|Borehole Tool for the Comprehensive Characterization of Hydrate-bearing Sediments
||Last Reviewed 12/11/2014
The objective of the project 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.
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. A borehole tool will be designed to comprehensively characterize hydrate-bearing sediments in situ. 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 permeabilities 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 such as:
- 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)
- 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.
The first prototype of the downhole tool was designed and constructed.
Current Status (December 2014)
Researchers designed and built the first prototype of the downhole tool, a stackable type system made of a train of modules and constructed of 316 stainless steel to meet stress and chemical resistance requirements. Some of the tool’s components include a penetration module, a resistivity module, a soil sampler, a strain gauge, and a porous ring for water pore pressure measurements. The penetration and soil sampler modules were successfully tested in shallow beach sand sediments in Lake Acworth, Georgia. The fluid sampler was designed to be filled with an inert gas at a pressure slightly higher than the dissociation pressure for methane hydrate so that sampling will not cause dissociation. Calibration tests of the electrical resistivity module conducted with salt solutions show good agreement with tabletop resistivity measurements. Future work includes additional testing of the various modules and further development of the system electronics.
Project Start: October 1, 2013
Project End: September 30, 2016
Project Cost Information:
Phase 1 – DOE Contribution: $138,944; Performer Contribution: $39,980
Phase 2 – DOE Contribution: $176,572; Performer Contribution: $41,979
Phase 3 – DOE Contribution: $161,509; Performer Contribution: $44,078
Planned Total Funding – DOE Contribution: $477,025; Performer Contribution: $126,037
NETL – Skip Pratt (firstname.lastname@example.org or 304-285-4396)
Georgia Tech Research Corporation – Carlos Santamarina (email@example.com or 404-894-7605)
Quarterly Research Performance Progress Report [PDF-4.17MB] July - September, 2014
Quarterly Research Performance Progress Report [PDF-2.39MB] April - June, 2014
Quarterly Research Performance Progress Report [PDF-1.11MB] January - March, 2014
Quarterly Research Performance Progress Report [PDF-545KB] October - December, 2013