Hydrate-Bearing Clayey Sediments: Morphology, Physical Properties, Production and Engineering/Geological Implications

Project Number

DE-FE0009897

Last Reviewed Dated

01/01/2018

Goal

The primary goal of this research effort is to contribute to an in-depth understanding of hydrate bearing, fine-grained sediments with a focus on investigation of their potential for hydrate-based gas production.

Performer(s)

Georgia Tech Research Corporation, Atlanta GA

Background

Fine-grained sediments host more than 90 percent of global gas hydrate accumulation. Yet hydrate formation in clay-dominated sediments is less understood and characterized than other types of hydrate occurrence. There is an inadequate understanding of hydrate formation mechanisms, segregation structures, hydrate-lense topology, system connectivity, and physical macro-scale properties of clay-dominated hydrate-bearing sediments. This situation hinders further analyses of the global carbon budget as well as engineering challenges/solutions related to hydrate instability and production.

Research on hydrate-bearing clay-dominated sediments is needed to enhance fundamental understanding of hydrate formation and resulting morphology, develop laboratory techniques to emulate “natural” hydrate formations in this type of material, develop and assess analytical tools to predict physical properties, evaluate engineering and geological implications, and advance understanding of the potential for gas production from these sediments.

Impact

The project will add significant data and knowledge to the body of hydrates science. An enhanced understanding of the occurrence and behavior of hydrates in clay-dominated sediments will inform discussions of both the role of hydrates in the global carbon cycle and the potential feasibility of production from a portion of the hydrate resource base not currently considered producible.

Accomplishments (most recent listed first)

Key findings from this detailed investigation into the nature and behavior of fine grained hydrate bearing sediments include the following:

Hydrate Formation and Morphology in Fine-Grained Sediments

Hydrate nucleation in small pores is limited by guest molecules
Hydrate morphology in fines is segregated, mainly governed by mechanical equilibrium
Hydrate phase boundary shifts due to both pore size, pore shape, and effective stress
Gas supply for hydrate formation comes by diffusion and gas-driven fracture
Freshly formed hydrate is highly porous and structured
Gas hydrate morphology is not equivalent to that found in initial ice lenses
Mineral surface and capillarity affects hydrate formation

Physical Properties of Hydrate in Fine Grained Sediments

Dominant morphology is particle-displacive; dominant interface is rough and jagged
Assumptions in effective media models are extremely important
Physical properties vary with hydrate lens orientation, volume fraction, and the total number of lenses
Strength is increased through sediment consolidation and hydrate cementing, but decreased due to particle slippage
Over-consolidation leads to altered physical properties
The morphology of THF hydrate in kaolinite is governed by mechanical and
thermodynamic conditions
The self-consistent model (patchy) is still effective in predicting the small-strain stiffness of heterogeneous specimens like hydrate-bearing clayey sediments
High acoustic damping in hydrate-bearing sediments is most likely caused by high damping hydrate crystals; the quality factor (i.e., damping) of s-wave is effective in quantifying hydrate saturation particularly for heterogeneous and anisotropic specimens

Gas Production from Hydrate in Fine Grained Sediments

Capillarity hinders gas production
Capillarity and effective stress govern the gas percolation patterns
Chemical stimulation is constrained by chemicals injected and ability to transport
Depressurization approach to production for hydrates in fine grained sediments: pressure drop occurs within limited zone in sediments with low permeability
High stress in the system leads to porosity decrease, which leads to high capillarity and low gas flow rate
Overall, potential production of gas from hydrate contained in fine grained sediments is extremely challenging and is impacted by a number of different factors in this type of system
Surface mining after thermal stimulation is a potential strategy of harvesting methane from hydrate-bearing clayey deposits, but would require extensive further validation and assessment of peripheral impacts

Current Status

(January 2018)
All activity under the project has been completed and project results are documented in a final scientific/technical report, which can be accessed from the additional information section below.

Project Start

10/01/2012

Project End

09/30/2017

DOE Contribution

$627,393

Performer Contribution

Cost Share Contribution: $182,774

Planned Total Funding: $810,167

Contact Information

NETL – Richard Baker (Richard.Baker@netl.doe.gov or 304-285-4714)
Georgia Tech – Sheng Dai (Sheng.Dai@ce.gatech.edu)

Additional Information