Free Gas Layer Research Articles

Research on Production Behavior of A Fractured Well in Gas Hydrate Reservoirs Considering Multilayer

Abstract Natural gas hydrates are internationally recognized as a new clean energy source with high prospects for commercial development. However, the vast majority of hydrates are hosted in oceanic clayey silty sediments, which are inefficient to exploit due to the extremely low effective permeability. In this paper, a novel development mode, that is, multilayer commingled production with a hydraulically fractured well, is proposed for the multilayered reservoir where hydrate and free gas coexist, to enhance productivity. Especially, the co-production behavior was numerically investigated, with the multilayered reservoir containing a hydrate-bearing layer, a three-phase layer, and a free gas layer located in the Shenhu Area as the geological background. The results indicated that the fracture provided flow channels for gas production in the multilayer, as well as greatly increasing the pressure drop spreading zone and changing the hydrate decomposition mode from around the wellbore to along the fracture surface. Compared with improving the fracture conductivity, increasing the fracture length is more effective for improving hydrate decomposition efficiency and co-production capacity. Specifically, when the fracture half-length was 30 m and the fracture conductivity was 100 D·cm, the cumulative gas production reached 949×104 m3 at 3600 days, which was 3.28 times that of the unfractured scenario. Additionally, fracturing the free gas layer hardly affects productivity as the free gas can be well-recovered by the wellbore. Overall, the proposed mode is promising for multilayered gas hydrate reservoirs, provides references for the co-production plan design, and contributes to the scale mining of hydrates.

Stimulation Behavior of Fracture Networks in the Second Hydrate Trial Production Area of China Considering the Presence of Multiple Layers

The fracture network’s stimulation of China’s second hydrate trial production area was investigated. First, the stimulation potential of the fracture network and the influence of well arrangement on hydrate development were explored. Second, the fracture distributions’ influence on development behavior was investigated. Results showed that the fracture network could cause the trial production reservoir to reach the commercial production rate. The average CH4 production rate of unit horizontal well length using the depressurization method and depressurization combined with thermal stimulation (combined method) were 61.3 and 151.5 m3/d with the fracture network and 23.7 and 14.3 m3/d without the fracture network. In addition, without the fracture network, the development behavior of wells arranged in the mixed layer was better than that of wells arranged in the hydrate layer. However, with the fracture network, the result was reversed. With the depressurization method, the best production behavior was obtained by fracturing in the hydrate layer; however, for the combined method, the best production behavior was obtained by fracturing in the hydrate and mixed layer, while fracturing in the free gas layer was useless. This study provides a valuable reference for the hydrate development of China’s trial production reservoir.

Gas production from a promising reservoir of the hydrate with associated and shallow gas layers in the low permeable sediments

The gas production rate from hydrate trials is still below commercial criterion. To increase the production rate, a promising geological system consisting of hydrate, associated and shallow gas layers was explored recently. Herein, the gas production of this complex geological system through depressurization was numerically investigated. The result showed a high gas production rate in the first tens day, and a subsequently slow decrease with an increasing water production rate under the immediate depressurization condition. The free gas layer contributed the most of gas production while the least is from hydrate reservoir. For water production, the most was from the associated gas layer and a moderate from hydrate layer. Among all factors, the depressurization rate affected greatly the initial gas rate, and slight depressurization caused a high and stable rate. The permeability, gas saturation and irreducible water saturation of the shallow gas layer affected dramatically the gas rate and obviously the corresponding water rate. Special attention should be paid to the hydrate forming in the shallow gas layer. This hydrate barrier caused a decrease of gas rate when reducing production pressure. The production of the complex system enhances the economic benefit, and it becomes a prospective system of exploration.

Numerical simulation of gas production behavior of class Ⅰ, class Ⅱ and class Ⅲ hydrate reservoirs for different well locations

The exploitation of natural gas hydrate, an unconventional natural gas, has drawn attention on a global scale due to increasing imbalance between energy supply and demand. Horizontal wells are considered to have a better production performance, while vertical wells have been mostly employed in previous field tests and laboratory research. Therefore, based on the representative properties of three kinds of hydrate reservoirs, a hydrate decomposition model is built to study the gas generation behaviors of various hydrate reservoirs with different horizontal well-spacing strategies in this work. The results show that for Class I hydrate reservoirs, placing the production well near the free gas layer can improve gas generation by 47%, and GWR (gas-water ratio) to 346.0 and maintain higher temperature in hydrate reservoir than that with placing the well in the hydrate reservoir. For Class Ⅱ hydrate reservoirs, placing the producing well away from the free water layer can cut down water production by 92%, while gas production could be also elevated, causing GWR increasing to 175.8. In Class Ⅲ reservoirs, the reduction of 30% in water production, and increment in GWR from 81.5 to 118.0 can be achieved by placing the well on the top of the hydrate layer, rather than that on the bottom. In addition, the presence of free gas layer, free water layer can promote the pressure-drop interface spread, provide sensible heat, and then accelerate hydrate decomposition further.

Sensible heat aided gas production from gas hydrate with an underlying water-rich shallow gas layer

Increasing the efficiency of gas production from marine gas hydrate still faces significant problems. Based on the geological survey of marine reservoirs, gas hydrates are generally associated with underlying free gas layers with high temperature and water saturation. Here the effect of this gas layer and its characteristics on the gas and water production from the hydrate layer are studied. It was found that a large temperature difference existed between the two layers during gas production due to the different heat demand and consumption in each layer. Slower gas production rate was observed in case of dense distribution of hydrates in the hydrate-bearing layer and the resulting sluggish gas permeation and enormous heat supply. Notably, this was not present when the free gas layer was more water-saturated. The resulting maximum gas production rate could be effectively enhanced by 41 % at most as well. This was attributed to the increased sensible heat available from the pore water and the interbedded heat exchange. It was thus indicated that a hydrate reservoir with an underlying water-rich layer could be more favorable for gas production in terms of heat supply.

Symmetry Energy in the Inner Crust Region of Neutron Stars: A Study Around the Neutron Drip Density Point using the Compressed Liquid Drop Model

The properties of neutron star’s inner crust have been investigated using the Compressible Liquid Drop Model, particularly around the neutron drip density region, which is the boundary between the outer and inner crust. Symmetry energy in the equations of state SLy4 and BSk3 was calculated to determine the density data between the outer and inner crusts. The properties of the inner crust can be understood through parameters such as the change in the number of nucleons in the atomic nucleus, the asymmetry parameter in surface energy, and volume energy. It was shown that the choice of the symmetry energy expansion coefficient (L) of order-1 results in a distinct energy range of 9-11 MeV within the neutron drip region. This contrasts significantly with the energy symmetry observed around saturation density, which reaches (30 ± 4) MeV in the reference models used. Furthermore, it was found that symmetry energy affects the neutron composition in the inner crust. As the density increases, neutron numbers rise, while proton counts exhibit relative stability within the range of 40 to 50 for each atomic nucleus. Importantly, we observe a marked decrease in proton fraction at the onset of the neutron drip region, where ???? ≅10 MeV, suggesting electron capture processes transforming protons into neutrons. This phenomenon contributes to the presence of neutron and free neutron gas layers within the inner crust.

Numerical Simulation of Improved Gas Production from Oceanic Gas Hydrate Accumulation by Permeability Enhancement Associated with Geomechanical Response

In the Shenhu Area of the South China Sea, although some numerical studies are conducted on the gas production at well SHSC-4, the geomechanical responses have not been taken into account, and the associated impact of permeability enhancement on gas production has not been thoroughly investigated. In this study, pTOUGH+HYDRATE V1.5 coupled with the RGMS is applied to account for geomechanical responses. Based on actual geological conditions, the reservoir model has five layers: the hydrate-bearing layer (HBL), the three-phase layer (TPL), the free gas layer (FGL), the overburden, and the underburden. The numerical results match the trial production data, validating the numerical model. The analysis shows that gas production from the FGL contributed the most (72.17%) to the cumulative gas production (Vg), followed by the TPL (23.54%) and the HBL (4.29%). The cumulative water-to-gas ratio (RwgT) gradually decreased during gas production, with the HBL exhibiting the highest value. Permeability enhancement can improve gas production, with the FGL being the most responsive to such enhancement. It increased Vg by 87% and reduced RwgT to 85%. To achieve more realistic production schemes and better enhance energy recovery, it is advisable to conduct numerical investigations that incorporate geomechanical considerations due to the intricate nature of hydrate-bearing sediments.

Numerical analysis of coupled thermal-hydro-chemo-mechanical (THCM) behavior to joint production of marine gas hydrate and shallow gas

Low gas production efficiency and high cost significantly impede the commercial viability of exploiting marine gas hydrate. To address this, we propose joint production of hydrate and shallow gas, focusing on previously unexplored characteristics such as fluid seepage and local deformation arising from interlayer interface. In this study, we investigate the coupled multiphysics response during depressurization in joint production. Our findings reveal that the joint production enables gas production rates to surpass commercialization threshold, with the minimum proportion of free gas in total production exceeding 0.5 during depressurization stage. Free gas stored in the reservoir promotes the energy recovery, which is correlated with permeability. We observe the water block effect, a type of interlayer interference, leading to local gas accumulation in three phase layer and heterogeneous gas effective permeability change within reservoir. Regarding geomechanical behavior, the maximum displacement occurs in the free gas layer during the 100-day test. Simultaneous compaction occurs in the upper part of the wellbore, whereas dilation is observed in the lower part. This study offers crucial insights into the characteristics and challenges of hydrate and shallow gas joint production related to interlayer interference.

Numerical analysis on gas production performance by using a multilateral well system at the first offshore hydrate production test site in the Shenhu area

Multilateral well technique is a promising approach to enhance gas recovery, especially in heterogeneous hydrate reservoirs with underlying free gas. However, little is known about the optimal deployment for multilateral wells on hydrate production. Herein, a 3D numerical model for predicting the combined production performance of hydrate reservoirs by using multilateral wells is proposed. The results indicate that the horizontal branch deployed at the interface between three-phase layer and free gas layer shows the best production potential when one branch is available. Then, effects of geometric parameters including branch deployment location, spacing, length, phase angle, and branch number on production behaviors are analyzed through orthogonal designs. The analysis shows dual-branch and quad-branch scenarios are most influenced by deployment location and branch length, and the corresponding optimal combinations are suggested respectively. By contrast, dual-lateral wells have the most favorable yield-increasing effects due to the synergistic depressurization, of which total gas production and productivity index are 123% and 81% higher than those of vertical wells. Additionally, well interference may exist between branches, which is unfavorable for gas recovery between the lateral branches and exacerbates with an increase in branch number. This research gives an in-depth insight into the industrialized co-production of hydrate and free gas.

Numerical simulation of gas hydrate production in shenhu area using depressurization: The effect of reservoir permeability heterogeneity

An accurate description of the reservoir characteristics is essential to the precise prediction of gas production from nature gas hydrate (NGH) deposits. In most numerical studies related to large-scale onshore or offshore NGH production cases, the reservoir permeability was usually assumed to be homogeneous. In this work, a multi-layered heterogeneous-permeability reservoir model (including a hydrate-bearing layer, a three-phase layer, and a free gas layer) was established, and the gas production behavior was analyzed by using the TOUGH + HYDRATE simulator. It is found that hydrate and free gas tend to be scatteredly distributed in this reservoir model. Reservoirs with heterogeneous permeability have better gas production performance than homogeneous ones. The 10-year cumulative gas production from the heterogeneous reservoir with the heterogeneity degree of 0.4μ (622 × 104 m3) is 15.19% higher than that from the homogeneous reservoir (540 × 104 m3). Moreover, the layered production results show that the free gas layer contributes the most to gas production among the three layers. The effect of heterogeneity on gas production in high-permeability reservoirs is more obvious than that in low-permeability reservoirs. Therefore, the permeability heterogeneity of the reservoir, especially the permeability heterogeneity of the free gas layer, should be considered in the long-term prediction of NGH production.

Numerical investigation of fracturing fluid invasion into hydrate reservoirs during hydraulic-fracturing stimulation

Hydraulic fracturing is a potentially promising stimulation technology employed for enhancing gas productivity and energy efficiency of low-permeability hydrate reservoirs. At present, most studies in the field of hydrate reservoir fracturing have mainly focused on the fracturing feasibility and recovery efficiency without considering the effects of fracturing fluids on hydrate reservoirs. However, fracturing fluid will inevitably invade hydrate reservoirs driven by high fracturing pressure, which may cause hydrate phase transitions and consequently affects fracturing. In this study, the dynamic process of fracturing fluid invasion into hydrate reservoir was simulated using the TOUGH+HYDRATE software, primarily focusing on the differences between the fracturing fluid invasion into the gas hydrate-bearing layer (GHBL), three-phase layer (TPL), and free gas layer (FGL). The results showed that a secondary hydrate column was formed within 2–10 m around the fracture by the fracturing fluid/free water and free gas during fracturing fluid invasion into the TPL and FGL, which was mainly driven by the large driving force exerted by high fracturing pressure. But the exothermic reaction of hydrate formation can provide negative feedback to the formation and expansion of the secondary hydrate column, leading to a state of phase equilibrium in the secondary hydrate formation region and the outward expansion of the secondary hydrate column in a “three-phase equilibrium” mode. It should be noted that secondary hydrate formation did not occur during fracturing fluid invasion into GHBL because of the absence of free gas, and fracturing fluid invasion into GHBL only affected reservoir temperature and pressure, which was similar to the fracturing fluid invasion into unconventional oil and gas layers. These results will provide important guidance for the potential application of hydraulic fracturing in the field tests of hydrate reservoirs and its scheme formulation.

Coupled thermal–hydrodynamic–mechanical numerical simulation of natural gas hydrate horizontal well depressurization production: Method and application in the South China Sea

In order to produce natural gas hydrate safely and efficiently, it is quite crucial to research the stability of hydrate reservoir in the process of its exploitation. The coupled thermal-hydrodynamic-mechanical (THM) numerical simulation can clearly present the mechanical response laws in the process of hydrate exploitation by horizontal well, but the model is often simplified as a profile vertical to the production well, so the evolution characteristics of real formation deformation space cannot be described sufficiently. To this end, this paper develops a coupled THM simulator applicable to the large-scale hydrate exploitation by horizontal well by introducing interactive interface to the FLAC mechanics program based on the hydrate exploitation program TOUGH + HYDRATE. Then, based on the field data of second hydrate production test in South China Sea, the gas and water production and formation deformation laws under the middle- and long-term development conditions of horizontal wells are studied by taking the actual gas production of horizontal well during the production test as the constraint of coupled THM model. And the following research results are obtained. First, when the production pressure is 7 MPa and the horizontal well length is 300 m, the gas production of horizontal well can reach 1190 × 104 m3, the pressure drop has a larger influence range in the free gas layer, the produced gas mainly comes from the free gas layer and the hydrate layer and the hydrate dissociation range is not large. Second, it is predicted that the seafloor settlement is about 0.16 m after 60 days' production test and 0.52 m after osne year's production. In conclusion, hydrate exploitation by horizontal well can cause a large range of seafloor settlement. The seafloor surface settles linearly and continuously and the spatial settlement distribute is in the shape of ellipse. What's more, the greatest deformation (vertical displacement) occurs at the horizontal well and above it, where formation damage happens the easiest. It is recommended to study seafloor deformation and landslip risk under the conditions of middle and long-term production based on seafloor topography, valley distribution and nonuniform spatial thickness of mineral ores.

Estimation of the gas hydrate saturation from multichannel seismic data on the western continental margin of the Chukchi Rise in the Arctic Ocean

A multichannel seismic survey was conducted to investigate the geophysical characteristics of gas hydrates along the western continental margin of the Chukchi Rise around an ARAON mound cluster, which was first recovered in 2016. In the seismic data, gas hydrate-related bottom simulating reflection was widely distributed along the western continental margin of the Chukchi Rise. High-precision seismic P-wave velocity was obtained to investigate the geophysical characteristics of the gas hydrate structures in the BSR areas. Iterative migration velocity analysis was used to construct a detailed P-wave velocity model from the acquired seismic data. The gas hydrate and free gas layers have abnormally high- and low-seismic P-wave velocities; the precise velocity model allows us to understand the detailed spatial distribution of gas hydrate and free gas structures. The effective medium theory model enables estimations of the gas hydrate saturation from constructed seismic P-wave velocity model. We propose the P-wave velocity and gas hydrate saturation models from acquired multichannel seismic data in the western continental margin of the Chukchi Rise for the first time.

Numerical investigation of natural gas hydrate production performance via a more realistic three-dimensional model

Numerical simulation plays a crucial role in the prediction of natural gas hydrate production performance. However, most existing models are two-dimensional or three-dimensional with idealized geometries and uniform parameter assignments, which cannot depict the effects of stratigraphic undulation and spatial variability of reservoir physical parameters on gas production. Therefore, a convenient method to convert the image information (more accessible) into parameter attribute values (required for model construction) was proposed in this study. Using the converted data of reservoir depth, thickness, and porosity, a more realistic three-dimensional model was innovatively constructed. Then, the influences of reservoir fluctuations and spatial variability of physical parameters on production performance were quantitatively analyzed. It was found that placing the production well in an elevated area can facilitate gas production. Specifically, Well 1 (located in the highland) had a 34.1% higher normalized gas production rate (i.e., production rate per unit well length) and a 14.9% lower normalized water production rate than Well 3 (located in the flat area) in the free gas layer. In addition to reservoir fluctuations, the exploitation efficiency of the gas hydrate-bearing layer was also affected by the thickness. The spatial variability of hydrate saturation and that of gas saturation in the study area were not very prominent, and the gas production rate obtained by the heterogeneous scheme was approximately 10% different from that of the homogeneous scheme. However, although the spatial variability of porosity was also not great (no more than 2%), when the cubic law was used to calculate the corresponding permeability, the gas production rate obtained by the heterogeneous scheme was nearly 20% different from that of the homogenous scheme. This study demonstrates the need to use a more realistic three-dimensional model for gas hydrate production performance prediction and is expected to provide an important reference for well location selection.

Experimental study on the dual-gas co-production from hydrate deposit and its underlying gas reservoir

Short gas production periods and high production costs are two main challenges for the commercial exploitation of natural gas hydrates (NGHs). The NGHs deposit with enriched underlying free gas has drawn more attention, because the dual-gas co-production from hydrate zone and underlying free gas zone are expected to increase gas yields. We designed a method to prepare this kind of hydrate deposits that a hydrate layer over a free gas layer, and performed a series of dual-gas co-exploitation experiments to investigate its gas production characteristics via depressurization method. Results demonstrate that the temperature of hydrate layer and free gas layer exhibit different variation tendency during gas production process and lower production pressure attributes to higher gas production rate and gas recovery ratio. The wellbore set at underlying free gas layer is recommended because it can avoid lower initial local permeability around the well and prevent ice plug or hydrate reformation during gas production process. Meanwhile, it enhances the movement of hydrate decomposition front and further improves gas production efficiency. Compared with the NGHs reservoir with a single hydrate zone, the dual-gas co-production has higher gas production efficiency and lower temperature decrease to maintain the driving force of hydrate dissociation.

Two-Phase Modeling Technology and Subsection Modeling Method of Natural Gas Hydrate: A Case Study in the Shenhu Sea Area

It is found that natural gas hydrate is not only a pore-filling material but also exists in the reservoir in the form of rock skeleton particles. Therefore, the traditional petrophysical simulation method cannot well describe the physical properties of natural gas hydrate reservoir. At the same time, the physical properties of the hydrate layer and its associated free gas layer are quite different, so it is difficult to fit the physical properties of the two media using traditional modeling methods. The two-phase modeling technology used in this paper is the equivalent medium modeling technology based on BK solid substitution theory and Gassmann fluid substitution theory, which simulates hydrate particles in rock skeleton and hydrate filling in pores, respectively. The forward simulation results show that the two-phase simulation technology of natural gas hydrate can well fit the P-wave and S-wave velocity information of the medium. At the same time, the equivalent medium model of the free gas reservoir is established by using only Gassmann fluid substitution theory. The practical application shows that the subsection modeling method can well solve the problem of the too large difference between the two sets of reservoir physical properties and make the calibration results of forward modeling synthetic records more accurate.

Long-term numerical simulation of a joint production of gas hydrate and underlying shallow gas through dual horizontal wells in the South China Sea

Recent field tests to recover natural gas from marine gas hydrate reservoirs in Japan and China have exhibited worldwide attention to this strategic energy form; significant challenges still remain in improving the accumulative gas yield for a better economic efficiency. According to the geological survey in marine hydrate reservoirs, there exists a concomitant free gas layer underlying the gas hydrate reservoir. Consequently, here we propose a new scheme to jointly produce the gases from hydrate layer and its underlying shallow gas layer. It was found that a dual horizontal well deployment respectively in the corresponding two layers could contribute to a 4.1 times cumulative gas yield comparing that of a single vertical well scenario. This implies a remarkable enhancement of gas productivity via making full use of the gases in the shallow gas layer. Notably, a potential risk of interlayer failure could occur upon the great interbedded pressure difference (maximum 10.7 MPa) arising from the varying behavior of pressure propagation in the layers. This can be effectively alleviated by separately controlling the depressurization scheme in different layers; a mild step-wise depressurization was suggested in the more permeable shallow gas layer while the hydrate layer with a lower permeability should experience a sharper pressure drop. This was found beneficial reducing the interbedded pressure difference by about 70% without intervening the gas production. An energy return on investment (EROI) analysis showed a promising positive energy harvest of our optimized layer-dependent pressure scheme. It could be therefore a potential method to be applied in the field tests in the South China Sea to improve the economic efficiency without disturbing the reservoir stability.

Quantification of CO2 Replacement in Methane Gas Hydrates: A Molecular Dynamics Perspective

Extraction of methane from natural gas hydrates whilst storing CO2 via gas replacement is a promising approach for reducing anthropogenic CO2 emissions during energy generation. In this study, molecular dynamic simulations were performed to identify the influence of temperature, pressure, and the initial CO2 concentration of sweep gas on the gas replacement characteristics. Simulations were performed under selected pressure and temperature conditions using five different initial CO2 concentrations. The simulation results clearly portray the replacement phenomena where methane molecules are released into the free gas layer while CO2 get enclathrated in hydrate structure. During gas replacement, minor structural changes in hydrate structure can also be observed, but they are quite insignificant as demonstrated through the alterations in Tetrahedrality order parameter. The variations of the number densities of gas and water molecules during gas replacement were used to quantify the methane recovery and CO2 storage. Based on the numerical comparisons, the replacement process is found to be strongly dependant on the temperature, yielding a higher methane recovery at higher temperatures; however, the CO2 storage capacity is found to be diminishing with increasing temperature. Having a higher initial CO2 concentration in the sweep gas may facilitate greater penetration of CO2 into the hydrate structure, eventually resulting in a higher methane recovery and improved CO2 storage.

Gas origin linked to paleo BSR

The Central-South Chile margin is an excellent site to address the changes in the gas hydrate system since the last deglaciation associated with tectonic uplift and great earthquakes. However, the dynamic of the gas hydrate/free gas system along south central Chile is currently not well understood. From geophysical data and modeling analyses, we evaluate gas hydrate/free gas concentrations along a seismic line, derive geothermal gradients, and model past positions of the Bottom Simulating Reflector (BSR; until 13,000 years BP). The results reveal high hydrate/free gas concentrations and local geothermal gradient anomalies related to fluid migration through faults linked to seafloor mud volcanoes. The BSR-derived geothermal gradient, the base of free gas layers, BSR distribution and models of the paleo-BSR form a basis to evaluate the origin of the gas. If paleo-BSR coincides with the base of the free gas, the gas presence can be related to the gas hydrate dissociation due to climate change and geological evolution. Only if the base of free gas reflector is deeper than the paleo-BSR, a deeper gas supply can be invoked.

Energy recovery behavior of low-frequency electric heating assisted depressurization in Class 1 hydrate deposits

Class 1 hydrate deposits are characterized by a free gas layer (FGL) underneath the hydrate-bearing layer (HBL) and are considered as the most potential target for commercial exploitation. To improve the contribution of hydrate decomposition to gas production, an efficient development method of low-frequency electric heating assisted depressurization under five-point well pattern is proposed for Class 1 hydrate deposits, which involves the implementation of electric heating after a certain period of depressurization. Based on the geological data of Messoyakha gas field, the numerical simulation model is established. Then the energy recovery behaviors under single depressurization and the proposed method are investigated through numerical simulation approach. Results indicate that the gas production rate of Class 1 hydrate deposits is extremely high at the initial stage of depressurization, but decreases sharply due to insufficient reservoir energy. After the implementation of electric heating, hydrate decomposition and gas production are significantly improved, and a considerable energy efficiency ratio is obtained. Under the same heat input, the linear decreasing voltage mode exhibits better production performance than the constant voltage mode, and can avoid the continuous high temperature near the wellbore to damage the electrode elements, which has greater potential for the exploitation of hydrate deposits. At the end of 10 years of production, a cylindrical hydrate decomposition zone with a radius of about 40 m is formed around each production well. The simulation results confirm the feasibility of the proposed method and provide new insights for enhancing gas recovery in Class 1 hydrate deposits.