Kinetics Of Hydrate Decomposition Research Articles

The effect of decomposition of natural gas hydrate on deep-water drilling

One of the significant challenges in deep-water drilling is calculating BHP during kickoff caused by natural gas hydrate decomposition. In this paper, the heat transport theory, seepage mechanics, and hydrate decomposition kinetics serve as the foundation for the hydrate decomposition and bottom hole pressure model. Research shows 42.8 m3 of gas have entered Well X cumulatively, resulting in a 1.66 MPa pressure decrease and a 6.9-hour-recovery period. The monitoring of high saturation and porosity formations needs to be strengthened, and drilling parameters need to be modified to protect the stability of the wellbore, according to the analysis of formation parameters and drilling parameters.

Effect of Cage Occupancy on Stability and Decomposition of Methane Hydrate.

Gas hydrates usually contain a certain number of empty cages that will both affect the hydrate stability and reduce the gas storage capacity. In this work, by MD simulations, we found that the hydrate stability is related to the cage occupancy, the empty cage types, and especially the distribution of empty cages. With the decrease of overall occupancy, the stability of hydrate becomes worse. Under the same overall occupancy, the more concentrated the empty cages are, the more unstable the hydrate is and hence the faster it decomposes. The methane molecules may migrate between distorted cages during the decomposition, resulting in a temporary increase in the stability of hydrate. Hydrates with different empty cage distributions show different decomposition mechanisms: when empty cages are concentrated, the melting rate is fast first due to the rapid decomposition of empty cages, but the remaining filled cages will reduce the melting rate; when empty cages are separated on the contrary, the early melting is slow because of the high local occupancy, and the following melting will be accelerated because of the high melting surface area. It indicates that the empty cage distribution plays a controlling role in hydrate decomposition kinetics at different stages.

Experimental and Modeling Study of Kinetics for Hydrate Decomposition Induced by Depressurization in a Porous Medium

The hydrate decomposition kinetics is a key factor for the gas production from hydrate-saturated porous media. Meanwhile, it is also related to other factors. Among them, the permeability and hydrate dissociation surface area on hydrate dissociation kinetics have been studied experimentally and numerically in this work. First, the permeability to water was experimentally determined at different hydrate saturations (0%, 10%, 17%, 21%, 34%, 40.5%, and 48.75%) in hydrate-bearing porous media. By the comparison of permeability results from the experimental measurements and theoretical calculations with the empirical permeability models, it was found that, for the lower hydrate saturations (less than 40%), the experimental results of water permeability are closer to the predicted values of the grain-coating permeability model, whereas, for the hydrate saturation above 40%, the tendencies of hydrate accumulation in porous media are quite consistent with the pore-filling hydrate habits. A developed two-dimensional core-scale numerical code, which incorporates the models for permeability and hydrate dissociation surface area along with the hydrate accumulation habits in porous media, was used to investigate the kinetics of hydrate dissociation by depressurization, and a “shrinking-core” hydrate dissociation driven by the radial heat transfer was found in the numerical simulations of hydrate dissociation induced by depressurization in core-scale porous media. The numerical results indicate that the gas production from hydrates in porous media has a strong dependence on the permeability and hydrate dissociation surface area. Meanwhile, the simulation shows that the controlling factor for the dissociation kinetics of hydrate switches from permeability to hydrate dissociation surface area depending on the hydrate saturation and hydrate accumulation habits in porous media.

Macroscopic defects upon decomposition of CO2 clathrate hydrate crystals.

Micrometer- and submicrometer-sized pores and macroscopic defects like cracks and tubular channels can be found in a variety of clathrate hydrates (hydrates for short) during formation and decomposition. Their origin, their evolution in time, and their effect on hydrate decomposition kinetics are unclear. We used time-lapse micro computed tomography (μCT) in combination with temperature control and pressure monitoring to study the formation and evolution of pores and macroscopic defects in decomposing CO2 hydrates at subzero (Celsius) temperature. Our results suggest that the decomposition of hydrates is always accompanied by the formation of pores and an increase of the apparent hydrate volume by more than 3%. Hydrate decomposition often starts with the formation of cracks inside the hydrate and not necessarily at the free surface of the hydrate, which frequently remains intact for a long period and seems to be self-preserved in some regions. Decomposition spreads out from these cracks in a uniform fashion yielding a variety of macroscopic features. In some cases, the propagating decomposition front seems to get blocked by planar barriers inside the hydrate yielding regions with high resistance against decomposition. This, together with a generally heterogeneous distribution of decomposition resistant regions, challenges the shrinking core model of hydrate decomposition as well as the popular ice-rind theory used to explain the effect of self-preservation.

Effect of polyvinylpyrrolidone at methane hydrate-liquid water interface. Application in flow assurance and natural gas hydrate exploitation

Polyvinylpyrrolidone (PVP) is one of the most studied low dosages hydrate inhibitor (LDHI), while its hydrate inhibiting effect is well known, its surface active properties by which PVP molecules alters the hydrate-liquid water interface has not been understood properly. In the present work, influence of PVP molecules at the hydrate-liquid water interface was studied at molecular level using molecular dynamics (MD) simulation. In addition, impact of various molecular weights (or chain length) of PVP molecules was also investigated. The force field parameters for PVP monomer (F4) and polymers were developed and validated against PVP physical properties. The free energy of binding of PVP with methane hydrate and methane hydrate decomposition kinetics was studied in presence of PVP at hydrate-water interface. Structural properties of hydrate were analyzed using four body order parameter and mutually coordinated guest order parameter (MCG-OP). The decomposition rate of methane hydrate in presence of PVP molecules (in bulk water near hydrate interface) was studied, it was observed that PVP polymer changes the surface properties of hydrate and enhances the hydrate decomposition rate.

Theoretical Study of Gas Hydrate Decomposition Kinetics: Model Predictions

In order to provide an estimate of intrinsic gas hydrate dissolution and dissociation kinetics, the Consecutive Desorption and Melting Model (CDM) was developed in a previous publication (Windmeier, C.; Oellrich, L. R. J. Phys. Chem. A 2013, 117, 10151-10161). In this work, an extensive summary of required model data is given. Obtained model predictions are discussed with respect to their temperature dependence as well as their significance for technically relevant areas of gas hydrate decomposition. As a result, an expression for determination of the intrinsic gas hydrate decomposition kinetics for various hydrate formers is given together with an estimate for the maximum possible rates of gas hydrate decomposition.

Theoretical Study of Gas Hydrate Decomposition Kinetics—Model Development

In order to provide an estimate of the order of magnitude of intrinsic gas hydrate dissolution and dissociation kinetics, the "Consecutive Desorption and Melting Model" (CDM) is developed by applying only theoretical considerations. The process of gas hydrate decomposition is assumed to comprise two consecutive and repetitive quasi chemical reaction steps. These are desorption of the guest molecule followed by local solid body melting. The individual kinetic steps are modeled according to the "Statistical Rate Theory of Interfacial Transport" and the Wilson-Frenkel approach. All missing required model parameters are directly linked to geometric considerations and a thermodynamic gas hydrate equilibrium model.

1-D MATHEMATICAL MODELING OF HYDRATE DECOMPOSITION IN POROUS MEDIA BY DEPRESSURIZATION AND THERMAL STIMULATION

This paper describes a one-dimensional numerical model for natural gas production from the dissociation of methane hydrate in a hydrate-capped gas reservoir under depressurization and thermal stimulation. The mathematical equations that can describe this type of reservoir include mass balance, heat balance, and kinetics of hydrate decomposition. These nonlinear partial differential equations are solved using the finite-difference fully implicit scheme to obtain the distribution of pressure and saturation of gas, water, and hydrate in the reservoir. In addition, the effect of convection an conduction heat transfer, variation change of formation porosity, the effect of using different equations of state [Peng-Robinson (PR) and modified Esmaeilzadeh-Roshanfekr (ER) equations of state (EOS)], variation change of thermal conductivity of rock, and the effect of using different fluids for thermal stimulation including steam, hot methane, and hot water injection are considered. For thermal stimulation, nine different cases are considered. The results of calculations show that the gas production rate is a sensitive function of well pressure and temperature, and the flow rate of the injected fluid. The results of the model are compared with those of the numerical models of Holder et al. (1982), Moridis (2002), and the HYDRSIM simulator. The results of the proposed model are in good agreement with those of the HYDRSIM simulator.

Experimental determination of permeability in the presence of hydrates and its effect on the dissociation characteristics of gas hydrates in porous media

Abstract Although there are many uncertainties in hydrate dissociation process in porous media, numerical simulation gives useful information in evaluating economically feasible gas recovery processes from gas hydrate reservoirs. Furthermore, there are several unknown parameters involved in the numerical model and determination of accurate values of these parameters is essential for reliable production forecasts. One of these parameters is the variation of permeability of the porous media in the presence of hydrates. In this study the permeability to gas was experimentally determined at varying hydrate saturations in a porous medium made of packed glass beads. By comparing the experimentally determined permeability with those calculated using the empirical permeability correlations it was found that for initial water saturations less than 35%, hydrate tends to form on the grain surfaces. However, for initial water saturations greater than 35%, the experimental results indicate a pore filling tendency of hydrate formation. The experimental permeability values were also correlated with the Masuda et al.'s (1997) permeability model and a value of 3.0 was obtained for the permeability reduction exponent. To evaluate the impact of permeability reduction exponent on the dissociation process, a one-dimensional numerical model was developed for dissociation of gas hydrates in porous media by depressurization. The numerical model includes the three mechanisms i.e. kinetics of hydrate decomposition, heat transfer and fluid flow; that might be associated with the dissociation of hydrates in porous medium. The effect of permeability reduction exponent on the dissociation characteristics of hydrate was analyzed using this simulator.

Effect of Hydrates on Sustaining Reservoir Pressure in a Hydrate-Capped Gas Reservoir

Abstract A hydrate-capped gas reservoir is defined here as a reservoir that consists of a hydrate-bearing layer underlain by a two-phase zone involving mobile gas. In such a reservoir, hydrates at the top contribute to the produced gas stream once the reservoir pressure is reduced by gas production from the free-gas zone. Large gas reservoirs of this type are known to exist in Alaska and Siberia and are expected to exist in the Mackenzie Delta of the Northwest Territories in Canada. Gas production from a hydrate-capped gas reservoir is a process governed by a combination of mechanisms of heat transfer, fluid flow, thermodynamics and kinetics of hydrate decomposition. Using a comprehensive numerical simulator, an extensive simulation study indicates that some of the non-linear processes involved in gas production from hydrate reservoirs (i.e. the convective heat transfer and the kinetics of hydrate decomposition) have a negligible effect on the overall physics of the process. This significantly reduces the complexity of the heat and fluid flow equations and legitimizes the construction and use of simplified models. In this work, we invoke the above approximations and develop a generalized gas material balance equation. This equation has two significant differences from the material-balance equation for conventional gas reservoirs, including the incorporation of:the effect of cooling due to endothermic decomposition of the hydrate; andthe effect of generated gas and water from the hydrate decomposition. In this model, it is assumed that a mobile phase exists in the hydrate zone; thus, no sharp hydrate dissociation interface is assumed. Considering the sensible heat of the hydrate zone and heat transfer from cap and base rocks, the gas and water generation rates are determined on the basis of the equilibrium rate of the decomposition process. Verification of the solution is obtained by comparing results with those of a comprehensive hydrate reservoir numerical simulator. The model developed here can be used as an approximate engineering tool for evaluating the role of hydrates in improving the productivity and extending the life of hydrate-capped gas reservoirs. Introduction Natural gas hydrates are solid molecular compounds of water with natural gas that are formed under certain thermodynamic conditions. There is evidence that enormous amounts of natural gas exist in the form of hydrate deposits in many regions of the world(1). These deposits occur in sub-oceanic sediments as well as in arctic regions. Every unit volume of gas hydrate has the potential to contain 170 to 180 volumes of gas at standard conditions, making the energy content of one cubic metre of a hydrate reservoir more than other types of unconventional gas reservoirs(2). In view of the large untapped resources of natural gas hydrates, extensive research and development work is underway to determine what fraction of this resource is recoverable. A number of recovery processes have been suggested for producing gas from hydrates in sediments. Sloan(3) and Makogan(4) have presented an extensive review of the suggested methods including depressurization, thermal stimulation and inhibitor injection.

Simulation of Depressurization for Gas Production From Gas Hydrate Reservoirs

Abstract Gas hydrates as a significant resource of natural gas have attracted considerable attention in recent years. However, the severe environmental conditions of gas hydrate reservoirs and the solid form of hydrates require extensive technological development before commercial gas production becomes possible. Numerical studies often give useful information for predicting the potential and technical viability of a recovery process. This paper presents a 2D cylindrical simulator for gas production from hydrate reservoirs. The model includes the equations for gas-water two-phase flow, conductive and convective heat transfer, and intrinsic kinetics of hydrate decomposition. The simulator is used to model a hydrate reservoir where the hydrate- bearing layer overlies a free gas zone, such as those discovered in the arctic. A well is drilled and completed in the free gas zone. Pressure reduction in the free gas zone leads to the decomposition of the overlying hydrate and subsequent production of the generated gas. In this paper, we study the impact of the overlying hydrate in improving the production performance of the underlying gas reservoir and investigate the effect of various parameters on gas production behaviour. The rate of gas generated and produced, pressure, temperature, and saturation distributions are studied to investigate the sensitivity of results on individual input parameters. The results suggest that the development of gas reservoirs with overlying hydrates can lead to significant production rates and that the top hydrates have a large impact on increasing the reserve and improving the productivity of the underlying gas reservoir. Introduction Today, increasingly more stringent environmental considerations require that clean sources of energy be found. It is therefore anticipated that the demand for natural gas will continue to increase significantly. Some studies indicate that the amount of methane trapped in gas hydrates in natural settings is 100 times that of conventional gas reserves(1, 2). Therefore, gas hydrates are being considered as a potential source for natural gas production. However, it is not clear what percentage of this huge resource is recoverable, and the technologies for recovering natural gas from hydrates are still under development. Sloan(3) has presented an extensive review of some suggested methods, including depressurization, thermal stimulation, and inhibitor injection. The least energy intensive process is thought to be the depressurization method, since in this method the heat of decomposition is provided by the surrounding formation. Modelling of gas production from hydrate reservoirs involves solving the coupled equations of mass and energy balances. A review of analytical and numerical models given by Hong et al.(4) suggests that two approaches with respect to conditions at the decomposition zone have been taken: equilibrium and non-equilibrium. In models using the equilibrium approach, the three-phase hydrate-gas-water interface is at a thermodynamic equilibrium. The underlying assumption in these models is that the intrinsic rate of hydrate dissociation is fast enough so that the overall rate of hydrate dissociation is controlled by other mechanisms, i.e., fluid flow or heat transfer. In non-equilibrium models however, the condition at the hydrate-gas-water interface is kinetically approaching equilibrium.

Determination of the intrinsic rate constant and activation energy of CO 2 gas hydrate decomposition using in-situ particle size analysis

Experimental data on the rate of decomposition of CO 2 gas hydrates has been obtained using a semi-batch stirred tank reactor, with an in-situ particle size analyser, at temperatures ranging from 274 to 281 K and pressures ranging from 1.4 to 3.3 MPa . A method for calculating the moments of the particle size distribution has been presented. The experimental data was analysed using the kinetic model of Clarke and Bishnoi (Determination of the intrinsic kinetics of gas hydrate decomposition kinetics using particle size analysis, Presented at the Third International Conference on Gas Hydrates, Salt Lake City, Utah, July 18–22, 1999; Chem. Eng. Sci. 55 (2000) 4869) in its differential form in order to account for the slight change in temperature during the decomposition of CO 2 hydrates. The applicability of the new instrument for measuring gas hydrate decomposition kinetics was examined by conducting experiments with ethane at conditions similar to those encountered by Clarke and Bishnoi (2000). It was seen that the previously obtained rate constants for ethane hydrate decomposition were able to predict the new obtained data. A new procedure for regressing the intrinsic rate constant and activation energy has also been described and it is seen that the activation energy is 102.88 kJ/ mol and the intrinsic rate constant is 1.83×10 8 mol/( m 2 Pa s ) for CO 2 gas hydrate decomposition.

Analytical Modelling of Gas Production From Hydrates in Porous Media

Abstract Gas hydrates are being considered as an alternative energy resource of thefuture since they exist in enormous quantities in permafrost and offshoreenvironments. However, gas production potential from hydrate reservoirs throughdifferent production schemes has not been fully investigated yet. This workintroduces a simple analytical model for simulating gas production from hydratedecomposition in porous media by a depressurization method. We consider the heat transfer to the decomposing zone, intrinsic kinetics ofhydrate decomposition, and gas-water two-phase flow as the three primarymechanisms involved in hydrate decomposition in porous media. In this study, the relative importance of these mechanisms is compared over a realistic rangeof the physical properties. It is shown that for the cases studied, the effectof two-phase flow is significantly smaller than the heat transfer and theintrinsic kinetics of hydrate decomposition. Considering the rate-controllingmechanisms, an analytical model is developed to predict the performance ofdecomposition of gas hydrates in porous media. The model is used to performsensitivity studies to investigate the feasibility of commercial gas productionfrom hydrate reservoirs. The results suggest that significant quantities of gascan be produced from gas hydrate reservoirs where the hydrate overlies the gaszone. Such reservoirs have been found in the permafrost regions of Siberia, Alaska, and Canada. Introduction The enormous natural gas reserves associated with the in situ gas hydratesin permafrost regions and offshore environments of the earth is expected to bean energy resource of the future. The gas could be produced from the hydratedissociation by depressurization, thermal stimulation, solvent injection, or acombination of these methods. The potential for gas production from hydratereservoirs through different production techniques is still uncertain and underinvestigation. One method of investigation is with the help of mathematicalmodels. For a mathematical model to be representative, it should include theimportant mechanisms. In a depressurization scheme considered in this study, three important mechanisms are involved: intrinsic decomposition of the hydratethat results in reduced temperature; heat flow towards the cooled zone thatprovides the necessary energy for further decomposition; and, flow of thedecomposed gas and water through the porous rock.

Upper Limits on the Rates of Dissociation of Clathrate Hydrates to Ice and Free Gas

The Hertz-Knudsen-Langmuir equation is used to calculate the maximum possible rate at which clathrate hydrates can dissociate. Since hydrate decomposition is endothermic, heat must be added to keep the sample temperature constant. The prediction of the Hertz-Knudsen-Langmuir equation for the rate of dissociation is used to determine the heat flux necessary to keep the sample temperature constant, and thereby maintain this maximum rate of production of gas from the hydrate. Such considerations may be relevant both to the study of the rate of hydrate decomposition and to the eventual efficient production of natural gas from hydrate deposits. In addition, experimental results available in the literature on hydrate decomposition rates and the kinetics of hydrate decomposition are discussed in light of the work done by Langmuir and others on endothermic decomposition reactions. These earlier studies suggest that dissociation experiments in which the sample is exposed to vacuum could help to explore the kinetics involved in hydrate decomposition.

Analogy between Effect of Inhibitors on Hydrate Equilibrium Thermodynamics and Hydrate Decomposition Kinetics

Annals of the New York Academy of SciencesVolume 715, Issue 1 p. 463-467 Analogy between Effect of Inhibitors on Hydrate Equilibrium Thermodynamics and Hydrate Decomposition Kinetics VIDYADHAR A. KAMATH, VIDYADHAR A. KAMATH Petroleum Development Laboratory University of Alaska Fairbanks Fairbanks, Alaska 99775–5880Search for more papers by this authorSHIRISH L. PATIL, SHIRISH L. PATIL Petroleum Development Laboratory University of Alaska Fairbanks Fairbanks, Alaska 99775–5880Search for more papers by this author VIDYADHAR A. KAMATH, VIDYADHAR A. KAMATH Petroleum Development Laboratory University of Alaska Fairbanks Fairbanks, Alaska 99775–5880Search for more papers by this authorSHIRISH L. PATIL, SHIRISH L. PATIL Petroleum Development Laboratory University of Alaska Fairbanks Fairbanks, Alaska 99775–5880Search for more papers by this author First published: April 1994 https://doi.org/10.1111/j.1749-6632.1994.tb38859.xCitations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume715, Issue1Natural Gas HydratesApril 1994Pages 463-467 RelatedInformation

Kinetics of methane hydrate decomposition

The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.