Natural Gas Hydrate Decomposition Research Articles

Research progress on the effects of nanoparticles on gas hydrate formation.

Gas hydrate has great application potential in gas separation, energy storage, seawater desalination, etc. However, the intensity of mass and heat transfer is not enough to meet the needs of efficient hydrate synthesis. Nanoparticles, different from other liquid chemical additives, are considered as effective additives to promote hydrate formation due to their rich specific surface area and excellent thermal conductivity. This work summarizes the effect of the nanoparticles on the thermodynamics and kinetics of hydrate formation. And also, this work probes into the mechanism of the effect of the nanoparticles on the formation of hydrate as well as provides some suggestions for future research. It is found that it's difficult for nanoparticles to effectively promote the formation of the gas hydrate without the use of surfactants, because the adhesion characteristics of the nanoparticles make them easily agglomerate or even agglomerate in solution. In addition, at present, the research on the influence of nanoparticles on the formation and decomposition of natural gas hydrate is still very fragmented, and the micro mechanism of the influence is not clear, which requires more systematic and specific research in the future. At the same time, the development of nanoparticles that can promote the formation of natural gas hydrate should also become the focus of future research.

Can low hydration heat cement prevent the decomposition of natural gas hydrate under high pressure and low temperature?

In this article, an in-house device is used to study the prevention of natural gas hydrate (NGH) decomposition performance and the mechanism of the low-heat cement for cementing. The results show that the natural gas hydrate can decompose to different degrees due to the hydration heat of the G-class oil well cement at the experimental conditions of 281.15 K & 8 MPa and 277.15 K & 6.5 MPa. Decomposition occurs within the period of hydration heat peak. The visualization window allows observing the decomposition and reduction of natural gas hydrate. The low-heat cement can effectively prevent the decomposition of natural gas hydrate at the experimental conditions of 281.15 K & 8 MPa, 277.15 K & 6.5 MPa, and 273.15 K & 4.5 MPa. The hydration heat experiment found that with the decrease in the hydration environment temperature, the hydration temperature rise appeared significantly later, the induction period was delayed into the acceleration period, the maximum of hydration temperature rise exhibited a decreasing phenomenon, and the hydration temperature rise of low hydration heat cement was far lower than that of the G-class oil well cement.

Design of a drilling unit for deep-sea stratum drilling robot

Marine natural gas hydrate has attracted much attention due to its broad energy prospects. With the deepening of research on natural gas hydrate, researchers have found that the decomposition of natural gas hydrate is an important inducer for many natural disasters. This paper proposes a design idea of a deep-sea stratum drilling robot used in gas hydrate test mining area. It can carry out long-term and effective real-time monitoring of the surrounding terrain and environmental changes. The specific structure and function of each component of the robot are introduced, and the locomotion principle of the drilling robot is elaborated. This paper focuses on a drilling unit as one of the key technologies for developing the robot, and the design of drilling unit of robot will be presented in detail. Then, the feasibility of the robot movement and the effect of the drill bit rotation on the soil are obtained through mechanical analysis and simulation. The work of this paper provides guidelines for the development of deep-sea stratum drilling robot in the future.

Molecular and Carbon Isotopic Characteristics during Natural Gas Hydrate Decomposition: Insights from a Stepwise Depressurization Experiment on a Pressure Core

Molecular and Carbon Isotopic Characteristics during Natural Gas Hydrate Decomposition: Insights from a Stepwise Depressurization Experiment on a Pressure Core

Effect of electrolytes on the self-protection of natural gas hydrate decomposition

Abstract This paper presents an experimental study of methane hydrate decomposition with different concentrations of electrolytes Na+ and K+, with the aim of exploring the electrolyte's behaviour characteristics shown in its effect on the self-protection effect of methane hydrate during decomposition. The study used an experimental device for hydrate synthesis and decomposition. It focuses on the effect of electrolytes on the self-protection effect of methane hydrate during the self-protection effect during methane hydrate decomposition. (i) Na+ ions have an inhibitory effect on self-protection, whereas K+ ions do not have a significant effect. (ii) There is a negative correlation between the hydrate self-protection effect and the concentration of Na+ ions. However, an excessive Na+ concentration can inhibit the hydrate gas production rate. (iii) The synergistic system of Na+ and K+ ions has a better inhibitory effect on the hydrate's self-protection effect than a single Na+ ion solution. As the concentration of the synergistic system increased, the hydrate gas production rate was not inhibited. However, in contrast to a single Na+ ion solution, when the concentration of the synergistic system was too high, the methane hydrate gas production rate was not inhibited because of the coexistence of cations.

Study on mechanical properties of natural gas hydrate production riser considering hydrate phase transition and marine environmental loads

A dynamic analysis model for natural gas hydrate (NGH) production riser was established considering the internal phase transition of hydrate multiphase flow and the external marine environmental loads. The model was numerically discretized by the finite element method (FEM) and solved by Newmark β method. The correctness of the analysis model was verified by an experiment and field testing data. The results indicate that the NGH begins to rapidly decompose in the middle of the riser, causing the sudden pressure drop in the riser. The internal NGH decomposition will significantly increase the axial tension and Von Mises stress of the riser. The Von Mises stress reaches maximum at the top end of the riser subjected to the distribution of effective axial tension. The lateral displacement and bending moment of the riser increase with the increase of flow rate and mixed fluid density in the middle and lower sections, and the stress decreases with the increase of flow rate and mixed fluid density. The increase of hydrate content and seawater temperature will decrease the lateral displacement and bending moment and the upper part stress of the riser, but it will significantly increase the stress in the lower part.

Investigation of the Formation and Decomposition Processes of the Sredneviluisky GCF Natural Gas Hydrates in Dispersed Media

In this paper the processes of formation and decomposition of natural gas hydrates in wet salted sand samples were studied. Investigations of phase transitions were performed on a specially assembled DTA installation. It is shown that with decrease of the humidity and increase of the salinity of media the degree of supercooling decreases, and the amount of the gas bound to hydrate decreases. It has been found that in comparison with the water-gas system in dispersed rocks there is a shift of thermobaric conditions of hydrate formation to the area of high pressures and low temperatures.

Review of natural gas hydrate dissociation effects on seabed stability

As a high-energy clean energy substance, natural gas hydrate (NGH) has a high value of development and utilization. However, NGH is extremely easy to decompose during its exploitations, thereby leading to the destruction of seabed stability. In this paper, the distribution and significance of NGH, the mechanism of decomposition and formation, the effect of seabed stability, and the influencing factors are studied and analyzed. Studies show that NGH reserves are large, and they are easy to decompose. The dissociation of NGH is the main factor of seabed instability. During the decomposition of NGH, the strength parameters (cohesion and friction angle) of seabed soil are reduced, and the pore water pressure of seabed increases. The seabed structure exhibits soft sliding surface and large deep cracks, leading to the instability of sediments and serious seabed landslide. The factors affecting the decomposition of NGH include environmental change, human activities, structure difference in seabed itself, and sea solute difference. This paper aims to better understand the decomposition mechanism of NGH for analyzing the influencing mechanism of seabed stability and for providing a direction for the study of marine geological hazards.

Investigating the Interaction Effects between Reservoir Deformation and Hydrate Dissociation in Hydrate-Bearing Sediment by Depressurization Method

Natural gas hydrate (NGH) has been widely focused on having great potential for alternative energy. Numerous studies on gas production from hydrate-bearing sediments have been conducted in both laboratory and field. Since the strength of hydrate-bearing sediments depends on the saturation of NGH, the decomposition of NGH may cause the failure of sediments, then leading to reservoir deformation and other geological hazards. Plenty of research has shown that the reservoir deformation caused by hydrate decomposition is considerable. In order to investigate this, the influence of sediment deformation on the production of NGH, a fully coupled thermo-hydro-chemo-mechanical (THMC) model is established in this study. The interaction effects between reservoir deformation and hydrate dissociation are discussed by comparing the simulation results of the mechanical coupling and uncoupled models on the laboratory scale. Results show that obvious differences in behaviors between gas and water production are observed among these two models. Compared to the mechanical uncoupled model, the mechanical coupling model shows a significant compaction process when given a load equal to the initial pore pressure, which leads to a remarkable decrease of effective porosity and reservoir permeability, then delays the pore pressure drop rate and reduces the maximum gas production rate. It takes a longer time for gas production in the mechanical coupling model. Since the reservoir temperature is impacted by the comprehensive effects of the heat transfer from the boundary and the heat consumption of hydrate decomposition, the reduced maximum gas production rate and extended gas production process for the mechanical coupling model lead to the minimum reservoir temperature in the mechanical coupling model larger than that of the mechanical uncoupled model. The reduction of the effective porosity for the mechanical coupling model causes a larger cumulative water production. The results of this paper indicate that the reservoir deformation in the gas production process should be taken into account by laboratory and numerical methods to accurately predict the behaviors of gas production on the field scale.

The potential utilization of lecithin as natural gas hydrate decomposition inhibitor in oil well cement at low temperatures

Inhibiting natural gas hydrate (NGH) decomposition is a crucial challenge in NGH strata cementation. Lecithin can inhibit the decomposition of NGH, however, before lecithin is added to oil well cement to create a cement slurry system that inhibits NGH decomposition, the effects of lecithin on the mechanical properties of oil well cement must be considered. Therefore, in this research, the effects of lecithin on the mechanical properties of oil well cement were studied. The elastic modulus and compressive strength were measured to evaluate the mechanical properties. The changes in the mechanical properties of cement with different lecithin concentrations were experimentally studied. Through experimental research and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis, it was confirmed that a 1.5% lecithin concentration in the cement slurry inhibits NGH decomposition. Quantitative calculations determined the ratio of lecithin to calcium silicate hydrate (CSH) gel in an atomic model when the lecithin concentration was 0, 0.5%, 0.8%, 1.0%, 1.2% and 1.5%, and the lecithin–CSH gel atomic model was established with different concentrations. According to molecular dynamics simulations and experimental analyses, the influence mechanism of lecithin on the mechanical properties of cement was revealed. The experimental and simulation results demonstrated that as the lecithin concentration increased, the elastic modulus and compressive strength of cement decreased, and the interfacial adsorption energy between lecithin and CSH gel increased. The decalcification of CSH gel by lecithin and the migration of calcium to the surface result in decreases in the elastic modulus and compressive strength of cement. The mechanical properties of cement can be enhanced by increasing the calcium content and reducing the number of calcium migration channels of calcium. Finally, we evaluated the impact of lecithin on the rheological properties and setting time of cement slurry. The research results are significant for the further development of cement slurry systems with NGH decomposition resistance.

Changes in relative permeability curves for natural gas hydrate decomposition due to particle migration

It is very important to study the fluid flow in a natural gas hydrate (NGH) reservoir for hydrate exploitation. During the decomposition of NGH, some particles fall off and flow with the fluid as a result of poor cementation, which usually leads to sand production in the hydrate mining process. In this study, a three-dimensional pore network model (PNM) was established to simulate the three-phase flow of the gas phase (CH4), water phase, and solid phase (particles). Relevant parameters were set considering the deposition, blockage, and flow in the process of particle migration. Then, the gas–water relative permeability curves under different hydrate saturations, particle diameters, and particle numbers were obtained, considering the influence of the change in the pore-throat space during the hydrate decomposition process. The results showed that the gas–water relative permeability equal points (isotonic points) first turned toward the left and then to the right. The analysis results showed that particle deposition and blockage mainly influenced the relative permeability curves during the early period of the hydrate decomposition process. An increase in the pore-throat space was the main factor affecting the relative permeability curves in the late period of the hydrate decomposition process. Moreover, increasing the particle diameter and number of particles caused the isosmotic points of the relative permeability curves moving to the left as a whole because the pore-throat space decreased. Increasing the number of particles first affected the fluid flow in the hydrate reservoir when the temperature was 280 K, pressure was 5.76 MPa, and hydrate saturation was 0.48. In the actual hydrate mining process, this could cause sudden changes in the relative permeability and production. Thus, this condition needs to be avoided. It has important significance in reference to the process of hydrate mining with sand production.

Kinetics of Formation and Decomposition of Natural Gas Hydrates in Synthesis from Shaped Ice

The results of investigations into the kinetics of formation and decomposition of natural gas hydrates obtained from shaped ice using the thermocycling method are reviewed. These data make it possible to find the weight distribution, specific gas content, and features of decomposition of different hydrate shapes synthesized in a reactor.

Preparation and evaluation of micro-encapsulated thermal control materials for oil well cement slurry

Abstract In the process cementing of deep water, cement particles react with water to produce a lot of hydration heat, which can lead to decomposition of natural gas hydrate. We synthesized a kind of micro-capsule thermal control material with paraffin wax as the base material and calcium carbonate as the skeleton support material. At first, the chemical structure and chemical element composition of thermal control material were obtained by FTIR and EDS, respectively. Secondly, the phase change properties of MPCM-1 were measured by using DSC. As a result, it was shown that phase change temperature and phase change enthalpy of thermal control material is 31.11 °C and 88.59 J/g, respectively. Simultaneously, the thermal stability of IPCM-1 was obtained by using a synchronous thermal analyzer. Then, the micro-encapsulated thermal control material is introduced into the cement slurry system, and the hydration heat and maximum hydration temperature rise of the cement slurry were investigated by a self-made hydration heat test device. As a result, compared with cement slurry CB, the hydration heat released to the environment by cement slurry CS12.0% decreased by 44.16% (at 48 h), and the maximum hydration temperature of cement slurry CS12.0% is reduced by 25.4 °C. Besides, compared with cement slurry CB, the compressive strength of cement slurry CS12.0% increased by 5.9% (24 h) and 9.8% (48 h). The thermal control material was added into the cement slurry, and a low hydration heat cement slurry system was successfully prepared.

Experimental model of pockmarks from gas hydrate decomposition by aeration

The decomposition of gas hydrates releases gas and water at volumes much larger than the original volume. The gas escapes violently, which destroys seabed sediments and can even cause geological disasters. To explore the effect of natural gas hydrate decomposition on underwater slopes, laboratory experiments were conducted to observe the features of slope failure. Aeration was used to model the gas that was produced by hydrate decomposition, and the results were as follows. (a) Once air filled into the bottom of the underwater slope, the pore pressure at the slope was altered, which eventually caused the slope to fail. (b) The formation of pockmarks corresponded to the variations in the pore-water pressure. (c) The theoretical analysis results showed that the sedimentation rate of fine particles (d < 0.4 mm) was lower than the water flow velocity, indicating that these particles were carried away with the air–liquid two-phase flow, which eventually caused the pockmarks to develop into craters.

Mechanical study on the wellbore stability of horizontal wells in natural gas hydrate reservoirs

Currently, the exploration of natural gas hydrates (NGHs) is regarded as a worldwide research focus. Due to multiple characteristics of NGH reservoirs (such as weak bonding, low strength and high degradability), wellbore instability is extremely likely to occur during drilling operations. Based on the thermodynamic characteristics of NGHs, a heat–fluid–solid coupling numerical model of horizontal wells in NGH reservoirs that considers the decomposition of hydrates was established. Additionally, the evolution of stress fields and plastic zones induced by changes in the temperature–pressure field and the mechanical properties of NGHs before and after their decomposition were analyzed. The results showed that stress was reduced in the zone where NGHs were completely decomposed, due to the weakening of elastic parameters, and that the strata close to the wellbore were in a state of plastic flow because of stress concentration there. Moreover, the stress was dramatically increased in the transition zone for the decomposition of NGHs due to the change in the mechanical properties of the strata. Hence, the secondary stress concentration was formed in the strata where NGHs did not undergo decomposition, and part of this strata would be subjected to plastic deformation. With the further decomposition of NGHS, the extent of the strata with completely decomposed NGHs in the plastic stage was also increased, and the secondary stress concentration effect formed in the zone with NGHs that did not undergo decomposition, in the strata far from the wellbore. If NGHs were decomposed under the selected drilling conditions, the small wellbore was more affected by the decomposition of hydrates, with a greater risk of collapse. Moreover, the effect of the wellbore size became more significant with increased drilling time; thus, selecting a large wellbore for drilling was more favorable for the stability of the wellbore.

Research of Formation and Decomposition Processes of Natural Gas Hydrates of Different Composition in Model Stratum Waters of a Bicarbonate-Sodium Type

The paper presents the results of an experimental study of the behaviour of formation and decomposition of natural gas hydrates of the Srednevilyuiskoe and Otradninskoe gas condensate fields depending on the concentration of sodium bicarbonate solution. Natural gases used in the hydrate formation process differ in their component composition and physicochemical properties. It was found that with increasing concentration of solutions, the gas pressure at which the hydrate formation process ends is increased. During hydrate formation, the initial dry natural gas of the Srednevilyuiskoe field turns into semi-wet gas, and that of the Otradninskoe field turns into wet gas. The decomposition of natural gas hydrates is described by sigmoid curves without an induction period. For the decomposition reaction of hydrates formed by natural gas of the Srednevilyuiskoe field, the reaction acceleration period is shorter than the deceleration period, while the opposite is observed for the Otradninskoe field. Therefore, in the first case, hydrates decompose faster than in the second. Thus, it was found that the hydrate formation process in model solutions of the sodium bicarbonate type and the decomposition reaction of the resulting hydrates depend on the composition of natural gas.

RETRACTED ARTICLE: Modeling and molecular simulation of natural gas hydrate stabilizers

ABSTRACT Uncontrolled decomposition of natural gas hydrate may lead to serious marine geological disasters and air pollution. The model of natural gas hydrate and lecithin was established. The stability mechanism of lecithin to structure hydrate was studied by molecular dynamics simulation. The consistent valence force field (CVFF) and TIP3P potential models are used to define the interaction between CH4-CH4 and water-water species, respectively. The simulations are performed on a combination of a 2 × 2 × 4 unit cell of sI hydrate and a water liquid phase with lecithin. The results of the simulations indicate that lecithin molecules adsorb on the hydrate surface with their hydrocarbon chains crossing and forming a net structure, easily producing the hydrate memory effect, which will narrow the available space for hydrate methane and water movement. Compared to the pure water-hydrate model, the mean square displacement (MSD) values of hydrate methane and water molecules are much lower, indicating that the hydrate dissociates more slowly.

Effects of structural properties of alcohol molecules on decomposition of natural gas hydrates: A molecular dynamics study

Natural gas hydrates, which are mainly distributed at the sea floor and in permafrost regions, are expected as a future but untapped energy resource. Design of effective chemicals for promotion of the gas hydrate decomposition is one solution of achieving sustained and steady exploitation of natural gas hydrate. Among possible additives, alcohols are commonly used. However, the effectiveness is limited and few studies have been conducted to understand the effects of molecular structure of alcohols on the hydrate decomposition. Here, with the aid of molecular dynamic simulations, we systematically investigate the effects of chain length, hydroxyl position and hydroxyl number of alcohols on the decomposition of methane hydrates. Combining variations of potential energy, radial distribution functions, and mean square displacement, the influences of alcohol structural properties on the hydrate decomposition are evaluated. Simulation results show that 1-pentanol, 2-pentanol and 3-pentanol are added, methane hydrates decompose completely at 1420 ps, 1300 ps and 1500 ps respectively. Alcohol with short branched chains is conducive to promoting the decomposition of methane hydrate. However, adding methanol, ethanol, 1-propanol, 1,2-propanediol and glycerol, methane hydrates decompose completely at 1530 ps, 1650 ps,1700 ps, 1500 ps and 900 ps respectively and methane hydrate can’t completely decompose at 2000 ps adding 1-butanol. The result indicates that shortening the chain length of alcohols and increasing the hydroxyl number of alcohols are beneficial to improving the promotion effect on methane hydrate decomposition. Our results thus provide useful guidelines for future design of alcohol-based molecules for promoting gas hydrate decomposition.

Research on pressure‐stabilizing system for transfer device for natural gas hydrate cores

AbstractTo broaden the analysis means for natural gas hydrate (NGH)‐pressured cores, long‐columnar cores are usually cut into smaller segments with a pressure‐retaining transfer device for NGH. The pressure‐stabilizing system is the core part of a transfer device for NGH, providing a stable high‐pressure environment for the transfer process to avoid NGH decomposition. In this study, the characteristics of the pressure‐stabilizing system were thoroughly studied, and the factors affecting the pressure fluctuations in the transfer device were discussed. Accordingly, the pressure‐stabilizing system was modeled with AMESim software, and the model parameters were set according to the actual working conditions. The simulated pressure fluctuations in the transfer process of transfer device for NGH confirm the theoretical results, which indicate that the precharge pressure of the accumulator should be 0.8‐0.9 times the working pressure. In addition, an increased accumulator volume decelerates the response of the system. Experiments were conducted to test the reliability of the pressure‐stabilizing system. During the transfer process of the NGH sample, the operating pressure can reach 20 MPa, and the fluctuations of the inner pressure are below 20%.

Preparation of low hydration heat cement slurry with micro-encapsulated thermal control material

During the cementing process of natural gas hydrate (NGH) layer, the hydration heat of cement slurry can easily cause decomposition of NGH which leads to cementing risk. A thermal control material of phase change micro-capsule (PCM-1) with paraffin as the core material and urea-formaldehyde resin as the wall material was successfully synthesized, and then a low hydration heat cement slurry was prepared by using PCM-1. The basic performances of PCM-1 were characterized by using DSC, FTIR, SEM and TG, and the results show that the performances meet designed requirements. Then, the PCM-1 was introduced into cement slurry system, and the hydration heat (Q) and hydration temperature rise (Tr) were measured by using the self-developed semi-adiabatic test equipment. As a result, it was confirmed that the Q and the Tr decrease with the increase of PCM-1 content. The Tr of cement slurry CP15% was 25.4 °C, lower than that of cement slurry CB. Meanwhile, compared with cement slurry CB, at 24 and 48 h hydration heat of cement slurry CP15% were decreased by 7.68 × 104 and 7.28 × 104 J, respectively. Therefore, the decomposition of NGH was avoided attribute to the smaller Q of cement slurry, and the cementing operation risk in deep water was reduced.