Recognizing the importance of methane hydrate research and the need for a coordinated effort, the United States Congress enacted the Methane Hydrate Research and Development Act of 2000. At the same time, the Ministry of International Trade and Industry in Japan launched a research program to develop plans for a methane hydrate exploratory drilling project in the Nankai Trough. India, China, the Republic of Korea, and other nations also have established large methane hydrate research and development programs. Government-funded scientific research drilling expeditions and production test studies have provided a wealth of information on the occurrence of methane hydrates in nature. Numerous studies have shown that the amount of gas stored as methane hydrates in the world may exceed the volume of known organic carbon sources. However, methane hydrates represent both a scientific and technical challenge, and much remains to be learned about their characteristics and occurrence in nature. Methane hydrate research in recent years has mostly focused on: (1) documenting the geologic parameters that control the occurrence and stability of methane hydrates in nature, (2) assessing the volume of natural gas stored within various methane hydrate accumulations, (3) analyzing the production response and characteristics of methane hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural methane hydrates, (5) analyzing the methane hydrate role as a geohazard, (6) establishing the means to detect and characterize methane hydrate accumulations using geologic and geophysical data, and (7) establishing the thermodynamic phase equilibrium properties of methane hydrates as a function of temperature, pressure, and gas composition. The U.S. Department of Energy (DOE) and the Consortium for Ocean Leadership (COL) combined their efforts in 2012 to assess the contributions that scientific drilling has made and could continue to make to advance our understanding of methane hydrates in nature. COL assembled a Methane Hydrate Project Science Team with members from academia, industry, and government. This Science Team worked with COL and DOE to develop and host the Methane Hydrate Community Workshop, which surveyed a substantial cross section of the methane hydrate research community for input on the most important research developments in our understanding of methane hydrates in nature and their potential role as an energy resource, a geohazard, and/or as an agent of global climate change. Our understanding of how methane hydrates occur in nature is still growing and evolving, and it is known with certainty that field, laboratory, and modeling studies have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information needed to advance our understanding of methane hydrates.

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Integrated Ocean Drilling Program Expedition 311 was conducted to study gas hydrate occurrences and their evolution along a transect spanning the entire northern Cascadia accretionary margin. A transect of four research sites (U1325, U1326, U1327, and U1329) was established over a distance of 32 km, extending from Site U1326 near the deformation front to Site U1329 at the eastern limit of the inferred gas hydrate occurrence zone. In addition to the transect, a fifth site (U1328) was established at a cold vent setting with active fluid and gas expulsion, which provided an opportunity to compare regional pervasive fluid-flow regimes to a site of focused fluid advection. In this synthesis, a revised gas hydrate formation model is proposed based on a combination of geophysical, geochemical, and sedimentological data acquired during and after Expedition 311 and from previous studies. The main elements of this revised model are as follows:1. Fluid expulsion by tectonic compression of accreted sediments at nonuniform expulsion rates along the transect results in the evolution of variable pore water regimes across the margin. Sites closer to the deformation front are characterized by pore fluids enriched in dissolved salts at depth, where zeolite formation from ash diagenesis is dominant. In contrast, the landward portion of the margin shows a freshening of pore fluids with depth as a result of the progressive overprinting of diagenetic salt generation with freshwater generation from the smectite-to-illite transition at greater depth. 2. In situ methane produced by microbial CO 2 reduction within the gas hydrate stability zone is the prevalent gas source for gas hydrate formation. 3. Some minor methane advection from depth is required overall to explain the occurrence of gas hydrate (and the associated downhole isotopic signatures of CH 4 and CO 2 ) within the sediments of the accretionary prism and the absence of gas hydrate within the abyssal plain sediments. In contrast, methane migrating from depth is a dominant source for gas hydrate formation at the cold vent Site U1328 (Bullseye vent). 4. Gas hydrate preferentially forms in coarser grained sandy/silt turbidites, resulting in very high local gas hydrate concentrations. Typically, gas hydrate occupies <5% of the pore space throughout the gas hydrate stability zone. Higher gas hydrate saturations were observed in intervals with abundant coarse-

Abstract:The thermal-stimulation test conducted on the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well in March of 2002 was designed to increase the in situ temperature of a portion of a well defined and constrained gas hydrate reservoir above the gas hydrate stability point, while maintaining constant pressure. Data collected, including surface and downhole instrumentation readings and data from advanced logging and seismic programs, were then used to calibrate numerical gas hydrate reservoirsimulation models and determine the kinetic and thermodynamic properties of the in situ gas hydrate.The thermal-stimulation test was successful: bottomhole temperature was increased to greater than 50°C during the test; gas from dissociated gas hydrate was produced, sampled, and flared at surface; and significant amounts of real-time downhole temperature and pressure data, as well as other scientific measurements, were obtained. L'essai de stimulation thermique a été une réussite : on a pu accroître la température au fond du puits à plus de 50°C durant l'essai; on a produit, échantillonné et brûlé à la surface du gaz naturel provenant de la dissociation des hydrates de gaz; et on a généré, entre autres données scientifiques, une quantité considérable de mesures de température et de pression, acquises en temps réel dans le puits.

A unique set of high-quality downhole shallow subsurface well log data combined with industry standard 3D seismic data from the Alaminos Canyon area has enabled the first detailed description of a concentrated gas hydrate accumulation within sand in the Gulf of Mexico. The gas hydrate occurs within very fine grained, immature volcaniclastic sands of the Oligocene Frio sand. Analysis of well data acquired from the Alaminos Canyon Block 818 #1 (''Tigershark'') well shows a total gas hydrate occurrence 13 m thick, with inferred gas hydrate saturation as high as 80% of sediment pore space. Average porosity in the reservoir is estimated from log data at approximately 42%. Permeability in the absence of gas hydrates, as revealed from the analysis of core samples retrieved from the well, ranges from 600 to 1500 millidarcies. The 3-D seismic data reveals a strong reflector consistent with significant increase in acoustic velocities that correlates with the top of the gas-hydrate-bearing sand. This reflector extends across an area of approximately 0.8 km 2 and delineates the minimal probable extent of the gas hydrate accumulation. The base of the inferred gas-hydrate zone also correlates well with a very strong seismic reflector that indicates transition into units of significantly reduced acoustic velocity. Seismic inversion analyses indicate uniformly high gas-hydrate saturations throughout the region where the Frio sand exists within the gas hydrate stability zone. Numerical modeling of the potential production of natural gas from the interpreted accumulation indicates serious challenges for depressurization-based production in settings with strong potential pressure support from extensive underlying aquifers.

In the Mallik 2002 Gas Hydrate Production Research Well Program, formation tests with a Modular Formation Dynamics Tester (MDT)TM tool were conducted and the test results were analyzed using conventional pressure-transient test-analysis methods. The reliability of the reservoir-parameter estimates, however, is uncertain because of the abrupt change in gas hydrate saturation associated with gas hydrate dissociation during the tests. To investigate the applicability of these methods, the bottomhole-pressure responses during MDT tests in the hypothetical and actual gas hydrate zones were predicted using a numerical simulator and then analyzed by conventional test-analysis methods. This study revealed that the conventional methods might indicate the average effective permeability over the area of gas hydrate dissociation, and that they might accurately suggest the radius of gas hydrate dissociation only when applying appropriate multiphase-fluid properties and production rates to the cases with high gas hydrate saturation.

The JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well was drilled in February and March, 1998, in the Mackenzie Delta, Northwest Territories, Canada, to a depth of 1150 m. The scientific program was conducted through a collaborative agreement between the Japan National Oil Corporation and the Geological Survey of Canada with key participation by the Japan Petroleum Exploration Company and the United States Geological Survey. A primary objective of the well was to undertake a comprehensive scientific research program to study an arctic gas hydrate accumulation. Field research conducted as part of the Mallik 2L-38 program included collection of permafrost and gas-hydrate-bearing core samples, downhole geophysical logging, and a vertical seismic profile survey. Laboratory and modelling studies undertaken during the field program, and subsequently as part of a post-field research program, documented the sedimentology, biostratigraphy, physical/petrophysical properties, pore-water and gas geochemistry, geophysics, and reservoir characteristics of the Mallik field gas hydrate accumulation.

Molecular and isotopic composition of gases from the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well demonstrate that the in situ gases can be divided into three zones composed of mixtures of microbial and thermogenic gases. Sediments penetrated by the well are thermally immature; thus the sediments are probably not a source of thermogenic gas. Thermogenic gas likely migrated from depths below 5000 m. Higher concentrations of gas within and beneath the gas hydrate zone suggest that gas hydrate is a partial barrier to gas migration. Gas hydrate accumulations occur wholly within zone 3, below the base of permafrost. The gas in gas hydrate resembles, in part, the thermogenic gas in surrounding sediments and gas desorbed from lignite. Gas hydrate composition implies that the primary gas hydrate form is Structure I. However, Structure II stabilizing gases are more concentrated and isotopically partitioned in gas hydrate relative to the sediment hosting the gas hydrate, implying that Structure II gas hydrate may be present in small quantities.