The non-isothermal hydrogen reduction kinetics of the MoS2–CaO system (molar ratio 1:2) were investigated using TG-DSC under a 50% H2Ar atmosphere at heating rates of 5–20 °C/min. The apparent activation energy was determined by the FWO and KAS isoconversional methods, and the reaction mechanism functions were screened using the Šatava–Šesták method. The reduction process exhibits a clear three-stage characteristic with a critical boundary at 450 °C, dividing the process into physical desorption (<200 °C), surface structure adjustment (200–450 °C), and bulk reduction with crystal phase evolution (>450 °C). Stage II (200–450 °C) is identified as a surface-controlled pre-reaction stage with an average activation energy of 258.76 kJ/mol, following the Anti-Jander eq. (D5) for three-dimensional reverse diffusion (A = 1.985 × 1017 s−1). Stage III (>450 °C) is the bulk reduction stage characterized by multi-step coupling, with an average activation energy of 224.95 kJ/mol, following the Avrami-Erofeev equation (n = 3) for nucleation and growth (A = 5.360 × 107 s−1). XRD analysis reveals a complex reaction pathway: initial reduction to Mo and CaS (≥700 °C), followed by intermediate CaMoO4 (≥800 °C) and stable CaMo6S8 (Chevrel phase, ≥950 °C). The transition in mechanism functions from D5 to A3 quantitatively reveals the promoting mechanism of CaO, shifting the rate control from surface diffusion to bulk nucleation and growth. This work provides the first quantitative kinetic framework describing CaO's dual role—surface activation in Stage II and deep reduction promotion via in-situ sulfur fixation in Stage III—while identifying competing reaction pathways leading to stable Chevrel phase formation. These findings offer theoretical insights for optimizing clean molybdenum extraction processes.

To address the key challenges of low thermal efficiency, poor displacement performance, and the unclear enhancement mechanism of single-gas-assisted steam flooding in heavy oil reservoirs, a comprehensive study integrating high-temperature and high-pressure PVT experiments, one-dimensional tubular displacement tests, and three-dimensional physical simulations was conducted. The objective was to reveal the synergistic enhancement mechanism between multi-component composite gas (20% CO2 + 80% N2) and steam, thereby promoting the efficient and environmentally sustainable development of heavy oil resources. First, a PVT apparatus was used to determine the dissolution behavior of the multi-component composite gas in crude oil under different temperature and pressure conditions, as well as its effects on heavy oil physical properties, such as viscosity and expansion coefficient. Second, one-dimensional displacement experiments were conducted to compare the oil displacement efficiencies of pure steam flooding and composite gas-assisted steam flooding, and to optimize injection parameters including temperature and total gas injection volume. Finally, three-dimensional physical simulation experiments were employed to investigate the production performance and steam chamber expansion behavior during composite gas-assisted steam flooding, and to quantitatively evaluate its contribution to enhanced oil recovery. As indicated by the research results, under reservoir conditions of 50 ℃ and 4 MPa, the solubility of the multi-component composite gas reached 15.5 m3/m3, reducing heavy oil viscosity by 72.76% and exhibiting a pronounced synergistic effect of viscosity reduction through gas dissolution and volumetric expansion. The one-dimensional displacement experiments determined an optimal injection temperature of 250 ℃ and an optimal total injection volume of 0.6 PV, under which the oil displacement efficiency of multi-component composite gas-assisted steam flooding was 12%-18% higher than that of pure steam flooding. The three-dimensional physical simulation experiments confirmed that co-injection of the multi-component composite gas increased the steam chamber expansion rate by 25%, expanded the heating area (100 ℃ isotherm) from 68.98% under pure steam flooding to 82.21%, and raised the final oil recovery to 49.49%, representing an improvement of 7.95% over pure steam flooding. Multi-component composite gas-assisted steam flooding significantly enhances heavy oil mobility and sweep efficiency through multiple synergistic mechanisms, including viscosity reduction by CO2 dissolution, pressure maintenance by N2, gas phase displacement of residual oil in small pores, and steam chamber expansion.

Efficient desulfurization of high-sulfur bauxite is crucial for its green resource utilization. Addressing issues in traditional roasting technologies such as low mass transfer efficiency, high energy consumption, and narrow operating windows, this study innovatively proposes and constructs a three-stage cyclone desulfurization reactor system. Combining experimental research with Computational Particle Fluid Dynamics (CPFD) numerical simulation, the effects of reaction temperature (800–1000 K) and gas velocity (5.0–7.0 m/s) on desulfurization performance were systematically investigated and compared with a single-stage system. Experimental results show that under optimal conditions (1000 K, 7.0 m/s), the total sulfur desulfurization rate of the three-stage system reached 70.97 %, and the sulfide-type sulfur desulfurization rate reached 90.11 %, representing improvements of approximately 27.6 % and 6.2 %, respectively, compared to the single-stage system. This study established a reliable CPFD modeling approach for the inter-stage airlock valves using the CPFD method, ensuring the authenticity of the gas–solid flow simulation in the multistage system. SEM analysis revealed that the roasting process reconstructed the microstructure of bauxite from a dense state to a loose and porous structure, significantly enhancing the reaction mass transfer efficiency. CPFD simulations further revealed the synergistic velocity-temperature effect and parameter decoupling regulation characteristics within the system, identifying the optimal operating range as an inlet gas velocity of 6.5–7.0 m/s and an inlet gas temperature of 1000–1050 K. This study provides a solid theoretical and experimental foundation for the industrial scale-up and optimal design of the three-stage cyclone reactor.

Addressing the dual challenges of oily wastewater treatment and solid waste valorization, this study pioneers a resource-efficient strategy to fabricate high-performance ceramic membranes from hazardous industrial residues. We demonstrated the synergistic utilization of gold tailings and electroplating sludge-two abundant yet underutilized solid wastes-as part of the raw materials for membrane fabrication through an energy-efficient dry-pressing and in-situ sintering process conduct at relatively low temperatures (950-1100 degrees C). This approach significantly reduces energy consumption compared to conventional high-temperature sintering techniques while valorizing waste streams. The membrane after raw material ratio optimization (1:1 waste ratio, 1050 degrees C) have good performance in terms of water permeance (71.4 L.m(-2).h(-1).bar(-1)) and oil rejection (95.4 %) for high-loading (2000 mg/L) oil-in-water (O/W) emulsions, surpassing most reported waste-derived membranes. Further innovation was realized through surface engineering: Secondary sintering was used to deposit a hydrophilic alpha-Fe2O3 coating on the membrane, modifying its surface pores. The resulting membrane demonstrated underwater superoleophobicity (oil contact angle >150 degrees) and achieved an oil rejection of 98.2 %. Long-term cyclic tests confirmed robust stability (>85 % flux recovery efficiency after cleaning) and minimal ecotoxicity. Fouling analysis revealed dominant cake-layer formation, enabling effective membrane regeneration. This work establishes a scalable "waste-treats-waste" paradigm, transforming environmental liabilities into functional materials. The process aligns with circular economy principles by cutting material costs, reducing sintering energy, and eliminating waste disposal burdens. It presents a commercially viable pathway for industrial oily wastewater remediation while advancing dual-carbon goals through integrated resource recovery and emissions reduction.

To meet the traffic control demands of highway merging areas and address the accuracy error of traffic flow prediction models, a cooperative control strategy based on adaptive prediction horizon Model Predictive Control (MPC) has been proposed for variable speed limits (VSL) and dynamic hard shoulder running (HSR). Firstly, the METANET model was improved based on the characteristics of merging areas and the impact of cooperative control strategy. Secondly, to mitigate the negative impact of the METANET prediction errors on control effectiveness, a fuzzy rule-based adaptive prediction horizon controller is designed. Thirdly, a cooperative control strategy for VSL and dynamic HSR is formulated under the MPC framework, aiming to optimize Total Time Spent(TTS)and Total Travel Distance (TTD), using genetic algorithms equipped with sliding time windows for resolution. Finally, using actual traffic flow data from Changtai Highway, simulation experiments are conducted, involving four scenarios: HSR-VSL control, VSL-only control, HSR-only control, and no control. In the cooperative control scenario, both adaptive and fixed prediction horizon approaches are considered. Results show that the proposed HSR-VSL control strategy with fixed prediction horizon reduces the total travel time and mainline density by 20.02% and 10.78% respectively, outperforming single strategies (only HSR or VSL). Compared to a fixed prediction horizon, the VSL-HSR with adaptive prediction horizon delivers even better results, reducing total travel time and mainline density by 24.53% and 12.94% respectively, proving the effectiveness of the cooperative control strategy and the adaptive prediction horizon controller.

During the CO2 flooding process in fractured low-permeability oil reservoirs, the injected CO2 is prone to channeling along fractures due to severe reservoir heterogeneity, resulting in poor development effect. The CO2-responsive gel system shows dual advantages in achieving CO2 capture and plugging gas channeling to enhance oil recovery. This paper constructed a system with good CO2 sensitivity based on long-chain alkyl amide propyl dimethyl tertiary amine first. Subsequently, the properties of the system before and after the response were evaluated through rheological test, and its microstructure was characterized by Cryo-TEM. The system exhibited good CO2 responsiveness, transitioning from low-viscosity solution system to high-viscosity CO2-responsive gel system upon contact with CO2, with its viscosity increasing by nearly five orders of magnitude. The CO2-responsive gel demonstrated excellent shear resistance, viscoelasticity and shear self-repairing ability. The change of microstructure further verified the mechanism of molecules self-assembly in the system under the action of CO2. Then, a series of core physical simulation experiments were carried out to comprehensively evaluate the effects of different factors on the injection capacity, plugging characteristics, dynamic filtration damage performance and EOR effect of CO2-responsive gel. The gel maintained injectability while achieving an exceptional deep plugging effect, and the plugging rate reached 98.77%. It showed good characteristics of low filtration and permeability damage in low permeability reservoirs, effectively ensuring the fracture plugging effect. After the fracture was plugged by gel, the sweep range of CO2 to the matrix significantly expanded, and the gas flooding recovery increased by 18.19–21.7%. Finally, the matrix-fracture dual-media chip model was used to conduct microfluidic experiment, the oil displacement characteristics in different displacement stages were visually clarified, and the synergistic plugging and oil displacement mechanism between the CO2-responsive gel and CO2 was summarized. The research results can provide important insights for the green and efficient application of CO2-responsive gel in fractured low-permeability reservoirs.

Gel foam exhibits excellent applicability in fractured-vuggy reservoirs, effectively plugging flow channels and enhancing oil recovery. However, due to the harsh high-temperature environment and the complex and variable fracture-vuggy structure in reservoirs, gel foam may undergo structural changes during its migration, which can affect its flow properties and plugging efficiency. Therefore, investigating the migration characteristics of gel foam in fractured reservoirs through visual experiments is of significant practical importance. In this study, migration experiments with different foam systems were conducted using the visualized vuggy model. The migration stability of foam was characterized by combining the sweep range and liquid drainage rate, and the impact of temperature on the migration characteristics of gel foam was explored. Additionally, a profile control experiment was performed using the fractured-vuggy network model, analyzing and summarizing its mechanisms for enhancing oil recovery in fractured-vuggy reservoirs. The results showed that, in the vuggy model, compared with ordinary foam and polymer foam, gel foam showed a lower drainage rate, higher foam retention rate and wider sweep range, and could form stable plugging in fractured-vuggy reservoirs. An increased temperature accelerated the thermal expansion of gas and changes in liquid film characteristics, which led to the expansion of foam migration speed and sweep range. Although a high temperature increased the liquid drainage rate of foam, it was still lower than 3%, and the corresponding foam retention rate was higher than 97%. In addition, the gel foam had a strong profile control ability, which effectively regulated the gas migration path and improved the utilization degree of remaining oil. Compared with the first gas flooding, the recovery of subsequent gas flooding was increased by 18.85%, and the final recovery of the model reached 81.51%. Comprehensive analysis revealed that the mechanism of enhanced oil recovery by gel foam mainly included density control, foam regeneration, flow redirection, stable plugging, and deep displacement by stable gel foam. These mechanisms worked synergistically to contribute to increased recovery. The research results fully demonstrate the application advantages of gel foam in fractured-vuggy reservoirs.

To realize efficient treatment of oily wastewater, various super-wetting materials have been developed. Oily wastewater is often complex and may contain both oil-in-water and water-in-oil emulsions. However, most of the current studies focus on the treatment of single emulsions, and there are fewer studies on the simultaneous separation of oil-in-water and water-in-oil emulsions. In this paper, by removing hemicellulose and lignin from bamboo processing waste powder (BPWP), the treated bamboo powder (TBP) containing mainly cellulose was obtained. TBP has superoleophobicity underwater and superhydrophilicity underoil, which can separate not only various oil-in-water emulsions stabilized by surfactants, but also water-in-oil emulsions stabilized by different surfactants, and the separation efficiency is higher than 99 %. The separation efficiencies of TBP for different water-in-oil emulsions were all higher than 99 %. On this basis, we have established an intelligent device that makes full use of underwater super-hydrophobic and under-oil super-hydrophilic properties to realize the purification of water and de-watering and recycling of floating oil in complex oil–water systems. This work provides a very promising direction for industrial application in practical oily wastewater treatment and fuel recovery.

Addressing the challenges of uranium extraction from seawater (UES) requires innovative strategies to overcome ultralow concentration (3.3 ppb) and thermodynamic limits. Herein, we propose a regioisomeric engineering strategy to design vinylene-linked covalent organic frameworks (COFs) for synergistic adsorption-photocatalytic UES. Two isomeric COFs, beta-PTTN-AO and alpha-PNNB-AO, were synthesized by tuning the substitution positions of amidoxime (AO) groups on olefin bonds. The beta-PTTN-AO isomer achieves a remarkable UES capacity of 12.74 +/- 0.21 mgg-1 in nature seawater, surpassing its alpha-positioned counterpart (8.9 +/- 0.18 mgg-1) and outperforming most reported photocatalysts. Combined experiments and density functional theory (DFT) theoretical studies correlate regioisomeric configurations with electronic structure modulation and photocatalytic activity. Specifically, beta-PTTN-AO enhance pi-electron delocalization and strengthen built-in electric fields, promoting exciton dissociation, charge separation, and uranium reduction. This work establishes a molecular design paradigm for COF photocatalysts, advancing sustainable nuclear energy through structural isomerism.

The water flooding potential of the target reservoir in Nanpu 3–2 zone has been distinctly declining year by year, making it difficult to achieve effective development. There is an urgent need to explore alternative displacement methods to improve oil recovery. Based on the petrophysical characteristics of the reservoir, artificial cores were made. The oil-saturated cores were prepared according to actual reservoir forming. After fully displacing oil-saturated cores with brine, the cores were displaced by N2, CO2, and hydrocarbon gas, respectively, and the displacement effectiveness of the three gases was evaluated. To explain the differences in the displacement effects, minimum miscibility pressure and nuclear magnetic resonance experiments were conducted. This study finds that gas flooding significantly modifies the flow channels, reducing the resistance caused by the flow channels during displacement, but it has a minimal impact on the overall porosity of the rock. Compared to water flooding, gas flooding can enhance oil recovery, but N2 struggles to reach the miscible state, leading to only a 5% improvement. Both CO2 and hydrocarbon gas can reach a miscibility state, allowing to displace oil from smaller pores, with oil recovery increasing by over 30%. During the displacement process, CO2 encounters greater resistance from water, resulting in a larger pressure differential, which enables it to penetrate tiny pores and displace oil from them. An alternating method of water flooding and hydrocarbon gas flooding is recommended to enhance the reservoir recovery. This research would provide insights for water-alternative-gas flooding with similar reservoirs.

The escalating energy demand has prompted nations to prioritize the development of high-viscosity and challenging-to-extract heavy and extra-heavy oil reserves. Consequently, the technique of in-situ combustion in oil reservoirs by injecting air to ignite heavy oil resources, leveraging the generated heat to enhance recovery rates, is a particularly critical extraction method. However, simulation studies of in-situ combustion techniques are still primarily conducted at a macroscopic level. Therefore, conducting more detailed numerical simulation studies holds significant importance. This paper establishes a mathematical model for heat transfer within reservoirs during in-situ combustion, thoroughly investigating the effects of inlet temperature, injection pressure, injection duration, and porosity on the heat transfer processes inside the reservoir. The research demonstrates that the reservoir’s internal temperature gradually rises as the injection duration increases. Additionally, porosity (an increase from 0.1 to 0.3 enhances the heat propagation rate by 15%) and injection pressure (an increase from 5 MPa to 8 MPa boosts the heat propagation rate by 25%) significantly affect the heat transfer rate.

Some aging expressways with limited lanes are unable to provide sufficient service resources when encountering sudden traffic surges caused by incidents or emergencies. Effectively utilizing existing hard shoulder emergency lanes for dynamic resource supply has become a new objective in the context of intelligent capacity expansion. A dynamic hard shoulder resource supply method is proposed. Firstly, a scenario model for basic expressway mainline lanes and hard shoulders is established using the Cell Transmission Model (CTM). Then, a fully centralized multi-agent system for hard shoulder control is constructed, and a reinforcement learning-based strategy is developed for dynamic resource supply. Finally, a series of simulation experiments are conducted to compare the proposed strategy with the baseline strategies of full opening and full closure. The results demonstrate that the proposed method reduces the average vehicle cell travel time by 51.7 % and the congestion dissipation time by 39.6 %, effectively supporting dynamic resource supply.

Abstract Foamy oil flow is a pivotal aspect of the cyclic solvent injection (CSI) process, yet the influence of water and foam stabilizers, such as nanoparticles, on its efficacy remains insufficiently elucidated. Consequently, a profound comprehension of how waterflooding and nanoparticles impact CSI performance is imperative for advancing oil recovery strategies. This study conducted a meticulously designed experimental investigation to investigate the roles of water and nanoparticles in a CO2-based CSI process. Three distinct tests were executed utilizing a cylindrical sandpack at varying injection pressures. Test 1 entailed a standard CO2-based CSI process for baseline comparison. Test 2 involved a waterflooding process with an injection volume of 1.5 PV, succeeded by a CO2-based CSI process. Test 3 featured a hybrid process comprising the sequence: CSI-waterflooding-CSI-Nanoparticle solution flooding-CSI. Key parameters including injection rate, injection volume, sandpack pressure, production rate, cumulative production, and water cut were meticulously monitored and recorded. Thorough data analytics were then employed to scrutinize the impact of water and nanoparticles, identifying mechanisms for enhancing the CSI process. Laboratory results revealed that the total oil recovery in Test 2 CSI process exceeded that of Test 1 by 7.9%, underscoring the increased efficiency of Test 2. This efficiency was attributed to a 33.2% lower oil saturation after the waterflooding process in Test 2 compared to Test 1. The positive impact of waterflooding on CO2-based CSI processes extended to Test 3, where the oil recovery factor of the CSI phase following waterflooding increased by 7.1% compared to the pre-waterflooding CSI phase. After nanoparticle solution flooding, the subsequent CSI phase yielded an additional 5.9% original oil in place (OOIP), demonstrating the nanoparticles' capacity to enhance foam stability even after multiple second oil recovery (SOR)/ enhanced oil recovery (EOR) processes. As the combined process progressed, the instantaneous gas-oil-ratio increased, facilitated by expanded space for CO2 injection amid heavy oil production. The amalgamated process achieved an impressive total oil recovery factor of 69.5%, more than doubling that of the CSI process in isolation.

Abstract In this study, a self-designed microchip system was used to visually study the pore-scale salt crystallization and migration, and a high-performance optical microscope was used to dynamically observe the salt precipitation process and results. The results show that pore-scale salt crystals mainly precipitate in the residual water phase, and mainly present two forms of occurrence, large-grained salt crystals and small-grained aggregated crystals, respectively. In addition to growing in the brine phase, large-grained salt crystals also nucleate and grow at the gas-liquid interface, and the maximum salt crystal size can reach the order of the pore size. This phenomenon was discovered for the first time and has not been mentioned in the existing literature. In addition, this study also observed an interesting phenomenon. The salt crystals formed in the wetting brine film and the brine phase can migrate under the combined influence of displacement pressure and capillary force, and eventually accumulate and precipitate inside the pores. Injection flow rate and salinity have a strong influence on the pore-scale salt crystallization kinetics. There is a critical value for the injection flow rate, and the critical injection rate causes the salt precipitation to be significantly aggravated. Under the same injection flow rate, an increase in salinity leads to an increase in the amount of salt precipitation.

High-viscosity paraffin-based crude oil is prone to wax deposition at low temperatures, hindering development and transportation efficiency while posing safety risks. Microbial technology offers a safe, eco-friendly, and economically viable solution. In this study, strain B-1 is isolated and cultivated optimally using statistical multifactorial synergistic optimization. Species identification reveals strain B-1 to be a new Gram-positive aerobic bacterium. After optimization, strain B-1′s growth activity increases by 11.5 %. Lipopeptide surfactants produced by strain B-1 reduce wax content and viscosity of the crude oil by 37.29 % and 23 %, respectively. It also shows a significant impact on long carbon chain heavy component hydrocarbon substrates, degrading C17-C40 hydrocarbons by 37.93 % on average. Moreover, strain B-1 transforms aggregated wax crystals into dispersed microcrystals, improving flowability. These findings offer a promising solution for enhancing reservoir development efficiency and ensuring pipeline transportation safety.

Combining multiple secondary oil recovery (SOR)/enhanced oil recovery (EOR) methods can be an effective way to maximize oil recovery from heavy oil reservoirs; however, previous studies typically focus on single methods. In order to optimize the combined process of ethane-based cyclic solvent injection (CSI) and water/nanoparticle-solution flooding, a comprehensive understanding of the impact of injection pressure, water, and nanoparticles on CSI performance is crucial. This study aims to provide such understanding through experimental evaluation, advancing the knowledge of EOR methods for heavy oil recovery. Three approaches (an ethane-based CSI process, water flooding, and nanoparticle-solution flooding) were applied through a cylindrical sandpack model with a length of 95.0 cm and a diameter of 3.8 cm. Test 1 conducted an ethane-based CSI process only. Test 2 conducted a combination approach of CSI–water flooding–CSI–nanoparticle-solution flooding–CSI. Specifically, the injection pressure of the first CSI phase in Test 2 was gradually increased from 3500 to 5500 kPa. The second and the third CSI phases had the same injection pressure as Test 1 at 5500 kPa. The CSI process ceased once the oil recovery was less than 0.5% of the original oil in place (OOIP) in a single cycle. Results show that the ethane-based CSI process is sensitive to injection pressure. A high injection pressure is crucial for optimal oil recovery. The first CSI phase in Test 2, where the injection pressure was increased gradually, resulted in a 2.9% lower oil recovery and five times as much ethane consumption compared to Test 1, which applied a high injection pressure. It was also found that water flooding improved the oil recovery in the CSI process. In Test 2, the oil recovery factor of the second CSI phase increased by 57% after the water flooding process, which is likely due to the formation of water channels and a dispersed oil phase that increased the contact area between ethane and oil. Although the nanoparticle-solution flooding only had 0.3% oil recovery, after that the third CSI phase stimulated another 10.8% of OOIP even when the water saturation achieved more than 65%. This demonstrated that the addition of nanoparticles can maintain the stability of the foam and enhance the transfer of ethane to the heavy oil. Finally, Test 2 reached a total oil recovery factor of 76.1% on a lab scale, an increase of 45% compared to the single EOR method, which proved the combination process is an efficient method to develop a heavy oil field.

Underground pipelines buried deeper than 1.5 m or in specific soil conditions are susceptible to microbial corrosion and dynamic alternating current (AC) interference. Yet, research on the coupled effects of these factors remains limited, leaving their mechanisms unclear. The study employed microbial activity tests, electrochemical experiments, and microscopic morphology characterization to elucidate the coupled effect of sulfate-reducing bacteria (SRB) and dynamic AC interference on buried metallic pipelines. Results show that sinusoidal AC significantly reduces SRB growth activity. Initially, the active microbial film produced by microbial metabolism inhibited corrosion but later exacerbating it as the microbial film detachment. Microscopic examination reveals as the interference time increases, the corrosion morphology changed from pitting corrosion to honeycomb/ulcer shapes, under SRB and different AC interference conditions. Moreover, sulfide corrosion products and iron phosphide formation accelerate corrosion, while rectification and alternating electric field effects further aggravate the process. These findings provide insights into the complex mechanisms of microbial and AC corrosion in buried pipelines, aiding in anti-corrosion strategies and layout optimization.

Mineral carbonation with serpentine can offer a sustainable and safe process option for simultaneous CO2 emission reduction and utilization of nature mineral. In this study, a sustainable process for CO2 mineral sequestration was proposed by using serpentine and ammonium sulfate as feedstocks. The mixture of feedstocks was subjected to roasting with temperature ranging from 390 degrees C to 480 degrees C, converting magnesium into the corresponding sulfate. Then, water leaching was employed to dissolve the magnesium sulfate from the roasted samples. Finally, through a mineralization reaction, the corresponding magnesium bicarbonate was generated after sequestrating CO2. Under the optimal roasting-leaching conditions, i.e. roasting temperature of 420 degrees C, roasting time of 2 hours, and mass ratio of ammonium sulfate/serpentine of 3; leaching temperature of 80 degrees C, leaching time of 1 hour, and a liquid-to-solid ratio of 1, the magnesium extraction efficiency reached 76 %. Thermodynamics and experimental results demonstrated that during the sulfation roasting process, the products generated during roasting, magnesium sulfate and silicon dioxide, adhered to the surface of the serpentine, thus inhibiting the mass transfer process and impeding the progress of the reaction. However, the liquid-solid reaction facilitated by molten ammonium sulfate and the gas-solid reaction provided by the decomposition of ammonium salts into SO2 played a promoting role in the sulfation roasting reaction. The carbonation of sulfated serpentine results indicated that the optimal CO2 storage capacity can reach 204 kg/t serpentine.

Carbon Capture Utilization and Storage (CCUS) has been widely accepted to be an effective technology to control anthropogenic greenhouse gas emissions globally. For CO2 geo-sequestration, the key is to understand the caprock integrity to assure the safety of the long term sealing effect. However, many caprock integrity studies do not consider the effects of geochemical reactions among CO2, formation brine and caprock. In this work, we used the Lloydminster heavy oil region as the target area and studied the effects of geochemical reactions on the caprock integrity. We collected caprock core samples from both Waseca heavy oil layer and the Deadwood saline aquifer in this area. Then, static tests (Caprock submerged into formation brine over-saturated with CO2 for 40 days) were conducted in the autoclave system under the reservoir pressure (Waseca: 5.4MPa, Deadwood: 11.5MPa) and temperature (Waseca: 25⁰C Deadwood: 35⁰C) to mimic the process of CO2 storage in two candidate formations. Finally, triaxial tests were conducted to compare the change in rock strength between core samples before and after CO2 treatment. Meanwhile, XRD analysis has also been conducted to provide the information of mineral composition change on caprock samples before and after CO2 treatment. Triaxial test results showed that caprock strength has increased (higher axial stress and lateral stress) and fracture pressure increased by 15.84% and 5.45% on average in Waseca and Deadwood formation respectively. Mineralogy analysis indicated that a large amount of carbonate minerals reacted with CO2-saturated brine and stable minerals were generated which help tighten the caprock structure, triggering the self-sealing effect thus caprock strength was enhanced. The research outcomes indicate that in the future site selection for CCS projects, reservoirs with caprocks containing carbonated minerals can be competitive candidates.