Depressurization Rate Research Articles

Experimental studies and pore-scale modeling of hydrate dissociation kinetics at different depressurization rates in a cubic hydrate simulator

Natural gas hydrate (NGH) is a promising energy resource that has triggered a race for scientific innovation in energy and environmental research. However, there still faces the challenges of low-efficiency hydrate dissociation and unstable gas production during the hydrate production. Clarifying the kinetic mechanism of hydrate dissociation is the key to improving the efficiency of “phase-transition to gas-supply” in hydrate-bearing sediment. This study successfully conducts hydrate dissociation experiments with different depressurization rates in the Cubic Hydrate Simulator (CHS). A novel dissociation kinetic model integrating the hydrate pore-scale morphology and its evolutions are established, and the sensitivities of the kinetic and thermal parameters are discussed in detail. The mathematical relationship between the hydrate saturation and reaction area is quantitatively analyzed for the hydrate formation and dissociation kinetics. The history matching simulation with the newly developed model achieves an excellent agreement with the experimental results. The full-lifecycle kinetic behaviors of the hydrate dissociation in the depressurization experiments are finely characterized. It is found that the evolutions of the hydrate saturation (SH) and temperature (T) spatial distributions exhibit strong heterogeneous characteristics in the vessel due to the phase transition and heat transfer effects. In addition, this reveals that the relatively high depressurization rate can lead to a more significant dissociation rate in the depressurization stage. This provides a new reliable and adaptable method for describing the hydrate dissociation kinetics in the porous media.

Modeling and Experimental Validation of Cell Morphology in Microcellular-Foamed Polycaprolactone.

This study investigates the modeling and experimental validation of cell morphology in microcellular-foamed polycaprolactone (PCL) using supercritical carbon dioxide (scCO2) as the blowing agent. The microcellular foaming process (MCP) was conducted using a solid-state batch foaming process, where PCL was saturated with scCO2 at 6 to 9 MPa and 313 K, followed by depressurization at a rate of -0.3 and -1 MPa/s. This study utilized the Sanchez-Lacombe equation of state and the Peng-Robinson-Stryjek-Vera equation of state to model the solubility and density of the PCL-CO2 mixture. Classical nucleation theory was modified and combined with numerical analysis to predict cell density, incorporating factors such as gas absorption kinetics, the role of scCO2 in promoting nucleation, and the impact of depressurization rate and saturation pressure on cell growth. The validity of the model was confirmed by comparing the theoretical predictions with experimental and reference data, with the cell density determined through field-emission scanning electron microscopy analysis of foamed PCL samples. This study proposes a method for predicting cell density that can be applied to various polymers, with the potential for wide-ranging applications in biomaterials and industrial settings. This research also introduces a Python-based numerical analysis tool that allows for easy calculation of solubility and cell density based on the material properties of polymers and penetrant gases, offering a practical solution for optimizing MCP conditions in different contexts.

Enhanced strategies for depressurization in offshore natural gas hydrate exploitation: An in-depth investigation into pathway optimization and production stability mechanisms

Natural gas hydrates have garnered widespread attention as a high-quality energy resource. Recent offshore extraction experiences suggest that depressurization is a technically mature and economically viable option. However, challenges such as reservoir temperature reduction, reservoir subsidence, secondary hydrate formation, and insufficient dynamics in later-stage hydrate decomposition still require improvements to the depressurization method. This study, based on field data from Japan's first offshore natural gas hydrate extraction, utilizes a self-developed numerical simulator to model and validate reservoirs at the field scale. Long-term production rate stability, total production, secondary hydrate formation, reservoir subsidence, evolution of permeability, and temperature-pressure paths were analyzed and optimized for the three mainstream depressurization modes: steady depressurization, stepwise depressurization, and cyclic depressurization. The results indicate that, under the condition of equal total work done throughout the entire depressurization process, steady depressurization with an effectively lower depressurization rate is the optimal choice. Cyclic depressurization, due to the formation of secondary hydrates reducing the permeability of certain reservoir zones, adversely affects gas production efficiency during the long-term stable production phase. This study enhances insights into the coupled evolution of multiple physical fields during the depressurization of offshore natural gas hydrates, providing valuable guidance for future on-site extraction plan designs.

CH4 hydrate dissociation and CH4 leakage characteristics: Insights from laboratory investigation based on stratified environment reconstruction of natural gas hydrate reservoir

Submarine natural gas hydrates (NGHs) are one of the largest methane reservoirs on Earth, offering huge potential as an alternative energy source and serving as a crucial global carbon sink. However, the substantial risk of methane leakage during NGH development seriously threatens marine and global ecological and environmental safety, presenting a major challenge for commercial NGH exploitation. Focusing on the unknown leakage mechanisms, this study employed a new simulation device to construct a stratified environment and to investigate the characteristics of hydrate dissociation and methane leakage during depressurization production, under conditions of varied fracturing in overlying sediment. A movable module was used to dynamically isolate and connect the hydrate reservoir with the overlying layer. The results showed that the intrusion of overlying water decelerated the reservoir depressurization rate, leading to a mass of hydrate reformation. The invasion locations and flow paths of the overlying water were influenced by the fracture scale of the overlying sediment. Benefiting from the additional sensible heat and reservoir space occupation of the overlying water in the later production stages, the methane recovery ratio in the fracture-containing systems were not significantly affected. However, the leakage methane increased as fracture channels enlarged, reaching up to 9.90 % of the total methane content in the hydrate reservoir. The leakage mechanism primarily involved local overpressure, buoyancy effects, and diffusion. The research, for the first time, experimentally revealed the response relationship between methane leakage and hydrate dissociation, providing foundational data and theoretical support for the safe and efficient NGH development.

Extinction of Ammonium Perchlorate: Similarity Between Rapid Depressurization and Low-Pressure Deflagration Limit

ABSTRACT The extinction of Ammonium Perchlorate (AP) monopropellant due to two transient processes, namely rapid depressurization and Low-Pressure Deflagration Limit (LPDL), was studied. The critical depressurization rate was determined experimentally using silica grease on the sides of the AP pellet to reduce convective heat loss. The critical depressurization rate was found to lie between 1820 and 1950 MPa/s. The computed critical depressurization rate was found to be 1450–1500 MPa/s with variable thermal properties in the condensed phase. The extinction of AP due to LPDL was studied using different heat fluxes imposed on the surface. Case I involved the constant heat flux imposed on the surface and suddenly reduced to zero, while case II involved constant heat flux imposed on the surface and linearly reduced to zero. The combustion stability was checked for both cases, and it was found that the combustion remains in a stable regime. For case I, the AP did not burn below 5.0 MPa when the imposed heat flux of 3 MW/m2 was suddenly reduced to zero in 0.1 s. However, for case II, the AP was found to burn up to 1.6 MPa when the imposed heat flux of 3 MW/m2 was linearly reduced to zero in 0.5 s. The extinction boundaries of two unsteady processes, extinction by rapid depressurization and extinction due to LPDL, were determined, and the two processes were shown to have similar physical behavior.

Upward migration of the shallow gas enhances the production behavior from the vertical heterogeneous hydrate-bearing marine sediments

Low gas production rates and insufficient gas yield hinder the large-scale production from natural gas hydrates; a joint production of gas hydrate and its underlying shallow gas is expected to address this limitation. This study focuses on the interaction between heterogeneous hydrate reservoirs and the upward migration of the shallow gas. The results indicated a 38.4 % increase in production efficiency with the assistance of the shallow gas. Specially, the melt water generated from extensive hydrate decomposition could potentially induce a lateral migration of the shallow gas at the interfacial zones of the heterogeneous reservoirs. Further investigation revealed that a lower production pressure would help the release of the shallow gas as well as the hydrate decomposition, thereby contributing to a 64.55 % shorter t90. A faster depressurization rate could facilitate the temperature recovery by intensifying the lateral movement of the shallow gas in the junction layer. Consequently, a proper control of the upward channeling of the shallow gas was suggested in the field test for a successive and secure gas production. Our results could be of help in elucidating the interlayer interference mechanisms and the selection of the depressurization strategy for a better recovery efficiency from the multi-gas source reservoirs.

Collaborative Fabrication of High-Quality Perovskite Films for Efficient Solar Modules through Solvent Engineering and Vacuum Flash System.

The vacuum flash solution method has gained widespread recognition in the preparation of perovskite thin films, laying the foundation for the industrialization of perovskite solar cells. However, the low volatility of dimethyl sulfoxide and its weak interaction with formamidine-based perovskites significantly hinder the preparation of cell modules and the further improvement of photovoltaic performance. In this study, we describe an efficient and reproducible method for preparing large-scale, highly uniform formamidinium lead triiodide (FAPbI3) perovskite films. This is achieved by accelerating the vacuum flash rate and leveraging the complex synergism. Specifically, we designed a dual pump system to accelerate the depressurization rate of the vacuum system and compared the quality of perovskite film formed at different depressurization rates. Further, to overcome the limitations posed by DMSO, we substituted N-methylpyrrolidone as the ligand solvent, creating a stable intermediate complex phase. After annealing, it can be transformed into a uniform and pinhole-free FAPbI3 film. Due to the superior quality of these films, the large area perovskite solar module achieved a power conversion efficiency of 22.7% with an active area of 21.4 cm2. Additionally, it obtained an official certified efficiency of 22.1% with an aperture area of 22 cm2, and it demonstrated long-term stability.

Effects of stepwise depressurisation rate on methane hydrate dissociation dynamics at pore scale using microfluidic experiments

Methane hydrate, recognized as a potential alternative energy source, faces challenges in achieving efficient production. Stepwise depressurisation has emerged as a viable technique for enhancing productivity, yet optimizing the depressurisation rate remains a complex issue. This study employs pore-scale experiments using microfluidic chips to examine the dissociation characteristics of methane hydrate under varying stepwise depressurisation rates. At a high depressurisation rate of 0.4 MPa/15 min, the dissociation process exhibits a three-stage pattern: stabilisation, rapid dissociation, and slow dissociation. During these stages, the mass transfer limitation in the water phase significantly impedes the dissociation rate. The gas-water migration triggered by depressurisation can mitigate this limitation. As the depressurisation rate is reduced to 0.2 MPa/15 min, the rapid dissociation stage splits into two due to a decrease in gas-water migration intensity. The dissociation rate decreases by 45% compared to the 0.4 MPa/15 min case. This results from an insufficient driving force for dissociation, necessitating another depressurisation step. Further reduction of the depressurisation rate to 0.1 MPa/15 min leads to a less pronounced gas-water migration, which is inadequate to significantly counteract the mass transfer limitation. As a result, the rapid dissociation phase occurring at a depressurisation rate of 0.4 MPa/15 min, which exhibits an average dissociation rate of 0.2%/s, subsequently transitions into a more uniform and slower dissociation stage, where the average rate of dissociation declines to below 0.07%/s. The experimental results offer valuable insights for guiding hydrate exploration strategies during the stepwise depressurisation process by adjusting the depressurisation rate to regulate production.

Nanofluids with superhydrophobic nanoparticles for improved depressurization mechanism in low permeability reservoirs

Decreasing injection pressure and increasing water injection are crucial methods to enhance oil recovery in low permeability reservoirs. However, the high injection pressure, constrained by the reservoir's low porosity and permeability, limits the amount of injected water, consequently resulting in low recovery. In this study, inspired by the ''lotus effect'' of superhydrophobic wettability, we synthesized superhydrophobic nanoparticles by grafting fluorine-containing long chains onto the surfaces of SiO2 nanoparticles. Nanofluids with small particle size (7 nm), high stability, and strong hydrophobicity (162°) were prepared by compounding modified SiO2 nanoparticles with surfactants. The functional properties of the nanofluids revealed a depressurization rate of 23.13 % and the 23.90 % increase in flow rate at the channel center. Modified nanoparticles altered the surface wettability from hydrophilic to superhydrophobic. Surface free energy, determined using a three-probe-liquid method, demonstrated a significant reduction after hydrophobic modification. The surface hydrophobic interaction was tested and quantified by AFM measurements. The results show that the adhesion force is much larger than that of the unmodified hydrophilic surface. Through these analyses, we propose an efficient depressurization mechanism facilitated by the superhydrophobic layer formed by modified SiO2 nanoparticles. This work offers technical and theoretical support for the efficient development of low permeability reservoirs.

Supercritical Impregnation of PETG with Olea europaea Leaf Extract: Influence of Operational Parameters on Expansion Degree, Antioxidant and Mechanical Properties.

PETG (poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate)) is an amorphous copolymer, biocompatible, recyclable, and versatile. Nowadays, it is being actively researched for biomedical applications. However, proposals of PETG as a platform for the loading of bioactive compounds from natural extract are scarce, as well as the effect of the supercritical impregnation on this polymer. In this work, the supercritical impregnation of PETG filaments with Olea europaea leaf extract was investigated, evaluating the effect of pressure (100-400 bar), temperature (35-55 °C), and depressurization rate (5-50 bar min-1) on the expansion degree, antioxidant activity, and mechanical properties of the resulting filaments. PETG expansion degree ranged from ~3 to 120%, with antioxidant loading ranging from 2.28 to 17.96 g per 100 g of polymer, corresponding to oxidation inhibition values of 7.65 and 66.55%, respectively. The temperature and the binary interaction between pressure and depressurization rate most affected these properties. The mechanical properties of PETG filaments depended greatly on process variables. Tensile strength values were similar or lower than the untreated filaments. Young's modulus and elongation at break values decreased below ~1000 MPa and ~10%, respectively, after the scCO2 treatment and impregnation. The extent of this decrease depended on the supercritical operational parameters. Therefore, filaments with higher antioxidant activity and different expansion degrees and mechanical properties were obtained by adjusting the supercritical processing conditions.

Impact of Varied Depressurization Rates on Gas Production and Heat Supply in Hydrate Dissociation

Impact of Varied Depressurization Rates on Gas Production and Heat Supply in Hydrate Dissociation

Transient Liquefaction on the Lunar or Martian Surface Operational Demonstration

As developments of local production of cryogenic fluids on the Lunar or Martian surface progress, it is important to understand transient system responses to help with the balancing of process plant power and understanding system-level operations. During the Cryogenic Fluid In-situ Liquefaction for Landers (CryoFILL) testing, a series of transient oxygen liquefaction tests were completed. These tests included varying liquefaction flow rate, environmental temperature, tank fill level, and effective cryocooler lift while allowing the tank pressure to respond to the input controls. An additional transient test was run at the 90% fill level to determine the impact of injecting the gaseous oxygen at the bottom of the tank, allowing the vapor to bubble up through the liquid. Tests were run in a cyclical nature varying one variable at a time. The control variable was set in a manner to increase tank pressure for a period of time and then subsequently changed in a manner to decrease the tank pressure back to its original value with multiple cycles run for all tests. Tank pressure and system temperature responses were tracked as a function of time with an emphasis on repeatability. Results indicate that of the four variables tested, the environmental temperature is the least important. As expected, the bubbling of the liquefaction gas significantly decreased the pressurization and depressurization rates in the tank at the 90% full level.

Geomechanical responses of sand–clay interbedded gas hydrate-bearing deposits under depressurization-driven gas production at site UBGH2-6 in Ulleung Basin, offshore Korea

This study explores geomechanical responses of sand-clay interbedded hydrate reservoirs subjected to depressurization. A thermo-hydro-mechanically (T-H-M) coupled simulation code was created to simulate T-H-M interactions in layered hydrate reservoirs, utilizing an explicit two-way coupling scheme. The code was then used to model a hydrate reservoir analogous to a hydrate deposit system in Ulleung Basin, Offshore Korea (Site UBGH2-6). Hydrate reservoirs comprising thin and interbedded sand-clay layers exhibit unique geomechanical responses due to the localized gas hydrate dissociation along sand-clay layer interfaces. The localized dissociation pattern leads to accelerated sediment consolidations along the layer interfaces. The simulation results also reveal development of shear deformation along the sand-clay interfaces, which implies the layer interfaces may act as the main sources of sand productions and fines migration within a depressurized hydrate reservoir. Additional simulations are conducted to further investigate the effects of depressurization rate and formation wettability on gas productivity. Although faster depressurization speeds up initial gas production, ultimately, the production rate is governed by the final bottom hole pressure, regardless of the depressurization rate. Nonetheless, slower depressurization appears more favorable, given its capacity to mitigate initial geomechanical responses, such as reservoir compaction and sand production, thus preserving the long-term production potential of a hydrate reservoir. On the other hand, a cyclic depressurization scheme also proves to be able to mitigate the level of initial geomechanical responses, but only at the cost of reduced gas productivity. A comparative analysis with varying wettability indicates that water-wet reservoirs may be more favorable target for gas hydrate exploitation than gas-wet reservoirs. The presented results enhance understanding of complex hydrate reservoir dynamics and contribute to advancement of sustainable and efficient hydrate production techniques.

A Blowdown Critical Heat Flux Experimental Vehicle

In the most challenging nuclear power plant accidents, transient critical heat flux (CHF) is a primary phenomenon that drives peak cladding temperature, and ultimately, fuel failure. It has not yet been determined whether the use of steady-state CHF methods can accurately predict transient CHF under the conditions of a blowdown due to a loss-of-coolant accident. There are limited comprehensive experiments at prototypic conditions. To address this deficiency, a quality separate-effects test facility was built to simulate an electrically heated rod under blowdown conditions. Testing reached full pressurized water reactor thermal-hydraulic conditions. With scaled break sizes as large as a double-end cold leg break, CHF was repeatedly measured with depressurization rates ranging from 7 to 17 MPa s−1. These measurements at prototypic conditions acquired in a controlled methodology are novel to the body of knowledge. Several steady-state CHF methods and heater models were evaluated using RELAP5-3D simulations and the Dakota framework. The results showed that many steady-state CHF methods performed inadequately, but that recently developed wide-ranged, look-up table methods had the most acceptable results. Additionally, the results showed no significant correlation between prediction accuracy and the depressurization rates tested.

Influence of foaming-induced crystallization behavior on the structure of poly(butylene adipate-co-terephthalate) supercritical foamed beads

The crystallization behavior during foaming directly affects the foaming properties. For crystalline polymers, there is no consensus on the influence of the crystallization behavior during foaming process on the stabilization of the cell structure. In this work, PBAT foamed bead and unfoamed pellets were prepared by controlling the saturated temperatures in supercritical CO2, soaking step (one or two) and the depressurization rate, respectively. Double melting peaks were observed in the DSC curve of supercritical CO2 foamed PBAT beads. By comparing the outgassing rates we find that the stretching-induced crystallization caused by the rapid expansion of the gas during foaming plays an important role in the stabilization of the cells. Although the crystalline perfection or crystal size at this time is much smaller than that of the crystalline grains formed during static cooling, the rapid crystallization is effective in stabilizing the cell structure of the foamed pores. Compared to normal supercritical foaming processes, the two-step foaming process of soaking CO2 at high temperatures followed by foaming at low temperatures results in an increase in cell size and expansion ratio. At high temperatures, more CO2 diffuses into the PBAT pellets, increasing the instantaneous gas concentration in the pellets for foaming, and the rapid stretching produces stretching-induced crystallization that raises the average size of the cells, further increasing the expansion multiplicity of individual cells. The average cell size of foam beads rises from 37.8 to 48.8 µm and the expansion ratio also increases to 8.6 with saturated temperature increasing form 95 to 105°C. The two-step soaking foaming method is a more efficient way of manufacturing industrial foamed beads, allowing for the preparation of better foam beads at low temperatures.

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.

Foaming of 3D-Printed PLA/CaCO3 Composites by Supercritical CO2 Process for Sustainable Food Contact Materials.

In the last decade, among the emerging technologies in the area of bioplastics, additive manufacturing (AM), commonly referred to as 3D printing, stands out. This technology has gained great interest in the development of new products, mainly due to its capability to easily produce customized and low-cost plastic products. This work aims to evaluate the effect of supercritical foaming of 3D-printed parts based on a commercial PLA matrix loaded with calcium carbonate, for single-use sustainable food contact materials. 3D-printed PLA/CaCO3 parts were obtained by 3D printing with a 20% and 80% infill, and two infill patterns, rectilinear and triangular, were set for each of the infill percentages selected. Supercritical fluid foaming of PLA/CaCO3 composite printed parts was performed using a pressure of 25 MPa, a temperature of 130 °C for 23 min, with a fast depressurization rate (1 s). Closed-cell foams were achieved and the presence of CaCO3 did not influence the surface of the foams or the cell walls, and no agglomerations were observed. Foam samples with 80% infill showed subtle temperature fluctuations, and thermogravimetric analysis showed that samples were thermally stable up to ~300 °C, while the maximum degradation temperature was around 365 °C. Finally, tensile test analysis showed that for lower infill contents, the foams showed lower mechanical performance, while the 80% infill and triangular pattern produced foams with good mechanical performance. These results emphasize the interest in using the supercritical CO2 process to easily produce foams from 3D-printed parts. These materials represent a sustainable alternative for replacing non-biodegradable materials such as Expanded Polystyrene, and they are a promising option for use in many industrial applications, such as contact materials.

Experimental Analysis on Thermodynamic and Kinetic Characteristics of Water‐Saturated Natural Gas Hydrates by Depressurization Decomposition

Natural gas hydrate has attracted worldwide attention for its abundant availability and clean and nonpolluting combustion products. The actual environment of marine methane hydrates is water‐saturated, but present researches on water‐saturated hydrates are relatively few. This study prepares water‐saturated hydrate sediment of ≈70% saturation and mainly focuses on the thermodynamic and kinetic characteristics of decomposition process using different depressurization rates. Compared with gas‐saturated hydrates, both the thermodynamic evolution and the decomposition kinetics of water‐saturated hydrates get weakened due to the inhibition of water molecules surrounding hydrate crystals on heat and mass transfer. In all experimental cases of water‐saturated hydrates, the temperature still decreases at most 0.5 °C in several minutes after the pressure has become constant, indicating the delay effect of depressurization in water phase. The results show that the increase in depressurization rate strengthens both temperature decrease and pressure delay of water‐saturated hydrate‐bearing sediment. In addition, the decomposition rate of water‐saturated hydrates in depressurization stage is constant and positive to the depressurization rate, while the decomposition rate in constant pressure stage is a function of residual hydrate amount. This study is significant for decomposition control of hydrate mining under actual marine environment.

On the Influence of Fine Particle Migration and Deposition on Gas Hydrate Production: Insights from the First Trial Production in the South China Sea

Summary As a promising alternative energy source with vast reserves, the primary challenge in exploiting natural gas hydrates (NGHs) lies in achieving long-term safety and efficiency. Several production tests conducted globally have demonstrated that the production of solid particles is one of the main factors contributing to this issue. However, most studies on assessing NGH production capacity have overlooked this phenomenon and its impact on production performance, potentially compromising the accuracy of simulation results. Therefore, this study aims to quantitatively analyze the impact of fine particle migration and deposition on gas production by numerically examining the first NGH production test conducted in the Shenhu area of the South China Sea (SCS). Through comparison of simulation results with the reconstructed gas production curve, the model was calibrated and enabled an explanation of unique gas production performance during field testing. It is found that the deposition of solid particles reduced the gas production rate by nearly an order of magnitude during the initial stage of exploitation. Long-term simulation results indicate that only the three-phase layer (TPL) remains partially unobstructed and serves as the primary source of gas production in later stages. Sensitivity analysis reveals that both depressurization and particle control strategies exert significant effects on particle migration, which in turn affects gas production. Specifically, the increase in depressurization amplitude does not necessarily lead to improved gas production behavior beyond a certain threshold (approximately 6 MPa). This study illustrates the inherent trade-off between preventing particle production and increasing gas production, highlighting the need for a safe and efficient production scheme that strikes a balance between these two objectives. Based on the current study, it is preliminarily recommended to maintain a depressurization amplitude of approximately 6 MPa with a maximum depressurization rate of 3 MPa/d and ensure a fine particle filtration ratio of no less than 95%.

Influence of depressurization mode on natural gas hydrate production characteristics: One-dimensional experimental study

The latest research suggests that using depressurization methods and their enhancements could be the most effective way to produce natural gas hydrates efficiently in marine areas. Therefore, it's crucial to investigate the gas production behavior and the changes in temperature and pressure within natural gas hydrate reservoirs under different depressurization methods. In this paper, the self-developed one-dimensional natural gas hydrate production simulation test system was utilized to conduct one-dimensional depressurization production tests during two depressurization modes of significant depressurization and slow depressurization. The findings indicated that the minimum temperature increment-depressurization rate curves in significant depressurization tests exhibited irregular patterns, primarily due to the frequency and intensity of hydrate reformation, while the smaller the depressurization rate, the larger the minimum temperature increment and the smaller the maximum dissociation rate under slow depressurization. In addition, when maintaining a fixed hydrate saturation level, the peak gas production rate showed a decline with decreasing depressurization rate. However, the exact correlation between the peak gas production rate and the depressurization rate remained uncertain due to the unpredictable nature of the “armoring” effect.