Methane Gas Recovery Research Articles

The effects of rhamnolipid on the formation of CH4 hydrate and separation of CH4/N2 via hydrate formation

Rhamnolipid (Rha) is an efficient green surfactant that is able to promote hydrate generation, it can be applied to the hydrate method of separating. However, the effect of rhamnolipid on the separation of methane and nitrogen by the hydrate method is not clear. Therefore, in this paper, we investigated the effect of rhamnolipid on methane hydrate formation and the separation between methane and nitrogen via hydrate method. Firstly, the effects of five concentrations (0 ppm, 200 ppm, 400 ppm, 600 ppm and 800 ppm), temperatures and pressures on methane hydrate formation were studied separately. The rate of methane hydrate formation was positively correlated with experimental pressure. The gas consumption increased rapidly with the rhamnolipid concentration, and then increased slowly to a steady state. The final gas consumption above 200 ppm rhamnolipid concentrations could be increased more than five times compared with pure water conditions. The promotion of methane hydrate production is most pronounced at 274.15 K, mainly depending on the diffusion of gas molecules in solution and the ease of hydrate nucleation. Then, the interfacial tension at different concentrations was measured by the suspension drop method, and the relationship between the interfacial tension and the rate of hydrate formation was studied. Hydrate formation rate shows a multiplicative power function with the interfacial tension. What’s more, the kinetics of hydrate formation and gas separation effect of 3:1 CH4/N2 at 274.15 K and 7 MPa were studied with five concentrations. And 200 ppm was found to be the optimum concentration for separation, the separation factor is 8.25. Finally, the kinetics and thermodynamics of hydrate formation and gas separation effect of 1:1 CH4/N2 at 274.15 K and 9 MPa were also investigated, and the separation factor reached a maximum of 12.7 at 800 ppm, and the methane gas recovery rate also reached the maximum at 40.46%. The results of this study can provide some theoretical guidance for the optimal selection of green surfactants in separation by hydrate method.

CH4/N2Adsorptive Separation by a ZSM-5 Zeolite Packed Multicolumn VPSA Process with the SMB Operation Mode for High-Purity Methane Production

ZSM-5 zeolites with a high Si/Al molar ratio are commercially available sorbents with a high specific surface area, well-developed microporous structure, good hydrophobic properties, and water resistance, which would be safer and more efficient sorbents to deal with the recovery of flammable methane gas from coalbed gas, shale gas, etc. In this article, ZSM-5 zeolites are used as sorbents, matched with the multicolumn vacuum pressure swing adsorption (VPSA) process with the simulated moving bed (SMB) operation mode to separate CH4/N2 for high-purity methane production. Based on the process design, five-column, six-column, and seven-column VPSA experimental apparatuses have been set up in the laboratory, which are operated with the SMB mode at a fully automatic control platform. According to experimental results, it is found that the switching time of inlet and outlet stream ports can be shortened, and the column number may be also reduced in the proposed VPSA process with ZSM-5 zeolites as sorbents. High-purity methane product gas (99% CH4) can be obtained continuously from 30–60% CH4 feed gas with an above 90% methane recovery efficiency and 1.06–1.64 mol/kg/h methane productivity at 250 kPa and ambient temperature by the developed VPSA process with ZSM-5 zeolites. Compared with our previous work using activated carbon sorbents, the separation performance of CH4/N2 by ZSM-5 zeolites is improved obviously, having a broad prospect for the recovery of low-grade methane gas from unconventional natural gases.

The Influence of Particle Size and Hydrate Formation Path on the Geomechanical Behavior of Hydrate Bearing Sands

Determining the geomechanical properties of hydrate-bearing sands (HBS), such as strength and stiffness, are critical for evaluating the potential for the economic and safe recovery of methane gas from HBS reservoirs. To date, results from numerous independent laboratory studies on synthesized HBS have shown that strength and stiffness are largely influenced by hydrate saturation, the method adopted for hydrate formation, and to a lesser extent, the confining stresses applied during testing. However, a significant scatter is observed in the data even when these conditions are similar. These include recent studies on natural HBS where sands with larger particle size distribution (PSD) exhibited higher strengths despite lower hydrate saturation. To investigate the impact of PSD, and the role that specific hydrate formation conditions might impose, on the strength and stiffness of HBS, a series of laboratory tests were carried out on sand specimens formed with different particle size distributions and utilizing different approaches for forming gas saturated HBS. The laboratory apparatus included a resonant column drive head to measure the small-strain stiffness of the specimen during hydrate formation, and subsequent drained compressional shearing to capture the stress-strain response of the HBS. Results indicate that the PSD significantly affects both the stiffness evolution (during hydrate formation) and peak strength at failure after formation compared to the effect of the methodology adopted for hydrate formation. These observations improve our understanding of the geomechanical behavior of laboratory-synthesized HBS and allow more robust relationships to be developed between them and natural HBS. This may aid in the development of economic and safe methane gas production methods to help realize the energy resource potential of HBS reservoirs.

Experimental study on the effect of hydrate reformation on gas permeability of marine sediments

Permeability is a crucial parameter determining methane gas recovery. Hydrate reformation has a significant impact on reservoir permeability during methane hydrate (MH) exploitation and it is often ignored. In this paper, the effect of hydrate reformation on gas permeability was investigated by remolded cores with different hydrate saturations and effective stresses. The results show that hydrate reformation exacerbates the heterogeneous distribution and reduces the reservoir permeability. The permeability damage rate (PDR) of hydrate reformation is greater than the hydrate first formation owing to the inhomogeneity of water caused by hydrate decomposition. When hydrate saturation is increased from 22.26% to 40.44%, the PDR range caused by hydrate formation varies from 19.89% to 98.02%. In addition, the permeability after hydrate decomposition decreases with increasing effective stress. When the effective stress is absent or small, the permeability after secondary decomposition is lower than the first decomposition at the same hydrate saturation. However, the opposite is true when the effective stress is reached 3 MPa. Due to the memory effect of MH in marine sediments, the hydrate reformation induction time is shorter and the reformation rate is faster. However, the gas consumption of the hydrate reformation is less than the first, causing lower hydrate saturation. This work supports the exploitation of gas hydrate and numerical simulation studies in marine sediments.

Coupled THMC modeling of dissociation induced deformation of gas hydrate bearing media

Methane gas recovery from hydrate bearing sediment (HBS) by depressurization causes significant pore pressure decrease, loss of solid load bearing hydrate from pores and small temperature drop. The decrease in pore pressure increases the effective compressive stress arising from overburden load on the HBS and thus causes the settlement of the HBS. The reduction of medium strength by the loss of load bearing hydrate and thermal contraction also influences the deformation of HBS. We have developed a THMC solver to simulate the complex geomechanics problem along with hydrate phase change kinetics, non-isothermal multiphase flow in porous media, and the alteration of porosity, permeability and bearing capacity. The deformation behavior of the hydrate-bearing media depends on the host sediment and hydrate morphology, effective porosity and critical porosity. We have included the influence of loss of load bearing hydrate and compaction due to increase of effective compressive stress as the result of pore pressure decrease, fraction of hydrate morphology, effective porosity and critical porosity on the effective medium bulk and shear moduli using a modified effective medium model. The effects of hydrate saturation decrease and effective compressive pressure increase on the deformation of HBS are thoroughly investigated. We have performed numerical simulations to understand the deformation behavior for different porosities and matrix supporting hydrate fractions. Our results show that the deformation is about 20% less when the fraction of matrix supporting hydrate increases from 0.1 to 0.4 because of increased soil bonding.

Retracted: CO2 Sequestration and Enhanced Shale Gas Recovery by CO2 Injection: Numerical Simulation Method

In previous decades, shale gas production has been given special attention as a clean source of energy. Technological advancements in multi-well especially horizontal drilling and hydraulic fracturing, have raised more research on how to produce shale gas commercially while studying its challenges. CH4 gas production by using CO2 injection is a combination of several parameters, including both fracking and geologic parameters. This paper investigated the influence of aligned and staggered multiwell placement patterns to enhance CH4 gas recovery and CO2 sequestration. A three-dimensional reservoir model was built and simulated, and the influence of reservoir and fracking parameters was analyzed. The results revealed that the staggered well pattern is the best pattern for CH4 gas recovery during continuous injection, with a 37% increase of recovery with late CO2 breakthrough, compared with the aligned well pattern, which had 31% increase recovery, associated with early CO2 breakthrough. In terms of CO2 gas storage, the aligned well pattern had a significant amount of CO2 storage during continuous injection and huff and puff injection by storing 4% more carbon dioxide during continuous injection and 7% more during huff and puff injection than that in the staggered well pattern. Different injection timings of 1, 2, and 3 years, and injection cycles of one, three, and five cycles were analyzed during huff and puff injection. The results showed that five cycles of injection had the highest methane gas recovery, 23% and 21%, in aligned and staggered well patterns, respectively. Furthermore, the influence of injection start time also was analyzed, and results showed that injection after 10 years of production produced higher methane gas recovery and CO2 storage in both aligned and staggered well patterns, followed by injection after 5 years of production, after 3 years of production, and during the first year of production. Sensitivity analysis revealed that horizontal matrix permeability, vertical matrix permeability, initial reservoir pressure, reservoir temperature, injection pressure, injection rate, fracture porosity, and fracture spacing played a vital role in both methane gas recovery and carbon dioxide gas storage in both well patterns. In addition, results showed that methane recovered during continuous injection is higher than during huff and puff injection in both aligned and staggered well patterns. Results obtained from this paper can help to improve shale gas production in multiwell placements, and save time and cost. This paper should motivate more research into the mitigation of global warming through CO2 geosequestration.

Converting Carbon Dioxide in to Methane Gas and Enhance Oil Recovery by using Biotechnology Process

Using biotechnology in petroleum industry has many advantages .for example , Microbiologically Enhanced Oil Recovery (MEOR) increase of the productivity of the oil field and decrease the viscosity of the crude oil . It's known that atmosphere has considerable amount of CO2 gas as a result of industrial activities (crude oil production). CO2 gas plays a role in increasing atmosphere temperature and causing global warming. Bioremediation is a viable Biotechnology function for Re-producing depleted wells and global warming. It means Bioremediation uses metabolic adaptation of microorganism, a promising approach, using this technique employs of Methanogenic bacteria to convert CO2 gas in to CH4. Therefore turns carbon dioxide in to carbon which is added to crude oil (so contribute decrease the viscosity for heavy crude oil, This mechanism is a part of the promotion of oil production.it is apart an operation EOR. and Second reacts with Hydrogen by Bacteria to produce methane gas. The aim study, advantage this method increase production. and removal global warming. In this review, we discuss the role of Methanogenic bacteria in transforming CO2 gas into methane gas , that it has a role in crude oil production . Methanogenic bacteria have an important role in petroleum industry and environment during decreasing CO2 amount in the atmosphere and increasing reservoir pressure. MEOR technology uses strains that have a role in crude oil production; these bacterial strains produce biogases (Methane) that increase reservoir pressure. In this study, six strains were isolated from Rumaila oilfield, south of Iraq. These strains were identified based on microscopic and morphological observations. These strains were Methanogenic bacteria. The main part of this study includes identification of bacteria that can consume CO2 gas and making continual lab experiments to isolate and determine the best genus to do this process in oil field. Experiments were done in specific bio-labs for two years, Methanogenic bacteria strains were isolated by using specific selective growth media. The second part of this study is using these strains for bioremediation process of oil wells, which includes providing anaerobic conditions for these strains to transform CO2 gas to methane . Morphological and microscopic observations were conducted to these strains and showed the best kind of these strains according to the ability of transformation of CO2 to methane. The isolated bacteria were called BRS11 strain showed high efficiency in transformation of CO2 to methane.

Effect of NaCl concentration on depressurization-induced methane hydrate dissociation near ice-freezing point: Associated with metastable phases

Methane hydrate (MH) has been viewed as an earth-abundant potential energy resource and attracted worldwide research attentions. Among such studies, the metastable performance of gas hydrates systems, i.e. gas hydrates decompose at slow rates or preserve for long periods of time out of the corresponding stable pressure-temperature conditions, was claimed to lead to the retarded hydrates dissociation and affect the recovery efficiency and sediment safety during exploitations. A mechanism proposed that MH decomposes and transform to supercooled water and gas below ice-freezing point before the formation of ice, which is a dominant factor of the related metastability. In this work, the influence of NaCl concentration on depressurization-induced MH dissociation behavior in porous sediments and the associated metastable property of the MH system near ice-freezing point were experimentally investigated. Effects of the metastability on methane gas recovery were studied. The results show that possible metastable states of supercooled water-MH-gas system can exist during the dissociation process of MH with NaCl concentrations of 0 wt%, 1 wt%, and 3 wt% under production pressures of 2.0 MPa and 1.9 MPa, leading to a prolonged gas production process. While a higher NaCl concentration of 5 wt% and a lower production pressure of 1.8 MPa showed no obvious system metastability. The formation of ice would drive the system out from the metastable region and accelerate the production of gas. The effect of NaCl concentration on formation of ice at 2.0 MPa and 1.9 MPa seems to be stochastic, but exhibit negative effect on the temperature-increase amplitudes of the sediment by ice formation at 1.8 MPa. This work present fundamental lab-scale experimental results of effects of NaCl concentrations on possible metastability of the MH system and ice formations for exploitation of MH under submarine brine environment.

Organo-Lithotype Controls on Cleat/Fractures, Matrix-Associated Pores, and Physicomechanical Properties of Coal Seams of Raniganj Coalfield, India.

The organo-lithotype properties of Barakar and Raniganj Formation coal seams have been investigated to assess the process of cleat origin, occurrence, and their influence on strength properties. Coal cleats have wide applications in coalbed methane gas recovery, underground mine strata mechanics, beneficiation, and pulverization. However, there is very limited information available on the cleat occurrence and controlling parameters of Indian coals. In this view, a total of 31 coal samples were retrieved from eight exploratory boreholes intersecting coal-bearing formations like Barakar and Raniganj in the Raniganj Coalfield. We identified four distinct lithotypes in coal seams: (i) B, bright coal; (ii) Db, dull banded coal; (iii) Bb, bright banded coal; and (iv) Bd, banded coal. The abundance of bright-band-associated lithotype indicates organic matter that attained the early anoxic conditions after deposition. The cleat system in Barakar coal is comparatively better than in Raniganj coal controlled by the lithotype, type of organic matter, thermal maturity, and gelification extent. The carbon enrichment process in coal mainly controls the megascopic cleat genesis pattern. The positive trend of cleat intensities with the depth of coal seams as determined by megascopic, microscopic, and scanning electron microscope (SEM) studies postulates that the macro- to nanocleats are interdependent and developed during devolatilization due to loss of plasticity. The field emission scanning electron microscopy (FE-SEM) photographs have shown intricate microfractures and pore structures owing to the epigenetic characteristics. Vitrinite bands indicate that it comprises the partially deformed planer cleat system. The resistance to quartz weathering nature attributed to coal brittleness properties also contributed to cleat genesis. The total clay content exhibits an inverse relationship with different cleat intensities, suggesting that hydrous clay swells due to its inherent ultrafine characteristics, thus not supporting the cleat construction. However, it ropes the development of the irregular crack when organo–inorganic matter achieves the dry thermal conditions. The microfractures linked with different pore structures in studied coals can be classified into seven types: (i) vitrite-associated regular open-slit pores, (ii) vitriinertite-char allied irregular pores, (iii) irregular fracture-pore partially filled with clay, (iv) fissile pores along bedding planes of clay, (v) organic pores evolved due to external heat received from intrusives, (vi) deep organic pores evolved during compaction and thermal transformation, and (vii) pore fractures blocked by boghead algae. The clay content showed a positive relationship with physicomechanical properties, signifying the cementing characteristics of clay holding fractures and pores. There is significant variation in the strength properties of Barakar and Marren measures coal influenced by thermal maturity, lithotype characteristics, and organo–inorganic content.

Study on the factors affecting the sealing performance and mechanical stability of CO2 hydrate cap during gas production from methane hydrate

An innovative idea of “reservoir reformation” was proposed earlier and verified to be feasible for enhancing methane gas recovery efficiency and CO2 sequestration by constructing an artificial impermeable CO2 hydrate cap between the methane hydrate reservoir and overburden. However, the effects of different factors on the sealing performance and mechanical stability of the CO2 hydrate cap need to be further clarified for the optimization of this new technology. In this study, experiments were conducted to simulate methane hydrate gas production by depressurization and analyze the influence of CO2 emulsion injection temperature, injection rate and overlying pressure by controlling these variables. The results indicated that the desired CO2 hydrate cap was formed by decreasing the injection temperature and rate. A cyclic process of “hydrate formation-fracture-regeneration” was proposed at a controlled injection rate of 3 mL/min. The degeneration rate of the CO2 hydrate layer was accelerated with an increase in the overlying pressure. The mechanical stability of CO2 hydrate cap was determined by the combined effects of methane hydrate decomposition and an increase of axial load.

Study for the Bio-CNG Recovery of Methane Gas in the Anaerobic Co-digestion Using Malaysian POME (Palm Oil Mill Effluent)

Study for the Bio-CNG Recovery of Methane Gas in the Anaerobic Co-digestion Using Malaysian POME (Palm Oil Mill Effluent)

Fracture Reactivation Modeling in a Depleted Reservoir

Injection-induced fracture reactivation during hydraulic fracturing processes in shale gas development as well as coal bed methane (CBM) and other unconventional oil and gas recovery is widely investigated because of potential permeability enhancement impacts. Less attention is paid to induced fracture reactivation during oil and gas production and its impacts on reservoir permeability, despite its relatively common occurrence. During production, a reservoir tends to shrink as effective stresses increase, and the deviatoric effective stresses also increase. These changes in the principal effective stresses may cause Coulomb fracture slip in existing natural fractures, depending on their strength, orientation, and initial stress conditions. In this work, an extended finite element model with contact constraints is used to investigate different fracture slip scenarios induced by general reservoir pressure depletion. The numerical experiments assess the effect of Young’s modulus, the crack orientation, and the frictional coefficient of the crack surface on the distribution of stress and displacement after some reservoir depletion. Results show that the crack orientation significantly affects the state of stress and displacement, particularly in the vicinity of the crack. Slip can only occur in permitted directions, as determined by the magnitudes of the principal stresses and the frictional coefficient. Lastly, a larger frictional coefficient (i.e., a rougher natural fracture surface) makes the crack less prone to shear slip.

2-06 MICPを応用したメタンハイドレート由来のメタンガス回収支援手法に関する検討

2-06 MICPを応用したメタンハイドレート由来のメタンガス回収支援手法に関する検討

Insights into Cage Occupancies during Gas Exchange in CH4+CO2 and CH4+N2+CO2 Mixed Hydrate Systems Relevant for Methane Gas Recovery and Carbon Dioxide Sequestration in Hydrate Reservoirs: A Thermodynamic Approach

Carbon dioxide injection for methane replacement from hydrate reservoirs is considered as one of the effective techniques for both methane production and carbon dioxide sequestration. To understand...

Natural Gas Production from a Marine Clayey Hydrate Reservoir Formed in Seawater Using Depressurization at Constant Pressure, Depressurization by Constant Rate Gas Release, Thermal Stimulation, and Their Implications for Real Field Applications

The depressurization approach of methane production from a natural gas hydrate reservoir has been identified as the most energy-efficient production approach. However, some of the field-scale studies involving constant pressure depressurization (CPD) did not yield significant success. To address this, the constant rate gas release (CRD) depressurization approach was used to overcome the drawbacks of the CPD approach. The experimental investigations of these methods with and without thermal stimulation (TS) have not yet been investigated in detail for marine clayey hydrate reservoirs formed in seawater to understand their comparative effectiveness for methane gas recovery. Although common production approaches have been studied by many researchers on hydrate-bearing sand sediments, energy recovery from hydrate-rich clayey sediments has not yet been investigated in detail, which form the major dominant hydrate reservoirs of the hydrate resource pyramid across the globe. This work investigates in detail the ...

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

Abstract In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO2. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO2/CH4 molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO2 molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO2 concentration in the aqueous phase may not result in faster growth of CO2 hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO2, the growth for carbon dioxide hydrate was very slow in the beginning.

An Experimental Investigation of Gas-Production Rates During Depressurization of Sedimentary Methane Hydrates

Summary Sedimentary methane hydrates contain a vast amount of untapped natural gas that can be produced through pressure depletion. Several field pilots have proved the concept with days to weeks of operation, but the longer-term response remains uncertain. This paper investigates the parameters affecting the rate of gas recovery from methane-hydrate-bearing sediments. The recovery of methane gas from hydrate dissociation through pressure depletion was studied at different initial hydrate saturations and different constant production pressures in cylindrical sandstone cores. Core-scale dissociation patterns were mapped with magnetic resonance imaging (MRI), and pore-scale dissociation events were visualized in a high-pressure micromodel. Key findings from the gas-production-rate analysis are that the maximum rate of recovery is only to a small extent affected by the magnitude of the pressure reduction below the dissociation pressure, and that the hydrate saturation directly affects the rate of recovery, where intermediate hydrate saturations (0.30 to 0.50) give the highest initial recovery rate. These results are of interest to anyone who evaluates the production performance of sedimentary hydrate accumulations and demonstrate how important accurate saturation estimates are to prediction of both the initial rate of gas recovery and the ultimate-recovery efficiency.

Efficiency enhancements in methane recovery from natural gas hydrates using injection of CO2/N2 gas mixture simulating in-situ combustion

Thermal stimulation was combined with an injection of a mixture of CO2 (85%) + N2(15%) to investigate efficiency enhancements from pure thermal stimulation and thermal stimulation with CO2 injection approaches. Tests were performed at initial hydrate saturation of 10% and 300 ml/min CO2 + N2 injection rate with three different heating rates of 20, 50 and 100 W. The results indicate that thermal stimulation with CO2 + N2 injection is the most efficient method available for methane gas recovery. At 10% Hydrate Saturation (SH) and 100 W heating rate, the number of moles of CH4 recovered increased from 8.5 to 16 to 20 in the case of thermal stimulation, thermal stimulation with CO2 exchange and thermal stimulation with CO2 + N2 exchange respectively. The experimental results reported here are aligned with model and Raman spectroscopy predictions in terms of replacement mechanism and recovery efficiency, reported in the literature. The results obtained from CO2/N2 composition ratio show that in the exchange process, CO2 first replaces CH4 in the large cages of Structure I hydrates followed by N2 targeting CH4 in the small cages of Structure I hydrates. This replacement mechanism has been predicted in the literature by Liu et al. (2016) using Molecular Dynamics simulations. It is also found from this work that N2 is selectively captured in hydrate cages below 12 °C. The values of carbon sequestration index (defined as moles of CO2 sequestered divided by moles of CH4 recovered) were 0.32, 0.52 and 0.85 respectively for 100, 50 and 20 W heating tests. The data obtained from our work in terms of gas composition, methane recovery and CO2 sequestered is consistent with the key findings reported in the literature.

The Environmental Impact Assessment of a Municipal Landfill - A Study on the Leachate

The increase in consumption draws the need to quickly assess the problem of the municipal solid wastes. On the short term, the easiest way to deal with this stringent problem seems to be landfilling. This method was always a controversial one. Thus, making it more environmentally friendly was the logical next step. The recovery and utilization of methane gas, the recovery and treatment of the liquid generated by the landfill and, finally, the sealing of the landfill by the end of its utilization made it possible to deal the waste problem more environmentally friendly. However, no matter how “green” a landfill might be, every time such type of site is planned, a thoroughly environmental impact assessment must be conducted to anticipate, avoid and ameliorate the impact on the environment. This paper presents some aspects regarding an environmental impact assessment of a landfill, focusing mainly on the possible impact on water, the effect of leachate treatment and, finally, the future alternatives to landfilling.

Impact of formation and dissociation conditions on stiffness of a hydrate-bearing sand

Methane gas recovery from gas hydrate–bearing sands requires dissociation of the hydrate. Understanding changes in the stiffness of the sand is essential if future production scenarios are to be modelled realistically. This paper reports the results of resonant column tests conducted to measure changes in shear and flexural Young’s modulus (stiffness) of sand specimens during the formation and dissociation of hydrate within the pore space. Factors such as hydrate saturation, effective stress, and dissociation method (thermal stimulation and depressurization) were evaluated. Results show a nonlinear relationship between stiffness and hydrate volume, with hydrate formation and dissociation giving markedly different changes in stiffness. Stiffness increases more slowly during the initial stages of hydrate formation, compared to later stages, with the eventual stiffness being independent of the effective stress applied at the start of formation. In contrast, the onset of dissociation leads to a rapid reduction in stiffness, with thermal stimulation giving a greater reduction compared to depressurization for similar changes in hydrate volume. These results highlight the impact of hydrate morphology on changes in stiffness during the hydrate formation process or its dissociation. We present and discuss a conceptual model to explain the differences observed.