The following review focuses on those studies that are most relevant to the assess­ment of gas hydrate resource potential.

1.1.1 Synopsis of Global Research Activities

Japan took a leading role in the effort to explore the potential of geologic hydrate deposits as an energy source by establishing a research program in 1995, which led to the drilling and installation of the first well in marine gas hydrate deposits in the Nankai Trough offshore Japan at a water depth of 945 m [114, 190, 199, 203]. This was succeeded by a larger multi-well exploration program [114], and is probably the most advanced program in the world in terms of proximity to commercial produc­tion. As part of this program, 36 wells were recently drilled in gas hydrate-bearing sand reservoirs at the same location [189]. Fujii et al. [47,48] and Saeki et al. [172] described the variety of gas hydrate occurrence found in the Nankai region, and Kurihara et al. [94, 96] discussed the technical challenges and the relative economic favorability of GH in different geologic settings. Production is expected to begin around 2016. Japan has also collaborated with Canada and other nations to conduct scientific studies and production tests from GH in the Canadian Arctic. Canada has
established a large gas hydrate research and development program that resulted in the Mallik production field test [35], the most significant to-date development in the quest for gas production from hydrates (see later discussion).

In the United States, studies on GH as a resource began in 1980s, and Collett [19] conducted the first systematic assessment. He estimated the 50% probability (mean) estimate of hydrate resources within the United States at 9 x 1015 m3 of CH4 (with the 95% probability estimate at 3 x 1015 m3 and the 5% probability estimate at

1.9 x 1016 m3), i. e., the mean value indicates 300 times more hydrated gas than the gas in the total remaining recoverable conventional resources. The Methane Hydrate Research and Development Act (MHR&D Act) of Congress in 2000 authorized funding to uncover the physical nature, economic potential, and environmental role of naturally occurring GHs. Over the first 10 years of the MHR&D Act, hydrate sci­ence advanced significantly, both in terms of knowledge of natural hydrate occur­rences, hydrate physical/chemical properties, and in the tools available to researchers. Researchers gained a greater understanding of the complexity of hydrate accumula­tions through laboratory work [40, 56, 86, 204,215], numerical simulation analyses [88, 129, 131-134, 136, 137], and national and international collaborative field experiments [35], and began the development of the precursors to tomorrow’s hydrate exploration and evaluation technologies. By 2005, it was clear that, given certain reservoir conditions, production of methane from hydrate was technically feasible and potentially commercially viable through specially tailored application of existing technologies [8]. Current research activities in the United States include laboratory experiments and simulation studies [8], in addition to field studies that focus on onshore Alaska and the offshore Gulf of Mexico (GOM)-i. e., sites of proven exploration targets in the United States [19-21]. Major federal-industry part­nerships have been formed in both the GOM and on the North Slope of Alaska [20]. It is likely that the first US domestic production from hydrates may occur in Alaska because of easier access, although the possibility of first production from GHs in the GOM cannot be discounted because of pipeline capacity and easier access to markets.

The government of India is funding a large national GH program to meet its growing gas requirements. Earlier seismic data from the Indian continental margin and GH occurrences that had been accidentally discovered during drilling for con­ventional oil and gas resources [20] provided the impetus for a hydrate-focused scientific expedition in the summer of 2006. This expedition confirmed large GH deposits at four offshore locations, from which many hydrate-bearing cores were obtained. Most notable was the 130-m thick fractured shale occurrence in the Krishna-Godowari basin that contained GH saturations SH previously unseen in shale-dominated reservoirs [ 28, 29 ] .

China has pursued gas hydrates R&D for more than a decade [44] , and con­ducted its initial drilling and coring program in the South China Sea in early 2007. That expedition found GH occurrences with SH up to 40% in clay-dominated sedi­ments at several sites [224]. As in the 2006 India expedition, these results were unexpected, and indicated that, given adequate sources of gas, hydrates are remark­ably effective at filling any available pore space.

Korea has established a significant research program that aims to assess the potential hydrate resources in the Korean East Sea. Preliminary surveys conducted by the Korea Institute of Geoscience and Mineral Resources (KIGAM) between 2000 and 2004 suggest a significant potential for gas hydrate occurrence in the Ulleung Basin [146], and numerical simulation studies have raised intriguing possibilities about the production potential of these deposits [136] . In late 2007, a drilling and coring program in Korea’s East Sea reported several 100-m thick occurrences [105].

Other countries (e. g., Norway, Russia, Mexico, Taiwan, Vietnam, Malaysia) have either embarked on, or are investigating the viability of, government-sponsored research programs to investigate the potential of gas production from national hydrate deposits. This list is only expected to grow. In Europe, research programs like Hydratech and Hydramed have focused primarily on scientific and environ­mental issues.

Recently, a growing number of deep sea drilling expeditions have been dedicated to locating marine GHs and obtaining a greater understanding of the geologic con­trols on their occurrence. The earliest projects were those of the Ocean Drilling Program (ODP) and the Integrated Ocean Drilling Program (IODP), including ODP Legs 164 [149] and 204 [194] and IODP Expedition 311 [162], as well as the 1998 and 2005 drilling programs conducted in the Nankai Trough by the MH21 consor­tium [47, 181]. More recently, the Gumusut-Kakap project offshore Malaysia [57], the Department of Energy (DOE)-sponsored drilling Legs I and II under the Joint- Industry Project in the GOM [9, 13, 166], and the India NGHP Expedition 01 [23, 28,29], as well as those in the offshore of China [218] and South Korea [147], have continued to expand the GH knowledge base.

Given the difficulty and the large costs of conducting field studies on hydrates, significant effort is invested in international collaborative projects. The most well known (and probably the most important, in terms of knowledge generated) was the 2002 Mallik project, conducted at that site in Canada’s Mackenzie Delta (Northwest Territories) by an international consortium that included seven organizations from five countries, as well as the International Continental Scientific Drilling Program. Current international collaborative projects include the Mallik 2007-2008 project [33, 37] (Japan and Canada), as well as other bilateral collaborations, e. g., US-India [27] and US-China [218].