Charting the Future of Methane Hydrate Research in the United States (2004)

Field research in the Arctic has advanced to production testing of a concentrated gas hydrate reservoir (Dallimore et al., 2002). The technology has stepped from a concern solely with geology, geochemistry, and geophysics to a concern with the engineering of production. In the near future, major advances in innovation to recover hydrated energy, first in permafrost form and then in more dispersed form in oceanic sediments, should be expected.

The next decade will probably see several additional production tests to validate and calibrate different approaches to extracting methane from natural gas hydrate. Initially the focus will continue to be in the Arctic, moving eventually to the more challenging marine environment. Views of how to identify gas hydrate in nature using geologic and geophysical tools have also evolved. It is clear that gas hydrate distribution in nature is very heterogeneous. Better models for the temporal evolution of natural gas hydrate systems and remote sensing techniques that can identify and quantify concentrated gas hydrate deposits must be developed. It is clear that fundamental advances and findings essential to this program have resulted from modest investments in international collaboration.

Because commercial production of gas from hydrate is expected to have a long time horizon (20-30 years), most of the professionals practicing today cannot be expected to be active when and if commercial production becomes a reality. It is therefore important that the Department of Energy (DOE) Methane Hydrate Research and Development (R&D) Program place major emphasis on educating a new generation of scientists and engineers to ensure a future pool of appropriate expertise in all aspects of hydrate systems. As discussed in Chapter 3, this can be accomplished through a program of graduate assistantships and fellowships as well as a program of postdoctoral fellowships. The postdoctoral fellowships might be patterned after DOE’s successful Hollander Fellowship program, but be modified to include opportunities for research experience involving cooperation between academia, government, and industry.

As specified in the original enabling legislation, an overarching goal of the Methane Hydrate R&D Program is to conduct applied research to identify, assess, and develop methane hydrate as a source of energy. The Methane Hydrate Research and Development Act of 2000 listed activities in a number of areas (P.L. 106-193, Section 3(b); Box ES.1). This section suggests research areas for future program emphasis based on the research conducted since initiation of the Methane Hydrate R&D Program by the act. These priorities are based on addressing the poorly understood aspects of the potential of hydrate as a future resource and optimizing the potential impact given the currently available program funding (~$9 million per year). This research should include both fundamental science and technology development and should involve periodic peer review as specified in A Strategy for Methane Hydrates Research and Development (DOE, 1998). Specifically, the research areas are:

• future field experiments, drilling, and production testing with consideration of testing offshore hydrate that might be considered to be of sufficiently large quantity to be potentially commercial;

• hydrate deposit identification and characterization;

• reservoir modeling;

• technology recovery methods and production;

• understanding the natural system and climate change potential;

• geological hazards; and

• transportation and storage.

Although they are not ranked in order of importance, each research area is discussed below in terms of the most important issues that should be addressed within that area in a future research program.

Given the large unknowns, pursuit of experimental drilling, multi-year time-series measurements of gas hydrate systems, and experimental production clearly would be the most effective way to advance this program. Field studies should be viewed as an integral part of the learning process and should proceed using the best information available on hydrate deposit identification, reservoir modeling, recovery methods, and production techniques. A major product of the drilling program should be new technologies that reduce risks and allow efficient and environmentally sound development of hydrate resources. These drilling experiments are extremely expensive and should be available to the community of researchers, to leverage both the cost and the scientific advantages of such an effort. There is a clear record showing that major fundamental advances and findings essential to this program have resulted from modest investments in international collaboration. Future research should build on and continue to emphasize successes resulting from international cooperation.

Before production can commence, it is necessary to select optimal test sites that will not only demonstrate feasible production but also provide for the broadest application of results for future drill sites and optimal production. To accomplish this, better estimates are needed of the location of rich hydrate zones, layers, or geological blocks (“sweet spots”), the amount and concentration of hydrate in situ before drilling, and the mobility of methane once production commences.

In the marine realm, the absence of known large, concentrated accumulations of methane hydrate most likely means that the nation cannot look to the U.S. exclusive economic zone (EEZ) as a promising region to supply some of its future energy resource needs through gas hydrate production. Given that the petroleum industry has shown little

interest in exploring for large marine accumulations of hydrate, the DOE Methane Hydrate R&D Program should enable efforts to identify the likely formative setting of hydrate and where it might be found, and then assemble information about reported or suspected large deposits.

If large, potentially exploitable bodies of marine hydrate exist, they most likely will be found off the continental shelf within the hydrate stability field, embracing reservoir sequences of clastic, carbonate, or siliceous sediment on the U.S. continental slopes and adjacent fans. The occurrence of large, concentrated hydrate accumulations in these deposits most likely will require a stratigraphic or structural connection to underlying thermogenic (i.e., petroleum) sources of methane. Other prospective areas are the thickly sedimented abyssal plains of ocean margin basins where turbidite sections have accumulated and are overlain by productive surface waters (e.g., the Gulf of Mexico, Caribbean, Shikoku Basin, Sea of Okhotsk, Bering Sea).

A main thrust of the Methane Hydrate R&D Act is to focus research on the likely locations of large accumulations of marine methane hydrate and also to field-test ideas and locate and characterize these deposits. The DOE Methane Hydrate R&D Program should therefore sponsor a workshop focused on specific aspects of required research, for example, finding sweet spots or monitoring the evolution of gas hydrate deposits over time in the context of the Ocean Observatories Initiative (OOI).

To these ends it is crucial to do the following:

• Enhance efforts to adapt and/or modify existing geophysical techniques, such as seismic acquisition and processing methods, to obtain much higher resolution of subsurface structural and petrophysical details. This may require the use of higher seismic frequencies in three-dimensional seismic surveys.

• Invest in developing more rigorous approaches to the calibration of surface seismic data interpretation techniques to identify hydrate in situ (e.g., comparing well logs and core information to surface seismic data). The use of pressure core barrel vertical seismic profiling surveys and seismic dipole logs could also be extremely useful.

• Develop petroleum system models that incorporate concepts of accumulation and loss.

• Develop processes to identify hydrate sweet spots based on integrated geological and geophysical site data and generic knowledge from other sites as well as theory and laboratory results.

All of the above require a systematic scientific approach using wells not only for calibration of seismic data but also for controls to characterize reservoir properties away from the well. This requires coordinated laboratory studies of fluid and rock physical properties, including core analysis of physical properties in specialized laboratory settings and field laboratories.

Before sustainable economic production of gas hydrate can commence, a realistic model-based estimate is required to optimize safe and efficient production procedures, determine suitable layout and design of production wells, and ultimately predict the expected rate of reservoir production. Accurate hydrate reservoir models, tested against field experience, provide an extremely cost-effective alternative to field experiments in economic assessment of hydrated energy production techniques. Suitable reservoir simulation models must accurately quantify the unique physical, chemical, and geomechanical properties of gas hydrate, free gas, and water-saturated porous media systems and their response to production stimulation. Although progress has been made in the area of reservoir modeling (Box 3.1), key research questions must be addressed in order to move this field forward. These include the following:

• resolving knowledge gaps in the kinetics of gas hydrate dissociation and the relative permeability of the rock-gas hydrate-fluid system—to date there has been minimal work on reservoir sediments (e.g., sands, silts, shales) aimed at understanding the response of gas hydrate to production stimulation and the flow response of the produced gas as hydrate breaks down into methane and water in different reservoir rock types; and

• determining the influence on recovery of spatial subsurface heterogeneities in rock and fluid systems, including the effects of variability in porosity, permeability, hydrate concentration, rock compressibility, sand-clay ratio, fracture or fault systems, in situ stress, and the effects of pore pressure and temperature, as well as their changes with time and production.

While the potential of hydrate as a major energy resource in the future appears promising, viable techniques for recovery are currently in the planning stage. It is essential that recovery techniques be investigated and tested, first in laboratory-hydrated sediments and then in controlled and carefully monitored field tests. Incentives should also be provided for investigating unconventional recovery techniques—techniques that are truly different from existing oil and gas methods.

An understanding of the role of methane hydrate in the methane and the carbon cycle remains poor and elusive. Important issues that require vigorous investigation include the following:

• determining what factors and mechanisms control hydrate for-mation and dissociation in nature and the rates of those processes;

• determining the extent of natural hydrate deposits, how dynamic they are, and how estimates of the global inventory of natural hydrate can be refined;

• ascertaining how the dissociation of hydrate influences the atmospheric inventory of methane in the short term and climate in the long term and what the climate system response will be to chronic as well as episodic methane releases from dissociating hydrate, as well as, developing methods to evaluate the magnitude of episodic releases and determining the climate impacts of these responses;

• establishing the role of microbial processes in controlling methane released by hydrate dissociation and determining whether the “oxidizing gauntlet” is effective in limiting releases of methane to the atmosphere;

• developing techniques and instruments for continuous monitoring of releases of methane from both natural deposits and hydrate deposits under development—both diffusive and advective environments have to be studied; these efforts should emphasize development of new technologies such as continuous acoustic sounding, electronic monitoring, deployment of sensitive ther-

mometer arrays, and methods for continuous measurement of methane concentration and isotope distributions and subsequent ground-truthing of these measurements; and

• ascertaining whether there are unique organisms or communities associated with hydrate deposits and vents, whether they have distinctive molecular signatures, and whether biological or chemical methods offer potential as means of locating hydrate deposits.

Understanding the temporal evolution of gas hydrate systems will require installation of long-term observatories on and beneath the seafloor. The DOE Methane Hydrate R&D Program should collaborate with the National Science Foundation (NSF), especially with the OOI and the Ocean Research Interactive Observatory Network (ORION) (http://www.coreocean.org/orion; NRC, 2003), to implement this aspect of the program. The OOI would provide the infrastructure needed to carry out in situ seafloor and subseafloor observations of gas hydrate and its associated micro- and macrobiological communities in a variety of different settings over extended periods. It would provide the measurements of methane flux both beneath the seafloor and from the seafloor into the ocean that are needed to determine how dynamic this reservoir is. This infrastructure would enable rapid-response surveys to study short-term phenomena and provide the power needed to enable perturbation experiments on the seafloor. Current ORION plans call for cable installations well situated to study gas hydrate on the continental margin of the Pacific Northwest. Additional installations in the Gulf of Mexico and on the southeast margin of the United States would be desirable for obtaining comprehensive coverage of different gas hydrate environments. Such studies would contribute to understanding the relationship between seafloor hydrate and seeping gas for resource exploration and production, as well as for slope stability and global climate change. The DOE Methane Hydrate R&D Program should sponsor a workshop focused on specific aspects of required research—for example, finding sweet spots or monitoring the evolution of gas hydrate deposits over time in the context of the OOI.

Geological hazards associated with gas hydrate relate on a fundamental level to the reduction of soil strength incurred as a result of gas hydrate dissociation and the fate and effect of the free gas produced (Kennett et

al., 2003). More fundamental research is required in the general field of geomechanics of hydrate deposits.

Gas hydrate has been implicated as the possible cause of large- and small-scale marine slope failures. Unique seafloor features such as pock marks or gas hydrate outcroppings may also be a hazard under some circumstances. Research should be conducted that locates and provides analytical verification of the correlation with past hydrate decomposition and slope instability and other observed geohazards.

Most germane to the DOE Methane Hydrate R&D Program, gas hydrate also represents a geohazard adjacent to bottom-founded structures, where the occurrence of gas hydrate near the seafloor may present foundation problems. Finally, the geohazard risk posed by gas hydrate must be considered carefully when hydrocarbon exploration or production facilities, either conventional or hydrate specific, penetrate gas hydrate and have the potential to induce coincident gas flows, casing strain, or ground surface settlements.

The DOE Methane Hydrate R&D Program has undertaken valued work in this field—for example, in the Gulf of Mexico research is expected to provide a better understanding of the safety hazards involved in drilling and producing oil and gas through hydrate-containing sediments in the deep water. It is recommended that work be focused on the future development of gas hydrate; thus, issues such as ground surface settlement should be considered as well as the design of safe and effective leak-free production casings.

This area is important, but it is not the exclusive domain of hydrate research. This area is given a relatively low priority, but it is recognized that this priority might change rapidly if commercially viable hydrate deposits are discovered.

The overriding focus of the DOE Methane Hydrate R&D Program in the future should be on the potential importance of hydrate as a future energy resource for the nation and the world.

To optimize the potential impact of the amount of hydrate research funding available (~$9 million per year), such a focused program should systematically address the following research areas that are poorly, or only partly, understood.

• Future field experiments, drilling, and production testing, with consideration of testing offshore hydrate that might be considered to be of sufficiently large quantity to be potentially commercial

• Hydrate deposit identification and characterization

• Reservoir modeling

• Technology recovery methods and production

• Understanding the natural system and climate change potential

• Geological hazards

• Transportation and storage

Collaboration between the DOE Methane Hydrate R&D Program and other agencies, to augment infrastructure, will facilitate the achievement of program goals. For example, collaboration with NSF, especially with the OOI and ORION, would be useful to implement studies geared toward understanding the temporal evolution of gas hydrate systems using long-term observatories on and beneath the seafloor (http:www.coreocean.org/orion; NRC, 2003).

The DOE Methane Hydrate R&D Program should sponsor a workshop focused on specific aspects of required research, for example, finding sweet spots or monitoring the evolution of gas hydrate deposits over time in the context of the OOI.

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