The project goal is to conduct a review of hydrate-bearing sediment properties and the inherent effects of in situ sampling for the purpose of designing, developing, and field-testing a new borehole tool to comprehensively characterize hydrate-bearing sediment in situ.

In Phase 1 of the project, researchers will review and update the database of hydrate-bearing sediment properties at Georgia Tech in order to develop robust correlations with index parameters. The resulting information will be incorporated into a tool for optimal field characterization. The design will recognize past developments, build on past characterization experience, and benefit from inspiring examples from nature and other fields. In Phase 2, researchers will design the tool’s electronics and instrumentation, construct a full-scale prototype, and initiate laboratory testing on hydrate sediment analogs. Finally, in Phase 3, the borehole tool will, in collaboration with industry, be deployed in the field to characterize both hydrate-bearing and hydrate-free sediments.

Georgia Tech Research Corporation, Atlanta GA 30332

While earlier research focused on the properties of the hydrate mass per se (Sloan Jr and Koh 2007), studies during the last decade have increasingly explored hydrate formation in both marine and permafrost sediments, their properties (Santamarina and Ruppel 2008; Waite et al. 2009), and production strategies. Reservoir simulators require reliable material parameters to anticipate reservoir response and production rates. Hydrate saturation governs initial properties and gas recovery; strength and stiffness before and after dissociation determines the deformation field and stability conditions; liquid and gas permeability and their variation with saturation define flow rates; and heat capacity and conduction limit dissociation.

The study of methane hydrate-bearing sediments currently relies on wireline logging or sampling. Logging while drilling (LWD) and measure while drilling (MWD) provide valuable information, but material properties required for analysis and design are inferred through correlations. On the other hand, sampling permits direct measurement of properties but faces pronounced challenges due to sampling disturbance followed by inherent difficulties with core handling and testing under pressure/temperature stability conditions.

Inherent sampling disturbance presents the greatest challenge to geo-analyses and engineering production strategies. Drilling, wall shear, core recovery, specimen extrusion from the sampler, and trimming and insertion into test chambers produce sediment “destructuration” and have a pronounced effect on all sediment properties (Baligh et al. 1987; Hight et al. 1992; Hvorslev 1949; La Rochelle et al. 1981; Ladd and DeGroot 2003; Landon 2007; Santagata and Germaine 2005; Santagata and Germaine 2002; Shogaki and Kaneko 1994). Furthermore, classical recompression techniques often considered in hydrate-free sediments will not reproduce the original stress–strain conditions when sampling alters the sediment structure, as is expected in all unconsolidated sediments (Tanaka 2000; Tanaka et al. 2002). The sources of sampling disturbance that affect hydrate-free sediments affect hydrate-bearing sediments as well. The presence of hydrates aggravates sampling effects (even when pressure core technology is used) due to pressure- and temperature-dependent hydrate dissolution and dissociation and time-dependent hydrate relaxation. A new borehole tool for characterizing hydrate-bearing sediments in situ will help researchers avoid the inherent difficulties and biases in sampling sediments, which are exacerbated when sampling hydrate-bearing sediments.

The proposed research reflects a convergence of multiple favorable conditions including sensor miniaturization,the availability of extensive data gathered from multiple laboratory and field studies, and past experience in characterizing hydrate-bearing sediments. The proposed sampling tool and characterization methodology will have profound impacts in the field including:

• direct measurement of sediment properties in situ to avoid sampling disturbance;
• the most comprehensive site characterization tool for characterizing hydrate-bearing sediments;
• the ability to robustly and reliably determine sample characteristics in situ complemented with pre-existing knowledge and post-sampling lab characterization (when plugs are recovered); and 
• a characterization tool and approach designed to provide information needed for reservoir simulations and analysis tools used for resource recovery, seafloor stability studies, and environmental evaluations.

Such information plays a critical role in the design of strategies for resource recovery, seafloor instability analyses, and environmental studies.

• Researchers successfully conducted two field tests of the borehole tool in the shallow waters of the Red Sea.
• The borehole tool was successfully tested at the King Abdullah University of Science and Technology (KAUST-Saudi Arabia) marina on the Red Sea. 
• The penetration and soil sampler modules were successfully tested in shallow beach sand sediments in Lake Acworth, GA.
• The first prototype of the borehole tool was designed and constructed.

(June 2018)
The project ended on September 30, 2017. The Principal Investigator gave a closeout presentation summarizing the results to NETL personnel. The final report is available below under "Additional Information."

The final report is available below under Additional Information. 

Phase 1 – DOE Contribution: $138,944
Phase 2 – DOE Contribution: $176,572
Phase 3 – DOE Contribution: $161,509
Planned Total Funding – DOE Contribution: $477,025

Phase 1 – $39,980
Phase 2 – $41,979
Phase 3 – $44,078
Planned Total Funding – Performer Contribution: $126,037

NETL – Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396)
Georgia Tech Research Corporation – Sheng Dai (sheng.dai@ce.gatech.edu or 404-385-4757)

Final Scientific/Technical Report [PDF-5.26MB] February, 2018