[1] Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.

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Physical properties of hydrate-bearing sediments

Investigation into gas production from natural gas hydrate: A review

[1] Review of the literature reveals that the nature of pore-scale interactions between gas hydrates and porous media remains a matter of controversy. To clarify the situation, nuclear magnetic resonance (NMR) measurements have been made on methane hydrate-bearing sandstones. The samples were synthetically prepared within the gas hydrate stability zone, at or near the seafloor in Monterey Bay, California. The method simulated natural hydrate deposition by gas flows that are not in thermodynamic equilibrium with the surrounding earth. The efficiency of hydrate production was variable, as has been observed elsewhere. When substantial hydrate saturations were achieved, NMR relaxation time measurements indicated that hydrate tended to replace water in the largest pore spaces. The relative permeability to water, as determined by an NMR-based correlation, was significantly reduced. The magnitude of this reduction was also consistent with formation of hydrate in the centers of pores, rather than with hydrate coating the grains. The growth habit suggested by these results is consistent with creation of hydrate nodules and lenses in coarse, unconsolidated sediments. It is also consistent with scenarios in which methane gas is delivered efficiently to the atmosphere as a result of seafloor slope failure, thereby strengthening global warming feedback mechanisms.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003JB002389

Deep sea NMR: Methane hydrate growth habit in porous media and its relationship to hydraulic permeability, deposit accumulation, and submarine slope stability

Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Simulation-Based Evaluation of Technology and Potential George J. Moridis, SPE, Lawrence Berkeley National Laboratory; Timothy S. Collett, SPE, US Geological Survey; Ray Boswell, US Department of Energy; M. Kurihara, SPE, Japan Oil Engineering Company; Matthew T. Reagan, SPE, Lawrence Berkeley National Laboratory; Carolyn Koh and E. Dendy Sloan, SPE, Colorado School of Mines This paper was prepared for presentation at the 2008 SPE Unconventional Reservoirs Conference held in Keystone, Colorado, U.S.A., 10–12 February 2008. Abstract Gas hydrates are a vast energy resource with global distribution in the permafrost and in the oceans. Even if conservative estimates are considered and only a small fraction is recoverable, the sheer size of the resource is so large that it demands evaluation as a potential energy source. In this review paper, we discuss the distribution of natural gas hydrate accumulations, the status of the primary international RD Klauda and Sandler, 2005). Given the sheer magnitude of the resource, ever increasing global energy demand, and the finite volume of conventional fossil fuel reserves, gas hydrates are emerging as a potential energy source for a growing number of nations. The attractive- ness of gas hydrates is further enhanced by the environmental desirability of natural gas (as opposed to solid or liquid) fuels. Thus, the appeal of gas hydrate accumulations as future hydrocarbon gas sources is rapidly increasing and their production potential clearly demands technical and economic evaluation. The past decade has seen a marked acceleration in gas hydrate RD Paull et al., 2005), reservoir lithology, and rates and

Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Simulation-Based Evaluation of Technology and Potential

https://digital.library.unt.edu/ark:/67531/metadc837805/m2/1/high_res_d/1004414.pdf

Status of the TOUGH-FLAC simulator and recent applications related to coupled fluid flow and crustal deformations

TOUGH+HYDRATE v1.0 is a new code for the simulation of the behavior of hydrate-bearing geologic systems. By solving the coupled equations of mass and heat balance, TOUGH+HYDRATE can model the non-isothermal gas release, phase behavior and flow of fluids and heat under conditions typical of common natural CH{sub 4}-hydrate deposits (i.e., in the permafrost and in deep ocean sediments) in complex geological media at any scale (from laboratory to reservoir) at which Darcy's law is valid. TOUGH+HYDRATE v1.0 includes both an equilibrium and a kinetic model of hydrate formation and dissociation. The model accounts for heat and up to four mass components, i.e., water, CH{sub 4}, hydrate, and water-soluble inhibitors such as salts or alcohols. These are partitioned among four possible phases (gas phase, liquid phase, ice phase and hydrate phase). Hydrate dissociation or formation, phase changes and the corresponding thermal effects are fully described, as are the effects of inhibitors. The model can describe all possible hydrate dissociation mechanisms, i.e., depressurization, thermal stimulation, salting-out effects and inhibitor-induced effects. TOUGH+HYDRATE is the first member of TOUGH+, the successor to the TOUGH2 [Pruess et al., 1991] family of codes for multi-component, multiphase fluid and heat flow developed at the Lawrence Berkeley National Laboratory. It is written in standard FORTRAN 95, and can be run on any computational platform (workstation, PC, Macintosh) for which such compilers are available.

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TOUGH+Hydrate v1.0 User's Manual: A Code for the Simulation of System Behavior in Hydrate-Bearing Geologic Media

Class 1 hydrate deposits are characterized by ahydratebearing layer underlain by a two-phase zone involving mobile gas.Two kinds of deposits are investigated. The first involves water andhydrate in the hydrate zone (Class 1W), while the second involves gas andhydrate (Class 1G). We introduce new models to describe the effect of thepresence of hydrates on the wettability properties of porous media. Wedetermine that large volumes of gas can be readily produced at high ratesfor long times from Class 1 gas hydrate accumulations by means ofdepressurization-induced dissociation using conventional technology.Dissociation in Class 1W deposits proceeds in distinct stages, while itis continuous in Class 1G deposits. To avoid blockage caused by hydrateformation in the vicinity of the well, wellbore heating is a necessity inproduction from Class 1 hydrates. Class 1W hydrates are shown tocontribute up to 65 percent of the production rate and up to 45 percentof the cumulative volume of produced gas; the corresponding numbers forClass 1G hydrates are 75 percent and 54 percent. Production from bothClass 1W and Class 1G deposits leads to the emergence of a seconddissociation front (in addition to the original ascending hydrateinterface) that forms at the top of the hydrate interval and advancesdownward. Inboth kinds of deposits,more » capillary pressure effects lead tohydrate lensing, i.e., the emergence of distinct banded structures ofalternating high-low hydrate saturation, which form channels and shellsand have a significant effect on production.« less

Depressurization-induced gas production from Class 1 hydratedeposits

EOSHYDR is a new module for the TOUGH2 general-purpose simulator for multi-component, multiphase fluid and heat flow and transport in the subsurface. EOSHYDR is designed to model the non-isothermal CH{sub 4} release, phase behavior and flow under the conditions of the comrilon methane hydrate deposits (i.e., in the permafrost and in deep ocean sediments) by solving the coupled equations of mass and heat balance. As with all other members of the TOUGH2 family of codes, EOSHYDR can handle multidimensional flow domains and cartesian, cylindrical or irregular grids, as well as porous and fractured media. EOSHYDR extends the thermophysical description of water to temperatures as low as -30 C. Both an equilibrium and a kinetic model of hydrate formation or dissociation are included. Two new solid phases are introduced, one for the CH{sub 4}-hydrate and the other for ice. Under equilibrium conditions, water and methane, as well as heat, are the main components. In the kinetic model, the solid hydrate is introduced as the fourth component. The mass components are partitioned among the gas, liquid and the two solid phases. The thermodynamic phase equilibrium in EOSHYDR is described by the P-T-X diagram of the H{sub 2}O-CH{sub 4}system. Phase changes and the corresponding heat transfers are fully described. The effect of salt in pore waters on CH{sub 4} solubility and on the growth and decomposition of gas hydrates is also taken into account. Results are presented for three test problems designed to explore different mechanisms and strategies for production from CH{sub 4}-hydrate reservoirs. These tests include thermal stimulation and depressurization under both permafrost and suboceanic conditions. The results of the tests tend to indicate that CH{sub 4} production from CH{sub 4}-hydrates is technically feasible and has significant potential. Both depressurization and thermal stimulation seem to be capable of producing substantial amounts of CH{sub 4} gas.

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EOSHYDR: A TOUGH2 Module for CH4-Hydrate Release and Flow in theSubsurface

The injection of grout into the subsurface can be used to encapsulate contaminated regions of an aquifer, or to form underground barriers for the isolation of contaminant sources and to prevent the spreading of existing plumes. This requires identifying grouts, or barrier fluids, which when injected into the subsurface exhibit a large increase in viscosity and eventually solidify, sealing the permeable zones in the aquifer. Simulation and modeling analysis are indispensable tools for designing the injection and predicting the performance of the barrier. In order to model flow and transport in such systems, the thermophysical properties of the fluid mixtures have to be provided, and the governing mass- and energy-balance equations for multiphase flow in porous media have to be solved numerically. The equation-of-state module EOS11 described herein is an extension of the EOS7 module of the TOUGH2 code for flow of saline water and air. In the modeling approach, the chemical grout is treated as a miscible fluid the viscosity of which is a function of time and concentration of the gelling agent in the pore water. If a certain high viscosity is reached and the movement of the grout plume ceases, the gel is assumed to solidify, leadingmore » to a new porous medium with changed soil characteristics, i.e. reduced porosity and permeability, increased capillary strength for a given water content, and changed initial saturation distribution.« less

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A TOUGH2 equation-of-state module for the simulation of two-phase flow of air, water, and a miscible gelling liquid

Permeation grouting with colloidal silica gel is a potentially effective means for creating hydraulic barriers to prevent the advective migration of radioactive contaminants in shallow permeable sediments. However, the effectiveness of silica gel grouted barriers in controlling transport of fission product radionuclides through sorption and diffusion is unknown. To resolve this question, static-batch sorption measurements with Cs + and Sr 2 + were conducted at ambient temperature (23 °C) and for times up to 96 days on silica gel and on two kaolinitic sediments from the Savannah River Site in South Carolina. Sorption experiments on the latter were conducted both in the presence and in the absence of silica gel. Cesium and strontium concentrations were varied between 10 - 3 to 10 - 8 M (mol/L) and 10 - 4 to 10 - 8 M, respectively. The pH values after one day varied for each experiment and ranged from 3.6 to 6.6. The pH of the solutions were, however, buffered by the sediments and/or silica gel, and changed little over the duration of the experiments. The fraction of both cesium and strontium retained on the solids increased with decreasing radioelement concentration. The sorption data were fitted to the Freundlich isotherm model.

George J. Moridis

Papers

TOUGH+Hydrate v1.0 User's Manual: A Code for the Simulation of System Behavior in Hydrate-Bearing Geologic Media

Depressurization-induced gas production from Class 1 hydratedeposits

EOSHYDR: A TOUGH2 Module for CH4-Hydrate Release and Flow in theSubsurface

A TOUGH2 equation-of-state module for the simulation of two-phase flow of air, water, and a miscible gelling liquid

Sorption of fission product radionuclides, 137Cs and 90Sr, by Savannah River Site sediments impregnated with colloidal silica