Project Objective

Observe hydrate formation and dissociation phenomena in various porous media and characterize hydrate-bearing sediments by estimating physical properties (kinetic parameters for hydrate formation and dissociation, thermal conductivity, permeability, relative permeability, and mechanical strength) to enhance fundamental understanding on hydrate formation and accumulation and to support numerical simulations and potential gas hydrate production

YONGKOO SEOL – NETL OFFICE OF RESEARCH & DEVELOPMENT
JEONG CHOI – OAK RIDGE INSTITUTE FOR SCIENCE AND EDUCATION
JONGHO CHA-VIRGINIA POLYTECH INSTITUTE

Project Location

National Energy Technology Laboratory - Morgantown, West Virginia

Project Description

Laboratory experiments to be performed include:

1. Hydrate re-formation experiments and core-scale simulations
2. Kinetic study for hydrate re-formation and induction
3. Gas migration within saturated hydrate bearing porous media
4. Gas exchange studies for methane production and CO2 sequestration

HYDRATE RE-FORMATION EXPERIMENTS AND CORE-SCALE SIMULATIONS

Experiments will be performed to validate existing and forthcoming results from reservoir simulations that predict hydrate re-formation during gas production. Important aspects of this research, which will be determined in collaboration with on-going simulations, include: (1) observation of hydrate re-formation during gas production in core-scale laboratory experiments, (2) identification of major variables of the experimental system that mimic the natural hydrate reservoir system subjected to gas production, (3) estimatation of the impact of the hydrate re-formation on the gas production efficiency, and (4) understand hydrate behavior (dissociation and re-formation) upon changes in PT conditions in non-uniform porous medium.

KINETIC STUDY FOR HYDRATE RE-FORMATION AND INDUCTION

Laboratory experiments will be designed and implemented to obtain kinetic information on secondary hydrate formation and induction dynamics in the presence of geological sediments and other porous media. Previous studies show that hydrate nucleation is stochastic, unpredictable, particularly under low driving force conditions, and time-dependent with the thermal history of the water, the degree of agitation, the presence of foreign particles, interface area of the two phases, and the rate of heat or mass transfer. In this study, the hydrate formation experiments will focus on characterizing the nature of hydrate induction and growth in the presence of various porous media including geological sediments which are obtained from potential hydrate production sites. The goal of the experiments will be generating reproducible and applicable kinetic data on hydrate induction and re-formation for numerical simulations on hydrate productions. This research will be performed in a new multi-reactor device that is designed for use in NETL CT scanning facilities. The experiments will provide a better understanding on the kinetic nature of hydrate formation and dissociation as hosting porous media and other parameters vary. X-ray CT observations will provide visual evidence for uniformity assumptions on hydrate formation and help to develop techniques for uniform hydrate formation in porous media. The experiment measurements will provide kinetic relations of hydrate formation to be incorporated into the numerical simulator for general simulations of hydrate production.

GAS MIGRATION WITHIN SATURATED HYDRATE-BEARING POROUS MEDIA

This study is intended to visualize hydrate accumulation patterns depending on sediment characteristics and geological conditions. Laboratory experiments utilizing x-ray CT scanning facilities will be designed to visualize gas migration in water-saturated deformable media under hydrate-stability conditions and to observe hydrate formation behavior at the phase boundary between gas and water in various situations encountered in potential hydrate reservoir and during production of hydrate-bearing sediments. Porous media will be packed according to predesigned configurations that simulate natural stratification and heterogeneity. This will include alternating layers with different grain sizes, horizontal/vertical or inclined boundaries between layers, sharp or gradual grain-size contrasts, and continuous or interrupted fissures and boundaries. The results will help better understand field observations of methane hydrates in natural systems and identify major mechanisms determining hydrate distribution patterns.

GAS EXCHANGE STUDIES FOR METHANE PRODUCTION AND CO₂ SEQUESTRATION

Gas hydrate production via CO₂ injection has been recently explored as a supplemental technique for traditional methane production such as depressurization, which faces a number of scientific uncertainties and technical hurdles. A recent report on the technique delivers promising results, including: (1) relatively rapid CH₄ release and CO₂ hydrate formation in conjunction with N2 injection and (2) the exchange occurs with no observable free water being generated. However, these findings should be confirmed and extended through additional experimental studies, modeling studies, and field trials, so that the exchange process can be adapted for a potential production technique to simultaneously and elegantly resolve some of the key hurdles facing methane production and CO₂ sequestration. The primary goal of the experiment is to examine (1) the effect of the presence of free water on the CO₂ hydrate formation, (2) kinetic mechanisms of the formation of CO₂ hydrate and CH₄ hydrate dissociation within deep CH₄ hydrate stability zone, and (3) experimental measurements of mechanical properties of porous media bearing mixed gas hydrates.

RESEARCH FACILITIES

The gas hydrate laboratory located in Morgantown is equipped with gas hydrate experiment station (Figure 1) with which gas hydrate can be formed and dissociated under various conditions relevant to hydrate phase stability. The laboratory is situated in proximity to the X-ray CT scanner facility (Figure 2) in Morgantown. The experiment station was designed to be mobile between the two laboratories. The experiment station is equipped with three ISCO syringe pumps to controlpressure and fluid flow through pressure vessels designed for X-ray scanning. The experiment system is monitored at all times for pressure and temperatures using multiple pressure transducers and thermocouples via Labview.

• Hydrate re-formation tests have been performed and the secondary hydrate formation has been confirmed with laboratory test and numerical simulations
• The heterogeneity in the hydrate saturation would result in non-uniform fluid flow during dissociation and gas production.
• Image processing procedure to develop 3-D porosity and phase saturation maps using X-ray CT scan images has been developed utilizing macro functions in ImageJ® and programming with MATLAB. The porosity and phase saturation maps will be used for core-scale simulations.
• Difference in variability of hydrate induction times between regular sand and hydrophobic sand was identified. Hydrate within hydrophobic sand was formed earlier compared to regular sand. The variation on hydrate induction time was also large in the hydrophobic sand under 1000 psi/3 °C for regular sand. The experiments with using hydrophobic sand with different hydrophobicities and mixtures (regular vs. hydrophobic) are currently in progress.

• Core-scale numerical simulation using the numerical mesh developed based on X-ray CT image is currently in progress. The simulation will examine the hydrate re-formation phenomena using actual detailed heterogeneity of the porous media.
• The more experimental quantifications on hydrate induction time are in progress. The experiments will consider using hydrophobic sand with different hydrophobicities and mixtures (regular vs. hydrophobic).
• Tests for gas migration have been performed with 10 µm silica sand which was dry-packed into rubber sleeve under 1000 psi confining pressure, 700 pore pressure, and 10 psi increment on injection pressure. The test using X-ray CT scanning confirmed that gas migration through the silt mainly through fracture under the test condition while flow through coarse particle goes through pore networks.
• Raman spectroscopy analysis to examine CO2-CH4 exchange mechanism is under progress.

FY09: $334,000 (no prior year funding, project started in FY09)
FY2010: ~$400,000

In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].

Publications

Seol, Y. and T. J. Kneafsey, Methane hydrate induced permeability modification for multiphase flow in unsaturated porous media, Journal of Geophysical Research, 2011, In Press.

Seol, Y. and E. Myshakin, Experimental and numerical observations of hydrate reformation during depressurization in a core-scale reactor, Energy Fuels, 2011 25(3), pp. 1099-1110.

Kneafsey, T.J., Y. Seol, A. Gupta, and L. Tomutsa, Permeability of laboratory-formed methane hydrate bearing sand; Measurements and observations using x-ray computed tomography.139525, Society of Petroleum Engineer Journal, 16(1), 2011, pp. 78-94

Kneafsey, T. J., Y. Seol, G. J. Moridis, L. Tomutsa, and B. M. Freifeld, 2009, Laboratory measurements on core-scale sediment and hydrate samples to predict reservoir behavior, in T. Collett, A. Johnson, C. Knapp, and R. Boswell, eds., Natural gas hydrates—Energy resource potential and associated geologic hazards: AAPG Memoir 89, p. 705–713.

Seol, Y., E. Myshakin, E., and T.J. Kneafsey, 2010, Core-scale heterogeneity of hydrate distribution and its impact of gas production, Fire In The Ice, NETL Methane Hydrate R&D Program Newsletter, pg. 6-8, August, 2010

Seol, Y. and R. Boswell, 2009. Methane Hydrate: Fire in the Ice, in press on G.I.T. Laboratory Journal Europe, September/October.

Moridis, G.J., Reagan, M.T., Kim, S.-J., Seol, Y., and Zhang, K. Evaluation of the Gas Production Potential of Marine Hydrate Deposits in the Ulleung Basin of the Korean East Sea. SPE Journal, 2009,14 (4), pp. 759 - 781.

Seol, Y. and Kneafsey, T.J., X-ray CT observations of water flow through anisotropic methane hydrate-bearing sand, Journal of Petroleum Science and Engineering, (2009), pp. 121-132

Kneafsey, T.J., L. Tomutsa, G.J. Moridis, Y. Seol, B.M. Freifeld, C.E. Taylor, and A. Gupta, “Methane Hydrate Formation and Dissociation in a Core-Scale Partially Saturated Sand Sample”, Journal of Petroleum Science and Engineering, 56, 2007 108-126.

Presentations

Choi, J., Y. Seol, and R. Boswell, 2010, Experimental Simulations of Methane Gas Migration Through Water-Saturated Sediment Cores, American Geophysical Union, Fall Meeting, December 6, 2010, San Francisco, CA

Seol, Y. T.J. Kneafsey, Emily L. Jones, X-ray CT Observations of Methane Hydrate Distribution in Natural Sediments and Laboratory Formed Compacted Sand Samples, AGU Fall Meeting, December 12-17, 2010, San Francisco, CA

Seol, Y. Characterization of Hydrate Bearing Sediment at NETL, Hydrate Meeting 2010, January 25-29, 2010, Atlanta, GA.

Seol, Y. and Timothy J. Kneafsey, Characterization and Preservation of Methane Hydrate Samples, Presented in US-Korea Gas Hydrate Workshop, April 28-29, 2009, Berkeley, California.

Seol, Y. and Timothy J. Kneafsey, Relative Permeability Parameter Estimation for Laboratory-Formed Hydrate-Bearing Sediments, Presented in American Association of Petroleum Geologist Annual Convention, June 7-10, 2009, Denver, Colorado

Seol, Y. Timothy J. Kneasey, and Emily V.L. Rees, X-ray CT observations of methane hydrate distribution in natural sediment and laboratory formed compacted sand samples, American Geophysical Union, December 15-18, 2009, San Francisco, California.

Crandall, D., Seol, Y., Bo. Hu, and Gyovai, K. Conversion of CT scans of geological media to heterogeneous computational fluid dynamics models, 3rd international workshop on x-ray CT for geomaterials, March 1-3, 2010. New Orleans, Louisiana.