Hydrate Exploitation Research Articles

Molecular dynamics-based analysis of the factors influencing the CO2 replacement of methane hydrate

The benefits of large reserves, wide distribution, and high combustion energy density of natural gas hydrates are of great practical importance to alleviate the energy tension, enhance the existing energy system in China and reduce the greenhouse effect. The CO2 replacement method is a critical way to develop natural gas hydrate, while traditional experimental methods are difficult to reveal the microscopic mechanism of the replacement system. An MD (molecular dynamics) technique was utilized in this work to simulate the process of carbon dioxide replacement of gas hydrates. This simulation investigates the effects of temperature, pressure, and CO2 purity during the CO2 replacement process. CO2, different concentrations of CO2/H2O, and CO2/NH3 are used as the injected fluid. The simulation results show that the influence of temperature on the CO2 replacement of natural gas hydrate is more significant than that of pressure. Within the temperature and pressure range specified in the simulation, H2O inhibits the replacement of CO2, owing to the inhibitory effect increasing as the concentration of H2O increases; NH3 promotes the process of CO2 replacement under the temperature conditions of 250 K and 260 K, and the promotion effect becomes more significant as the concentration of NH3 increases. However, adding NH3 inhibits the CO2 replacement process with hydrate when the temperature lifts to 270 K. These findings provide new ideas to improve the efficiency of the CO2 replacement method and provide theoretical insight for the engineering exploitation of hydrates.

Application of infrared thermal imaging technique in in-situ temperature field measurement of hydrate-bearing sediment under thermal stimulation

Natural gas hydrate is a green energy with great development prospects. The exploitation of natural gas hydrate has been attracting much attention. The temperature field distribution of hydrate-bearing sediment is a crucial indication on the heat or mass transfer characteristics and thermal properties of hydrate-bearing sediment during hydrate exploitation. However, to date, the acquisition means of temperatures of hydrate-bearing sediment have been limited to the discrete temperature measurement by using the contact-type temperature sensors inserted into hydrate sediment. The continuous evolution of temperature field of hydrate-bearing sediment can be hardly achieved. Thus, in this study, a new method applying the non-contact and non-destructive infrared thermal imager was developed and applied in the in-situ measurement of the continuous evolution of temperature field of hydrate-bearing sediment. The results confirm the feasibility of application of the infrared thermal imaging technique in the hydrate-related research. The complete continuous temperature fields of hydrate-bearing sediment and non-hydrate-bearing sediment under thermal stimulation were imaged and compared. The results indicate that the temperature field distribution of hydrate sediment is predominately controlled by the effective thermal conductivity of hydrate-bearing sediment. In addition, the effects of the type of hydrate-bearing sediment, heating power and particle size of sediment were investigated.

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

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

"Ladetes"-A novel device to test deformation behaviors of hydrate-bearing sediments.

Natural gas hydrate (NGH) exploitation is severely restricted by geotechnical problems. Deformation behaviors of the hydrate-bearing strata (HBS) control the occurrence and evolution of geotechnical problems during extracting natural gas from HBS. In this paper, a novel approach named Ladetes is introduced to evaluate the lateral deformation behaviors of the near-wellbore and fracture-filling regions of the HBS. The pressuremeter test and the flat dilatometer test are designed to simulate the inner boundaries of an NGH-producing well and an artificial stimulation fracture for the first time. The device can realize the in situ hydrate formation prior to the experiment and axial loading application throughout the experiment. Both the strain control mode and the stress control mode can be achieved to estimate the deformation characteristics of HBS under different downhole conditions. Prime experiments proved their adaptability and reliability. The Ladetes provides an effective and alternative way of obtaining geotechnical parameters for HBS.

Experimental study on the effect of hydrate reformation on gas permeability of marine sediments

Permeability is a crucial parameter determining methane gas recovery. Hydrate reformation has a significant impact on reservoir permeability during methane hydrate (MH) exploitation and it is often ignored. In this paper, the effect of hydrate reformation on gas permeability was investigated by remolded cores with different hydrate saturations and effective stresses. The results show that hydrate reformation exacerbates the heterogeneous distribution and reduces the reservoir permeability. The permeability damage rate (PDR) of hydrate reformation is greater than the hydrate first formation owing to the inhomogeneity of water caused by hydrate decomposition. When hydrate saturation is increased from 22.26% to 40.44%, the PDR range caused by hydrate formation varies from 19.89% to 98.02%. In addition, the permeability after hydrate decomposition decreases with increasing effective stress. When the effective stress is absent or small, the permeability after secondary decomposition is lower than the first decomposition at the same hydrate saturation. However, the opposite is true when the effective stress is reached 3 MPa. Due to the memory effect of MH in marine sediments, the hydrate reformation induction time is shorter and the reformation rate is faster. However, the gas consumption of the hydrate reformation is less than the first, causing lower hydrate saturation. This work supports the exploitation of gas hydrate and numerical simulation studies in marine sediments.

Numerical Investigation of Depressurization through Horizontal Wells in Methane-Hydrate-Bearing Sediments Considering Sand Production

Sand production has been identified as a key reason limiting sustained and commercial gas production in methane-hydrate-bearing sediments. Production tests in Canada and Japan were terminated partially because of excessive sand production in pilot wells. It is meaningful to carry out numerical investigations and sensitivity analyses to improve the understanding of sand production mechanisms during the exploitation of methane hydrates. This study introduces a numerical model to describe the coupled thermal–hydraulic–mechanical–chemical responses and sand production patterns during horizontal well depressurization in methane-hydrate-bearing sediments. The model is benchmarked with a variety of methane hydrate reservoir simulators. Results show that the spatial and temporal evolution patterns of multi-physical fields are different and the hydromechanical evolutions are the fastest. Gas production and sand production rates are oscillatory in the early stages and long-term rates become stable. Gas production is sensitive to rock physical and operational parameters and insensitive to rock mechanical properties such as cohesion. In contrast, sand production is sensitive to cohesion and insensitive to rock physical and operational parameters. Although cohesion does not directly affect gas productivity, gas productivity can be impaired if excessive sand production impedes production operations. This study provides insights into the sand production mechanism and quantifies how relevant parameters affect sand production during the depressurization in methane-hydrate-bearing sediments.

Re-definition of the region suitable for CO2/CH4 replacement into hydrates as a function of the thermodynamic difference between CO2 hydrate formation and dissociation

The replacement of methane with a theoretically equal quantity of carbon dioxide, probably represents the most promising solution for natural gas hydrate exploitation. However, the real efficiency is far from the ideal value. This article aims to focus the attention on the thermodynamic area considered suitable for replacement. Because the formation and dissociation of hydrates always show differences between each other and, in particular, the formation always requires more severe conditions to occur, the region effectively suitable for replacement is still more narrow than what currently believed and consists of the area between the dissociation curve of methane hydrates and the formation curve of CO2 hydrates. The present hypothesis was confirmed by carrying out the replacement process both above and below this latter curve. It was found that the methane recovery was more than one order of magnitude higher in the first case: 43.32 against 4.19 vol%.

Molecular simulation studies on the water/methane two-phase flow in a cylindrical silica nanopore: Formation mechanisms of water lock and implications for gas hydrate exploitation

The water/gas two-phase flow is a frequently encountered question in the percolation field, and is especially important for the exploitation of natural gas hydrates because their decomposition products are exactly liquid water and natural gas. We studied the water/methane two-phase flow in a hydrophilic cylindrical nanopore by performing molecular simulations, and obtained high-quality nanoflows under different water saturation (Sw) thanks to the newly established nano-manometer method to control pressure difference accurately. With increasing Sw, the methane flow decreases almost linearly until a sudden stop when Sw ≥ 0.52. The formation of the water lock accounting for this phenomenon is observed clearly, and the larger Sw, the earlier formation of the water lock as well as the longer water lock. Based on careful data analysis, a water lock model and its formation mechanism are newly proposed with two pieces of strong evidence — the continuous reduction of the surface area of the water/gas interface when the water lock forms and the existence of maximum thickness of water film for different Sw. Thus, the competition between the surface tension of the water/gas interface and the adsorption of the water/wall interface controls the development of the water lock. These findings are very helpful for understanding the two-phase percolation and optimizing the gas production and water removal schemes during hydrate exploitation. In addition, the nano-manometer can be widely used in other nanoflow simulations for measuring the local pressure accurately.

An analytical model of time-dependent elastoplasticity with hydraulic–mechanical coupling for wellbore stability in hydrate exploitation

Natural gas hydrates have potential economic and environmental significance. However, wellbore instability likely occurs during drilling due to the deterioration in the geomechanical properties of formation caused by hydrate dissociation. In this study, a time-dependent elastoplastic analytical model for wellbore stability is proposed under overbalanced and underbalanced drilling, considering the hydrate dissociation-induced changes in the geomechanical properties and full coupling between hydraulic–mechanical fields. The analytical solutions are verified with the finite element results under the same conditions and validated with the results from complex numerical simulations. According to the analytical solutions, the difference in pore pressure relative to the initial pore pressure decreases, and accordingly, the incremental displacement decreases (by approximately 39.54% for the maximum displacement) after the influence of the mechanical field on pore pressure is considered. The influence is greater far from the wellbore and smaller around the wellbore due to the constant drilling fluid pressure. The risk of wellbore instability increases with time, and the safe drilling window of drilling fluid pressure will be narrowed by hydrate dissociation (by −5.90%), the increase in the drilling fluid temperature (by −12.64% from the temperature of 20 °C to 30 °C) and the reduction in cohesion (by −47.43% at most).

A mesoelastic-plastic damage model for hydrate-bearing sediments with various hydrate-growth patterns

A mesoelastic-plastic damage mechanical model (Gurson-DP) is proposed to simulate the progressive failure caused by damage accumulation in hydrate-bearing sediments (HBS) under engineering disturbances. HBS is regarded as a complex of the matrix phase, inclusion phase and void phase. A combination of the Reuss and Voigt bounds is used to predict the macroscopic modulus of HBS. First, a mesodamage mechanical model is established based on Weibull random failure theory and Gurson plastic damage theory. Next, the analytical biphasic Hill equation of the yield stress for dilatation-softening HBS and equations describing void growth and nucleation are proposed to study the behavior of the matrix phase and void phase. Finally, the accuracy and validity of the model are verified by triaxial compression tests. The results show that our proposed model can simulate the entire stress-strain process of HBS from plastic yielding to softening. The model can accurately characterize the mechanical behavior of HBS, such as dilatation softening and cementation failure, and reasonably reflects its mesoscopic failure mechanism under complex stress paths. This paper comprehensively studies the complex mechanical response of HBS and provides a theoretical basis and technical means for improving hydrate exploitation.

Optimization of the depressurization rate and stepwise strategy for hydrate exploitation using a genetic algorithm-based depressurization method

Depressurization is one of the most effective methods for hydrate exploitation. Optimization of the pressure-drop strategy for improving the exploitation efficiency requires immediate attention. In this study, a hydrate decomposition model was for the first time combined with a genetic algorithm. The pressure-drop rate and strategy were optimized based on the exploitation efficiency. The depressurization rate of the continuous slow depressurization method was optimized. Subsequently, the best pressure-drop rate for stepwise depressurization was hypothesized and validated. In addition, the stepwise strategy was optimized. For the two depressurization methods, increasing the pressure-drop rate increased the exploitation efficiency, while increasing the number of pressure-drop stages in the stepwise depressurization method adversely impacted the exploitation efficiency. Prolonged constant-pressure intervals reduced the efficiency when there were few pressure-drop stages; however, the opposite trend emerged for a high number of depressurization steps. This study provides guidance for optimizing the production efficiency of hydrate exploitation via depressurization.

Modeling on the phase equilibrium of gas hydrate in electrolytes containing system

The phase equilibrium of gas hydrate is fundamental for flow assurance, energy exploitation, and hydrate concerning technique. In this study, the electrolyte NRTL equation coupled with the two-step hydrate model of Chen and Guo was successfully applied to predict the phase equilibrium of gas hydrate in the presence of single and binary mixed electrolytes. The predicted results were in good agreement with the available experimental data over a wide range of electrolyte concentrations when taking into account the contributions of long-range and short-range interactions in saline solution. Validated with 943 hydrate experimental data of pure gas and gas mixture formed in single and mixed electrolytes, the average absolute deviations in pressure are 5.42 % and 4.71 %, respectively. More importantly, it is further investigated that the proposed model shows a better performance for the high-concentration saline solution with concentration up to the near-saturation, with an average deviation of 0.59 K for methane hydrate. Therefore, the proposed model in this work is significant for comprehending gas hydrate phase behavior in saline solution, and provides better guidance for hydrate exploitation and industrial applications.

Decomposition characteristics of methane hydrate in porous media under continuous and intermittent microwave heating

Microwave stimulation is a new method for natural gas hydrate exploitation. In this study, methane hydrate was synthesized in quartz sand with a particle size of 106–150 μm, and the decomposition characteristics were investigated using continuous and intermittent microwave heating. During the initial stage of continuous microwave heating, methane hydrate decomposed immediately due to microwave stimulation. Subsequently, due to a decrease in microwave penetration depth, microwaves did not affect the areas further away from the microwave source and macroscopic heat transfer became the main heat source for hydrate decomposition. The microwave power used during the study ranged from 200 W to 500 W. The results indicated that hydrate decomposition time decreased as power increased, and the average gas production rate increased at the same time. However, the energy efficiency ratio did not vary with the microwave power. The maximum energy efficiency ratio was 1.320 at a microwave power of 400 W under continuous microwave heating. Compared with continuous microwave heating, intermittent microwave heating improved the efficiency ratio by 59.32 %, with a heating cycle involving microwave stimulation for 5 min (Microwave ON time) and no stimulation for 1 min (Microwave OFF period). As microwaves provide heat for hydrate decomposition, a high-speed gas production can be obtained. Heat reservoirs were utilized to maintain hydrate decomposition during the OFF period, which also resulted in energy saving. Although intermittent microwave heating reduced the average gas production rate slightly, it improved the energy efficiency significantly. Therefore, the number of heating cycles and microwave heating periods should be carefully considered to obtain high hydrate exploitation efficiency. Intermittent microwave heating is recommended for hydrate exploitation to improve extraction efficiency and save energy.

Study on Gas Hydrate Reservoir Reconstruction for Enhanced Gas Production in the Shenhu Area of the South China Sea Based on a 3D Heterogeneous Geological Model

Natural gas hydrate (NGH) has the huge exploitation potential for clean energy in the current world energy pattern. Its total organic carbon storage is about twice the sum of carbon content of oil, gas, and coal and hence attracts the attention of the world. China has carried out some gas hydrate exploitation works and delineation of three gas hydrate deposits whose reserve scale is over 100 billion cubic meters, and the NGH resource is abundant. The NGH reservoir in the South China Sea is of low porosity and permeability, is unconsolidated, has poor cementation, and is easy to fragment in hydrate production. On the one hand, the condition of low porosity and permeability around the well would severely reduce the production effect; on the other hand, the hydrate decomposition would more easily bring wellbore instability caused by stratum stress change. Therefore, to achieve safe and efficient exploitation of NGH, proper reservoir reconstruct technology needs to be chosen for enhancing the reservoir’s permeability and stability. This paper chose the Shenhu area of South China Sea as the research area, constructed the three-dimensional heterogeneous geological model of hydrate-bearing sediments which can be approximated realistically to depict, then used high-pressure jet grouting (HPJG) technology to reconstruct the hydrate reservoir, optimized the grouting hole direction, location, and spacing, and assessed the productivity increasing effect. The research results show the following: (a) Because of the higher hydrate saturation (SH) and lower permeability (k) around the well, the HPJG in the vertical direction was profitable for reservoir productivity. (b) Considering the heterogeneous SH and k in the horizontal direction, the HPJG in the front of the horizontal well was profitable for the reservoir productivity. (c) The HPJG spacing needs to be properly designed in combination with the absolute standard (VP), the relative standard (RGM), and the specific production index (J). (d) Under the conditions of this paper setting, the optimal HPJG reconstruction scheme is as follows: the HPJG in the vertical direction was arranged at the front of the horizontal well, and the spacing between the holes was 10 m. The productivity after reconstruction ranged up to 55.69% compared with before.

A novel technique for seabed strata deformation in situ monitoring

Seafloor strata deformation monitoring is important for gas hydrate exploitation and the monitoring and early warning of seabed instabilities. Due to the limitation of in situ monitoring technology, existing observations are carried out with geophysical methods to provide basic geomorphological characteristics and stratigraphic structures. However, it is of equal importance to study the in situ evolution mechanism of the process of strata deformation, which relies heavily on long-term in situ observations. An in situ monitoring instrument for seabed strata deformation monitoring is presented. Sufficient theoretical, numerical, and experimental studies were carried out to conduct a mechanical analysis on the entire deployment process of the instrument. The maximum penetration resistance and reaming pressure were calculated during the deployment process, and the stability and feasibility of the deployment method were verified. To validate the maximum penetration resistance obtained and the monitoring performance of the instrument, field tests were conducted on a tidal flat in Changzhi Island. The penetration resistance of the instrument and the strata deformation of the tidal flat were measured and obtained. The results demonstrate the feasibility of the presented instrument.

Hydrate phase equilibria in natural sediments: Inhibition mechanism and NMR-based prediction method

The hydrate phase equilibrium condition in natural sediments is an important prerequisite for gas hydrate exploitation and subsea sequestration of CO2. However, its rapid and accurate prediction remains a challenge. In this work, we proposed a novel method to predict the hydrate phase equilibria in various natural sediments using low-field NMR technology. Also, its potential inhibition mechanism was clarified from the perspective of different types of pore water. The results indicated the peaks of T2 spectra for all types of pore water shifted to lower transverse relaxation times during the hydrate formation, meaning that the formed hydrates act as solid matrices in sediments and thus reduce pore size. Furthermore, it was observed that hydrate formation from bound water was much more difficult than capillary water, even at the same pore size. More importantly, not all bound water participated in hydrate formation. During the hydrate dissociation, montmorillonite exhibited the greatest dissociation temperature depression, followed by SA sediments, while illite and kaolin showed a relatively low inhibition on hydrate phase equilibria. This difference in dissociation temperature depression is attributed to water adsorption on the mineral surface and interlayer cation hydration, in addition to the capillary effect. Among them, the capillary-induced phase equilibrium inhibition is the lowest, followed by interlayer cation hydration, and mineral surface adsorption shows the most strong inhibition. Finally, the feasibility and validity of the NMR-based method in predicting the hydrate phase equilibrium condition in natural sediments were verified. These findings not only add further insights into the hydrate phase behavior in clayey-silty sediments but also provide an effective tool for rapid and accurate predictions of hydrate phase equilibria.

Visual study on methane hydrate formation and depressurization-induced methane hydrate dissociation processes in a micro-packed bed reactor

Natural gas hydrate has become one of the most promising green alterative energies. The safe and efficient exploitation of natural gas hydrate is of importance. Depressurization method has been considered as one of the most feasible hydrate exploitation approaches. The methane hydrate dissociation by depressurization has been widely investigated by using a variety of reactors or simulators. However, the micro-packed bed reactor has been rarely used for the hydrate-related studies. The packing materials in the micro-packed bed reactor are useful for simulating the porous condition of sediments. The optical transparency of the microreactor can provide the direct visualization of phase behavior, morphology, interfacial phenomenon and fluid migration in pore spaces. Thus, a high-pressure transparent micro-packed bed reactor recently developed was used to investigate the methane hydrate formation and depressurization-induced methane hydrate dissociation behaviors in porous media in this study. The hydrate formation results identify the different patterns of methane hydrate formation caused by the various methane bubble dispersion conditions, such as size and distribution in pores. The depressurization-induced methane hydrate dissociation behavior was investigated by continuously extracting fluids after the methane hydrate formation in the micro-packed bed reactor. The hydrate reformation phenomenon was observed during the early stage of depressurization process. This was triggered by the methane escaping out of the collapsed hydrate shell. The impact of fluid extraction rate of depressurization was studied. The results indicate higher fluid extraction rate leading to more severe hydrate shell collapsing and significant gas migration, resulting in more significant methane hydrate reformation. The hydrate dissociation process and dramatic fluid migration phenomena in the pore spaces were also visualized during the later stage of depressurization.

Study on structure optimization and applicability of hydrocyclone in natural gas hydrate exploitation

With the development of economy and industry, the consumption of fossil energy is gradually increasing. Currently, natural gas hydrates (NGH) are considered to be an ideal alternative energy due to its large reserve and high energy density. However, the separation of hydrate slurry is a critical step in the exploitation of NGH. In this study, the optimization of the structural parameters based on the conventional three-phase hydrocyclone was carried out using numerical simulation and orthogonal design. At the same time, the separation efficiency criterion E was defined to evaluate the separation efficiency by calculating the sum of the discharge efficiency of water and gas. Analysis of the effect of individual structural factors on the flow field distribution characteristics inside the hydrocyclone using the single factor analysis method. The results showed that: with the combination of structural parameters of s was 2 mm2 × 12 mm2, dz was 28 mm, h was 20 mm, and li was 28 mm, the maximum E of the three-phase hydrocyclone was 1.46. The effect significance of each structural parameter on the separation efficiency from the highest to the lowest was the s, dz, h, and li. In the single-factor analysis, when the s was 2 mm2 × 12 mm2, the tangential velocity, axial velocity, and CH4 volume fraction in the flow field reached the maximum of 13.65 m/s, 4.35 m/s, and 12.4%, respectively. But the minimum water phase volume fraction was 69.9% under this structural parameter condition. When the dz was 36 mm, the maximum decrease value of axial velocity in the flow field was 3.57 m/s, the maximum CH4 volume fraction was 12.4%, and the water volume fraction reached a minimum of 66.3%. The li and the h only had significant effects on the axial velocity and the water volume fraction, respectively. The axial velocity reached a maximum of 4.75 m/s when the li was 32 mm, and the water phase volume fraction reached a maximum of 77.9% when the h was 10 mm. The study of the structural parameters and flow field characteristics of this three-phase hydrocyclone applicable to the solid fluidization exploitation of NGH provides some guidance and suggestions for the separation of hydrate slurry after solid fluidization exploitation of NGH.

Applications of the Discrete Element Method for Gas Hydrate-Bearing Sediments: Recent Advances and Perspectives

The understanding of the mechanical properties of hydrate-bearing sediments (HBSs) is fundamental to the safe and efficient exploitation of natural gas hydrates. HBSs are granular materials composed of detrital mineral particles and hydrates. The inherent heterogeneity, discontinuity, and anisotropy cannot be effectively treated by continuum-based numerical methods. The discrete element method (DEM) has been widely used for modeling geomaterials, such as soils and rocks. Recently, it has been increasingly applied to study the mechanical properties of HBSs at the particle level. This paper presents a comprehensive review of recent advances in studies of simulating hydrate-bearing sediment models using the DEM, including complex hydrate-bearing models and their applications. The contact models and micromechanical parameters used in the DEM models are summarized, and the various applications, including laboratory tests, submarine landslides, and hydraulic fracturing, are discussed. In addition, the advantages and challenges for future studies are discussed. This review is beneficial to help researchers thoroughly understand the state-of-the-art DEM modeling of HBSs.

Experimental investigation and modelling of synergistic thermodynamic inhibition of Diethylene Glycol and glycine mixture on CO2 gas hydrates

In this experimental and modelling study, Diethylene glycol (DEG) and Glycine (Gly) mixtures are introduced to hinder carbon dioxide hydrate formation by pushing the phase boundaries on the lower temperature side. The mixture of DEG and Gly with the ratio of 1:1 is experimented at 15, 10, and 5 wt% concentrations and the pressure vary from 2.5 to 4.0 MPa. The T-cycle method is employed to assess the effect of the studied blends on the CO2 hydrate by evaluating the hydrate dissociation temperature. Varied compositions of pure DEG and Gly as well as their mixtures are used to compute the synergistic effect. The studied system's thermodynamic hydrate inhibition (THI) influence is a concentration-driven phenomenon. Higher concentration can shift the hydrate liquid vapor equilibrium (HLVE) curve to lower temperatures and high-pressure regions. The outcomes depict that mixture of DEG and Gly at 15 wt%. Shows comparatively better results than the mixtures at 5 and 10 wt%, respectively. The obtained 10 wt% mixture results have also been compared with the conventional hydrate inhibitors and other THIs systems and provide a significant hydrate average suppression (ΔT) of 2.4 K. Furthermore, the freezing point-based Dickens and Quint Hunt model was also applied to predict the HLVE data of CO2 hydrates and satisfactory agreement found with maximum mean absolute error (MAE) of 0.498 K. A better inhibitory performance was seen when diethylene glycol and glycine were combined, demonstrating the potential of amino acids as synergistic inhibitors in the exploitation of hydrates, transportation of oil and gas, and flow assurance.