Hydrate Phase Research Articles

Granite Dust and Silica Fume as a Combined Filler of Reactive Powder Concrete

By volume, cement concrete is one of the most widely used construction materials in the world. This requires a significant amount of Portland cement, and the cement industry, in turn, causes a significant amount of CO2 emissions. Therefore, the development of concrete with a reduced cement content is becoming an urgent problem for countries with a significant level of production and consumption of concrete. Therefore, the purpose of this article is to critically investigate the possibility of using inert granite dust in combination with highly active silica fume in reactive powder concrete. The main physical and mechanical properties, such as the compressive strength at different curing ages and the water absorption, were studied using mathematical planning of experiments. The consistency and microstructure of the reactive powder concrete modified with granite dust in combination with silica fume were also analyzed. Mathematical models of the main properties of this concrete are presented and analyzed, and the graphical dependencies of the influence of composition factors are constructed. A more significant factor that affects the compressive strength at all curing ages is the silica fume content, increases in which to 50 kg/m3 lead to a 25–40% increase in strength at 1 day of age, depending on the granite dust content. In turn, an increase in the amount of granite dust from 0 kg/m3 to 100 kg/m3 in the absence of silica is followed by an increase in strength of 8–10%. After 3 days of curing, the effect of granite dust becomes more significant. Increases in the 28-day strength of 25%, 46% and 56% were obtained at a content of 50 kg/m3 of silica fume and 0 kg/m3, 100 kg/m3 and 200 kg/m3 of granite dust in concrete, respectively. It is shown that the effect of inert granite dust is more significant in combination with silica fume at its maximum content in the range of variation. The pozzolanic reaction between highly active silica and Ca(OH)2 stimulates the formation of hydrate phases in the space between the grains and causes the microstructure of the cement matrix to compact. In this case, the granite dust particles act as crystallization centers.

Advances, Applications, and Perspectives of Machine Learning Approaches in Predicting Gas Hydrate Phase Equilibrium

Advances, Applications, and Perspectives of Machine Learning Approaches in Predicting Gas Hydrate Phase Equilibrium

Study on the gas composition of hydrate phase and unreacted liquid phase for hydrate-based gas separation

Hydrate-based gas separation (HBGS) method is an environment-friendly gas separation technique. At the end of the hydrate formation stage, the system usually consists of gas phase, hydrate phase and residual unreacted liquid phase. The separation efficiency of HBGS is usually determined by measuring the gas composition of gas phase before and after hydrate formation. It is currently unclear the gas composition of hydrate phase and residual unreacted liquid phase, and how they will affect the gas separation efficiency of HBGS separately. This work developed a novel method for efficiently separating the hydrate phase and the unreacted liquid phase, making it possible to directly measure the gas composition in the hydrate phase and residual unreacted liquid phase for the gas mixture hydrate system. The influence factors, such as operation conditions, gas composition of feed gas and types of guest gas on the gas composition of liquid and hydrate phases were studied. The experimental results show the mole fraction of CO2 in both hydrate phase and liquid phase are higher than that in the feed gas. The increase of system pressure and the mole fraction of CO2 in feed gas will obviously lead to the increase of the mole fraction of CO2 in hydrate phase, while slightly affect the mole fraction of CO2 in the liquid phase. When the mole fraction of CO2 in feed gas exceeds 80 %, the mole fraction of CO2 in the water phase will reach over 96 %, resulting in other influence factors being negligible. The mole fraction of N2 in hydrate phase is higher than that of H2, while the mole fraction of N2 in water phase is close to H2.

Machine Learning Potential for Serpentines

AbstractSerpentines are layered hydrous magnesium silicates (MgOO) formed through serpentinization, a geochemical process that significantly alters the physical property of the mantle. They are hard to investigate experimentally and computationally due to the complexity of natural serpentine samples and the large number of atoms in the unit cell. We developed a machine learning (ML) potential for serpentine minerals based on density functional theory calculation with the SCAN meta‐GGA functional for molecular dynamics simulation. We illustrate the success of this ML potential model in reproducing the high‐temperature equation of states of several hydrous phases under the Earth's subduction zone conditions, including brucite, lizardite, and antigorite. In addition, we investigate the polysomes of antigorite with periodicity = 13–24, which is believed to be all the naturally existent antigorite species. We found that antigorite with larger than 21 appears more stable than lizardite at low temperatures. This ML potential can be further applied to investigate more complex antigorite superstructures with multiple coexisting periodic waves.

An assessment of the pozzolanic potential and mechanical properties of Nigerian calcined clays for sustainable ternary cement blends

This study investigates the potential of calcined clays from Nigerian deposits as supplementary cementitious materials. Clay materials were obtained from three sites namely: Ikpeshi, Okpilla and Uzebba. The raw clay samples were then calcined at 700°C and 800°C. Chemical and mineralogical compositions were determined for the raw and calcined clay samples using XRF and XRD respectively. The chemical composition by XRF confirmed these clays as potential pozzolans with SiO2, Al2O3, and Fe2O3 collectively exceeding 70%. XRD analysis identified kaolinite and quartz as major mineral phases in the raw clays, which transformed into metakaolin upon calcination. Thermo Gravimetric Analysis (TGA) indicated varying lime consumption levels among the clays, with Ikpeshi clay displaying the highest pozzolanic reactivity and Uzebba clay the least. Compressive strength investigation on mortar cubes prepared with 50% substitution of Portland cement with the calcined clay and limestone, showed that Ikpeshi clay at 800°C had the best strength performance, with strength activity index of 0.92 (at age 28 days), demonstrating superior pozzolanic potential. Strength development was more significant between 7 and 28 days, indicating the pozzolanic reaction's contribution to long-term strength. However, initial strength at 3 days was lower than the reference Portland cement due to a delayed pozzolanic reaction. XRD analysis of blended pastes revealed typical phases of hydration like portlandite, calcium silicate hydrate phase, strätlingite, and ettringite, with the calcined clay blends showing reduced portlandite content, indicating absorption by the pozzolan's alumina phase.

Electrically driven nucleation for enhanced control of salt hydrate hydrogel heat release in long-term thermal storage applications

Sodium acetate trihydrate (SAT) is a well-known salt hydrate phase change material (PCM) with large energy density and a high degree of supercooling, making it suitable for long-term thermal storage. However, effectively discharging heat from the supercooled SAT remains a challenge. This study delves into optimizing the electrical nucleation process in an SAT-based PCM, beginning with the validation of electrode pre-treatment and concluding with initiation under various conditions. The research identifies the optimal voltage and electrode spacing for nucleation. The crucial role of diffusion field interactions from growing crystals at different sites is highlighted, noting that their convergence creates a complex concentration gradient profile that hampers crystallization efficiency. Additionally, an increase in electrode pairs correlates with a more uniform heat distribution. Findings revealed that through material modification and nucleation strategy optimization, the theoretical crystallization time for SAT-based PCMs can vary significantly, ranging from 44 to 252 s. This variability, offering up to a 472.73 % extension in discharge time, underscores the PCM's adaptability for customized applications, especially in fields requiring variable discharge rates, such as residential heating and electronic thermal management.

Influence of magnesium oxychloride cement mortar with different strength grades: Fly ash as compensation material

Magnesium oxychloride cement (MOC) is widely used due to its high solid waste utilization efficiency. However, the demand for cement raw materials (MgO and MgCl2) in the lower strength gradation remains low, leading to excessive sand particles in the slurry, thus reducing the working performance of the MOC mortar. Fly ash (FA) has been used in the construction industry to improve the workability of the slurry. The focus and innovation of this work involved using FA as a compensation material to produce MOC mortar materials with different strength levels. In this study, FA was used as compensation material to form MOC mortar with different strength grades, and the effects of FA on the MOC mortar flow performance, setting time, hydration heat release, strength development, phase composition, pore structure, and micromorphology were investigated. Combined with the experimental analysis and referring to the strength grade law of silicate concrete, the grade classification of MOC mortar with FA as the compensation material could be simply divided by adding 20 %, 30 %, 40 %, and 50 % FA, which could serve as a reference for the use design of MOC in different environments.

Hydrate phase equilibrium of hydrogen with THP, DCM, TBAB+THF and sulfur hexafluoride +TBAB aqueous solution systems

Experimental hydrogen hydrate dissociation data with single thermodynamic additive: tetrahydropyran (THP, with oxygen-containing functional group) or dichloromethane (DCM, with halogen group), and thermodynamic additive mixtures: tetrahydrofuran (THF) + tetrabutylammonium bromide (TBAB) system and sulfur hexafluoride (SF6) +TBAB system were reported with temperature range from 275.33 to 282.98 K and pressure range from 1.65 to 12.63 MPa. Other experimental data were collected from the literature. The compared results showed that the oxygen-containing or halogen functional group can significantly affect the hydrogen bonding between water molecules, which present great promoting effects on hydrogen hydrates formation. Also, the promoting effects of mixture additives on the phase equilibrium of hydrogen hydrates were investigated. The results indicated that the combination of thermodynamic additives showed better promoting effects on hydrate formation compared to the individual ones. And the results obtained in this work would provide useful information to select suitable and effective thermodynamic additives for hydrate-based hydrogen storage technology.

Liquidus of SiO2 in the Li2O‐SiO2, Na2O‐SiO2, and K2O‐SiO2 systems

AbstractThe phase equilibria in the SiO2‐rich region of the Li2O‐, Na2O‐, and K2O‐SiO2 systems at 1550°C to 1650°C were experimentally studied to determine accurate liquidus of SiO2 in the systems. A classical equilibration/quenching method was used, and the equilibrated samples were analyzed by X‐ray diffraction (XRD) and electron probe microanalysis (EPMA). Samples were contained in sealed Pt crucibles and held at the target temperatures for 7–21 days to reach equilibrium condition. Sealed Pt crucibles were employed to avoid the volatile loss of alkali oxides during high temperature phase equilibration and hydration upon quenching. Accurate liquidus of SiO2 in alkali‐silicate systems was determined for the first time, and the results were analyzed using the limiting slope rule in order to understand the dissolution behavior of alkali oxides in SiO2 melt. It was confirmed that alkali oxide dissolves in SiO2 melt by producing Li+, Na+, and K+ cationic species rather than Li22+, Na22+ and K22+ species.

Characterisation of Fault-Related Mn-Fe Striae on the Timpa Della Manca Fault (Mercure Basin, Southern Apennines, Italy)

The Quaternary Mercure basin is a complex fault structure located in the Pollino region of the southern Apennines (Italy). A persistent seismic gap makes the Mercure basin structure one of Italy’s highest seismic risk zones. The southernmost termination of the Mercure basin is the Timpa della Manca fault. The fault’s mirror is characterised by distinctive, lineated, black-coloured striae decorating a cataclasite made of carbonate clasts. These black-coloured striae consist of a mixture of Mn phases, including hollandite, todorokite, birnessite, and orientite, which are associated with goethite and hematite along with minor amounts of phyllosilicates (chlorite, muscovite), quartz, and sursassite. This mineral association and their phase stability suggest that hydrothermal circulating fluids may have mobilised and re-precipitated low-temperature Mn hydrous phases within the shear zone, leaving remnants of higher-temperature minerals. Oceanic crust remnant blocks within the Frido Unit appear to be the most likely source of the Mn. The uniqueness of the Mn striae on the Timpa della Manca fault offers intriguing insights into fluid circulation within the Mercure basin tectonic system, with potential implications for the seismotectonic characteristics of the Pollino region.

Agro-industrial waste utilization in air-cured alkali-activated pavement composites: Properties, micro-structural insights and life cycle impacts

This study investigates the development and performance of agro-industrial waste-based air-cured alkali-activated composites (AC) for sustainable high-strength pavement applications. The calculated amount of Na2SiO3 and NaOH were employed with water to generate alkaline activator solution. Locally sourced materials, including blast furnace slag, construction and demolition (C&D) waste, and sugarcane bagasse ash (SBA), were utilized to examine mechanical properties, micro-structural behaviour, and life cycle impacts. Optimized AC mixes containing 50% recycled aggregates (RCA) and 15% SBA demonstrated superior compressive, tensile, and flexural strength, while significantly reducing embodied energy and carbon emissions. Microstructural analysis through XRD, SEM, EDAX, and TGA confirmed the formation of stable alumino-silicate hydrate phases, contributing to enhanced superior-strength. The life cycle analysis results indicated considerable environmental benefits compared to traditional OPC pavement concretes. This research presents a sustainable solution for pavement infrastructure, aligning with circular economy principles by promoting the reduction of resource consumption and greenhouse gas emissions.

High-performance superhydrophobic fly ash based geopolymers with graphene oxide reinforcement for enhanced durability and repellency

While high-performance fly ash geopolymers offer a demonstrably reduced carbon footprint in the construction industry, their inherent affinity for water (hydrophilicity) can facilitate the accumulation of moisture within the material matrix, potentially leading to the initiation and propagation of internal corrosion. The implementation of hydrophobic functionalization strategies on fly ash geopolymers demonstrably enhances their resistance to corrosive degradation. Nevertheless, a crucial challenge persists in the form of mitigating potential declines in mechanical strength. This investigation endeavors to attenuate the deleterious effects exerted by the hydrophobic aluminosilicate hydrate phase on the material's mechanical properties, while concurrently preserving its superhydrophobic character. Our approach involved the incorporation of a novel composite modifier, wherein polymethylhydrosiloxane (PMHS) served as the principal hydrophobic component. Graphene oxide (GO) was strategically introduced to achieve efficient pore filling, owing to its exceptional dispersibility. Furthermore, the presence of GO reinforces the mechanical performance of the composite due to its inherent superior mechanical properties. Additionally, the well-dispersed GO portion forms nano hydrophobic particles by covalently grafting hydrophobic groups, further enhancing the overall hydrophobicity of the composite. This synergistic interplay between PMHS and GO facilitated the successful development of a high-performance fly ash geopolymer composite characterized by exceptional mechanical strength, three-dimensional superhydrophobicity, and enhanced chemical stability. The graphene oxide reinforced high-performance three-dimensional superhydrophobic hybrid hydrogel geopolymer composites maintained high compressive strength while achieving a water contact angle of 153 ° and a water absorption rate of only 1.7 %. Remarkably, the geopolymer retains its high hydrophobicity even after 24 hours in an acid-base solution, with a contact angle exceeding 140° and water absorption rates lower than 4 %.

Hydrate management strategies for CO2 injection into depleted gas reservoirs

Sequestering CO2 in depleted gas reservoirs using carbon capture, utilization, and storage technologies has emerged as a viable strategy for mitigating global carbon emissions. However, CO2 hydrate formation during injection processes is challenging and poses a risk to the operational integrity and efficiency of sequestration projects. This study investigated CO2 hydrate formation dynamics within silica gel environments that closely mimicked the median pore size of natural sandstone reservoirs, particularly targeting depleted gas fields in the East Sea of Korea. Integrating kinetic insights into experimental hydrate formation assessments and molecular dynamics simulations provided a comprehensive understanding of the CO2 hydrate formation mechanisms, as well as the formation dynamics and stability of the CO2 hydrates. For example, the hydrate formation kinetics were significantly reduced in the small pores, suggesting the feasibility of implementing more economical hydrate inhibitor injection strategies during CO2 injection. Moreover, this study evaluated the inhibitory effects of NaCl and methanol on CO2 hydrate stability by accurately measuring the three-phase (H-Lw-V) equilibria and employing silica gels (6 nm pore size). The presence of methanol and amorphous silica significantly impacted hydrate formation, with methanol potentially influencing the local structure around the hydrate phase and silica hindering hydrate growth through dynamic interactions with CO2 molecules. In addition, we elucidated the complex interplay between CO2, water, and methanol (hydrate inhibitor) within the constrained environments of porous media, offering strategic insights for the development of effective CO2 injection and sequestration strategies. Integrating molecular-level observations with real-world geological modeling presents a novel methodology for enhancing the safety, efficiency, and environmental sustainability of carbon capture and storage operations. The findings of this study provide critical insights into hydrate phase behavior, highlighting the importance of precise equilibrium determination under simulated reservoir conditions to effectively anticipate and mitigate hydrate formation challenges.

Experimental study on infrared detection of debonding in concrete-filled steel tubular structure under acceleratory period of hydration heat action

Concrete-filled steel tubular (CFST) Structures often face challenges with debonding during construction, which can markedly compromise the structural integrity. The hydration of concrete can generate significant heat during construction, making the infrared thermography as a potential method for the defect detection. However, effects of concrete hydration behavior, debonding size, and environmental factors on the infrared thermal imaging of CFST debonding remains unclear. This study conducted experiments using four different hydration heating rates and three debonding sizes to simulate debonding detection using infrared imaging during the hydration phase of CFST. The feasibility of the simulation approach was validated through pair-to-pair comparison, and multiple linear regression analysis was employed to evaluate the impact of these factors. The findings highlight that absolute temperature difference has the most significant impact on detection effectiveness regardless of interaction effects. In regression models without interaction, heating rate demonstrated the least impact, Whereas the model considering the interaction showed that the interaction effect of heating rate and debonding size showed a secondary effect. Further examination indicated that interaction effects decrease as heating rate and debonding size decrease.

Hydrogen purification via hydrate-based methods: Insights into H2-CO2-CO hydrate structures, thermodynamics, and kinetics

Hydrate-based H2 purification is promising for removing impurities owing to the cage-like structures formed by water molecules. Understanding the competition mechanism of multicomponent gas molecule in hydrate is critical for improving gas purification efficiency. This study investigated the hydrate structure, thermodynamics, and kinetics of ternary gas mixture (H2–CO2–CO) from natural gas reforming products. The results identified H2–CO2–CO hydrate as type sI and determined the lattice parameters using X-ray diffraction. Raman spectroscopy results confirmed the presence of H2, CO2, and CO gas molecules in the hydrate phase. Increasing pressure, compared to cooling, enhanced CO2 content in hydrate phase. The phase equilibrium conditions and average hydrate dissociation enthalpy (53.47 J/g) were determined using a high-pressure microcalorimeter. Gas chromatography identified that the content of CO2 in the hydrate was the highest, followed by H2, and CO was the least abundant. The molecule dynamics simulation results show CO2 molecule numbers reflected trends in 51262 cages, H2 numbers correlated with changes in 512 cages, while CO numbers showed insignificant variation. Under the gas composition studied, the ability of gas molecules to be incorporated within hydrates decreases in the following order: CO2, H2, and CO.

Phase equilibria and guest gas occupancy characteristics of H2-DIOX sII hydrates based on calorimetric and Raman analysis

Hydrogen (H2) as the most abundant element offers a clean energy solution for a sustainable future. Thermodynamic hydrate promoters can enhance hydrate-based H2 storage under mild pressure conditions. 1,3-dioxolane (DIOX) as a low-toxicity promoter has attracted attention for its potential to improve H2 hydrate kinetics. However, the phase equilibria of H2-DIOX in the presence of DIOX and its thermodynamic promotion mechanism are not fully elaborated and warrant thorough investigation. In this study, the phase equilibria of H2-DIOX hydrates were measured for DIOX concentrations (CDIOX) ranging from 2.0 mol% to 5.56 mol%. The equilibrium temperature of H2-DIOX hydrates shifted rightward by 2.3 K at 15.0 MPa for 5.56 mol% DIOX compared to 2.0 mol% DIOX. The measured thermodynamic data were validated by fitting the H2-DIOX hydrate phase equilibira using the Clausius–Clapeyron equation. The cage occupancy of H2 and DIOX in H2-DIOX sII hydrates was revealed through Raman spectroscopy and DSC thermal analysis. Two types of hydrates (DIOX and H2-DIOX) were observed for all CDIOX. Single H2 molecules were enclathrated in the 512 cages of H2-DIOX hydrates and increasing CDIOX effectively enhanced DIOX molecules enclathration in the 51264 cages but had limited effect on the H2 molecules in the 512 cages. The findings of this study provide fundametnal thermodynamic data and cage occupancy charateristics for H2-DIOX sII hydrates below 15.0 MPa. The results provide guidance on the optimal thermodynamic promoter concentrations for future large-scale hydrate-based H2 storage application.

Hydrate formation and its influence on natural gas pipeline: Simulation study

Natural gas transportation is plagued with the twin problem of hydrate and corrosion that occurs when a hydrate prone gas is conveyed in such a manner that the pipeline operating conditions fall within hydrate formation region of the hydrate phase envelop. This study simultaneously studied this twin problem, establishing their interdependent using gas sample from Niger Delta that was meticulously simulated and analysed for hydrate formation possibilities with the aid of Unism software. CO2 corrosion was simulated using NORSOK M-506 standard model in matlab. Major factors considered are the relationship between corrosion rate and temperature, corrosion rate and PH, corrosion-temperature relationship for varying CO2 mole percent, and PH values. The result from this study established that both type I and type II hydrates could form at the operating conditions of 5OC and 60 bar. Rate of corrosion decreases and increases with increase in PH and temperature respectively to a certain temperature of approximately 78 OC, then a dip in rate of corrosion. Corrosion-temperature relationship for varying PH and CO2 mole percent shows a decrease in corrosion rate with an in increase in PH, and an increase with increase in CO2 mole percent, with a rise as high as 5,7 mm/year at a 3 mole percent. This value and trend portray a bad omen for the affected pipeline. This study recommends that natural gas to be transported by pipeline should be sweetened and processed to remove H2S, CO2 and mercaptans if present and also to satisfy maximum dew point specification.

Study of hydrophobic cemented paste backfill (H-CPB) to prevent sulphate attack

One of the challenges encountered in mining is acid mine drainage (AMD) in sulphurous ores in response to rainfall and groundwater. CPB one of the most prevalent waste management systems addresses this issue today. Nevertheless, in the long term, the concretion in CPB may become ineffective because of external factors, such as groundwater and rainfall. The relevant sources in the literature have no mention of AMD problems that may occur in the long term with CPB, particularly in metallic ores. Most studies indicate that the issue which can be prevented by using cement. However, due to the destructive effects of nature, cement alone would be insufficient. Consequently, the research's principal aim is to form CPB hydrophobic, thereby reducing the interaction between CPB and water. In the study, stearic acid was chosen as the hydrophobic agent and application method to the CPB and the changes in load-bearing capacity were studied. Specimens were tested by ion chromatography, X-ray diffraction (XRD), elemental analysis by combustion, water absorption, uniaxial compressive strength (UCS), and scanning electron microscopy (SEM). There was a decrease in the load-bearing capacity while gaining the hydrophobic properties of the material. The results confirm the validity of the selected agent and method and reveal that the effect of sulphate decreases with increasing hydrophobicity yet, there is no significant decrease in the 7, 14, and 28-day UCS tests. The optimal results were achieved when Stearic Acid (SA) was used at a concentration of 1.25 % for 7 % Portland cement and 0.75 % for 11 % Portland cement, with a UCS strength of 1.223 and 2.008 MPa, respectively. The expected benefit of stearic acid was realized as the water absorption value of the reference sample was 2.50 times higher in 7 % cement and 4.25 times higher in 11 % cement than the same value in Hydrophobic Cemented Paste Backfill (H-CPB). These results indicate that AMD formation can be prevented in the future with H-CPB. The results demonstrate that stearic acid, with the new methodology, forms the CPB hydrophobic, while only an acceptable strength loss was observed. Additionally, the outcomes point out that the methodology adopted does not consider a significantly adverse impact on hydration phase of concretation and can be utilized as an environmentally friendly backfilling method, thereby being evaluated as the cleaner backfilling for further CPB applications.

A Combined Experimental and Computational Study on the Effect of the Reactor Configuration and Operational Procedures on the Formation, Growth and Dissociation of Carbon Dioxide Hydrate

Clathrate hydrate-based technologies are considered promising and sustainable alternatives for the effective management of the climate change risks related to emissions of carbon dioxide produced by human activities. This work presents a combined experimental and computational investigation of the effects of the operational procedures and characteristics of the experimental configuration, on the phase diagrams of CO2-H2O systems and CO2 hydrates’ formation, growth and dissociation conditions. The operational modes involved (i) the incremental (step-wise) temperature cycling and (ii) the continuous temperature cycling processes, in the framework of an isochoric pressure search method. Also, two different high-pressure PVT configurations were used, of which one encompassed a stirred tank reactor and the other incorporated an autoclave of constant volume with magnetic agitation. The experimental results implied a dependence of the subcooling degree, (P, T) conditions for hydrate formation and dissociation, and thermal stability of the hydrate phase on the applied temperature cycling mode and the technical features of the utilized PVT configuration. The experimental findings were complemented by a thermodynamic simulation model and other calculation approaches, with the aim to resolve the phase diagrams including the CO2 dissolution over the entire range of the applied (P, T) conditions.

How shallow CO2 hydrate cap affects depressurization production in deeper natural gas hydrate reservoirs: An example at Site W17, South China Sea

The logging results from the Shenhu Sea show that the P-T conditions of NGH deposits are below the CO2 hydrate phase equilibrium curve. The burial depth difference between the CO2 hydrate stable zone and NGH deposits is usually above 100 m, which differs from the laboratory scale. Thus, whether CO2 hydrate caps can provide pore sealing and reinforcement of natural gas hydrate (NGH) overburden at the engineering scale is unknown. Based on this, we aimed to perfect research on the CO2 hydrate cap, including its formation process, effects on NGH exploitation, geomechanical response, and comprehensive benefit evaluation, by establishing a THMC model based on Site W17. Results indicate that (i) CO2 can form hydrates in the overburden layer with a conversion rate of about 28%, preventing the upward escape of residual liquid CO2 due to density difference. (ii) CO2 injection and CO2 hydrate cap formation can increase the decomposition driving force during depressurization to enhance production, but it fails to inhibit water invasion from the upper part of the NGH deposit due to the excessive depth difference. (iii) The CO2 hydrate cap causes strata uplift, thereby mitigating strata subsidence during depressurization production, especially for the cases of horizontal wells, where the subsidence is reduced by about 103.4%. (iv) Injecting too much CO2 may not benefit gas production, where part of the free gas will convert into NGH due to pressure rise. The optimal injection rate in this study is 40,000 m3/d. (v) Indicators like CO2 hydrate conversion rate, gas-water ratio, and maximum strata displacement show that horizontal well systems with CO2 hydrate caps are more beneficial than vertical well systems, and multi-branched well systems are more beneficial than single-direction well systems. These key findings may differ from the laboratory scale, which can provide a reference for applying CO2 hydrate caps in actual NGH exploitation.