Abstract A growing body of evidence indicates that a large volume of natural gas is stored in gas hydrates and that the production of natural gas from gas hydrates appears to be technically feasible. There are numerous research projects underway to investigate the geological origin of gas hydrate, their natural occurrence, the factors that affect their stability, and the possibility of using this vast resource in the world energy mix. Highly successful cooperative research projects, such as the various phases of the Mallik gas hydrate production project in northern Canada, have for the first time tested the technology needed to produce gas hydrates, and other highly successful gas hydrate research studies have been conducted in Japan, India, China, South Korea, northern Alaska, and the Gulf of Mexico. All of these projects have contributed greatly to an understanding of the energy resource potential of gas hydrates throughout the world.

Abstract The Gulf of Mexico gas hydrates Joint Industry Project (the JIP), a cooperative research program between the US Department of Energy and an international industrial consortium under the leadership of Chevron, conducted its “Leg II” logging-while-drilling operations in April and May of 2009. JIP Leg II was intended to expand the existing knowledge base on gas hydrates in the Gulf of Mexico to include the evaluation of gas hydrate occurrence in sand reservoirs. The selection of the locations for the JIP Leg II drilling was the result of a geological and geophysical prospecting approach that integrated direct geophysical evidence of gas hydrate-bearing strata with evidence of gas sourcing, gas migration, and occurrence of sand reservoirs within the gas hydrate stability zone. Logging-while-drilling operations for JIP Leg II included the drilling of seven wells at three sites. Despite drilling the deepest and most technically challenging well yet attempted in a marine gas hydrate program, the expedition was on time, under budget, and met all its scientific objectives. Minimal operational problems were encountered with the advanced LWD tool string, and the continual refinement of drilling parameters enabled the successful management of a range of shallow drilling issues, including borehole breakouts and shallow gas and water flows. Two wells drilled in Walker Ridge Block 313 (WR 313) confirmed the pre-drill predictions by discovering gas hydrates at high saturations in multiple sand horizons having reservoir thicknesses up to 50 ft. In addition, drilling in WR 313 discovered an unpredicted, thick, strata-bound interval of shallow finegrained sediments having abundant gas-hydrate-filled fractures. Two of three wells drilled in Green Canyon Block 955 (GC 955) confirmed the pre-drill prediction of extensive sand occurrence having gas hydrate fill along the crest of a structure associated with positive indications of gas source and migration. Well GC955-H discovered ~100 ft of gas hydrate in sand at high saturations. Two wells drilled in Alaminos Canyon Block 21 (AC 21) confirmed the pre-drill prediction of potential extensive occurrence of gas hydrates in shallow sand reservoirs at low saturations. Further data collection and analyses at AC 21 will be needed to better understand the nature of the pore filling material. The JIP plans to use the results of Leg II to plan Leg III drilling and coring operations anticipated to occur in 2010.

Abstract A strong upward trend exists for the consumption of all energy sources as people throughout the world strive for a higher standard of living. Someday, possibly soon, the earth's store of easily accessed hydrocarbons will no longer satisfy our growing economies and populations. By then, an unfamiliar but kindred hydrocarbon resource called natural gas hydrate may become a significant source of energy. Approximately 35 years ago, Russian scientists made what was then a bold assertion that gas hydrates, a crystalline solid of water and natural gas and a historical curiosity to physical chemists, should occur in abundance in the natural environment. Since this early start, the scientific foundation has been built for the realization that gas hydrates are a global phenomenon, occurring in permafrost regions of the arctic and in deep-water parts of most continental margins worldwide. The amount of natural gas contained in the world's gas-hydrate accumulations is enormous, but these estimates remain highly speculative. Researchers have long speculated that gas hydrates could eventually be a commercial producible energy resource, yet technical and economic hurdles have historically made gas-hydrate development a distant goal instead of a near-term possibility. This view began to change in recent years with the realization that this unconventional resource could possibly be developed with the existing conventional oil and gas production technology. The pace of gas-hydrate energy assessment projects has significantly accelerated over the past several years, but many critical gas-hydrate exploration and development questions still remain. The exploitation and potential development of gas-hydrate resources is a complex technological problem. However, humans have successfully dealt with such complicated problems in the past to satisf your energy needs; technical innovations have been key to our historical successes.

Abstract Hydrocarbon gas composition and isotopic composition of methane were analyzed from cutting samples obtained from industry oil wells penetrating the Eileen and Tarn gas-hydrate deposits. These gas-hydrate deposits overlie the Prudhoe Bay and Kuparuk River oil fields and are restricted to the updip part of a series of nearshore deltaic sandstone reservoirs in the lower Tertiary (Eocene) Mikkelsen Tongue of the Canning Formation and the Tertiary Staines Tongue of the Sagavanirktok Formation, respectively. The Eileen and Tarn gas hydrates are thought to contain a mixture of deep-source thermogenic gas and shallow, microbial gas (methane carbon isotopic composition ranges from —54 to — 46% in the gas-hydrate zone). Thermogenic gases likely come either from existing oil and gas accumulations or from source rocks within the oil- and gas-generating window that have migrated updip and or upfault and formed gas hydrate. The timing of gas source mixing is unknown. The microbial gases likely have a source contribution from biodegraded oil or gas in the underlying oil fields, as evidenced by the carbon isotopic composition of methane, ethane, propane, and carbon dioxide. The distribution of the Eileen and Tarn gas-hydrate accumulations appears to be controlled in part by the presence of large-scale regional faults that may have acted as vertical and lateral gas migration conduits.

Abstract A primary mechanism likely to control potential gas production from gas-hydrate-bearing porous media is the gas-water two-phase flow during dissociation. Gas-water relative-permeability functions within gas-hydrate systems are poorly understood, and direct measurements within gas-hydrate-bearing porous media are difficult. In this study, we developed a new method for measuring gas-water relative permeability for laboratory-synthesized gas hydrate within porous media. The new experimental design allows gas hydrate to form within a porous media and allows the measurement of effective permeability and relative permeability for different saturation values. The relative permeability to gas and water was determined by applying the Johnson-Bossler-Neumann method. Finally, effective permeability and relative permeability data of gas and water phases are reported for gas-hydrate-saturated consolidated Oklahoma 100-mesh sand and Alaska North Slope subsurface sediments. The results show significant reduction in permeability at increased gas-hydrate saturations. The results also suggest that the relative permeability determined from the unsteady-state core floods is primarily affected by gas-hydrate saturations. Furthermore, effective as well as relative permeabilities vary by the nature of gas-hydrate distribution for the same bulk saturation in different porous media. We believe that the experimental data obtained from this work will provide input data to reservoir modeling, fluid flow modeling, and development of relative-permeability-estimation methods for hydrate production. However, considerable additional experimental and theoretical work remains to develop an analytical or generalized model to predict the relative permeability for gas-hydrate reservoir simulation.

Abstract Although considerable uncertainty and disagreement prevail concerning the world’s gas- hydrate resources, the estimated amount of gas in those gas-hydrate accumulations greatly exceeds the volume of known conventional gas reserves. However, the role that gas hydrates will play in contributing to the world's energy requirements will ultimately depend less on the volume of gas-hydrate resources than on the cost to extract them. Gas hydrates occur in sedimentary deposits under conditions of pressure and temperature present in permafrost regions and beneath the sea in outer continental margins. The combined information from arctic gas-hydrate studies shows that in permafrost regions, gas hydrates may exist at subsurface depths ranging from about 130 m to 2000 m. The presence of gas hydrates in offshore continental margins has been inferred mainly from anomalous seismic reflectors (known as bottom-simulating reflectors) that have been mapped at depths below the seafloor ranging from approximately 100 m to 1100 m. Current estimates of the amount of gas in the world’s marine and permafrost gas-hydrate accumulations are in rough accord at about 20,000 trillion m 3 . Gas hydrate as an energy commodity is often grouped with other unconventional hydrocarbon resources. In most cases, the evolution of a nonproducible unconventional resource to a producible energy resource has relied on significant capital investment and technology development. To evaluate the energy-resource potential of gas hydrates will also require the support of sustained research and development programs. Despite the fact that relatively little is known about the ultimate resource potential of gas hydrates, it is certain that they are a vast storehouse of natural gas, and significant technical challenges will need to be met before this enormous resource can be considered an economically producible reserve.