another crucial aspect affecting CO2–brine–rock interactions under varying temperature, pressure, and salinity conditions, which is essential for ensuring long-term CO2 storage security and monitoring. Moreover, dual-energy CT scanning can provide deeper insights into geochemical interactions and their complexities. [ABSTRACT FROM AUTHOR]

The induction of accelerated carbonation curing (ACC) as carbon capture, utilization, and sequestration (CCUS) technique helps in achieving the net zero target. ACC is one of the potential techniques to sequester the CO2 in concrete. However, the usage of ACC in reinforced concrete is still debatable. This paper investigates the effect of ACC on mechanical, permeation, mineralogy, hydration and microstructural characteristics of concrete with the long-term performance of reinforced concrete using linear polarization resistance (LPR) and carbonation depth. In order to study the effect of ACC duration on the properties of concrete, the specimen was subjected to 6, 12, and 24 hours (h) of carbonation curing. The results were compared with conventional water-curing specimens. ACC at 12 h provided the best results for tested properties. The results were varied by statistical analysis using ANOVA and stoichiometry. Based on the best 12-h duration, 2.13 kg of CO2 can be sequestered in 1 m3 (0.89 kg/t) of concrete. [ABSTRACT FROM AUTHOR]

The aim of this study is to examine the CO2 gas adsorption capability of coals from Sohagpur coalfield, India. Coal bed CO2 sequestration is a technique utilized to mitigate carbon dioxide emissions and improve global warming. Various factors, including pore structure, pore volume, mineral composition, moisture content, cleats, coal quality, pressure, and temperature, influence the adsorption of CO2 in coal seams. To conduct this investigation, multiple coal samples were collected from the study area and subjected to proximate analysis, ultimate analysis, scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR), Brunauer – Emmett–Teller (BET), and measurement of CO2 adsorption rates on the coal samples. Samples were characterized based on their geochemical properties, then pore and fracture properties and maximum adsorption of CO2 gas were determined. The interrelationship between the genetic properties of coal with the adsorption rate of CO2 gas was established. These coals lie mesopore in category with the presence of fractures and hydrogen bonds. The result of BET and kinetics rate indicates that the adsorption of gas was unrestricted multilayer type, and the maximum adsorption of CO2 gas at 50 bar is 2.15 moles gas/kg sample, respectively. [ABSTRACT FROM AUTHOR]

In recent years, technical processes for the sequestration of CO2 through industrial waste mineral carbonation have been explored and developed. There is a large portfolio of carbon capture, utilisation, and storage (CCUS) techniques that have been employed in laboratories and at pilot scale. These include geological storage, ocean storage, and mineralisation by carbonate ores. In view of this, the main purpose of this research was to investigate and explore chemical variables, particularly ammonium salts as lixiviants for calcium mineral extraction from iron-making slag. The slag in use was acquired from a steel mill in the Vaal Triangle Region in Gauteng, South Africa. The experimental test work was conducted using different ammonium lixiviants, namely, NH4NO3, NH4Cl, and CH3COONH4, to understand the influence of anion type as well as possible differences in mechanisms of interactions. Lixiviant concentration as well as reaction time were varied in this research study. The three selected ammonium-based lixiviants showed different extents of calcium extraction owing to differences in the anion groups. NH4NO3, NH4Cl, and CH3COONH4 were found to be capable of dissolving 50% to 80% of the calcium from the selected slag for different molar concentrations. Anion type and leaching time also had significant influences on the leaching of calcium from the slag. Rapid pH degradation resulted in better calcium extraction capabilities. This work has shown that the selected ammonium salts have the potential to be lixiviants for calcium dissolution from iron-making blast furnace slags. These lixiviants would, therefore, be important to consider during calcium mineral carbonation for CO2 sequestration. [ABSTRACT FROM AUTHOR]

Sequestering CO2 in depleted oil reservoirs provides one of the most appealing measures to reduce greenhouse gases (GHG) concentration in the atmosphere. The remaining liquids after enhanced oil recovery (EOR) processes, including residual oil and remaining water, lead to the main challenges to this approach. How to effectively evacuate a depleted oil reservoir by recovering not only residual oil but also remaining water is a critical consideration for this type of CO2 sequestration. This paper presents conceptual investigations concerning the methods which effectively evacuate depleted oil reservoirs from both the displacement efficiency and the sweep efficiency points of view. To improve the displacement efficiency, surfactant slug and solvent slug injection was examined using a core scale numerical model. Investigations regarding improving sweep efficiency, such as horizontal well pattern infilling and foam injection, were carried out based on a typical row well pattern. Simulation results showed that surfactant slug which modified the relative permeability and capillary pressure remarkably reduced both residual oil saturation and remaining water saturation. A CO2 slug injected before surfactant slug can help improve the oil recovery. Solvent enriched CO2 slug also remarkably reduced the residual oil saturation to as low as 2%. Horizontal well pattern infilling had great advantage for thick or inclined reservoirs, and foam slug injection greatly improved CO2 storage capacity in thin reservoirs by improving the sweep efficiency. Maximum mobility reduction (MRF) is the most important parameter to maximize the storage capacity and the benefit. The variation of CO2 storage capacity along with CO2 slug size. Larger foam slug size will play a better storage performance. The conceptual simulation investigations confirmed that depleted oil reservoirs can be effectively evacuated for CO2 storage. Depleted oil reservoirs with maximum evacuation are the best candidates for CO2 sequestrations. [ABSTRACT FROM AUTHOR]

Climate change necessitates urgent actions to mitigate carbon dioxide (CO2) emissions from fossil fuel-based energy generation. Among various strategies, the deployment of carbon capture and storage (CCS) solutions is critical for reducing emissions from point sources such as power plants and heavy industries. In this context, cryogenic carbon capture (CCC) via desublimation has emerged as a promising technology. While CCC offers high separation efficiency, minimal downstream compression work, and integration potential with existing industrial processes, challenges such as low operating temperatures and equipment costs persist. Ongoing research aims to address these hurdles in order to optimize the desublimation processes for widespread implementation. This review consolidates diverse works from the literature, providing insights into the strengths and limitations of CCC technology, including the latest pilot plant scale demonstrations. The transformative potential of CCC is first assessed on a theoretical basis, such as thermodynamic aspects and mass transfer phenomena. Then, recent advancements in the proposed process configurations are critically assessed and compared through key performance indicators. Furthermore, future research directions for this technology are clearly highlighted. [ABSTRACT FROM AUTHOR]

This research explores nanomaterials' potential in CO2 capture and storage, emphasizing their role in CO2 diffusion and interfacial tension. We aimed to develop eco-friendly nanomaterials and evaluate their impact on CO2 sequestration, considering factors like pressure, temperature, salinity, and nanoparticle concentration. The research involved experimental measurements of CO2 diffusion in brine solutions and brine-based nanofluids containing green silica NPs and SiO2/Xanthan nanocomposites. CO2 diffusion coefficients were determined through practical pressure decay measurements using the Sheikha method. These measurements were conducted within a Fluid EVAL (PVT) cell, allowing CO2 interaction with each solution. The results of the study revealed significant improvements in the carbon dioxide (CO2) diffusion coefficients and reductions in interfacial tension when utilizing water/silica nanofluids containing 0.5 wt.% and 0.1 wt.% concentrations, in comparison with a brine solution without nanoparticles (NPs) and with a high salt concentration (20 wt.% NaCl). The CO2 diffusion coefficient increased from 2.15E-09 to 4.01E-09 m2/s. An even more significant enhancement was observed with 0.1 wt.% SiO2 NPs, where the CO2 diffusion coefficient reached 4.87E-09 m2/s. In addition, CO2 interfacial tension reduced from 44.3517 to 1.0388 mN/m and 0.9098 mN/m, respectively. The general trend of the measured carbon dioxide diffusion coefficient aligned with increased pressure and temperature. Additionally, when considering the transition to a supercritical state, the findings highlighted consistent behavior, independent of variations in pressure and temperature. Conversely, the interfacial tension between CO2 and nanofluids decreased in response to heightened pressure and temperature. Moreover, an increase in salinity led to a rise in interfacial tension. In conclusion, heightened CO2 diffusion and reduced interfacial tension improve CO2 sequestration, enhancing CO2 transport, absorption, and storage efficiency for successful long-term CO2 storage. [ABSTRACT FROM AUTHOR]

In recent years, the building industry has looked for technological ways to protect the environment and preserve natural resources. Since the COVID-19 epidemic, there has been a shortage of building materials, which has caused construction costs to go up. This has made it more important for sustainable development to be based on the principles of the circular economy. This gives an opportunity to utilise various reliable materials as substitutes, like construction and demolition (C&D) waste. (C&D) wastes are made up of a large chunk of all solid waste, which causes many environmental problems. The most important factor in the struggle against climate change is the reduction of CO2 emissions from the construction sector. At the same time, globally, climate change caused in part by carbon dioxide (CO2) emissions is an important problem that requires innovative carbon sequestration strategies. Because C&D waste is alkaline-rich (e.g., calcium hydroxide and calcium-silicate-hydrate (C-S-H)), it can be used to sequester CO2 by converting it into thermodynamically stable carbonates. Temperature, partial pressure of CO2, time, process route, humidity, and the water-to-solid ratio (w/s) can affect the CO2 sequestration over the C&D wastes. [ABSTRACT FROM AUTHOR]

In terms of the collaborative optimization of CO2 flooding for Enhanced Oil Recovery (EOR) and CO2 sequestration, previous studies have co-optimized both cumulative oil production and CO2 sequestration by various algorithms. However, these solutions fail to optimize the CO2 injection schemes for high-water cut oil reservoirs. This paper presents an optimization methodology for CO2 flooding and sequestration in high-water cut oil reservoirs. The production optimization was carried out by adjusting the injection and production rate. To solve the proposed objective functions, the simultaneous perturbation stochastic approximation (SPSA) algorithm is applied in this paper, and the CMG-GEM module is utilized to simulate the reservoir production performance. A typical high-water cut reservoir in the Shengli oilfield was used to verify the feasibility of the presented methodology. In this paper, the production performance and net present value (NPV) for continuous gas injection under different water cuts were analyzed. The optimal timing of transforming from water flooding to gas displacement for the high-water cut reservoir was optimized. In addition, the optimal water–gas ratios for Water-Alternating-Gas (WAG) flooding were determined. The sensitivity of NPV to gas injection price and carbon subsidy was analyzed. The results show that when the gas price is 0.178 $/m3 and the carbon subsidy is 0.0169 $/m3, the optimal timing of transforming from water flooding to gas injection should be earlier than the time when the water cut is 0.82. Through the combination of NPV, cumulative oil production rate, and CO2 sequestration volume for WAG flooding, the optimal WAG ratio should be 1:2. The presented method in this paper considers various economic indicators and can optimize CO2 flooding and sequestration in high-water cut oil reservoirs efficiently, which can provide some guidance for the design of CO2 flooding schemes in high-water cut oil reservoirs. [ABSTRACT FROM AUTHOR]

Microalgae have been highlighted as a contributor to CO2 sequestration due to their efficient photosynthetic system. However, calculations on their actual potential for CO2 sequestration are often lacking. Here, we calculated the potential of microalgae for the capture of CO2 by integrating it with a large emitter (gas-based energy plant) and a low emitter (dairy farms), and also discussed if such integrated systems can be considered as carbon sequesters given that the final use of the biomass often quickly releases the captured CO2. Moreover, the CO2 footprint of microalgal systems is highlighted as a critical point of attention for future developments. Such considerations are of utmost importance to avoid false promises that ultimately harm this sector, as large investments are made following untruthful claims that, when proven wrong, result in a loss of interest. Finally, key definitions are proposed to improve clarity and help in such discussions.

Over the years, Carbon Capture and Sequestration (CCS) has been recognized as a crucial element in the toolkit of measures to combat climate change. At the European Union (EU) level, CCS plays a vital role in climate policy, particularly in reducing CO2 emissions from hard-to-abate industries. However, no comprehensive legal framework covers all stages of CCS. These stages include carbon capture techniques, transportation by ships or pipelines, injection, site closure, and post-closure management. Each of these stages is regulated by different legal frameworks that address various topics such as geoengineering, climate change, industrial activities, property, transportation, port operations, waste management, dumping, health, and the environment. Critical legal questions remain unanswered, such as who is liable for discharges in the marine environment during the transportation of CO2 by ships and for the long-term management of sub-seabed storage sites. As the transportation of CO2 by ships will likely have transboundary implications, we explore the legal possibilities, limitations and risks associated with exporting CO2 streams for sequestration under the sub-seabed.

Abstract Sequestering CO2 in depleted oil reservoirs provides one of the most appealing measures to reduce greenhouse gases (GHG) concentration in the atmosphere. The remaining liquids after enhanced oil recovery (EOR) processes, including residual oil and remaining water, lead to the main challenges to this approach. How to effectively evacuate a depleted oil reservoir by recovering not only residual oil but also remaining water is a critical consideration for this type of CO2 sequestration. This paper presents conceptual investigations concerning the methods which effectively evacuate depleted oil reservoirs from both the displacement efficiency and the sweep efficiency points of view. To improve the displacement efficiency, surfactant slug and solvent slug injection was examined using a core scale numerical model. Investigations regarding improving sweep efficiency, such as horizontal well pattern infilling and foam injection, were carried out based on a typical row well pattern. Simulation results showed that surfactant slug which modified the relative permeability and capillary pressure remarkably reduced both residual oil saturation and remaining water saturation. A CO2 slug injected before surfactant slug can help improve the oil recovery. Solvent enriched CO2 slug also remarkably reduced the residual oil saturation to as low as 2%. Horizontal well pattern infilling had great advantage for thick or inclined reservoirs, and foam slug injection greatly improved CO2 storage capacity in thin reservoirs by improving the sweep efficiency. Maximum mobility reduction (MRF) is the most important parameter to maximize the storage capacity and the benefit. The variation of CO2 storage capacity along with CO2 slug size. Larger foam slug size will play a better storage performance. The conceptual simulation investigations confirmed that depleted oil reservoirs can be effectively evacuated for CO2 storage. Depleted oil reservoirs with maximum evacuation are the best candidates for CO2 sequestrations.

Objective Thermal energy storage and CO2 sequestration in depleted oil and gas reservoirs can not only solve the problem of seasonal solar thermal energy storage but also increase the share of renewable energy space heating and enhance the economy of CO2 geological sequestration. Methods A novel scheme of thermal energy storage for space heating and CO2 sequestration in depleted oil and gas reservoirs is proposed by storing solar thermal energy in depleted oil and gas reservoirs in summer and extracting thermal energy for space heating in winter using CO2 as the working medium. A mathematical model of the energy storage and release process is established, and the thermal performance and CO2 sequestration performance of energy storage system in depleted oil and gas reservoirs are analysed. Results The results show that (1) the novel scheme has excellent thermal performance, with a single-well thermal extraction power of 4 808.95 kW, a thermal energy storage capacity of 49 859.21 GJ per heating season and an energy storage density of 28 984.23 kJ/m3. (2) The novel scheme has an energy recovery efficiency of 95.84% and a thermal recovery efficiency of 83.66% due to the strong sensitivity of the CO2 density to temperature. (3) The solubility trapping of CO2 in formation water is accelerated by the energy storage process. The periodic injection and extraction of CO2 during the process of energy storage and release causes the repeated expansion and contraction of the gas-water interface, which increases the gas-water contact area and improves the driving force of mass transfer, thus leading to an increase in CO2 dissolution in the formation water. Compared with the CO2 sequestration model alone, the mass ratio of CO2 dissolution in formation water for the energy storage model increases from 0.26% to 2.22%. Conclusion Overall, the novel scheme has excellent thermal performance. It accelerates CO2 geological sequestration and is a high-value scheme for depleted reservoir utilization and renewable energy space heating. It has great potential for wide application.

Abstract In terms of the collaborative optimization of CO2 flooding for Enhanced Oil Recovery (EOR) and CO2 sequestration, previous studies have co-optimized both cumulative oil production and CO2 sequestration by various algorithms. However, these solutions fail to optimize the CO2 injection schemes for high-water cut oil reservoirs. This paper presents an optimization methodology for CO2 flooding and sequestration in high-water cut oil reservoirs. The production optimization was carried out by adjusting the injection and production rate. To solve the proposed objective functions, the simultaneous perturbation stochastic approximation (SPSA) algorithm is applied in this paper, and the CMG-GEM module is utilized to simulate the reservoir production performance. A typical high-water cut reservoir in the Shengli oilfield was used to verify the feasibility of the presented methodology. In this paper, the production performance and net present value (NPV) for continuous gas injection under different water cuts were analyzed. The optimal timing of transforming from water flooding to gas displacement for the high-water cut reservoir was optimized. In addition, the optimal water–gas ratios for Water-Alternating-Gas (WAG) flooding were determined. The sensitivity of NPV to gas injection price and carbon subsidy was analyzed. The results show that when the gas price is 0.178 $/m3 and the carbon subsidy is 0.0169 $/m3, the optimal timing of transforming from water flooding to gas injection should be earlier than the time when the water cut is 0.82. Through the combination of NPV, cumulative oil production rate, and CO2 sequestration volume for WAG flooding, the optimal WAG ratio should be 1:2. The presented method in this paper considers various economic indicators and can optimize CO2 flooding and sequestration in high-water cut oil reservoirs efficiently, which can provide some guidance for the design of CO2 flooding schemes in high-water cut oil reservoirs.

The technique of Enhanced Gas Recovery by CO2 injection (CO2-EGR) into shale reservoirs has brought increasing attention in the recent decade. CO2-EGR is a complex geophysical process that is controlled by several parameters of shale properties and engineering design. Nevertheless, more challenges arise when simulating and predicting CO2/CH4 displacement within the complex pore systems of shales. Therefore, the petroleum industry is in need of developing a cost-effective tool/approach to evaluate the potential of applying CO2 injection to shale reservoirs. In recent years, machine learning applications have gained enormous interest due to their high-speed performance in handling complex data and efficiently solving practical problems. Thus, this work proposes a solution by developing a supervised machine learning (ML) based model to preliminary evaluate CO2-EGR efficiency. Data used for this work was drawn across a wide range of simulation sensitivity studies and experimental investigations. In this work, linear regression and artificial neural networks (ANNs) implementations were considered for predicting the incremental enhanced CH4. Based on the model performance in training and validation sets, our accuracy comparison showed that (ANNs) algorithms gave 15% higher accuracy in predicting the enhanced CH4 compared to the linear regression model. To ensure the model is more generalizable, the size of hidden layers of ANNs was adjusted to improve the generalization ability of ANNs model. Among ANNs models presented, ANNs of 100 hidden layer size gave the best predictive performance with the coefficient of determination (R2) of 0.78 compared to the linear regression model with R2 of 0.68. Our developed ML-based model presents a powerful, reliable and cost-effective tool which can accurately predict the incremental enhanced CH4 by CO2 injection in shale gas reservoirs.

Changes in pH during CO2 injection into oceans can lead to significant negative environmental impacts, making it particularly important to track these changes. However, previous studies have not comprehensively investigated the development of machine learning models to estimate this parameter. To fill this research gap, this study developed 15 models comprising five machine learning methods: regression trees, support vector regression, Gaussian process regression, bagged trees, and boosted trees, and three optimization algorithms: random search, grid search, and Bayesian optimization. A total of 170 data points were used to develop these models. After data preprocessing and model development, it was determined that the boosted trees model optimized with grid search, with an R2 = 0.9964 and RMSE = 0.0156, performed the best, while the support vector regression model optimized with random search, with an R2 = 0.8426 and RMSE = 0.1030, had the lowest accuracy. The boosted trees model optimized with grid search was found to estimate all data points with a residual error of less than 0.15 and an absolute relative error of 4.62 %. The 95 % confidence interval for the RMSE was calculated based on the best model, showing that the error lies between 0.009060 and 0.023256 with 95 % confidence. Pearson correlation analysis was used for sensitivity analysis. The results showed that in all models, temperature, solubility, and pressure have a negative correlation with pH, while salinity has a positive correlation. Additionally, solubility and salinity exhibited the highest and lowest correlations, with average values of −0.9225 and 0.0594, respectively. Due to the accuracy of the developed models, these models can help to optimize the operation of injecting CO2 into oceans to reduce harmful environmental effects.

The properties of amorphous calcium carbonate (ACC) and its transformations to crystalline polymorphs are frequently studied in aqueous systems and in small quantities. In this study, synthetic calcium carbonate stones are created from bulk ACC and crystalline polymorphs, which were precipitated from gaseous CO2, at a gradient of end pH. Some of the ACCs hardened into stones which are durable against an abrasion and impact test, while some of the ACCs create fragile, friable stones. When ACCs which transform to durable stones and those which transform into fragile stones were subject to calorimetry, significant differences were observed. These stones, synthesized from gaseous CO2, can be used as a storage reservoir for utilized CO2 in construction and other infrastructure applications. [ABSTRACT FROM AUTHOR]

Extralow-permeability reservoirs have emerged as a significant area of focus for CO2 geological sequestration due to their stable subterranean structure and expansive storage capacity, offering substantial potential in addressing global climate change. However, the full extent of CO2 geological sequestration potential within these extralow-permeability reservoirs remains largely unexplored. To address this gap, this paper utilizes the Shahejie Formation (Es1 member) of the Shuang 229 block in the Liaohe oilfield, Bohai Bay Basin, as a case study. This section is characterized by its abundant oil-gas reserves and serves as an exemplar for conducting experimental research on CO2 storage within extralow-permeability reservoirs. The results demonstrate that the reservoir lithology of the Es1 member is fine sandstone and siltstone, with high compositional and structural maturity. Moreover, the average porosity is 14.8%, the average permeability is 1.48 mD, and the coefficient of variation of the reservoir is approximately 0.5, which indicates a low- to extralow-permeability homogeneous reservoir. In addition, the overburden pressure is >2.0 MPa, the fault can withstand a maximum gas column height of >200 m, and the reservoir exhibits favorable overburden and fault sealing characteristics. Notably, stepwise increasing gas injection in the Shuang 229-36-62 well reveals that the injected liquid CO2 near the wellhead exhibits a relatively high density, close to 1.0 g/cm3, which gradually decreases to approximately 0.78 g/cm3 near a depth of 2000 m underground. The injected fluid changes into a supercritical state upon entering the formation, and the CO2 injection speed is optimal, at 0.08 HCPV/a. According to these findings, it is predicted that the highest burial CO2 volume via the injection of 1.5 HCPVs in the Wa 128 block area is 1.11 × 105 t/year, and the cumulative burial volume reaches approximately 2.16 × 106 t. This shows that the CO2 sequestration potential of extralow-permeability reservoirs is considerable, providing confidence for similar instances worldwide. [ABSTRACT FROM AUTHOR]

Methods for quantifying the CO2 storage potential of recycled aggregates The necessity of utilizing CO2 sinks is becoming increasingly relevant for the construction industry, as the manufacturing of certain industrial goods will process‐related continue to produce emissions. An innovative approach to this is the utilization of waste concrete respectively recycled aggregates produced from it for CO2 sequestration, which expands the recycling of construction waste in the context of resource conservation (Urban Mining) to include climate compatibility. Initial implementations in practice have already occurred, and an increasing future application is emerging. One challenge lies in the uncertainty regarding the CO2 uptake potential of the recycled aggregates. Accurate assessment is essentially possible only after carbonation has taken place by determining the masses and monitoring the experimental conditions. The primary influencing parameters are the grain size and the time available for carbonation, as well as the concrete properties and exposure conditions of the available waste concrete. This article presents a practical method by which the respective carbonation potential can be determined prior to demolition of a structure providing a simple, manageable means to evaluate the effectiveness of the additional required processing step. [ABSTRACT FROM AUTHOR]

• Applied voltage and calcium addition increased biogas yield and CO 2 sequestration. • Wollastonite and CaCl 2 exhibited different CO 2 sequestration performances. • Wollastonite showed a better CO 2 sequestration effect with 2.22% CO 2 in biogas. • The contribution of chemical and biological CO 2 sequestration was clarified. The combination of microbial electrolytic cells and anaerobic digestion (MEC-AD) became an efficient method to improve CO 2 capture for waste sludge treatment. By adding CaCl 2 and wollastonite, the CO 2 sequestration effect with mineral carbonation under 0 V and 0.8 V was studied. The results showed that applied voltage could increase dissolved chemical oxygen demand (SCOD) degradation efficiency and biogas yield effectively. In addition, wollastonite and CaCl 2 exhibited different CO 2 sequestration performances due to different Ca2+ release characteristics. Wollastonite appeared to have a better CO 2 sequestration effect and provided a wide margin of pH change, but CaCl 2 released Ca2+ directly and decreased the pH of the MEC-AD system. The results showed methane yield reached 137.31 and 163.50 mL/g SCOD degraded and CO 2 content of biogas is only 12.40 % and 2.22 % under 0.8 V with CaCl 2 and wollastonite addition, respectively. Finally, the contribution of chemical CO 2 sequestration by mineral carbonation and biological CO 2 sequestration by hydrogenotrophic methanogenesis was clarified with CaCl 2 addition. The chemical and biological CO 2 sequestration percentages were 46.79 % and 53.21 % under 0.8 V, respectively. With the increased applied voltage, the contribution of chemical CO 2 sequestration rose accordingly. The findings in this study are of great significance for further comprehending the mechanism of calcium addition on CO 2 sequestration in the MEC-AD system and providing guidance for the later engineering application. [ABSTRACT FROM AUTHOR]

Reservoir simulation is traditionally based on the assumption that water is an inert phase, while hydrocarbon components split into oil and gas phases. This approach is usually reasonable when modeling conventional hydrocarbon recovery, but specific applications may require accounting for mass exchange between the water and hydrocarbon phases. We here present the extension of our Graphics Processing Units (GPUs) compositional reservoir simulator (Esler et al. SPE J. 27(01), 597–612, 2021) to support gas-water equilibrium. Specifically, the Søreide and Whitson equation of state (EoS) (Søreide and Whitson Fluid Phase Equilib. 77, 217–240, 1992) was implemented to compute mutual solubilities of hydrocarbon/brine mixtures. The impact of salinity on phase equilibrium is accounted for, with salt being treated as an active tracer. The simulator uses a mass-variables formulation, meaning that little modifications to the construction of transport equations and Jacobian assembly was required; most of the required code changes are localized in the EoS module for the computation of component fugacities, and phase properties such as partial molar fractions and partial molar volumes. Treating salt as an active tracer instead of defining a further pseudo-component has an important advantage with the Søreide and Whitson EoS. If salinity changes as in water vaporization processes, our choice ensures that flash iterations can still be cast as a Gibbs Minimization problem with salinity being a constant parameter. On the contrary, salinity would change as flash iterations progress, jeopardizing the thermodynamic consistency of the phase equilibria. The overall reservoir simulation system of equations is still accurate to first order in time, at the cost of possibly slight volume imbalances at the end of converged timesteps. In this paper, we focused on CO 2 sequestration in saline aquifers, where solubility trapping is a key mechanism. The accuracy of our implementation with respect to conventional CPU ones is first demonstrated on a synthetic box model. We then select an open-access aquifer model (Gassnova 2016) to illustrate its applicability in an industrial setting. Finally, we show how being able to seamlessly run high resolution models allows for modeling of convective mixing. A key conclusion of this work is that the extreme performance of GPU-based reservoir simulation naturally transfers to new fields of study, which is critical when modeling saline aquifers whose extent is an order of magnitude larger than that of typical oil and gas fields. [ABSTRACT FROM AUTHOR]

Objective Fracture systems in shale reservoirs have an important impact on CH4 production and CO2 sequestration, and different geological characteristics of reservoirs have their corresponding optimal fracturing schemes. The study aims to investigate the effect of artificial fracture parameters on CO2 sequestration and CH4 production of Yanchang formation shale reservoirs in Ordos Basin. Methods Based on the geological conditions of shale reservoirs of Yanchang formation in Ordos Basin, a dual-porosity, dual- permeability homogeneous model was established to analyze the effects of artificial fracture half-lengths, fracture width, fracture height, fracture spacing, and the number of fractures on CO2 sequestration and CH4 production in CO2-ESGR. Results The results showed that fracture half-length fracture width and fracture height were positively correlated with CO2 sequestration and CH4 production, among which fracture width had the greatest influence. When the fracture width increased from 5 mm to 25 mm. CO2 sequestration increased by 112.69% and CH4 production increased by 87.11% at most. Both fracture interval and fracture number increased CO2 sequestration and CH4 production. However, when the horizontal well length was the same, the increasing of fracture number had a far greater impact on CO2 sequestration and CH4 production than that of fracture interval. When the number of fracture increased from 2 to 6. CO2 sequestration increased by 151. 92% and CH4 production increased by 137. 81% at most. Conclusions During the development process, strategically enhancing the half-length, height, width and quantity of artificial fractures can facilitate efficient sequestration of CO2 and extraction of CH4. [ABSTRACT FROM AUTHOR]

Increased CO2 emissions have resulted in extreme climatic variations and as the forecast is that the global temperature will hit its highest-ever level in the next five years. This comes at a time when there is an urgent need for effective and smooth means of reducing greenhouse gas emissions. Geological Sequestration of Carbon (GCS) is a new alternative: the effective and safe storage of CO2 underground. The most critical part of the process is the leakage assessment and geological formation safety as a long-term sink of CO2. Caprock is important in this process as an efficient long-time sequester for CO2, as it is more permeable to CO2 than geological reservoirs. Of all the other processes involved in trapping, the most effective in the immediate phase after the injection of CO2 is capillary trapping. The CO2 remains stored under the caprock until the critical pressure that initiates movement is achieved. Traditional methods, such as mercury intrusion porosimetry and core flooding experiments, do not tend to be replicated correctly in-situ and often complicate the process. Measurements made in such a manner usually overestimate threshold pressures for one of many reasons, be it late flow signal recognition in the low permeability of caprocks or incompletely saturated cores. For these purposes, in-situ-type novel equipment was developed for easy and direct capillary pressure measurement, core saturation, and effortless reproduction of in-situ conditions at higher pressures. This new technique measures the pressure in the outflow directly, so the values of threshold pressure it gives are very exact. [ABSTRACT FROM AUTHOR]