The objective of this research is to measure physical, chemical, mechanical, and hydrologic property changes in methane hydrate-bearing sediments subjected to: injection of carbon dioxide (CO₂) and nitrogen (N₂), the effects of sediment layering, and the effects of relevant gradients (thermal, chemical , and capillary pressure) within the system.

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA 94720

Few studies have examined the hydrologic and physical/mechanical property changes that occur during a hydrate composition change. In the studies that have been conducted, researchers did not measure hydrologic properties; quantification of the effluent gas was crude and performed over a limited range of conditions (mostly dry hydrate) and failed to address important reservoir issues such as pressure increase upon injection and the effect of changes in gas composition in a system where the gas composition varies. This research will investigate processes associated with the injection of N₂, CO₂, and mixtures of these gases into methane hydrate-bearing porous media under non-stirred batch and flow-through conditions, and will attempt to quantify the exchange kinetics of the N₂ and CO₂ replacement into methane hydrate using flow-through reactors and breakthrough curve analysis. Permeability will be measured to detect changes, and geophysical property changes will be measured using either the Split Hopkinson Resonant Bar apparatus or a flow-through vessel with p- and s- wave transducers in the end platens.

Much of the investigated hydrate-bearing sediments that are thought of as potential energy targets are contained in layered sediments, having sands and silts or clay layers. Few laboratory studies have studied these layered systems. Layering affects the local and global permeability to both gas and water, further affecting gas and water flow, the location of hydrate formation and dissociation, and the impact of pressure signals. Layered systems are by nature complex, and simplification is required in laboratory studies to generate conceptual models that can be expressed numerically to aid in predicting gas production and mechanical changes of the sediments. Early studies have used fine and coarse sand, and sandstone and sand layers. Few laboratory tests of gas hydrate dissociation from layered systems have been performed. Also few tests have been performed examining important gradients. Tests with better quantification of processes are needed. This effort will measure physical, chemical, mechanical, and hydrologic property changes in layered sediments containing methane hydrate, water, and gas.

In addition to the studies of layered systems, numerical simulation of flow and mechanical properties of hydrate-bearing sands at the multigrain scale will be conducted here to extend earlier work by LBNL.

The primary benefits of this lab-based research is the provision of critical information for interpreting other laboratory and field tests including injection of CO₂ and N₂ into methane hydrate-bearing reservoirs, and production of methane from layered hydrate-bearing sediments, and systems under thermal, chemical, or capillary pressure gradients. Questions asked and answered on this project will be from a reservoir perspective understanding that many nonideal conditions can exist.

Overall Project

• Investigated flow and geophysical properties of hydrate bearing sediments undergoing gas exchange.
• Initiated development of computational rock mechanics capabilities. 
• Developed new laboratory tools and techniques, and performed numerous tests to examine methane hydrate behavior in increasingly more realistic environments including:
  1. Controlled Thermal Gradients/Chemical Gradients/Well Analogs
  2. Layered systems
• Contributed to eight papers and presentations, including invited talks at international meetings and session chair duties, and current code comparison study.

Budget Period 6 (July 2017–June 2018)

• Implemented a technique to create layered hydrate styems and tested the system on both hydrate-bearing and non hydrate-bearing sediments to evaluate particle flow within the system.
• Completed  lab experiments evaluating the effectiveness of vertical and horizontal wells for gas production from hydrate in a layered (sand/mud) hydrate-bearing system.

Budget Period 5 (July 2016–December 2017)

• Generated a preliminary working version of a new permeability code to be used in prediction of the behavior of a hydrate-bearing medium based on X-ray micro CT and three hydrate habits.
• Completed multiple tests on the hydrate dissociation point in saline systems providing indication that brine systems result in a hydrate equilibrium range rather than sharp equilibrium points.

Budget Period 4 (July 2015–June 2016)

• Completed a laboratory system to enable investigation of the effects of thermal gradients and gradient oscillation on hydrate system behavior.
• Completed development of new lab pressure cell with increased sample size and additional feed through to allow more efficient setup and control of additional temperature manipulation experiments. Completed investigation of the effect of thermal gradient and gradient oscillation on hydrate behavior using existing pressure cell.
• Completed multiple tests to examine the effect of thermal gradient on hydrate system behavior. Additional changes are needed to better control temperature gradient.
• Completed lab setup for experiments on gas production from layered hydrate system and conducted initial experimental runs.
• Completed a new system for the automated calculation of bulk and shear modulus for sub-volumes of a larger 3D image sequence as part of the effort focused on grain scale computation of HBS properties using MicroCT images.
• Developed MATLAB interface to allow utilization of ELAS3D finite element code in an automated context to be applied to evaluation of elastic properties of models of hydrate bearing sediments.

Budget Period 3 (June 2014–June 2015)

• Obtained all materials required for conducting a test of a layered system, and working to resolve leak path issues for the experimental setup.
• Rebuilt hydrate pressure vessel.
• Redesigned and built new temperature control jacket allowing Teflon coating of pressure vessel to eliminate external corrosion.
• Examined hydrate sample layering techniques using sand and available layered sandstone.

Budget Period 2 (June 2013–May 2014)

• Completed development of computational protocol to provide theoretical distribution of hydrates in an experimentally measured sediment matrix.
• Developed the permeability and diffusivity calculation codes for use in grain-scale computation of hydrate-bearing sediment properties based on micro CT sample descriptions.
• Completed initial experiments measuring kinetics of gas exchange between a CO₂/N₂ mixture and existing CH4 hydrate in a system with excess free water and comparing it to a system without excess free water.

Budget Period 1 (June 2012–May 2013)

• Completed and documented results of a series of lab tests to monitor changes (gas exchange rates, permeability, and geomechanical properties) in CH4 hydrate-bearing samples exposed to an N₂/CO₂ gas mixture.
• Designed and constructed an experimental system to measure kinetics of gas exchange in hydrate-bearing sediments.
• Established a new laboratory set-up (including a new CT scanner) capable of performing and monitoring hydrate exchange kinetics experiments.
• Please see the project page for ESD05-048 to view accomplishments from past, related efforts.

Final Status (March 2019)
Efforts under the project are complete.  A summary final report on activities and findings under the field work proposal is accessible via the link in the Additional Information section below  Lab-based gas hydrate studies will be ongoing at LBNL but new work will be conducted under new project number FP00008137.

Key Findings resulting from activities completed under this project include:

• CH₄ hydrate exposed to 77% N₂ 23% CO₂ gas experienced dissociation and physical property changes. A range of stable 3-phase states over temperatures from 4 C to 9 C at constant pressure was encountered from different hydrate compositions.
• In salty water, rapid mass transfer relative to rate of dissociation leads to salty water equilibrium conditions, whereas slow mass transfer relative to the melting process leads to fresh water equilibrium conditions.
• Without sand control, geomechanical failure of samples was likely under reasonable flow and effective stress conditions. With sand control, samples did not fail upon either fast (analog for vertical radial well with high flux) or slow depressurization (analog for horizontal well with lower flux).
• Hydrate in sand/mud layered systems formed in sand layer only. Mud layers tended to compact under effective stress changes.

$685,000

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NETL – Richard Baker (Richard.Baker@netl.doe.gov)
LBNL –Timothy J. Kneafsey (tjkneafsev@lbl.gov)
If you are unable to reach the above personnel, please contact the content manager.

Final Report [PDF] March, 2019

Topical Report : Behavior of Methane Hydrate Bearing Sediments Subjected to Changing Gas Composition [PDF-1.55MB]

CT scans of hydrate bearing system showing controlled temperature grasient