Mixed Hydrate Research Articles

The role of phase saturation in depressurization and CO2 storage in natural gas hydrate reservoirs: Insights from a pilot-scale study

The natural gas recovery and CO2 storage in natural gas hydrate (NGH) reservoirs is a promising integrated strategy for implementing clean energy production and CCUS. However, the fundamental characteristics (phase saturation) of NGH reservoirs on the feasibility and efficiency of the above-integrated processes remain unclear. In this study, we synthesized methane hydrate-bearing sediments (MHBS) with varying hydrate saturation (SH = 18–66 %) and aqueous saturation (SA = 7–92 %) at marine NGH conditions (T = 283.8 K, P = 11.0 MPa). The effect of phase saturation on depressurization-induced hydrate dissociation, and subsequent CO2 storage and hydrate restoration by CO2/N2 injection was investigated. The water-saturated MHBS with high SA can promote faster MH dissociation during the depressurization stage and prevent secondary hydrate formation, but a slower MH dissociation during the later stage due to slow heat transfer. A relatively high SH (> 63 %) results in sustained low temperatures due to insufficient heat supply slowing down MH dissociation. The CH4/CO2/N2 mixed hydrates (Mix-H) formation and CO2 storage in depleted MHBS after CO2/N2 injection initially increase and then decrease with post-mining SA (peak at SA = 54.5 %). The rate of Mix-H formation decreases as the post-mining SA increases. Higher pre-mining SH and CO2/N2 injection rate facilitates rapid gas phase mixing within the sediments, thereby improving the kinetics and homogeneity of Mix-H formation and hydrate-based CO2 storage efficiency. MHBS with relatively low SH and SA exhibit enhanced safety for the integrated process, offering reduced depressurization-induced sediment subsidence and increased hydrate restoration ratios (∼85 %) by Mix-H formation.

Thermodynamic stability and component heterogeneity of CO2/N2 mixed hydrates: Implications for hydrate-based CO2 capture and sequestration

Injecting CO2/N2 into marine sediments to form gas hydrates for CO2 storage is an emerging Carbon Capture and Storage (CCS) technology, holding the potential to significantly reduce the costs of CCS while simultaneously enhancing environmental persistence. However, there is currently a lack of comprehensive investigation into the critical parameters and stability evaluations of CO2/N2 mixed hydrates (Mix-H) formation. This study delves into the impact of gas–liquid ratios, pressure–temperature gradients, and hydrate formation degree on the phase equilibrium, formation kinetics, and thermodynamic stability of Mix-H. Experimental findings elucidate the excess water significantly enhances CO2 dissolution, increasing the thermodynamic barrier for Mix-H formation. Consequently, this leads to weakened kinetics and reduced total CO2 composition within the Mix-H (54.2%–96.4%). Raman spectroscopy confirmed varying heterogeneous compositions and thermodynamic stability of hydrate crystals within the bulk Mix-H. The heterogeneity is quantitatively assessed using a novel test – stepwise depressurization, which revealed increased heterogeneity with decreasing initial pressure–temperature as well as increasing gas–liquid ratios and hydrate formation degree. The heterogeneity of Mix-H significantly impacts the CO2 capture efficiency and long–term stability of CO2 sequestration under environmental disturbances. The results also pave the way for evaluating the performance of mixed hydrate application in hydrate–based chemical engineering and CCS technology.

Mechanical and acoustic characterization of carbon dioxide gas replacement of methane gas hydrate

CO2 replacement presents a promising approach for the extraction of natural gas hydrate, offering advantages in cleanliness and safety. In this study, CO2 replacement CH4 hydrate experiments were carried out by using the triaxial, hydrate specimens with varying replacement ratios were prepared through different methods, and triaxial tests were performed to evaluate the mechanical properties of sediments after replacement. The key findings are as follows: the shear damage behaviors of CH4, CO2, and their mixed hydrate specimens are similar. Acoustic data indicates that initial CO2 injection during replacement causes dissociation of CH4 hydrate, potentially reducing the failure strength of the reservoir. However, post-replacement hydrate specimens exhibited higher failure strength than their original counterparts. This study provides valuable insights into the mechanical stability of CH4 hydrate reservoirs during CO2 replacement process.

Determination of hydrate phase equilibrium (H-L-V) data for the binary CO2–CH4 gas mixture in the presence of 1,3 dioxolane

Present work details the determination of three phase hydrate equilibrium data (H-L-V) using temperature search method for the binary CO2/CH4 gas mixture (50:50 molar ratio) in presence of 1,3 dioxolane (DIOX). DIOX concentration used for phase equilibrium determination were 1,3 and 5.56 mol% respectively. In the presence of DIOX, it was observed that phase equilibrium curve was shifted right with respect to the curve using same gas mixture with no additive (pure water). This indicates that the presence of DIOX moderates the hydrate formation equilibrium conditions. Also, as DIOX concentration increases from 1 mol% to 5.56 mol%, a decrement in phase equilibrium pressure at same temperatures was observed, confirming the potential of DIOX as an effective thermodynamic promoter. Enthalpy of hydrate dissociation was calculated for CO2/CH4 gas mixture in presence of DIOX using Clausius- Clapeyron plot and it was found to be 90.81±6.55 KJ/mol which confirms the sII structure of CO2-CH4-DIOX mixed hydrate. Besides providing the phase equilibrium data of formed hydrates with CO2/CH4 gas mixture using different concentration of DIOX, the present study will aid in determining suitable experimental conditions for examining kinetics and performing separation studies of CO2/CH4 gas mixture through hydrate formation.

Predicting three phase (hydrate–liquid–vapour) equilibria of mixed hydrates in guest gas swapping: AI‐based approach versus physical modelling

Predicting three phase (hydrate–liquid–vapour) equilibria of mixed hydrates in guest gas swapping: <scp>AI</scp>‐based approach versus physical modelling

Pore-Scale Study on the Effect of SO2 on Hydrate-Based CO2 Sequestration in a High-Pressure Microfluidic Chip

Summary To mitigate the effects of greenhouse gases, the sequestration of greenhouse gases such as carbon dioxide (CO2) in seafloor sediments in the form of hydrates has become a safe and efficient method. If sulfur dioxide (SO2), one of the flue gas impurities, is also sequestered, the cost of CO2 purification and sequestration can be effectively reduced. However, there is a lack of in-situ observation of how SO2 affects the nucleation and growth process of CO2 hydrates. In this study, a visual microfluidic chip combined with in-situ Raman spectroscopy was used for the first time to investigate the impact mechanism of SO2 on the nucleation and growth kinetics of CO2 hydrates in porous media. The results indicate that SO2 could promote the nucleation and growth of CO2 hydrate in the following aspects: First, the diffusion of SO2 in solution induces spontaneous convection of the solution in the pores, which could promote the nucleation of mixed hydrates. After nucleation, dissolved SO2 acts as a “seed” for hydrate formation, and the pore solution is covered with hydrate microcrystals, providing heterogeneous nucleation sites for hydrate growth in solution. During the growth stage, SO2 could induce the preferential growth of mixed hydrates within the solution and enhance the growth rate of hydrates, acting as a promoter of hydrate formation. As CO2-SO2 mixed hydrates preferentially grow in solution and grow denser, it could quickly cement the pores, which could significantly improve the stability of the reservoir and form a strong hydrate barrier in the reservoir. These findings have important theoretical value and guiding significance for the synchronous sequestration of CO2-SO2 by hydrates.

Fundamental insights into multistep depressurization of CH4/CO2 hydrates in the presence of N2 or air

Exploitation of natural gas hydrates provides an alternative way to address energy crisis. Dilute CO2 gas (13–30mol%CO2 with remaining N2/Air) injection into CH4 hydrates for hydrate swapping (SW) allows cheaper and more practical CH4 recovery and in-situ CO2 sequestration. However, the roles of N2/Air in dilute CO2 gas during exploitation remain unknown. It is unclear whether depressurization should be coupled after SW and continued below CH4 hydrate stability pressure. This work employed multistep depressurization (MD) to dissociate the mixed hydrates formed after SW from 86.5 to 97.9 bar at 0.7–1.2 °C in bulk-water and sandpack with CH4 hydrate saturation of 4.1–25.3 %. Effects of N2/Air on exploitation were investigated by examining hydrate morphologies and gas compositions. Morphological results in bulk-water indicated higher N2 fraction in 20mol%CO2/N2 triggered more CO2-rich hydrate reformation and CH4-rich hydrate dissociation. Exploitation results in sandpack indicated 13mol%CO2/N2 produced the highest CH4 swapping percent (46.6 %) and CO2 hydrate sequestration percent (29.1 %). Air exerted weaker promoting effects on exploitation compared with equivalent N2. The promotion of N2/Air on exploitation was dominated by dilute CO2 gas injection altering mixed hydrate equilibrium which varied with time-dependent gaseous compositions during MD. l-methionine of 3000 ppm had stronger promoting effects on CO2 sequestration in sandpack than bulk-water depending on mass transfer and water availability. Ceasing points (13.9–31.4 bar) suggested MD could be continued below CH4/above CO2 hydrate stability pressures and before water production. For the first time, this study provided insights into the roles of N2/Air to determine injection gas types and depressurization schemes for efficient and safe hydrate exploitation in gas-rich hydrate-bearing sediment.

Synergistic CH4 recovery and CO2 sequestration through amino acid-assisted injection in methane hydrate sediments

Methane (CH4) hydrates exist on the seabed globally. This study explores the novel concept of methane recovery by CO2 exchange into CH4 hydrate through depressurization-assisted CO2 injection. For the first time, we demonstrate the effectiveness of CH4 recovery and CO2 sequestration using l-Leucine amino acid. Three different approaches of additive injection to assess feasible methane recovery were studied. The investigation focuses on the thermodynamic region between CH4 and CO2 phase equilibrium lines in the presence of 0.5 wt% leucine. The amino acid system shows a 5 % increase in CH4 recovery compared to the pure sediment system. Gas exchange kinetics suggest equilibration of released methane and injected CO2, prompting recrystallization into mixed hydrate. CO2 consumption correlates with initial CH4 hydrate conversion, with higher methane conversion resulting in lower CO2 intake. The amino acid system promotes quicker hydrate dissociation and greater stability of mixed hydrates, preventing induced melting during depressurization. Ex-situ Raman analysis performed after the CO2 exchange in 0.5 wt% Leucine system resulted in a four-wave number upward shift at 2919 cm−1 indicating partial distortion of small cages. The Large (L)/Small (S) cage intensity ratio of CH4 hydrate after swapping is 0.57, suggesting a 50 % methane replacement by CO2 with preferential CO2 occupying large cages.

Molecular insight on CO2/C3H8 mixed hydrate formation from the brine for sustainable hydrate-based desalination

Systematic molecular dynamics simulations have been performed to investigate the formation of CO2/C3H8 mixed hydrate in brine, to search for the optimal C3H8 content and elucidate the microscopic mechanism for hydrate-based desalination process. Simulation results indicate that the desalination process is significantly affected by the formation kinetics of CO2/C3H8 mixed hydrates due to the diverse physical properties of CO2 and C3H8 molecules in the brine. Specifically, CO2 molecules are more likely to leave the mixed gas nanobubbles and form hydrates, whereas most of C3H8 molecules remain in gas nanobubbles for a prolonged period. Interestingly, ions can form abnormal CO2-occupied and C3H8-occupied hydrate cages by replacing the water molecule in cages, and some ions can also be adsorbed on the surfaces of the cage-like hydrogen bond network or encapsulated between the hydrate solids. The presence of these ions presents a challenge to separating them due to the strong attraction from the water in hydrate solids. On the other hand, it is confirmed that the C3H8 content with 10 % is optimal for CO2/C3H8 mixed hydrate-based desalination, as it promotes the decomposition of mixed gas nanobubbles to form hydrates by suppressing the structural fluctuations in the system. These molecular insights into the effect of C3H8 content on CO2/C3H8 mixed hydrate formation in brine may help to develop hydrate-based desalination technology.

Molecular dynamics study on roles of surface mixed hydrate in the CH4/CO2 replacement mechanisms

The CH4/CO2 replacement method is a promising approach for the exploitation of natural gas hydrates, offering dual benefits of extracting CH4 and sequestering CO2. This technique not only facilitates the extraction process but also mitigates the greenhouse effect and maintains geological stability, thereby contributing to sustainable energy utilization and environmental preservation. Currently, there are multiple viewpoints about the replacement mechanism. Furthermore, mixed hydrates can form on the surface during the replacement process. The unclear mechanism of CH4/CO2 replacement and the obstruction of mass transfer caused by the mixed hydrate impede its practical applicability. Clarifying the effects of surface mixed hydrate in replacement mechanisms can offer valuable insights for identifying optimal operating conditions in practical exploitation applications. Therefore, the present study aims to reveal the significant roles of surface mixed hydrates in the replacement mechanism by employing the molecular dynamics simulation methodology. The results showed that under the mechanism of cage complete rupture, the surface mixed hydrate decomposes rapidly to form a thickening water zone. Additionally, each layer of the hydrate cage structure undergoes a process from deformation or partial rupture to sudden complete disintegration, which is concomitant with an abrupt change of potential energy. Under the mechanism of cage incomplete rupture, the surface mixed hydrates hinder mass transfer and decelerate the reaction rate. A similar situation arises when the number of the surface mixed hydrate layers is increased. Therefore, the key to distinguishing the replacement mechanism lies in whether the environmental conditions are sufficient to break the potential energy barrier of the surface mixed hydrate and disrupt its cage structure.

Coupling amino acid injection and slow depressurization with hydrate swapping exploitation: An effective strategy to enhance in-situ CO2 storage in hydrate-bearing sediment

Natural gas (mainly methane, CH4) hydrates are a prospective energy resource. CH4-CO2 hydrate swapping has the advantages of producing CH4 gas for clean energy recovery and simultaneously storing CO2 in-situ for carbon emission reduction. Depressurization is the most feasible strategy to recover CH4 from hydrate-bearing sediments. The combination of these two methods has been proved feasible to produce CH4-rich gas and store CO2-rich hydrate. However, the efficiencies of CH4 recovery and CO2 storage decrease significantly when the reservoir is depressurized to the points below CH4/CO2 mixed hydrate equilibrium pressure causing unwanted CO2-rich hydrate dissociation. In this work, amino acid injection (AAI) (L-tryptophan or L-methionine) was employed for CH4/CO2 mixed hydrate formation with enhanced CO2 storage, followed by slow depressurization in various controlled manners, i.e., multistep depressurization, constant-pressure depressurization or multistep constant-pressure depressurization (MCPD) to recover CH4 from the mixed hydrates. In-situ Raman and gas chromatograph (GC) were employed to confirm the compositions of mixed hydrates formed and mixed gases produced. The results showed that AAI decreased CO2 fraction from 30 mol% to 3.1–8.4 mol% in the residual gas, indicating the technique helped regaining reservoir pressure and kinetically promoting further hydrate formation. The pressure recovered by AAI compensated the performance discrepancy caused by different solutions injected. Raman spectra and GC results confirmed CO2-rich hydrate formation, and up to 91.3% CO2 was stored in the sediments. During mixed hydrate dissociation, slow depressurization maintained high CH4-rich gas production (CH4 fraction over 87.5 mol%), with 9.7–30.6% CH4-rich gas recovered and 5.8–17.9% water produced among various trials. The best performance of CO2 storage and CH4 recovery was achieved by AAI of 1000 ppm L-tryptophan at 33.2 bar and MCPD to 20.9 bar, showing a final CO2 storage efficiency of 82.3%, gas recovery percentage of 30.6% and gas/water production ratio of 37.9 STP m3/m3. These findings provided guidance to enhance CO2-rich hydrate storage and CH4-rich gas production by multiple AAI and slow depressurization at controlled depletion pressures after hydrate swapping.

Prediction of Phase Equilibrium Conditions and Thermodynamic Stability of CO2-CH4 Gas Hydrate

With the large-scale promotion and application of CO2 flooding, more and more engineering problems have emerged. Due to the high CO2 mole fraction, the associated gas of CO2 flooding very easily forms solid hydrates, compared to conventional natural gas. This has resulted in production decline or shutdown. Understanding the phase equilibrium conditions for hydrate formation in production fluids is crucial for hydrate prevention and control. In this study, accurate predictions of CO2-CH4 mixed gas hydrate formation conditions were performed using theoretical models. The temperature and pressure ranges for hydrate formation were calculated for different CO2 mole fraction, ranging from −11.5 °C to 20.85 °C and from 0.81 MPa to −28.1 MPa, respectively. Based on the calculated phase equilibrium data, a multi-parameter empirical model was developed using polynomial fitting. The calculation errors for the multi-parameter empirical model were 3.09%. The multi-parameter empirical model established in this study can avoid complex thermodynamic equilibrium calculations and has the advantages of simplicity, high accuracy, and wide coverage of downhole conditions. Based on the calculated phase equilibrium data, the dissociation enthalpy of CO2-CH4 hydrate below and above the freezing point of water was calculated. The results showed that an increase in CO2 mole fraction led to an increase in hydrate dissociation enthalpy and enhanced thermodynamic stability, making hydrate prevention more challenging. Our work can contribute to the optimization of CO2 production fluid treatment processes and the development of hydrate prevention and control technologies.

Polymorphisms in M2+AlF5(H2O)7 (M2+ = Fe2+, Co2+, or Ni2+): Syntheses, Crystal Structures, and Characterization of New Mixed Metal Fluoride Hydrates

Three new mixed metal fluoride hydrates, M2+AlF5(H2O)7 (M2+ = Fe2+, Co2+, or Ni2+), were synthesized and characterized. The crystals of M2+AlF5(H2O)7 were obtained using a hydrothermal method with a CF3COOH aqueous solution. The crystal structures displayed polymorphisms in C2/m (No. 12) or P-1 (No. 2) space groups, depending on temperature variations. The observed polymorphisms in M2+AlF5(H2O)7 are associated with changes in the bonding environment of [M(H2O)6]2+ and [AlF5(H2O)]2− octahedra, along with changes in hydrogen bonds and unit cell volumes. Infrared spectra and thermogravimetric analyses confirmed the presence of water molecules. The ultraviolet–visible spectra of M2+AlF5(H2O)7 revealed distinctive absorption bands dependent on the [M(H2O)6]2+ complex. This work provides a detailed account of the synthetic procedure, crystal structures, and spectroscopic characterization of M2+AlF5(H2O)7.

Tuning effect of DIOX on the thermodynamics and cage occupancy of CH4/CO2 + DIOX mixed hydrates

Hydrate technology could provide a novel approach to deliver convenient CO2-rich natural gas. The identification of a suitable and environmental-friendly promoter for enhancing CO2/CH4 hydrate kinetics is critical. In this study, we evaluated the thermodynamics, kinetics, and morphology of CH4/CO2 + DIOX mixed hydrates in the presence of a thermodynamic promoter 1,3-dioxolane (DIOX) at and below its stoichiometric concentration (SC, CDIOX = 5.56 mol%). Due to the thermodynamic preference of DIOX enclathration in mixed hydrates formation, a decrease in CDIOX in the unconverted solution was observed post nucleation below SC and the hydrates formed exhibit significant heterogeneity in cage occupancy. As CDIOX in the unconverted solution decreases, the DIOX concentration in hydrate (RDIOX) and the thermodynamic stability of the newly formed hydrates decreases. Based on the step-wise heating design, the thermodynamic stability of the hydrates formed below SC with high-RDIOX is close to that of hydrates formed at SC, while hydrates with low-RDIOX undergo dissociation at their P-T trajectories above the measured phase equilibria. Raman measurement indicates that the lower-RDIOX hydrates possess a higher CO2 composition. This study provides new insights into the tuning effect of DIOX on mixed hydrates formation and the basis for using low thermodynamic promoter concentration in hydrate-based technologies.

Evaluation of a Simplified Model for Three-Phase Equilibrium Calculations of Mixed Gas Hydrates

In this study, we perform an extensive evaluation of a simple model for hydrate equilibrium calculations of binary, ternary, and limited quaternary gas hydrate systems that are of practical interest for separation of gas mixtures. We adopt the model developed by Lipenkov and Istomin and analyze its performance at temperature conditions higher than the lower quadruple point. The model of interest calculates the dissociation pressure of mixed gas hydrate systems using a simple combination rule that involves the hydrate dissociation pressures of the pure gases and the gas mixture composition, which is at equilibrium with the aqueous and hydrate phases. Such an approach has been used extensively and successfully in polar science, as well as research related to space science where the temperatures are very low. However, the particular method has not been examined for cases of higher temperatures (i.e., above the melting point of the pure water). Such temperatures are of interest to practical industrial applications. Gases of interest for this study include eleven chemical components that are related to industrial gas-mixture separations. Calculations using the examined methodology, along with the commercial simulator CSMGem, are compared against experimental measurements, and the range of applicability of the method is delineated. Reasonable agreement (particularly at lower hydrate equilibrium pressures) between experiments and calculations is obtained considering the simplicity of the methodology. Depending on the hydrate-forming mixture considered, the percentage of absolute average deviation in predicting the hydrate equilibrium pressure is found to be in the range 3–91%, with the majority of systems having deviations that are less than 30%.

Investigation of Hydrate Formation and Stability of Mixed Methane-THF Hydrates: Effects of Tetrahydrofuran Concentration.

Effects of tetrahydrofuran (THF) concentration on the mixed methane hydrate formation, dissociation, and stability were investigated. The experiment was conducted at 286.2 K and 6 MPa in a quiescent reactor. The presence of THF below 2.5 mol% did not show the evidence of hydrate formation. However, the concentration above 2.5 mol% enhanced the methane formation rate and the methane consumption. Increasing the THF concentration decreased the induction time as the result of the decrease in the surface tension. Moreover, the methane uptake and formation rate increased with the THF concentration due to the higher degree of hydrate nucleation. The methane recovery after the dissociation experiment showed up to 96%. Furthermore, the hydrate stability increased, and the hydrate dissociation kinetics decreased with the increase in the THF concentration. The optimum THF concentration to enhance and improve the hydrate formation kinetics and stability is its stoichiometric concentration.

Research progress on the influencing factors and enhancement mechanism of CH4/CO2 mixture separation process by hydrate‐based technology: A review

AbstractThe separation of mixed gas by hydrate method can realize the efficient separation of CO2 gas from biological gas. However, the long period, slow rate, and low selectivity of hydration reaction have become the critical problems restricting the efficient separation of the gas mixture by hydrate method. In this review, the formation characteristics of CH4/CO2 mixed gas hydrate are systematically summarized, and the kinetic process and influencing factors of CH4/CO2 mixed gas hydrate formation are comprehensively analyzed. On this basis, the influence mechanism and law of temperature, pressure, gas–liquid ratio, gas component ratio, additives, and other factors on the CH4/CO2 mixed gas hydrate formation progress were described in detail, and the enhancement mechanism of CH4/CO2 mixed gas hydrate formation under the influence of different factors was analyzed. Finally, the shortcomings and future development directions of the purification and separation technology of CH4/CO2 mixed gas by hydrate method are pointed out. Further research is needed to understand the kinetic mechanism and enhancement mechanism of the CH4/CO2 mixture separation process by hydrate method. The relative results will provide valuable guidance for the separation of mixture gas by a hydrate‐based method.

Enthalpy of dissociation of the mixed methane + propane sII hydrate along the three-phase equilibrium line

ABSTRACT We present a detailed overview of the calculation of the enthalpy of dissociation of structure II pure propane or mixed methane + propane hydrates, focussing primarily on methods that are based on either the Clausius-Clapeyron equation or the direct calculation of the enthalpies of all the components that are involved in the hydrate dissociation reaction. Molecular dynamics simulations are used extensively in order to calculate the enthalpies and molar volumes of water, methane, propane, and the sII mixed hydrate (with variant degree of occupancy) at pressure and temperature conditions along the three-phase (Hydrate–Liquid water–Vapor or Hydrate–Liquid water–Liquid hydrocarbon) equilibrium line.

Quantification of mixed hydrate and free gas concentrations by the joint integration of velocity and conductivity information

Quantification of gas hydrates in marine sediments is crucial for understanding gas hydrate systems. By empirical relationships or effective medium modelling, gas hydrate concentrations can be derived from velocity and/or conductivity logs. However, these approaches do not take the co-occurrence of free gas and gas hydrate into account leading to large uncertainties in the calculated free gas and gas hydrate concentrations. To overcome this issue we adopt a joint elastic and electric self-consistent/differential effective medium model as the basis for a new joint inversion scheme that distinguishes between both phases. We apply this scheme to p-wave velocity and electric induction data measured by downhole-logging of boreholes at Formosa Ridge off Taiwan - a known hydrate province with an active gas conduit. Gaussian Mixture Modeling separates the background signal of the host medium from anomalies and allows to determine a background porosity as a probability density function of depth. We use this derived porosity to jointly invert electrical conductivity and velocity data for hydrate and free gas concentrations. At Formosa Ridge, we find two resistive anomalies, one in the shallow and another in the deep part of the borehole. Only the deep anomaly in conductivity coincides with a high-velocity anomaly. This is consistent with ∼30% hydrate with ∼1% free gas concentration. For the shallow anomaly, increased velocities due to hydrate concentrations of ∼15% are compensated by a decrease in velocity due to ∼1% of free gas. The method reconciles the different sensitivities of the two data types and yields hydrate and free gas concentrations that are largely consistent with geochemically derived values.

A new approach to producing a prospective energy resource based on coalmine methane

The paper describes topical issues of a prospective method for coalmine methane utilization for obtaining an additional valuable energy resource for the regional development of coal-mining areas. It is noted that the development of the extraction of methane resources is very urgent and is of great economic importance for ensuring the energy independence of Ukraine. The experience and technologies of using methane and coalmine gas by global coal-mining companies are analyzed. Modern prospects and opportunities for using coal gas are studied. There is a need to transform the coalmine methane removal system and directions for maximizing the use of its resources in a wide range of concentrations in the composition of gas-air mixtures based on the development of innovative technologies to improve the efficiency and cost-effectiveness of functioning coal-mining enterprises. Attention is focused on the advantages of using gas hydrate technologies for obtaining additional energy resource under conditions of changing coalmine methane concentrations. The specifics of the process of mixed gas hydrate formation from gas mixtures of various geneses have been studied. It has been revealed that it is the coalmine gas-methane composition that determines and forms the basic condition for hydrate formation. The thermobaric conditions for the hydrate formation process at different methane concentrations in gas mixtures of degassing systems have been experimentally determined. The results obtained are the basis for further research on efficiency of creating gas hydrates from coalmine methane and determining its minimum permissible concentration in the gas mixture of degassing systems according to the technological and economic criteria of hydrate formation.