The primary goal of this research is to develop analytical techniques capable of quantitatively evaluating the nature of methane hydrate reservoir systems through modeling of their acoustic response using techniques that integrate rock physics theory, amplitude analysis, and spectral decomposition.

Fugro GeoConsulting, Inc., Houston, TX

Past efforts under the DOE-supported Gulf of Mexico Joint Industry Project included the selection of well locations utilizing prospectivity analysis based primarily on a petroleum systems approach for gas hydrate using 3-D exploration seismic data and derivative analyses that produced predicted gas hydrate saturation volumes. Logging–while-drilling at those locations confirmed the presence of high saturation gas hydrate reservoirs at two boreholes in Green Canyon Block 955 (GC955) and two boreholes in Walker Ridge Block 313 (WR313) in the Gulf of Mexico. The success of the four wells was a significant achievement and legitimized the conceptual approach taken to prospect for potential producible methane hydrate reservoirs in deepwater that could be exploited with modifications to present-day technology.

The success of future hydrate research wells and, eventually, resource exploration wells, will depend on the continued evolution of the techniques employed to select successful drilling locations. It is anticipated that future prospecting for methane hydrate deposits will be driven by their potential for exploitation as an energy resource. Geophysical prospecting techniques will need to be developed to both identify potential gas hydrate accumulations and better delineate and characterize these potentially complex systems and reservoirs.

This research effort will focus on developing and refining techniques that integrate rock physics modeling, amplitude analysis, and spectral decomposition. The expected outcome of the research efforts will be an enhanced ability to quantitatively evaluate and prioritize potential gas hydrate accumulations that may be selected as exploration drilling targets based on 3-D seismic data. Potential enhancements that are expected to result from research efforts include:

• More reliable identification and delineation of seismic data that illustrates the existence of gas hydrate accumulations
• Determination of class type of gas hydrate reservoirs
• Delineation of interfaces between gas hydrates and free gas across the prospect area
• Determination of hydrate concentration
• Determination of hydrate volume
• Determination of subjacent free gas concentration
• Determination of subjacent free gas volumes

Enhanced prospecting techniques for detecting and characterizing hydrate occurrences using seismic data will help reduce the substantial costs and risks and increase the likelihood of success of hydrate-focused deepwater drilling programs. These techniques will be important for initial research-based hydrate drilling activities, but may also eventually play a critical role in drilling programs seeking to exploit hydrates as an energy resource. Reliable selection and prioritization of gas hydrate drilling targets could have the following benefits: reduced costs incurred for drilling “dry” wells, increased likelihood of intersecting economically recoverable gas reserves, reduced exploration cost per volume of recoverable gas reserves, and enhancement of support for investment in future exploitation of gas hydrates as an energy resource.

• Documentated the cutting- edge approaches and techniques for seismic analysis and interpretation employed in the project, as well as the results of those analyses through the final project technical report including characterization of the gas hydrate petroleum system for the study area, delineation of gas hydrate prospects, generation of gas hydrate distribution, and volume estimates for the gas hydrate prospects.
• Created spectral decomposition volumes for areas of interest within the research data and completed integration of nearby data for use as a rock property baseline.
• Identified a specific potential gas hydrate deposit in the eastern Gulf of Mexico dataset focused around a singular deep-seated fault.
• Completed review of the eastern Gulf of Mexico seismic data identifying potential gas hydrate deposits.
• Acquired suitable seismic data for the Lund and Elbow protraction areas (offshore Florida).
• Acquired the petrophysical and inversion software required for the project.
• Modeled mixtures of methane and thermogenic gas hydrate signatures against flux and geothermal gradients and depositional architecture.
• Completed investigation of available well log data.
• Selected the rock physics model to be used in the project.
• Developed the geostatistical/inversion analytical routines to be used in the project.
• Completed review of related scientific/industry research efforts.

(May 2018)
The project was completed at the end of March 2016. The scientific and technical results of the effort are documented in the projects final report, which is accessible from the link in the Additional Information section below.

This study reviewed gas hydrate interpretation techniques for identifying gas hydrate bearing sands and expanded on direct hydrocarbon indicators for high saturation gas hydrate sands. Results from the project make a case for the presence of a large gas hydrate deposit in the deepwater Eastern Gulf of Mexico. The research demonstrates that prospecting for high-saturation gas hydrate deposits can be greatly aided with improved approaches to seismic interpretation, especially if sets of seismic attributes can be shown as diagnostic or direct hydrocarbon indicators for high saturation gas hydrates in sands that would be of most interest for gas hydrate production.

The effort provides evidence that spectral decomposition methods may be effective for identifying gas hydrates in sands, as are other seismic attributes that detect attenuation and layered high energy in thin beds. Spectral amplitude is responsive to both impedance and thin layers. In spectral data corresponding to an impedance anomaly caused by gas hydrates, the spectral amplitudes will increase in amplitude at higher frequencies. In a gas sand, the spectral data corresponding to the gas impedance anomaly will increase in some low- to mid-frequency ranges, depending on the setting and decrease in amplitude at higher frequencies. Frequency attributes derived from spectral decomposition proved to be direct hydrocarbon indicators by pseudo-thickness that could only be reconciled by substituting gas hydrate in the pore space. The study emphasizes that gas hydrate exploration and reservoir characterization benefits from a seismic thin-bed approach.

$170,755

$42,689

Planned Total Funding: $213,444

NETL – Richard Baker (Richard.Baker@netl.doe.gov or 304-285-4714)
Fugro GeoConsulting Inc. – Dan McConnell (DMcConnell@fugro.com)

Final Technical Report [PDF-12.9MB] December 30, 2017