USGS Scientists Participate in Indian Ocean Gas Hydrates Drilling
During the summer of 2015, USGS Coastal and Marine Geology Program personnel participated in the Indian Government’s National Gas Hydrates Program (NGHP-02) drilling expedition offshore from eastern India (see map). NGHP-02 is one component of a long-term study of the potential for India’s marine gas hydrates to be an energy resource. Earlier this year, the program’s sponsor, India’s Directorate General of Hydrocarbons (DGH), and management agency, India’s Oil and Natural Gas Company (ONGC), made their initial public announcement about the results. A recent Sound Waves story provides additional expedition highlights.
What are gas hydrates?
Gas hydrates are a solid form of water and gas, stable at low temperature and elevated pressure. On Earth, the most abundant gas hydrate hosts methane, which is stable at the pressures and temperatures found in marine environments in the shallow subsurface, generally below ~350–400 meters of water (http://woodshole.er.usgs.gov/project-pages/hydrates/primer.html).
When brought to standard temperature and pressure, a given volume of methane hydrate will break down, or dissociate, releasing up to 164 times its volume in methane. The United States is among several countries engaged in testing the viability of extracting methane from gas hydrate as an energy resource.
Unprecedented scope of NGHP-02
Methane hydrate concentrated in the pore space of sands has the greatest potential as an energy resource. The NGHP-02 program extends the 2006 NGHP-01 project by specifically targeting sand-rich hydrate-bearing formations near the base of the continental slope.
The 2015 NGHP-02 drilling expedition was an ambitious, multi-component field study aboard the Japanese research-drilling vessel D/V Chikyu. From March 4 to April 27, 25 sites were logged while drilling, which generated high-resolution digital geophysical data that provided information about the sediments surrounding the borehole. Based on the logging-while-drilling results, gas hydrate-bearing sediment was identified across a range of depositional environments and sediment types. From April 28 to July 25, 10 priority sites were revisited for a combination of conventional and pressure coring, wireline logging, and vertical seismic profiling. During NGHP-02, approximately 6600 meters of subsurface were logged while drilling, and over 2200 meters of core material were collected.
The NGHP-02 expedition acquired 104 pressure cores, more than any gas hydrates drilling program completed over the past two decades. Unlike conventional cores, in which sediment is allowed to come to atmospheric pressure as the core is recovered, pressure cores use special technology to preserve sediments at the pressure they experienced in the seafloor. This is critical for maintaining gas hydrate within its stability field through the entire recovery process. Pressure cores are quickly cooled once on shipboard and can be stored for months or years at refrigerator temperatures prior to analysis without the hydrate breaking down.
The USGS Energy Resources Program and the Coastal and Marine Geology Program have participated in both of the Indian Government’s National Gas Hydrates Program expeditions. Timothy Collett (USGS Energy Resources Program) was the expedition chief scientist for both cruises. The USGS Coastal and Marine Geology Program supported coring components of NGHP-01 and NGHP-02 with geochemical and geophysical sampling and measurements. For NGHP-02, John Pohlman, Pamela Swarzenski, and Thomas Lorenson sailed in support of geochemical studies focused on determining the source of methane, the overall gas generation potential across the study region, and the downhole hydrate saturation. William Waite assisted in geophysical studies to support the reservoir modeling and borehole engineering required for effectively extracting methane as an energy resource.
Sample collection for USGS Coastal and Marine Geology Program post-cruise studies
Aboard the D/V Chikyu, USGS scientists collected samples from conventional and pressure cores for several post-cruise geotechnical and geochemical studies. Sediments from the conventional cores were sampled for index property measurements. These measurements provide insight into several processes that must be understood to safely and effectively extract methane from hydrate as an energy resource, such as how fluids and gas will flow in response to extracting methane from hydrates, and how much the sediment is likely to settle around a production well.
To measure how the presence of hydrate changes the sediment properties, assess the distribution and concentration of gas hydrate, and identify gasses contained within the hydrate, samples were also collected from pressure cores. Prior to sampling aboard the drillship, pressure cores were scanned to obtain initial X-ray, seismic velocity, and density profiles that were used to determine the distribution and saturation of gas hydrate in the sediments contained within the core and guide the subsampling locations for shipboard and post-cruise studies. Based on those initial scans, certain pressure-core subsections were depressurized in a controlled fashion to collect gas specimens for gas composition and origin studies, and to quantify the in-situ gas hydrate content. Twenty-five pressure-core sections were then stored for extensive post-cruise analysis by Japan’s National Institute of Advanced Industrial Science and Technology in Sapporo, Japan, and by the USGS at the Woods Hole Coastal and Marine Science Center. William Waite and Junbong Jang travelled to Sapporo in winter and spring 2016 to assist with the planning and execution of the NGHP-02 pressure-core analysis at Japan’s National Institute of Advanced Industrial Science and Technology.
Pressure-core analysis at the USGS Woods Hole Coastal and Marine Science Center
Five of the NGHP-02 pressure cores are earmarked for analyses by the USGS Gas Hydrates Project at a new facility being constructed at the Woods Hole Science Center with support from the U.S. Department of Energy. The facility is being built in a specially outfitted 40-foot refrigerated van set up adjacent to the Woods Hole Science Center core storage facility.
The new USGS pressure-core facility will house a suite of pressure-core characterization tools (PCCTs) originally built by J. Carlos Santamarina at Georgia Tech with U.S. Department of Energy support and now managed by the USGS Gas Hydrates Project on behalf of the U.S. hydrates community. The PCCTs make it possible to manipulate and measure properties of hydrate-bearing pressure core while continuously maintaining the pressure required to keep hydrate stable. Georgia Tech deployed the PCCT during a collaboration with USGS and the National Institute of Advanced Industrial Science and Technology in Sapporo, Japan, in January, 2013. The USGS is now modifying the tools in preparation for commencing analyses on the NGHP-02 pressure cores in autumn 2016. Researchers at the Woods Hole Science Center will use the PCCTs to measure geophysical, geotechnical, and hydraulic properties of the NGHP-02 pressure cores. The resulting data will inform reservoir modeling and borehole engineering plans currently underway as part of preparations for an eventual methane production test at the NGHP-02 sites (http://www.netl.doe.gov/file%20library/research/oil-gas/methane%20hydrates/MHNews_2016_Spring.pdf [10 MB PDF]).
Significance of NGHP-02 for Gas Hydrate Project goals
The broad scope of NGHP-02, covering multiple depositional environments and recovering hydrate-bearing sediment from a range of lithologies, is providing the USGS with an extensive collection of gas, water, and sediment samples. Post-cruise studies at the Woods Hole Science Center and Pacific Coastal and Marine Science Center are not only increasing our understanding of how the deposition of organic matter and sediment control the distribution and concentration of gas hydrates, but are also dramatically expanding our database linking chemical, mechanical, and transport properties to in-situ hydrate saturations. Together, these advances further refine our understanding of the geologic controls on the formation and properties of gas hydrate deposits, particularly those of potentially high energy-resource value (http://woodshole.er.usgs.gov/project-pages/hydrates/energy.html), while providing data for improving reservoir and borehole engineering models needed for effectively extracting methane from hydrate as an energy resource. NGHP-02 has provided the USGS with opportunities to significantly advance our understanding of hydrates in nature and further refine our sampling and measurement strategies ahead of domestic field projects being planned for the Alaskan North Slope and Gulf of Mexico.
USGS Gas Hydrates Project
The USGS Gas Hydrates Project is a globally recognized research effort focusing on energy, climate, and geohazard issues associated with natural-gas hydrates, and is jointly supported by the USGS Coastal and Marine Geology Program and Energy Resources Program. The Project’s research activities take place in the northern Gulf of Mexico, U.S. Arctic Ocean, the Alaskan North Slope, the U.S. Atlantic margin, and offshore Japan, India, and Korea (http://energy.usgs.gov/OilGas/UnconventionalOilGas/GasHydrates.aspx).
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