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A Multi‐Scale Experimental Investigation of Flow Properties in Coarse‐ Grained Hydrate Reservoirs During Production
Project Number
DE-FE0028967
Last Reviewed Dated
Goal

The objective of this project is to gain insight into the relative permeability behavior and depressurization response of coarse‐grained methane hydrate deposits subjected to perturbation through observation of behaviors at the macro- (core) scale and examination of the underlying processes controlling the behaviors at the micro- (pore) scale.

Performer

University of Texas at Austin, Austin, TX 78712

Background

Depressurization of coarse‐grained gas‐bearing reservoirs involves multiple processes that interact at multiple length and time scales. These include, but are not limited to, relative permeability, capillary, compaction, kinetic, and thermodynamic behaviors. Two properties that are poorly understood are 1) the relative permeability behavior of these systems as the hydrate and gas saturation change, and 2) the effect of local changes in pore water chemistry as hydrate dissociation occurs. These are macro scale behaviors that can be measured at the core scale, and they have a large impact on the production rate of methane from hydrate reservoirs. Accurate predictions of gas production from hydrates await a better understanding of these behaviors. This understanding will result from both a macro‐scale description of the behavior and a micro‐scale analysis of the underlying processes driving these macro‐scale behaviors.

This project will explore the relative permeability of coarse‐grained reservoirs and the response of these reservoirs to depressurization at the macro‐ (1 m) and micro‐ (1x10‐6 m) scale. At the macro‐scale (e.g., 0.1 m to 1 m sand‐pack cores, eventually moving to natural Gulf of Mexico cores), researchers will determine relative permeability and perform production tests (pressure dissipation). Simultaneously, they will perform micro‐CT and micro‐Raman analysis to understand the habit and phase distribution at the micro- (pore) scale and will examine the evolution of these properties during dissipation. The project will develop constitutive relationships to describe these processes and inform reservoir simulation efforts.

Impact

Methane hydrates within sand‐rich marine reservoirs represent a potentially enormous reservoir for methane. Previous drilling/logging in marine sand reservoirs within the Gulf of Mexico (GoM) has verified that methane hydrate filled sand reservoirs are present and that sand reservoirs can be identified from seismic analysis. DOE is now focusing on acquiring intact samples through its project “Genesis of Methane Hydrate in Coarse‐Grained Systems: Northern Gulf of Mexico Slope,” DOE Award No.: DEFE0023919. It is anticipated that the first conventional and pressurized cores of these reservoirs will be collected under that project in spring 2017.

Laboratory studies to determine the effect of solid phases (hydrate) on relative permeability are of the highest importance because this behavior has a large impact on gas recovery in hydrate bearing systems. Current modeling approaches are limited to relying on theoretical extensions of conventional multi‐phase flow models. It is vital now to go beyond these limitations and pursue an experimental program that will illuminate, at the core and the pore scale, the effect of methane hydrate on gas flow behavior and the process of hydrate dissociation due to perturbation. A successful testing program leading to analysis of intact cores (as is planned under this project) provides a pathway to this understanding. The learnings that result will provide a significant step forward in our ability to simulate hydrate production and make realistic estimates of the ability of the methane hydrate resource to be a viable energy source.

Accomplishments (most recent listed first)
  • Initiated hydrate formation experiments in natural GoM sandy silt sediment samples with micro-Raman observation
  • Completed initial methane hydrate growth experiment (with CT scanning) in loosely packed sandy silt sediment from natural GoM core
  • Completed depressurization of one intact pressure core section collected from GoM (Green Canyon 955)
  • Completed initial relative permeability experiments with simultaneous flow of gas and brine at a range of hydrate saturations using sandstone samples
  • Completed benchmark micro-scale petrochemistry analyses to characterize natural GoM sediment samples using Raman Spectroscopy
  • Completed initial macro-scale lab experiments in sand packs demonstrating capability to form methane hydrates at targeted saturations
  • Conducted macro-scale dissociation tests of hydrate bearing sand pack samples, both with and without CT monitoring
  • Measured intrinsic and relative permeability measurements for macro-scale samples (without brine flow)
  • Conducted multiple hydrate dissociation experiments (different hydrate saturations) monitored by x-ray CT in the Micro-CT device
  • Demonstrated capability to synthesize and dissociate methane hydrate with deionized water and glass beads in the static Micro-Raman cell
  • Developed a process to reliably transfer sand pack samples into Experimental pressure vessel with varying water saturations
  • Conducted Micro-CT measurements of sand pack samples using xenon hydrate to optimize system resolution
  • Completed the build and testing of a micro-consolidation device for use in lab experiments using Micro-CT
  • Completed the design and build of a static hydrate pressure vessel for use in Micro-Raman spectroscopy experiments and demonstrated formation of pure methane hydrate (without porous media), and measurement of Raman spectra of the hydrate
Current Status

Efforts in coming months will involve continued activity across project focus areas that include 1) steady state relative permeability measurements of sandstone hydrate samples using natural GoM sediments contained in intact pressure cores; 2) continued depressurization experiments of sand pack hydrate samples, focused on experiments with higher hydrate saturations; 3) continued controlled depressurization of targeted sections of intact GoM pressure cores including both sandy silt and clayey silt lithofacies; 4) continued hydrate formation and production experiments in natural GoM sediments with micro-CT observation utilizing improved sample packing methods; and 5) continued hydrate formation and production experiments with micro-Raman observation using different lithofacies of natural GoM sediments.

Project Start
Project End
DOE Contribution

$1,199,991

Performer Contribution

$300,000

Contact Information

NETL – Richard Baker (richard.baker@netl.doe.gov)
UTA – Dr. Peter Flemings (pflemings@jsg.utexas.edu)