The primary goals of this research effort are to develop a truly coupled numerical model that addresses the complex thermo-hydro-chemo-mechanical (THCM) phenomena in hydrate-bearing sediments through incorporation of proven constitutive relationships that also satisfy fundamental conservation principles (conservation of mass, energy, and momentum) and apply that model to analyze available data and further enhance understanding of the behavior of hydrate-bearing sediments in the context of field production experiments and the development of hydrate production approaches and technology.

Texas A&M University, College Station, TX
Georgia Tech Research Corporation, Atlanta, GA

The experimental study of hydrate-bearing sediments has been hindered by the very low solubility of methane in water (lab testing); the complexity of synthesizing hydrate-bearing sediments in the lab that are representative of those found in nature; and inherent sampling difficulties associated with depressurization and thermal changes to hydrate-containing samples during core extraction. This situation has prompted the need for more decisive developments in numerical modeling in order to help advance our understanding of hydrate-bearing sediments and investigate/optimize production strategies and their implications.

Project personnel will undertake an in-depth review of the properties of hydrate-bearing sediments and use the results to update a numerical model capable of simulating the complex thermo-hydro-chemo-mechanical behaviors of hydrate-bearing sediments. This updated model will be corroborated through the use of close-form analytical solutions and then used to analyze data available from past production related hydrate field experiments and develop optimized approaches for potential future field production studies in marine and permafrost environments.

Results will provide critical insights into the behavior of gas hydrate-bearing sediments caused by THCM perturbations such as those that can be triggered by environmental changes or activities aimed at the production of gas from hydrates. The results of the effort will assist in the development of optimal, technically viable strategies for methane production in both marine and permafrost settings and improve our understanding of the potential reaction of hydrate systems to natural or induced changes in their environment.

• Developed and validated a fully coupled THCM numerical model with refined constitutive expressions for the behavior of hydrate bearing sediment systems.
• Developed an IT tool for searching and tracking of properties of hydrate bearing sediments.
• Validation of the THCM hydrate code against close form analyses and available lab and field data.
• Published five articles in refereed journals on the results of the research with four more in review and four additional articles in preparatory stage.
• Completed evaluation (using the simulation code) of the volume expansion and compressibility of the constituent phases of gas hydrate during dissociation. 
• Performed initial efforts to model sand production during depressurization of hydrate bearing sediments.
• Upgraded the mechanical constitutive model to include the effect of gas hydrate dissociation during analysis.
• Completed testing of the updated model and its application to hydrate field production experiments (with favorable results).
• Completed review of the main governing evolution laws, parameters, and ratios governing hydrate dissociation through application of close-form analytical solutions.
• Completed initial validation of functions implemented in the code, including constitutive equations and phase relationships.
• Conducted numerical tests of the updated system to validate the numerical approach that was implemented, including one case involving the depressurization of hydrate-bearing sediment.
• Completed an update of the constitutive model for hydrate-bearing sediments to include dynamic effects of capillary pressure-saturation relationships.
• Updated the THCM-Hydrate code including validation of the incorporation functions capturing the effect of cryogenic suction on the mechanical behavior of frozen sediments.
• Completed testing the THCM-Hydrate code against the DOE Hydrate numerical simulator Code Comparison problem set. 

(June 2017)
Research efforts under the project were completed in September 2016 and project results are documented in a final scientific/technical report which can be accessed from the “Additional Information” section below.

$388,560

$97,140

Planned Total Funding (through all project phases): $485,700

NETL Project Manager – Richard Baker (Richard.Baker@netl.doe.gov)
Texas A&M University – Marcelo Sanchez (msanchez@civil.tamu.edu)

Final Project Report [PDF-4.54MB] February 2017