Gas Hydrate Formation Research Articles

Effects of Crystal Facets of Quartz on the Formation and Dissociation of Natural Gas Hydrates

Natural gas hydrates are non-stoichiometric crystalline compounds composed of natural gas and water, typically found in the pore spaces constructed by minerals. Mineral crystals exhibit significant variations in surface properties among different crystal facets. Despite the importance of these mineral crystal facets, previous studies have not reported their influence on natural gas hydrates. To address this gap, we focused on quartz, a vital component of hydrate reservoirs, and studied the process of natural gas hydrates formation and dissociation on its distinct crystal facets. In our investigation, we simplified pores as narrow gap spaces between two parallel quartz substrates, and captured the entire process with a microscope. The results indicate that the formation and dissociation of natural gas hydrates are notably influenced by the distinct crystal facets of quartz. The influences of quartz crystal facet on the hydrate formation are primarily attributed to two factors, wettability and hydroxyl concentration of quartz crystal facet. We have also revealed the mechanism of how quartz crystal facet influences the hydrate dissociation. This research provides a fundamental understanding of how mineral crystal facets influence the hydrate formation and dissociation, offering a novel perspective for the design of processes for extracting hydrate.

Load-bearing characteristics of surface conductor in deepwater gas hydrate formations

The surface conductor is the first structural casing in deepwater natural gas hydrate (NGH) development, bearing the top load while suspending the casings of various layers. NGH decomposition leads to formation settlement, changing the mechanical properties of the formation and reducing the bearing capacity of the surface conductor, threatening the safety and stability of the wellhead. Understanding the bearing characteristics of the surface conductor in the hydrate formation can guide the safe drilling operation in the field. By introducing the negative skin friction theory of pile foundations and based on conventional bearing capacity models, a method for calculating the bearing capacity of surface conductors in NGH formations was developed. Using an NGH drilling simulation apparatus, the accuracy of the bearing capacity theoretical model was verified, empirical coefficients under different conditions were obtained, and the influence of soil parameters, hydrate saturation, and decomposition temperature on the bearing capacity of surface conductors was quantified. The results indicated that compared to clay, sandy soils have higher porosity and significantly weakened strength after the decomposition of NGH; when the hydrate saturation in the formation is 20%, the reduction in bearing capacity of the surface conductor in sand exceeds 30%, and in clay soils, it decreases by 25% after complete decomposition of NGH; as the hydrate saturation increases, the reduction in the bearing capacity of surface conductors after decomposition becomes more significant. Verified through Experimentation, the error of the hydrate-bearing strata-bearing capacity model is around 10%. For short-term test production operations of NGH in water, the design depth for surface conductors is around 100 meters. These research results can provide a scientific theoretical basis for the design of conductor depth below the mud， and reduce operational risks.

Methane seepage activities in the Qiongdongnan Basin since MIS2

Gas hydrates are globally acknowledged as a significant strategic alternative energy source, and there is a consensus on the necessity to enhance their exploration. However, gas hydrates are highly prone to decomposition under variations in external environmental conditions, which can result in subsea methane seepage activities. Consequently, investigating subsea methane seepage activities holds substantial theoretical and practical significance for exploring gas hydrates. This paper evaluates the history of methane seepage activities in the Qiongdongnan Basin (QDNB) by analyzing the carbon and oxygen isotopic characteristics of benthic foraminifera and the geochemical properties of pore water from gravity sediment cores at sites QH-CL4 and QH-CL40. The results indicate that since the Marine isotope stage2 (MIS2), continuous micro-methane seepage activity has been present in the QDNB, characterized by a slight negative deviation in the carbon isotopes of benthic foraminifera. Methane seepage activity intensified during 14.6 ka BP and between 19.64–23.22 ka BP. This increase is thought to be associated with rising seawater temperature during the Bølling–Allerød interstadial and declining sea level during the Last Glacial Maximum, respectively. Moreover, current geochemical characteristics of pore water reveal strong methane seepage activity, with flux as high as 28.968 mmol·m-²·a-¹. This ongoing activity has led to gas hydrate formation within shallow layers while also causing negative deviations in pore water salinity.

Evaluation of the synergic effect of amino acids for CO2 hydrate formation and dissociation

Gas hydrate formation is a very challenging problem in the oil and gas industry. The chemical inhibition method is the best practicable hydrate mitigation method by injecting hydrate inhibitors such as Thermodynamic Hydrate Inhibitors (THIs) and Kinetic Hydrate Inhibitors (KHIs) into the pipeline. However, the hydrate inhibitors' biodegradability and limited data on dual functional inhibitor mixtures raise concerns in this study. This study aims to investigate and compare thermodynamic and kinetic inhibition on CO2 hydrate by using biodegradable amino acid inhibitor mixtures of Glycine and Alanine. In this study, the inhibitor mixtures were prepared by mixing Glycine and Alanine in 3 different mixture ratios, followed by the Thermodynamic and Kinetic inhibition tests. Thermodynamic Inhibition Test was conducted by using 10 wt% of inhibitor mixtures in a CO2-water system under pressure of 4.0, 3.5, 3.0 and 2.5 MPa, while Kinetic Inhibition Test was carried out by using 1 wt% of the sample in the CO2-water system at a constant pressure of 4.0 MPa and temperatures at 274.15K. The analysis methods for the Thermodynamic Inhibition Test were Hydrate Liquid-Vapor Equilibrium (HLVE) Curve, Average Depression Temperature and Molar Dissociation Enthalpy, while the Induction Time method, the number of CO2 moles consumed, the formation rate of CO2 gas hydrate and RIP were used in the Kinetic Inhibition Test. In this study, all inhibitor mixtures exhibit dual functional inhibition on the CO2 hydrate. For THI, 50% Gly: 50% Ala shows the best thermodynamic inhibition strength with an average depression temperature of 2.42 K. All the inhibitor mixtures for THI have the dissociation enthalpies within the CO2 hydrate enthalpy range, which show that the inhibition is due to the influence on the water molecules’ interaction only. For KHI, 75% Gly: 25% Ala shows the highest kinetic inhibition strength on CO2 formation with the longest induction time of 115.2 min and the highest RIP of 0.40. In the KHI experiment, there is a drop in the CO2 uptake capacity with the presence of inhibitors used, where the highest difference of CO2 moles consumed is 0.0057 mol. A synergistic effect of inhibitor mixtures was observed in this study on 50% Gly: 50% Ala for THI and 75% Gly: 25% Ala for KHI. However, the “degradation” effect was also exhibited on 75% Gly: 25% Ala and 25% Gly: 75% Ala for THI and 50% Gly: 50% Ala and 25% Gly: 75% Ala for KHI, where the performance of the inhibitor mixtures is poorer than the concentrated amino acids. The “degradation” effect of the inhibitor mixtures at certain ratios was not covered in this study and it requires a further understanding of the chemistry behind the inhibition mechanism.

Experimental Study of the Effect of HCO3– and Cl– Ions on Natural Gas Hydrate Formation in a Porous Medium

Experimental Study of the Effect of HCO3– and Cl– Ions on Natural Gas Hydrate Formation in a Porous Medium

Gas Hydrate Formation Assessment in Deadlegs and Jumpers: A Comprehensive Review and Field Case Study Analysis

Gas Hydrate Formation Assessment in Deadlegs and Jumpers: A Comprehensive Review and Field Case Study Analysis

Effect of Promoters on Associated Petroleum Gas Hydrate Formation Under Static Conditions

Effect of Promoters on Associated Petroleum Gas Hydrate Formation Under Static Conditions

Beyond gas supersaturation: Dissecting the secondary formation of methane hydrate

Rapid secondary formation of gas hydrate is a critical issue in gas transportation and at the same time has foreseeable potential in future gas storage. Despite the devoted research in the past decade, the intrinsic mechanism of the secondary formation of gas hydrate, is still an on-going subject of debate. Because the secondary formation of gas hydrate is commonly observed under conditions with extraordinarily high content of gas, gas supersaturation is hypothesized as one crucial mechanism. To dissect the gas supersaturation hypothesis, Molecular Dynamics simulations were conducted systematically with hydrate secondary formation in solutions with various gas concentrations covering supersaturation conditions. The effects of key parameters influencing the secondary formation of hydrate, including system temperature and local methane concentration, were explored. The results revealed for the first time a U-shape-like trend in the induction time of hydrate formation with the increase of gas concentration, pinpointing an optimal gas content with the given environmental temperature and pressure. Importantly, the findings highlighted the needed revision of the current gas supersaturation hypothesis in both methane hydrate mitigation and application. This work not only advanced the current understanding of the secondary formation of methane hydrate but also contributed to the fundamental knowledge essential for future gas storage by gas hydrates.

Methane hydrate formation between graphene oxide nanosheets: Insights from molecular dynamics simulations

This work focuses computationally on the role of graphene and graphene oxide nanosheets in improving the formation of methane gas hydrate and their potential as a promising alternative to traditional gas storage and transportation method. To evaluate methane gas mechanism storage between graphene and graphene oxide nanosheets including C8O-flat, C8O-polar, and C8(OH)2 surfaces, radial distribution function, mean squared displacement, number of hydrogen bonding, and coordination number were taken under consideration. Our results showed that methane hydrate is well formed between graphene, C8O-flat, and C8O-polar nanosheets. C8(OH)2 nanosheet has an inhibitory effect on the gas hydrate formation caused by the formation of hydrogen bonds between the hydroxyl functional groups of the sheets and water molecules. To further investigate the degree of hydrate formation, a four-body structural order (F4φ) was obtained. The values of the F4φ parameter for the C8O-flat, graphene, C8O-polar, and C8(OH)2 systems are 0.6, 0.55, 0.51, and −0.02, respectively. These values indicate the presence of an almost complete and regular network of methane hydrate between the first three mentioned sheets. However, the negative value of the F4φ parameter in the last one suggests the absence of significant hydrate formation by ice-like structure of water molecules. The effect of different temperatures on the formation of methane hydrate was also investigated. It is observed that the hydrate structure completely breaks down in the range of 300–400 K in the different structures.

Metal plate-based promotion on methane hydrate nucleation: Insights into the influence of metal type and surface properties

Hydrate-based technologies hold significant promise in the fields of gas storage, water desalination and gas separation, but their application is restricted by the long induction time and high degree of randomness associated with hydrate nucleation. In this study, we conducted experimental investigations to access the influence of metal plates (Mg, Al and Zn) on methane hydrate nucleation under both pure water and acidic conditions. The results demonstrated that Mg plate exhibited the strongest promotion effect on methane hydrate nucleation. The presence of acid significantly accelerated hydrate nucleation in the Zn plate system, but conversely reduced the promotion effect of Al plate. In conjunction with the in-situ morphology evolution of hydrate nucleation, methane-liquid–metal interface was found to play a crucial role in the metal-induced promotion effect. Two nucleation modes were proposed accordingly: (i) in pure water, hydrate nucleation initiated exclusively at the methane-liquid–metal interface without extra nucleation site (Mode 1), and (ii) in acidic condition, hydrate nucleation occurred with evident multiple nucleation sites (Mode 2). Furthermore, SEM imaging, AFM and contact angle characterization revealed that the surface properties of metal plate (e.g., hydrophilicity and roughness) were the key factors in determining the effectiveness of the promotion effect. Liquid climbing upward along the metal plate surface was vital for metal plates to promote gas hydrate formation. Overall, this study provides new insights into hydrate nucleation promotion and suggests a straightforward way to enhance hydrate nucleation by modifying surface properties

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.

A new set of gas-structure-dependent parameters to improve gas hydrate equilibrium calculations and structure descriptions by van der Waals-Platteeuw model

The traditional Kihara potential parameters employed in the van der Waals-Platteeuw (vdW-P) model were only related to the species of hydrate-forming gases. Although our previous study (Chemical Engineering Science 248, 117213) proposed a framework for optimizing the gas-dependent Kihara potential parameters in vdW-P model to improve the hydrate equilibrium calculations, the predictions for hydrate structures are barely satisfactory. Thus, this study provides a new set of Kihara potential parameters which are dependent on not only the gas species but also the hydrate structures. With the constraints on hydrate structure changes, a novel procedure for fitting the gas-structure-dependent parameters is developed. The calculation results show that the newly obtained parameters improve the performances of vdW-P model in predicting the hydrate equilibria for the pure-gas and gas-mixture systems. Besides, the vdW-P model coupled with gas-structure-dependent parameters can provide reliable temperature-composition phase diagrams and acutely detect the crystalline structures for various gas hydrates.

Gas hydrate inhibition by urea and its blends with vinyl lactam polymer: Paving the way to green hybrid inhibitors

Urea is an environmentally benign substance considered a promising gas hydrate inhibitor in flow assurance. Nevertheless, its effect on gas hydrate formation kinetics remains poorly understood. This study investigates the impact of urea and hybrid urea/polymer KHI samples on the nucleation and growth kinetics of sII natural gas hydrates. Hydrate formation was observed at a lower onset temperature with increasing urea and polymer concentration. The nucleation of sII hydrate in aqueous urea solutions occurred at a higher subcooling (7.50 ± 0.58 K at 30 mass%) than in pure water (5.17 ± 0.69 K). These findings indicate that urea acts as a nucleation inhibitor of sII hydrates, although its capacity is not as potent as that of polymer KHI.The analysis of the hydrate nucleation probability distributions revealed that the sII hydrate nucleation rate exhibited a significant decline, approximately one order of magnitude, at subcooling of 5.3–6 K for 20 mass% urea compared to water. A similar behavior was noticed in an aqueous solution of polymer KHI. Urea has succeeded in providing a total benefit of up to 10 K in hydrate onset temperature due to a shift in the hydrate stability zone and nucleation retardation.Consequently, urea is a green dual-acting anti-hydrate chemical that inhibits the formation of sII hydrates by thermodynamic and kinetic mechanisms. Besides, adding 10 mass% urea increases the cloud point temperature of vinyl lactam polymer Luvicap 55W by 14 K. Urea is an additive that considerably augments the stability of the polymer in aqueous solutions at elevated temperatures. These findings make urea an effective and environmentally friendly top-up inhibitor that significantly enhances the anti-hydrate properties of polymer KHI.

Insight into the micro-mechanism of hydrate-based methane storage from active ice

Gas hydrate formation in active ice holds significant potential for solidified natural gas storage, while the deep understanding of its micro-mechanism is required for the futural application of such a technology. In this study, the kinetics and micro-properties of methane hydrate formation enhanced by active ice (porous ice containing an unfrozen solution layer of sodium dodecyl sulfate) were investigated via experiments and molecular dynamics (MD) simulations. Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray diffraction (XRD) differential scanning calorimetry (DSC) characterization, and in-situ visual observation confirmed the formation of sI methane hydrate in the active ice system and the occurrence of single-crystal hydrate, and also indicated the occurrence of active water near the surface of porous active ice during the active ice formation. A sensitivity analysis of the hydrate kinetics experiments suggested that temperature is the primary driver of rapid methane hydrate formation in the active ice system. The shortest induction time and t90 for hydrate formation were recorded at 5 s and 5.5 min, respectively. Furthermore, MD simulations indicated that the direct hydrate nucleation and growth in the active water, heat transfer from gas hydrate to ice, and the diffusion of active water (1.24 × 10-9 m2/s) and methane (7.10 × 10-8 m2/s) into the porous ice structure are the primary mechanism that enhances hydrate formation kinetics and methane storage capacity. This work provides an essential microscopic mechanism of the “active ice → active water → gas hydrate” circulation that contributes to the deep understanding and futural application of the efficient hydrate-based solidified methane storage in active ice system.

Prediction of hydrate formation boundaries in pure water and salt/alcohol containing systems based on prior knowledge and artificial intelligence

As an efficient and clean energy source, natural gas plays a crucial role in optimizing the global energy consumption structure. However, the formation and accumulation of hydrates in pipelines during the exploitation and transportation of natural gas greatly jeopardize the production safety. Accurately predicting hydrate formation boundaries remains challenging due to the complex interation among various influencing factors. Although mechanistic models provide insights, they often fall short in accuracy. Conversely, machine learning models, while promising, may face limitations related to small sample sizes and a lack of physical interpretability. To overcome these limitations, this study proposed a physically guided neural network (PGNN) based on the Chen-Guo model, which integrated thermodynamic mechanisms with a neural network framework. This proposed model utilized pressure calculated from the Chen-Guo model as an input variable and incorporates physical inconsistencies into its loss function. A comparative analysis using literature data that PGNN achieved superior prediction accuracy, with an R2 value of 0.9768 for gas hydrate formation pressure prediction. The integration of thermodynamic mechanisms enhanced the prediction accuracy, as evidenced by an increase in the R2 value by 0.036, and a reduction in the MSE value by 5.56. Furthermore, the PGNN maintained a high level of prediction accuracy, ranging from 0.96 to 0.98, even with limited sample sizes, thus confirming its applicability and stability. This study validated the feasibility of PGNN for predicting gas hydrate formation conditions and offered insights into hydrate-based applications and hydrate management strategies.

Simulation of CO2 hydrate formation in porous medium and comparison with laboratory trial data

The storage of CO2 in gas hydrate form in the pore space in depleted natural gas reservoirs has been considered a method for greenhouse gas control. The formation of CO2 hydrate in porous medium is a strongly coupled Thermal-Hydraulic-Chemical (THC) problem under certain thermodynamic conditions. In this study, laboratory data on CO2 hydrate formation in silica sand, including the profiles of pressure, temperature, the amount of CO2, H2O, and CO2 hydrate, etc., were compared with results from numerical simulations. The minimized deviations between the simulation and experimental results, including the pressure drop, the significant temperature increase caused by hydrate formation, and the amount of CO2, water, and hydrate, were all less than 10 % in the numerical simulations. The sensitivities of the deviations between numerical simulations and experimental data to the domain discretization, thermal conductivity of the silica sand, absolute permeability, and kinetics of CO2 hydrate formation were analyzed. One of the major findings is that CO2 hydrate formation in the porous medium in this study is dominated by the kinetics of chemical reaction, rather than the heat or mass transfer. Another key finding of this study is the acquisition of the modeling parameters of the CO2 storage process in the laboratory-scale sand reservoir, including the thermal conductivity of the silica sand λs = 2.2 W/m/K, the absolute permeability k0 = 3.0 × 10−11 m2, and the kinetic constant Kf0 = 8.4 × 1011 kg/m2/Pa/s and the reduction exponent β = 5.3 in the kinetic model of CO2 hydrate formation. It is noteworthy that the mathematical models and the parameters faithfully fit three independent experiments of Run 1–3. The results of the experiments and corresponding numerical simulations provide a reliable method to evaluate the capacity, technical and commercial feasibility of CO2 storage in marine and permafrost reservoirs.

Insights into the dual effect of an amphiphilic additive on hydrate formation from a water structure perspective

Chemical additives play an important role in gas hydrate formation, which involves the transformation of water structure. However, the relationship between the effects of additives on water structure and hydrate formation is inconclusive, especially for amphiphilic molecules. Here, we investigate the changes in water structure caused by rhamnolipid (Rha) biosurfactants and the resulting effect on methane hydrate formation through kinetic experiments, morphological observation, and in situ Raman spectroscopy. The Gaussian peaks of strongly hydrogen-bonded and weakly hydrogen-bonded water are identified, of which the integrated intensity and position are compared. It is found that the dual effect of Rha on hydrate formation kinetics, namely nucleation inhibition and growth promotion, is attributed to the ordered arrangement of water molecules with stronger hydrogen bonding interactions induced by the charged head groups. The strongly hydrogen-bonded water inhibits nucleation but promotes growth. In addition, the adsorption of Rha on montmorillonite (MMT) eliminates the changes in water structure and the dual effect of hydrate formation kinetics, providing further evidence for the above conclusion. These insights pave the way for a deeper understanding of hydrate formation kinetics from a water structure perspective, as well as providing a scientific basis for the commercial application of surfactants.

EXPERIMENTAL STUDY OF HYDRATE FORMATION PECULIARITIES FOR CONDITIONS OF THE TURNO AND CENOMANIAN DEPOSITS: Part II

This paper is the second part of the research devoted to the study of hydrate formation features for the conditions of Turonian and Cenomanian deposits. The launch of new gas projects at the Turon and Senoman production facilities in Western Siberia provided a good opportunity to critically analyze the known methods of protecting production, gathering and transportation facilities of the gas field from the formation of solid gas hydrates. The paper presents the experience of implementing a program of laboratory studies of conditions of gas hydrate formation with their subsequent processing and in-depth analysis. The research program covered the area of thermobaric parameters typical for the conditions of Turon-Senoman deposits exploitation with localization of hydrate-hazardous areas in the conditions of Technological Regimes for full development. The description of laboratory studies is given, in which two gas compositions of Senoman and Turon objects, different variants of mineralization and ionic composition corresponding to formation and condensation water, as well as hydrate formation conditions under changing dosages of basic inhibitor on the basis of methanol were considered. The details of the experiment based on the method of swinging cells and the subsequent analysis of the results of the completed experiments to determine the thermobaric conditions of formation and decomposition of hydrates are given. The main features of the experiment are specified, estimates of the rate of change of the influencing parameters of the experiment on its quality are given. In the process of implementation of the experimental program, the optimal values of these parameters were selected, which allowed us to significantly reduce the variation of experimental results to determine the thermobaric conditions of hydrate formation. It is experimentally established that the temperature of hydrate decomposition is higher than the temperature of its formation at all investigated gas compositions and water mineralization.

Gas hydrate technological applications: From energy recovery to carbon capture and storage

Hydrates are crystalline structures that trap small gas molecules inside hydrogen-bonded water cages. These structures form at high pressure and low temperature. In recent years, there has been a growing interest in gas hydrates for technological applications, specifically in energy recovery, as well as carbon dioxide capture and storage. In the CO2/CH4 exchange using gas hydrates, researchers have reported a large amount of natural gas trapped in the form of gas hydrates under the ocean seafloor and permafrost regions. This large amount of natural gas trapped inside hydrate cages in oceanic and permafrost deposits has driven interest in the energy sector to investigate the possibility of safely harvesting gas hydrates as one of energy resources. However, there are still unanswered fundamental questions including the mechanism of natural gas recovery from gas hydrates. Another gas hydrate-based technology that has a growing interest is the use of gas hydrates for separation including carbon dioxide capture and storage. Carbon dioxide molecules have been shown to be preferentially trapped in the hydrate phase, demonstrating the possibility of the usage for carbon capture technology. Similarly, there are still underlying concerns of these applications, such as thermodynamics and stability of gas hydrates in porous materials, and the crystallization kinetics and mechanism of hydrate formation. This paper provides an overview of laboratory investigations conducted to understand the mechanism and evaluate the feasibility of energy recovery as well as discussion on recent advances in laboratory investigations on gas hydrate-based technology.

Long-Term Distributed Temperature Sensing Monitoring for Near-Wellbore Gas Migration and Gas Hydrate Formation

Summary Well integrity monitoring has always been a critical component of subsurface oil and gas operations. Distributed fiber-optic sensing is an emerging technology that shows great promise for monitoring processes, both in boreholes and in other settings. In this study, we present a case study of using distributed temperature sensing (DTS) technology to monitor a cemented and plugged well in the Alaska North Slope (ANS). The well was drilled as part of a long-term gas hydrate study, and the downhole DTS data were recorded over a period of approximately 2 years. By applying a temporal gradient and removing instrument instability noise, we reveal subtle (<0.001°C/h) thermal anomalies, which are characterized by brief warming periods followed by longer cooling periods at discrete depths along the borehole. The observed coherent events show an upward trajectory from deeper formations into the overlying permafrost interval, with the thermal anomalies concentrated in relatively coarse-grained sandstone layers. We also observe that the upward migration rate of the DTS anomalies varies with formation lithology and that there is a spatial and temporal correlation between the subsurface events and measured wellhead annular pressures. We interpret that the observed warming events represent the exothermic process of gas hydrate formation that is occurring in association with the upward migration of gas outside the well casing, and this interpretation is confirmed by numerical simulations. These observations demonstrate the ability of suitably processed DTS data to detect subtle processes and highlight the value of DTS technologies for wellbore integrity monitoring.