DE-FE0009963

Goal
The primary project objectives are to relate seismic and acoustic velocities and attenuations to hydrate saturation and texture. The information collected will be a unique dataset in that seismic attenuation will be acquired within the seismic frequency band. The raw data, when combined with other measurements (e.g., complex resistivity, micro-focus x-ray computed tomography, etc.), will enable researchers to understand not only the interaction between mineral surfaces and gas hydrates, but also how the hydrate formation method affects the hydrate-sediment system in terms of elastic properties.

An over-arching goal of this research is to calibrate geophysical techniques for hydrate exploration, evaluation, and production monitoring. Extensive field data of hydrate-bearing sediments exist, but quantitative estimates of the amount and distribution of hydrates are difficult to determine. In addition, in situ substitution of CO₂ for CH₄ has been proposed (and briefly tested) as a method of both extracting methane and sequestering carbon dioxide. Our suite of measurements can be systematically applied to both borehole and surface data to derive hydrate saturation.

Performer
Colorado School of Mines, Golden, CO 80401

Collaborators
United States Geological Survey (USGS), Denver, CO 80225

Background
Differences in gas hydrate generation methods influence hydrate habit and distribution in both natural and synthetic hydrate-bearing sediments and should impact the physical properties of the hydrate. However, mechanical interactions between hydrates and sediments and the controls exerted by the hydrate formation method are poorly understood. It is critical to understand and model these effects on seismic properties, since existence and indirect mapping of hydrate-bearing formations and hydrate saturations rely heavily on indirect seismic mapping techniques. The research will help to fill this gap via a series of well-defined experiments designed to calibrate the seismic response of hydrate-bearing sediments. The experiments comprise a series of petrophysical tests on laboratory-formed hydrate-bearing sediments, including frequency-dependent measurements of seismic velocities and attenuation. Various hydrate-formation methods will be tested, including methane injection into partially water-saturated sand, circulation of methane-saturated water, and the use of tetrahydrofuran as a hydrate former. These formation methods are expected to yield “cementing” and “non-cementing” hydrates and the resulting hydrate-bearing samples will represent end-members for effective medium models of mechanical and electrical properties. Micro-focus x-ray computed tomography will provide verification and quantification of hydrate distribution in the pore space and throughout the sample. Rock physics models that link the hydrate saturation and distribution to the elastic properties of the hydrated sediment will be developed based on laboratory results. Finally, available field data, such as sonic well-logs, will be inverted for attenuation as a function of frequency. The obtained attenuation data will be used in conjunction with velocity information and developed rock physics models to investigate targeted gas hydrate-bearing areas, specifically with respect to their potential formation history.

Impact
The project outcome should provide a means of calibrating geophysical field data and insight into the formation of natural gas hydrate deposits, improve our ability to detect and evaluate hydrates in the subsurface and, ultimately, help researchers design feasible, economic, and safe production schemes for natural gas hydrates.

Accomplishments
New project awarded on October 1, 2012

Current Status (November 2012)
Current laboratory equipment will be modified to allow researchers to synthesize and measure the parameters of various hydrate compounds. Phase stability of THF, CH₄ and CO₂-CH₄ hydrate will be modeled to establish an experimental range of conditions. Researchers will extract sonic attenuations, and assess the in situ hydrate saturations with logs obtained from areas of known hydrate occurrence, such as the North Slope of Alaska.

Project Start: October 1, 2012
Project End: September 30, 2015

Project Cost Information:
Phase 1 - DOE Contribution: $225,414, Performer Contribution: $65,167
Phase 2 - DOE Contribution: $215,629, Performer Contribution: $65,167
Phase 3 - DOE Contribution: $214,673, Performer Contribution: $65,167
Planned Total Funding - DOE Contribution: $655,716, Performer Contribution: $195,501

Contact Information:
NETL – Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396)
Colorado School of Mines – Michael Batzle (mbatzle@mines.edu or 303-384-2067)
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