Natural Gas Recovery Research Articles

Robust Metal–Organic Frameworks with High Industrial Applicability in Efficient Recovery of C3H8 and C2H6 from Natural Gas Upgrading

Developing efficient adsorbents with high uptake and selectivity for separation and recovery of C 2 H 6 and C 3 H 8 from natural gas is an important but challenging task. In this work, we demonstrate that high surface polarity and suitable pore diameter are two key factors that can synergistically enhance the separation performance, exemplified by metal–organic framework (MOF)-303 and MIL-160 (MIL: Matériaux de l’Institut Lavoisier), both possessing one-dimensional (1D) open channels with high density of heteroatoms and desired pore size (5∼7 Å). Significantly, the uptake of MOF-303 for C 3 H 8 is up to 3.38 mmol g −1 at 298 K and 5 kPa with a record-high C 3 H 8 /CH 4 (5:85, v/v) ideal adsorbed solution theory (IAST) selectivity of 5114 among all reported MOFs. In addition, MOF-303 also displays high C 2 H 6 uptake capacity (at 10 kPa) and C 2 H 6 /CH 4 (10:85, v/v) selectivity, reaching 1.59 mmol g −1 and 26, respectively. Owing to the larger pore diameter and lower density of heteroatoms within its 1D channels, MIL-160 shows apparently lower uptake and selectivity compared to those of MOF-303, though the values exceed those of majority of reported MOFs. Density functional theory (DFT) calculations verify that the high surface polarity and the suitable pore diameter synergistically enhance the affinity of the frameworks toward C 3 H 8 and C 2 H 6 , giving rise to the high loading capacity and selectivity for C 3 H 8 and C 2 H 6 . Both MOFs feature remarkable moisture stability without structural change upon exposure to 95% relative humidity (RH) for a month. In addition, synthesis of both compounds can be readily scaled up through one-pot reactions to afford about 5 g samples with high crystallinity. Finally, the substantial potential of MOF-303 and MIL-160 as advanced adsorbents for efficient separation of C 3 H 8 /C 2 H 6 /CH 4 has been demonstrated by ternary breakthrough experiments, regeneration tests, and cyclic evaluation. The excellent separation performance, high stability, low cost, and good scalability endow both MOFs promising adsorbents for natural gas purification and recovery of C 2 H 6 and C 3 H 8 .

A Multi-medium and Multi-mechanism model for CO2 injection and storage in fractured shale gas reservoirs

Under the background of “dual-carbon”, it is strategically significant to use shale gas reservoirs for CO2 injection and storage. Injection of CO2 into shale formations can improve natural gas recovery and achieve effective storage of CO2. However, due to the complex characteristics of shale reservoirs, like complex fractures and a variety of flow mechanisms, few work has been done to comprehensively consider those complex characteristics for accurate reservoir simulation of CO2 injection and storage. Therefore, to improve this situation, this paper establishes a fully coupled model of the matrix, natural fracture and hydraulic fracture, which considers multiple mechanisms, including adsorption/desorption, diffusion, stress sensitivity of fracture and stimulated reservoir volume (SRV). The embedded discrete fracture model (EDFM) is applied to describe the transfer flow between matrix-fracture, fracture-fracture and fracture-well. The finite volume and quasi-Newton iterative methods are used to solve the model. The model's reliability and practicability are verified by matching the production history of commercial software in shale gas reservoirs. The effects of various factors on the production curve and CO2 storage characteristics are analyzed, including adsorption/desorption, diffusion, stress sensitivity, well production pressure, CO2 injection rate, CO2 injection opportunity and fracture parameters. The results show that the model is reliable and practical and can be used to study the dynamic performances of enhanced shale gas recovery and CO2 storage.

Quantification of Amines in Refinery Process Water via Surface-Enhanced Raman Spectroscopy

Amines are used in crude oil production, natural gas recovery, and hydrocarbon refining as hydrogen sulfide scavengers, corrosion inhibitors, and pH control neutralizers. Residual amines can be detrimental to the refining process, such as forming heat-stable salts that lead to corrosion-inducing deposits or causing nitrification of wastewater streams. Traditional methods for amine analysis such as ion chromatography are complex, time-consuming, and not adapted to field deployment. We present a new method using surface-enhanced Raman spectroscopy for amine quantification with a focus on two problem-causing tramp amines: monoethanolamine and methylamine. This method is calibration-free, accurate across spectrometers, stable over years in laboratory-standard solutions and in real-world process samples, and can be performed by minimally trained operators within less than 5 min.

Review on the Mechanism of CO2 Storage and Enhanced Gas Recovery in Carbonate Sour Gas Reservoir

Carbonate gas reservoirs in the Sichuan Basin have many complex characteristics, such as wide distribution, strong heterogeneity, high temperature, high pressure, high H2S and CO2 content and an active edge or bottom water. In the late stage of exploitation of carbonate sour gas reservoirs, the underground depleted reservoirs can provide a broad and favorable space for CO2 storage. If CO2 is injected into the depleted carbonate sour reservoirs for storage, it will help to achieve the goal of carbon neutrality, and the CO2 stored underground can perform as “cushion gas” to prevent the advance of edge or bottom water, to achieve the purpose of enhanced natural gas recovery. Injecting CO2 into low permeability reservoirs for oil displacement has become an important means to enhance oil recovery (EOR). However, the mechanism of EOR by injecting CO2 into carbonate sour gas reservoirs is not clear and the related fundamental research and field application technology are still in the exploration stage. This paper reviews the main scientific and technical perspectives in the process of injecting CO2 into carbonate sour gas reservoirs for storage and enhancing gas recovery.

The role of microbial ecology in improving the performance of anaerobic digestion of sewage sludge.

The use of next-generation diagnostic tools to optimise the anaerobic digestion of municipal sewage sludge has the potential to increase renewable natural gas recovery, improve the reuse of biosolid fertilisers and help operators expand circular economies globally. This review aims to provide perspectives on the role of microbial ecology in improving digester performance in wastewater treatment plants, highlighting that a systems biology approach is fundamental for monitoring mesophilic anaerobic sewage sludge in continuously stirred reactor tanks. We further highlight the potential applications arising from investigations into sludge ecology. The principal limitation for improvements in methane recoveries or in process stability of anaerobic digestion, especially after pre-treatment or during co-digestion, are ecological knowledge gaps related to the front-end metabolism (hydrolysis and fermentation). Operational problems such as stable biological foaming are a key problem, for which ecological markers are a suitable approach. However, no biomarkers exist yet to assist in monitoring and management of clade-specific foaming potentials along with other risks, such as pollutants and pathogens. Fundamental ecological principles apply to anaerobic digestion, which presents opportunities to predict and manipulate reactor functions. The path ahead for mapping ecological markers on process endpoints and risk factors of anaerobic digestion will involve numerical ecology, an expanding field that employs metrics derived from alpha, beta, phylogenetic, taxonomic, and functional diversity, as well as from phenotypes or life strategies derived from genetic potentials. In contrast to addressing operational issues (as noted above), which are effectively addressed by whole population or individual biomarkers, broad improvement and optimisation of function will require enhancement of hydrolysis and acidogenic processes. This will require a discovery-based approach, which will involve integrative research involving the proteome and metabolome. This will utilise, but overcome current limitations of DNA-centric approaches, and likely have broad application outside the specific field of anaerobic digestion.

MIL-101-Cr/Fe/Fe-NH2 for Efficient Separation of CH4 and C3H8 from Simulated Natural Gas.

Adsorptive separation based on porous solid adsorbents has emerged as an excellent effective alternative to energy-intensive conventional separation methods in a low energy cost and high working capacity manner. However, there are few stable mesoporous metal-organic frameworks (MOFs) for efficient purification of methane from other light hydrocarbons in natural gas. Herein, we report a series of stable mesoporous MOFs, MIL-101-Cr/Fe/Fe-NH2, for efficient separation of CH4 and C3H8 from a ternary mixture CH4/C2H6/C3H8. Experimental results show that all three MOFs possess excellent thermal, acid/basic, and hydrothermal stability. Single-component adsorption suggested that they have high C3H8 adsorption capacity and commendable selectivity for C3H8 and C2H6 over CH4. Transient breakthrough experiments further certified the ability of direct separation of CH4 from simulated natural gas and indirect recovery of C3H8 from the packing column. Theoretical calculations illustrated that the van der Waals force proportional to the molecular weight is the key factor and that the structural integrity and defect can impact separation performances.

Full coupling of CO2–CH4 transport and sorption with solid deformation in gas shale enhances natural gas recovery and geological CO2 storage capacity

A thermodynamically rigorous constitutive model is used to describe the full coupling among the nonlinear processes of transport, sorption, and solid deformation in organic shale where the pore fluid is the binary mixture of carbon dioxide and methane. The constitutive model is utilized in a numerical solution that simulates injection of carbon dioxide in shale before producing carbon dioxide and methane from the same. The solution considers advection and diffusion as viable mechanisms of pore fluid transport where the latter comprises molecular, Knudsen, and surface diffusion in ultralow permeability shale. Results indicate that gas adsorption would be the main storage mechanism of sequestration in shale which may comprise up to 70% of the stored CO2 mass. A third of this storage capacity could be due to the geomechanical effects. Therefore, complete or partial exclusion of the coupling between sorption and solid phase deformation from the solution would result in underestimation of carbon dioxide storage capacity and natural gas recovery factor of the rock. Surface diffusion, sorption-induced deformation, as well as strain-induced changes in gas sorption capacities, are all conducive to both outcomes. Sensitivity analysis shows that the solution results are most sensitive to changes in adsorption capacities, followed by initial permeability, Young's modulus, Poisson's ratio, surface diffusivities, and initial pore radius.

Developing offshore natural gas hydrate from existing oil & gas platform based on a novel multilateral wells system: Depressurization combined with thermal flooding by utilizing geothermal heat from existing oil & gas wellbore

Offshore natural gas hydrate (NGH) is universally recognized as a new alternative energy resource. If methods can be found to commercially exploit it, it is expected to significantly impact the world's energy supply. In this work, an innovative method for developing offshore NGH from existing oil & gas platform is proposed, namely depressurization combined with thermal flooding utilizing geothermal heat from existing oil & gas wellbore based on a novel multilateral wells system. Meanwhile, a numerical simulation model is developed to investigate the natural gas recovery performance of the proposed method. The study shows that the average NGH concentration of the whole NGH bearing layer is reduced by about 25% after one year production by utilizing the innovative method, and 1.6 × 107 m3 natural gas is produced. Bottom hole pressure is the main controlling factor in the initial stage of NGH dissociation, while the formation temperature is the main controlling factor for the dissociation of NGH in the later stage of production, and increasing the fluid injection rate is an effective means to enhance the production performance. The study also shows that the production mode of continuous injection-intermittent production has the highest cumulative natural gas production, its production performance is proved to be the best.

Experimental Evaluation of Water Control for Continuous Packer in Buried Hill Fractured Gas Reservoir: A Case Study of HZ 26-6 Condensate Gas Field

Abstract Although research into water control completion techniques is now relatively mature, there are still difficulties in controlling water in fractured gas reservoirs in the sea. Unlike oil reservoirs, submerged gas reservoir development still faces some problems. To explore the water control mechanism of buried hill fractured gas reservoir, based on the parameters of well HZ26-6-2 in HZ 26-6 condensate gas field, the water control experiment of the continuous packer in the bottom water gas reservoir was completed through the design of experimental parameters, the design of buried hill fractured formation, and the process design of continuous packer. Studies have shown that the continuous packer water control technology delays the water coning rate and makes the water propulsion more uniform. The water breakthrough time and gas production are slightly different for different fractured gas reservoirs, and the network fracture model has a short gas recovery period and fast gas production speed. Continuous packer water control can improve natural gas recovery by 14.3% in fractured gas reservoir. Based on fracture dredging ability, sand accumulation and filling degree, and drilling and production strategy, the influencing factors of horizontal well water control effect in buried hill fractured gas reservoir are discussed and summarized. The research results are aimed at establishing a development model of water control for buried hill gas reservoirs and providing good technical support for rational and scientific water control of horizontal Wells in offshore condensate gas fields. The findings of this study can help for a better understanding of water control of horizontal wells in offshore condensate gas fields.

Supercritical carbon dioxide enhanced natural gas recovery from kerogen micropores

As the global energy demand increases, a sustainable and environmentally friendly methane (CH4) extraction technique must be developed to assist in the transition off of fossil fuels. In recent years, supercritical carbon dioxide (CO2) has been poised as a candidate for enhanced gas recovery (EGR) from CH4-rich source rocks, potentially with the reservoir serving as a carbon sink for CO2. However, the underlying molecular-scale mechanisms of CO2-EGR processes are still poorly understood. Using constant chemical potential molecular dynamics (CμMD), this study investigates the CH4 recovery process via supercritical CO2 injection into immature (Type I-A) and overmature (Type II-D) kerogens in real-time and at reservoir conditions (365 K and 275 bar). A pseudo-second order (PSO) rate law was used to quantify the adsorption and desorption kinetics of CO2 and CH4. The kinetics of simultaneous adsorption/desorption are rapid in immature kerogen due to better connected pore volume facilitating fluid diffusion, whereas in overmature kerogen, the structural heterogeneity hinders fluid diffusion. Estimated second order kinetic rate coefficients reveal that CO2 adsorption and CH4 desorption in Type I-A are about two times and an order of magnitude faster, respectively, compared to those of in Type II-D. Furthermore, overmature Type II-D kerogen contains inaccessible micropores which prevent full recovery of CH4. For every CH4 molecule replaced, at least two and six CO2 molecules are adsorbed in Type-II-D and Type I-A kerogens, respectively. Overall, this study shows that CO2 injection can achieve 90 % and 65 % CH4 recovery in Type I-A and Type II-D kerogens, respectively.

Study on the influence of various factors on dispersion during enhance natural gas recovery with CO2 sequestration in depleted gas reservoir

In CO2 enhanced gas recovery (EGR), physical dispersion occurs between CO2 and natural gas, which can pollute the produced natural gas. Therefore, accurate assessment of the dispersion process is important for the commercialization of EGR. Under reservoir conditions, the effects of gravity, impurities, and other factors on dispersion in porous media were systematically evaluated. Comparison of the apparent dispersion characteristics of sandstone and unconsolidated cores (sandpacks) revealed that the vertically upward dispersion coefficient was smaller owing to the greater permeability and homogeneity of the sandpacks. With horizontal and vertically downward displacement of CO2–CH4, gravity promotes CO2–CH4 dispersion. However, dispersion was suppressed with vertically upward displacement (opposite to the direction of gravity). Under the same experimental conditions, pure N2 exhibited greater dispersion than CO2 as a displacing fluid. Finally, CO2 was used to displace natural gas containing different impurities. The results show that the more impurities (CO2, C2H6) exist in the displaced phase, the greater the mixing degree in the displacement process and the larger the dispersion coefficient.

Experimental investigation on the mechanism of low permeability natural gas extraction accompanied by carbon dioxide sequestration

The injection of CO2 into natural gas reservoir is regarded can increase natural gas recovery accompanied with CO2 sequestration. In this work, we first demonstrated that the gas adsorption ability in the sampled plunger low permeability sandstone core was only about 1/10 of that in the core powders, the former was more representative for use. The existence of bound water substantially weakened the gas adsorption in the core. The CO2 diffusion coefficients in low permeability cores were in the order of 10−8-10−9 m2/s, which increased with decreasing pressure but dramatically decreased with the existence of bound water. Last, long core experiments for natural gas recovery through CO2 flooding showed that the CO2 injection substantially increased the natural gas recovery ratio R. And we for the first time demonstrated that due to the higher CO2 density than that of natural gas through experiments, the CO2 injection at the relative low position showed higher R than that at the high injection position. And with the highest CO2 sequestration amount (M) reached 64.36 kg/m3. The injection of CO2 into low permeability natural gas reservoir to realize both natural gas recovery and CO2 sequestration are tested feasible and effective.

Molecular dynamics of CH4/CO2 on calcite for enhancing gas recovery

AbstractThe effect of temperature and pressure on the adsorption of CO2 and CH4 gases on calcite (104) has been studied by means of classical molecular dynamics. The results show that carbon dioxide greatly improves methane desorption in the 323–373 K range, even at low CO2 concentrations. However, this effect is less pronounced for very high temperatures (423 K), where most of the methane is desorbed and CO2 tends to desorb in large quantities. Radial distribution function (RDF) analysis reveals two distinct peaks for CO2 (0.36 and 0.47 nm) and two for methane (0.87 and 0.57 nm) and the intensities of these peaks tend to decrease with increasing temperature. Such peaks are always clearly visible for CO2, while the methane profile gets very broad already for mild conditions of temperature and CO2 concentration. These results highlight how the CO2 geometry of adsorption is well defined and characterized by strong interaction, while methane adsorption is quite loose and depicts a very dynamic picture. Focusing on the effect of pressure, RDF peaks intensities increase, although this effect is limited to the 1–5 MPa range. Moreover, the high CO2 presence further decreases the effect of pressure on methane adsorption. In fact, from pure methane to 20/80 CO2/CH4, methane adsorption increases linearly with pressure. For gas mixtures with a CO2 concentration higher than 40%, higher pressure has less impact on methane adsorption. Overall, the results obtained yield important details to tune the gas composition and conditions for efficient and enhanced natural gas recovery and sequestration of CO2.

Unlocking the limits of diffusion and adsorption of metal-crosslinked reduced graphene oxide membranes for gas separation

Reduced graphene oxide (rGO) membranes have shown promising separation and purification in the fields of water treatment and gas capture due to their unique physicochemical characteristics. However, how to further reduce the transport resistance of rGO membranes and improve separation performance is still a thorny issue. In this work, the reported metal-crosslinked rGO membranes showed a reverse-selective separation behaviors for the adsorbed gas molecules at low pressure. The effect of metal ions on the membrane structure and the separation performance were investigated. Metal ions not only can improve the cross-linking structure and control interlamellar spacing of rGO membranes for the precise molecular sieve, but also can provide abundant metal sites to enhance the affinity, which led to a diffusion-controlled process for the targeted gas molecules. The resulting metal-crosslinked rGO membranes presented outstanding gas permeance and selectivity for gas pairs of the He/CO2, N2/CO2 and Kr/Xe, with the highest selectivity of 21, 11.4 and 4.1, respectively. The work will provide a new avenue towards specific molecule capture for the development of rGO membranes in the fields of natural gas purification and radioactive gas recovery.

Characteristics of Pore-Throat in Tight Sandstones of the Jurassic Ahe Formation in the Northern Tarim Basin

In order to clarify the characteristics of pore-throat in tight sandstone reservoirs in the Dibei area of the Kuqa Depression in the Tarim Basin (Northwest China) and to make clear its impact on reservoir quality and productivity, microscopic observation and quantitative analysis of 310 tight sandstones in the Kuqa Depression are carried out by using various methods. Microscopic observation shows that the shapes of the pores are flat, oval, and long-narrow. A great number of throats connect the nanoscale pores in the form of a network. Quantitative analyses including RCMP (rate-controlled mercury penetration), HPMI (high-pressure mercury injection), NA (nitrogen adsorption), and routine and stress-dependent core analysis show that the peak of pores radius ranges from 125 μm to 150 μm, and the throat radius is in the range of 1 μm-4 μm. The throat space accounts for about 2/3 of the total space of the tight sandstones, which is the major storage space for natural gas. The space shape has a great influence on the reservoir seepage capacity, particularly under the condition of overburden pressure. The pores with throat radius greater than 300 nm have free fluid, and they contribute more than 98% of the reservoir permeability. The pore spaces with throat radius among 300 nm-52 nm can release fluids by reservoir stimulation. The pore-throats with radius < 52 nm cannot release the irreducible hydrocarbon fluids. In addition, formation pressure is easy to destroy tight sandstone reservoir. The research results will provide insights into the efficient recovery of natural gas in tight sandstones.

Numerical Simulation and Optimization of CO2-Enhanced Gas Recovery in Homogeneous and Vertical Heterogeneous Reservoir Models

Abstract CO2-enhanced gas recovery (CO2-EGR) is a promising, environment-friendly technology to produce more natural gas from depleted reservoirs and simultaneously sequester CO2. The subsurface flow in the heterogeneous reservoir is usually different from homogenous one, and the heterogeneity significantly affects the gas recovery. The effects of heterogeneity and the optimization of CO2 injection strategy are the key factors in CO2-EGR. Thus, one of the goals of this paper is to conduct simulations of CO2-EGR in both homogeneous and heterogeneous reservoirs to evaluate the effects of reservoir heterogeneity on CO2-EGR. The second goal is to perform optimization studies to determine optimal CO2 injection time and injection rate for achieving optimal natural gas recovery. The CO2-EGR simulations were conducted in a 3D reservoir model with a 'five-spot' well pattern by using the multi-phase simulator TOUGH2. The results show that the layers with low permeability as well as gravity segregation retard upward migration of CO2 and promote horizontal displacement efficiency. The breakthrough time of CO2 and reservoir space of underexploited natural gas directly affect the gas recovery. The optimal injection time is determined as the depleted stage, and the corresponding injection rate is optimized by using a genetic algorithm (GA) integrated with TOUGH2. The optimization of CO2 injection parameters leads to recovery factors (RFs) reaching 62.83% and 64.75% in the homogeneous and heterogeneous cases while simultaneously obtaining the economic benefit of about 8.67 and 8.95 million USD. This study shows significant economic potential as well as environmental benefits of using CO2-EGR in the depleted gas reservoir by optimizing the CO2 injection parameters. The findings of this work could assist in determining the optimal injection strategy for using CO2-EGR in industrial scale gas reservoirs.

Methane separation and capture from nitrogen rich gases by selective adsorption in microporous Materials: A review

The rapid increase of natural gas consumption has induced imbalance between supply and demand of natural gas, and the continuous growth of methane emissions has severely exacerbated greenhouse effects and destroyed the atmospheric methane cycle. High-efficiency CH4 capture and separation from N2 rich gases has become a significant challenge for the recovery and utilization of low-grade natural gas and also industrial tail gas, which was important for sustainable energy and environment and attracted much attention from both researchers and engineers in recent years. This review provides an overview of selective separation techniques for N2 removal from natural gas including the benefits and drawbacks of these typical methods. Most notably, the review primarily outlines the progress of metal–organic frameworks, zeolites and activated carbons as superior adsorbents for separating CH4-N2 mixtures in worldwide laboratories, respectively, with an emphasis on the relationship of the pore size, surface chemistry and composition of adsorbents with the CH4/N2 selectivity and methane capacity. We also highlight the potential for the development of the new adsorbents with the best possible matching between aperture control and atomic-scale tuning of the composition for CH4 capture and separation from N2 rich gases, and indicate that the MOFs possess both the advantages of activated carbons and zeolites and will become one of the most promising candidates for high-efficiency CH4 separation from N2 rich gases in the future.

Full Coupling of Co2-Ch4 Diffusion and Sorption with Solid Deformation in Gas Shale Enhances Natural Gas Recovery and Geological Co2 Storage Capacity

Full Coupling of Co2-Ch4 Diffusion and Sorption with Solid Deformation in Gas Shale Enhances Natural Gas Recovery and Geological Co2 Storage Capacity

A review of research on the dispersion process and CO2 enhanced natural gas recovery in depleted gas reservoir

The dispersion coefficient is a key physical parameter for enhanced gas recovery (EGR) and reflects the degree of mixing between the displacing-fluid CO2 and natural gas. However, no comprehensive overview of existing research on EGR dispersion characteristics has been conducted to date. In this review article, previous experimental and simulation studies are summarized to provide an overview of the current research progress and, hence, to elucidate the limitations of EGR and identify directions for future research. The literature analysis reveals that temperature and flow rate promote CO2–CH4 dispersion, whereas pressure and residual-water salinity inhibit dispersion under supercritical conditions. The CO2–CH4 dispersion coefficient is smaller in porous media with high permeability. However, on the core scale, the effects of residual water on the CO2 dispersion and breakthrough time are controversial and further verification is required. To date, only limited research has been conducted on the effects of impurities under supercritical conditions, such as considering CO2 containing N2, and CH4 containing CO2, N2 and ethane. Existing pilot EGR trials are insufficient to provide standardized field operation instructions, for example, with regard to the wellhead layout. Field-scale simulations have verified the feasibility of EGR technology and economy. However, factors such as the permeability heterogeneity, initial water saturation distribution, connate water salinity, gas-reservoir non-isothermal conditions, and vertical stratification should be considered in simulations of actual gas reservoirs. More in-depth experimental and simulation-based investigations of EGR should be performed on various scales to accurately assess the dispersion characteristics and natural-gas recovery efficiency under gas-reservoir conditions.

Strengthening and weakening of methane hydrate by water vacancies

Gas clathrate hydrates show promising applications in sustainable technologies such as future energy resources, gas capture and storage. The stability of clathrate hydrates under external load is of great crucial to those important applications, but remains unknown. Water vacancy is a common structural defect in clathrate hydrates. Herein, the mechanical characteristics of sI methane hydrates containing three types of water vacancy are investigated by molecular dynamics simulations with four different water forcefields. Mechanical properties of methane hydrates such as tensile strength are dictated not only by the density but also the type of water vacancy. Surprisingly, the tensile strength of methane hydrates can be weakened or strengthened, depending on the adopted water model and water vacancy density. Strength enhancement mainly results from the formation of new water cages. This work provides critical insights into the mechanics and microstructural properties of methane clathrate hydrates under external load, which is of primary importance in the recovery of natural gas from methane hydrate reservoirs. Cited as: Lin, Y., Liu, Y., Xu, K., Li, T., Zhang, Z., Wu, J. Strengthening and weakening of methane hydrate by water vacancies. Advances in Geo-Energy Research, 2022, 6(1): 23-37. https://doi.org/10.46690/ager.2022.01.03