DOE/NETL Methane Hydrate Projects
Characterizing Baselines and Change in Gas Hydrate Systems using Electromagnetic (EM) Methods Last Reviewed November 2017

DE-FE0028972

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.

Performers
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)

  • 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 (November 2017)
Scientists from Scripps Institute of Oceanography conducted marine CSEM surveys over four methane hydrate prospects in the Gulf of Mexico, using the Research Vessel Point Sur from June 29 through July 11. The surveys used the deep-towed "Vulcan" system, developed by Scripps, for the express purpose of mapping seafloor gas hydrates. The team collected a total of 359 line kilometers of high quality data over Walker Ridge 313, Walker Ridge 100 (Orca Basin), Green Canyon 955, and Green Canyon 781 (Mad Dog).

USGS and LLNL completed a first round of conductivity measurements on pure methane hydrates. At the end of the run, the sample was partially dissociated through depressurization in order to produce a hydrate product with a coexisting liquid water phase. The sample was then quenched in liquid nitrogen for cryogenic scanning electron microscopy. The cryoSEM images show a very interesting texture that was not expected. Instead of being distributed around the methane hydrate grains, water is distributed in segregated patches. It is not known if this is a result of water migrating from dissociating hydrate grains and pooling, or if dissociation preferentially occurs in the patches. The texture of the methane hydrate grains, which appear eroded on the boundaries, does suggest some dissociation that is spread evenly through the sample.

During the next quarter, the team will continue to collect laboratory conductivity data at Menlo Park, and continue with processing and inversion of the CSEM field data.

Project Start: October 1, 2016
Project End: December 30, 2019

Project Cost Information
Phase 1 – DOE Contribution: $366,579, Performer Contribution: $180,484
Phase 2 – DOE Contribution: $116,986, Performer Contribution: $101,616
Phase 3 – DOE Contribution: $49,841, Performer Contribution: $80,399
Planned Total Funding–DOE Contribution: $533,406, Performer Contribution: $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:

Quarterly Research Performance Progress Report [PDF] July - September, 2017

Quarterly Research Performance Progress Report [PDF] January - March, 2017