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Characterizing Baselines and Change in Gas Hydrate Systems using Electromagnetic (EM) Methods
Project Number
DE-FE0028972
Last Reviewed Dated
Goal

The overall objectives of this work are (i) advance understanding of hydrate electrical conductivity as a function of sediment type and fluid content; (ii) quantify the conductivity changes associated with hydrate dissociation induced by increasing temperature or decreasing pressure; and (iii) collect baseline data sets in the field to illustrate the capabilities of the Vulcan instrument system, calibrate the relationship between conductivity inversions and well logs, and provide quantitative constraints on hydrate volume in situ.

Phase 1 objectives: Understand the effect of grain size on methane hydrate conductivity. Assess the impact on methane hydrate conductivity of dissociation associated with (a) decompression and (b) increased temperature. Image the electrical conductivity structure of 2 or 3 prospects in the Gulf of Mexico (GoM) using the Vulcan marine Controlled Source ElectroMagnetic (CSEM) system.

Phase 2 objectives: Interpret the Vulcan inversions to obtain quantitative estimates of total hydrate volume.

Phase 3 objectives: Complete the integration of field interpretations, laboratory conductivity studies, and any available logging/coring results. Publicize results and facilitate commercial application of the technology.

Performer

The Regents of the University of California – San Diego (UCSD), Scripps Institute of Oceanography, La Jolla, CA 92093

Collaborators
United States Geological Survey (USGS), Menlo Park, CA 94025
Lawrence Livermore National Laboratory, (LLNL), Livermore, CA 94551

Background

In order to clarify the processes by which gas hydrate deposits are formed, maintained, and evolve within geologic systems, it is important to develop tools other than drilling, seismology, and geochemistry to study hydrate systems, both in the field and in the laboratory. Much progress has been made in our understanding of hydrate systems using the existing tools, but adding electrical conductivity cannot fail to increase our understanding of gas hydrate systems. Combined with appropriate models obtained from laboratory studies, CSEM measurements can help quantify the saturation and total volume of hydrate within a known or suspected deposit. By adding geometrical constraints obtained from seismic reflection data, tradeoffs between total volume and peak saturation can be resolved. Currently our laboratory models are limited to pure hydrate and hydrate+sand. It is important to expand this library to include silt and fluids to the list. Basic data such as these will also improve the interpretation of resistivity well logs. A critical part of the proposed work is to use laboratory measurements to characterize and quantify changes in electrical conductivity of hydrate systems during dissociation induced by production (lowering pressure) or environmental change (increasing temperature). Combined with repeat field measurements to collect CSEM data, observed changes in conductivity can thus be interpreted in terms of changes in hydrate volume and extent. It is possible that climate- or production-induced changes in hydrate content may generate a more observable signal in electrical conductivity than in seismic properties.

Impact

By examining the role of grain size and fluids, the work proposed here will expand the application of our data to more complicated natural systems, and will help take the interpretation of well logs from a largely qualitative approach to something more quantitative. By collecting field data in locations where logging while drilling (LWD) data have already been collected, and coring data are likely to be collected in the future, we can further refine our ability to improve the interpretation of logs.

Accomplishments (most recent listed first)
  • An article on laboratory conductivity studies was published in the Summer 2018 issue of Fire in the Ice.
  • Posters on the preliminary results from the GoM field work were presented at the Fall American Geophysical Union (AGU) meeting in New Orleans, December 2017, and the Gordon Research Conference in Galveston, TX, March 2018.
  • A suite of conductivity runs have been made on hydrate, sand, and salt systems.
  • Inversions have been carried out for two of the four GoM prospects.
  • Completed a research cruise to collect CSEM data over four methane hydrate prospective areas in the GoM.
  • Researchers from LLNL and USGS collected a baseline set of electrical conductivity data from the conductivity cell, which was recently refurbished and installed at the USGS Gas Hydrate Laboratory at Menlo Park.
Current Status

Scientists at UCSD have started carrying out inversions of the GoM field data collected in July 2017. 2D inversions of two prospects, Walker Ridge 313 and Walker Ridge 100 (Orca Basin) have been completed. The results appear sensible and are consistent when compared with seismic data from the areas.

USGS and LLNL continue to collect electrical conductivity measurements and cryogenic electron microscopy on samples of gas hydrate with added salt, and now have results from five salt concentrations. The salt forms brine on the surface of the gas hydrate grains, which creates a connected electrical conduction path and increases the conductivity significantly over that of pure methane hydrate. At sufficiently low temperatures the brine freezes to form halite or hydrohalite, and this phase boundary is evident in the electrical conductivity data. Conductivity measurements have also been made of hydrate synthesized from flash frozen seawater. Results from this work to date were presented at two meetings in March 2017, the Gordon Research Conference in Galveston, TX, and the Scripps Seafloor Electromagnetic Methods Consortium annual meeting in La Jolla, CA.

During the next quarter, the team will continue to collect laboratory conductivity data of hydrate mixed with silt at Menlo Park, and will continue with inversion of the CSEM field data. Additionally, the team is preparing a journal article on the laboratory work. This article is nearly ready for submission.

Project Start
Project End
DOE Contribution

Phase 1 – $366,579

Phase 2 – $116,986

Phase 3 – $49,841

Planned Total Funding– $533,406

Performer Contribution

Phase 1 – $180,484

Phase 2 – $101,616

Phase 3 – $80,399

Planned Total Funding– $362,499

Contact Information

NETL – Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396) 
UCSD, Scripps Institute of Oceanography – Steve Constable (sconstable@ucsd.edu or 858-534-2409)

Additional Information