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1.
Drilling on Hydrate Ridge, offshore Oregon, during ODP Leg 204 enabled us to investigate fabrics of gas hydrate samples in
a wide depth range of the gas hydrate stability zone (GHSZ). X-ray computerized tomographic imaging on whole-round samples,
frozen in liquid nitrogen, revealed that layered gas hydrate structures are related to variable processes occurring at different
sediment depths. Shallow gas hydrates often form layers parallel or sub-parallel to bedding and also crosscut sedimentary
strata and other gas hydrate layers, destroying the original depositional fabric. The dynamic processes interacting with this
complicated plumbing system in this shallow environment are responsible for such highly variable gas hydrate fabrics. Gas
hydrate layers deeper in the sediments are most often dipping with various angles, and are interpreted as gas hydrate precipitates
filling tectonic fractures. These originally open fractures are potential candidates for free gas transportation, and might
explain why free gas can rapidly emanate from below the bottom-simulating reflector through the GHSZ to the seafloor.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
Drilling at the site UBGH1-9, offshore Korea in 2007, revealed varied gas-hydrate saturation with depth and a wide variety of core litholgies, demonstrating how the variations in the lithology are linked with those in gas-hydrate saturation and morphology. Discrete excursions to low chlorinity values from in situ background chlorinity level occur between 63 and 151 mbsf. In this occurrence zone, gas-hydrate saturations estimated from the low chlorinity anomalies range up to 63.5% of pore volume with an average of 9.9% and do not show a clear depth-dependent trend. Sedimentary facies analysis based on grain-size distribution and sedimentary structures revealed nine sediment facies which mainly represent hemipelagic muds and fine- to medium-grained turbidites. According to the sedimentary facies distribution, the core sediments are divided into three facies associations (FA): FA I (0–98 mbsf) consisting mainly of alternating thin- to medium-bedded hemipelagic mud and turbidite sand or mud beds, FA II (98–126 mbsf) dominated by medium- to very thick-bedded turbidite sand or sandy debris flow beds, and FA III (126–178 mbsf) characterized by thick hemipelagic mud without intervening discrete turbidite sand layers. Thermal anomalies from IR scan, mousse-like and soupy structures on split-core surfaces, non-destructive measurements of pressure cores, and comparison of gas-hydrate saturations with sand contents of corresponding pore-water squeeze cakes, collectively suggest that the gas hydrate at the site UBGH1-9 generally occurs in two different types: “pore-filling” type preferentially associated with thin- to medium-turbidite sand beds in the FA I and “fracture-filling” type which occurs as hydrate veins or nodules in hemipelagic mud of the FA III. Gas-hydrate saturation in the FA II is generally anomalously low despite the dominance of turbidite sand or sandy debris flow beds, suggesting insufficient methane supply. 相似文献
3.
T.S. Collett R.E. LewisW.J. Winters M.W. LeeK.K. Rose R.M. Boswell 《Marine and Petroleum Geology》2011,28(2):561-577
The BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well was an integral part of an ongoing project to determine the future energy resource potential of gas hydrates on the Alaska North Slope. As part of this effort, the Mount Elbert well included an advanced downhole geophysical logging program. Because gas hydrate is unstable at ground surface pressure and temperature conditions, a major emphasis was placed on the downhole-logging program to determine the occurrence of gas hydrates and the in-situ physical properties of the sediments. In support of this effort, well-log and core data montages have been compiled which include downhole log and core-data obtained from the gas-hydrate-bearing sedimentary section in the Mount Elbert well. Also shown are numerous reservoir parameters, including gas-hydrate saturation and sediment porosity log traces calculated from available downhole well log and core data. 相似文献
4.
G.J. Crutchley A.R. Gorman I.A. Pecher S. Toulmin S.A. Henrys 《Marine and Petroleum Geology》2011,28(10):1915-1931
Highly concentrated gas hydrate deposits are likely to be associated with geological features that promote increased fluid flux through the gas hydrate stability zone (GHSZ). We conduct conventional seismic processing techniques and full-waveform inversion methods on a multi-channel seismic line that was acquired over a 125 km transect of the southern Hikurangi Margin off the eastern coast of New Zealand’s North Island. Initial processing, employed with an emphasis on preservation of true amplitude information, was used to identify three sites where structures and stratal fabrics likely encourage focused fluid flow into and through the GHSZ. At two of the sites, Western Porangahau Trough and Eastern Porangahau Ridge, sub-vertical blanking zones occur in regions of intensely deformed sedimentary layering. It is interpreted that increased fluid flow occurs in these regions and that fluids may dissipate upwards and away from the deformed zone along layers that trend towards the seafloor. At Eastern Porangahau Ridge we also observe a coherent bottom simulating reflection (BSR) that increases markedly in intensity with proximity to the centre of the anticlinal ridge. 1D full-waveform inversions conducted at eight points along the BSR reveal much more pronounced low-velocity zones near the centre of the ridge, indicating a local increase in the flux of gas-charged fluids into the anticline. At another anticline, Western Porangahau Ridge, a dipping high-amplitude feature extends from the BSR upwards towards the seafloor within the regional GHSZ. 1D full-waveform inversions at this site reveal that the dipping feature is characterised by a high-velocity zone overlying a low-velocity zone, which we interpret as gas hydrates overlying free gas. These results support a previous interpretation that this high-amplitude feature represents a local “up-warping” of the base of hydrate stability in response to advective heat flow from upward migrating fluids. These three sites provide examples of geological frameworks that encourage prolific localised fluid flow into the hydrate system where it is likely that gas-charged fluids are converting to highly concentrated hydrate deposits. 相似文献
5.
《Marine and Petroleum Geology》2012,29(10):1915-1931
Highly concentrated gas hydrate deposits are likely to be associated with geological features that promote increased fluid flux through the gas hydrate stability zone (GHSZ). We conduct conventional seismic processing techniques and full-waveform inversion methods on a multi-channel seismic line that was acquired over a 125 km transect of the southern Hikurangi Margin off the eastern coast of New Zealand’s North Island. Initial processing, employed with an emphasis on preservation of true amplitude information, was used to identify three sites where structures and stratal fabrics likely encourage focused fluid flow into and through the GHSZ. At two of the sites, Western Porangahau Trough and Eastern Porangahau Ridge, sub-vertical blanking zones occur in regions of intensely deformed sedimentary layering. It is interpreted that increased fluid flow occurs in these regions and that fluids may dissipate upwards and away from the deformed zone along layers that trend towards the seafloor. At Eastern Porangahau Ridge we also observe a coherent bottom simulating reflection (BSR) that increases markedly in intensity with proximity to the centre of the anticlinal ridge. 1D full-waveform inversions conducted at eight points along the BSR reveal much more pronounced low-velocity zones near the centre of the ridge, indicating a local increase in the flux of gas-charged fluids into the anticline. At another anticline, Western Porangahau Ridge, a dipping high-amplitude feature extends from the BSR upwards towards the seafloor within the regional GHSZ. 1D full-waveform inversions at this site reveal that the dipping feature is characterised by a high-velocity zone overlying a low-velocity zone, which we interpret as gas hydrates overlying free gas. These results support a previous interpretation that this high-amplitude feature represents a local “up-warping” of the base of hydrate stability in response to advective heat flow from upward migrating fluids. These three sites provide examples of geological frameworks that encourage prolific localised fluid flow into the hydrate system where it is likely that gas-charged fluids are converting to highly concentrated hydrate deposits. 相似文献
6.
Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan 总被引：1，自引：0，他引：1
Sabine Kasten Kerstin N?then Christian Hensen Volkhard Spie? Martin Blumenberg Ralph R. Schneider 《Geo-Marine Letters》2012,32(5-6):515-524
The geochemical cycling of barium was investigated in sediments of pockmarks of the northern Congo Fan, characterized by surface and subsurface gas hydrates, chemosynthetic fauna, and authigenic carbonates. Two gravity cores retrieved from the so-called Hydrate Hole and Worm Hole pockmarks were examined using high-resolution pore-water and solid-phase analyses. The results indicate that, although gas hydrates in the study area are stable with respect to pressure and temperature, they are and have been subject to dissolution due to methane-undersaturated pore waters. The process significantly driving dissolution is the anaerobic oxidation of methane (AOM) above the shallowest hydrate-bearing sediment layer. It is suggested that episodic seep events temporarily increase the upward flux of methane, and induce hydrate formation close to the sediment surface. AOM establishes at a sediment depth where the upward flux of methane from the uppermost hydrate layer counterbalances the downward flux of seawater sulfate. After seepage ceases, AOM continues to consume methane at the sulfate/methane transition (SMT) above the hydrates, thereby driving the progressive dissolution of the hydrates “from above”. As a result the SMT migrates downward, leaving behind enrichments of authigenic barite and carbonates that typically precipitate at this biogeochemical reaction front. Calculation of the time needed to produce the observed solid-phase barium enrichments above the present-day depths of the SMT served to track the net downward migration of the SMT and to estimate the total time of hydrate dissolution in the recovered sediments. Methane fluxes were higher, and the SMT was located closer to the sediment surface in the past at both sites. Active seepage and hydrate formation are inferred to have occurred only a few thousands of years ago at the Hydrate Hole site. By contrast, AOM-driven hydrate dissolution as a consequence of an overall net decrease in upward methane flux seems to have persisted for a considerably longer time at the Worm Hole site, amounting to a few tens of thousands of years. 相似文献
7.
In western Canada gas hydrates have been thought to exist primarily in the Cascadia accretionary prism off southern Vancouver Island, British Columbia (BC). We present evidence for the existence of gas hydrate in folds and ridges of the Winona Basin up to 40 km seaward from the foot of the continental slope off northern Vancouver Island. The occurrence of a bottom-simulating reflector (BSR) observed in a number of vintage seismic reflection profiles is strongly correlated to faulted, and folded sedimentary ridges and buried folds. The observed tectonic structures of the Winona Basin are within the rapidly evolving Juan de Fuca - Cascadia - Queen Charlotte triple junction off BC. Re-processing of multi-channel data imaged mildly to strongly deformed sediments; the BSR is confined to sediments with stronger deformation. Changes in the amplitude character of sediment-reflections above and below the depth of the base of gas hydrate stability zone were also used as an indicator for the presence of gas hydrate. Additionally, regional amplitude and frequency reduction below some strong BSR occurrences may indicate free gas accumulations. Gas hydrate formation in the Winona Basin appears strongly constrained to folds and ridges and thus correlated to deeper-routed fluid-advection regimes. Methane production from in situ microbial activities as a source of gas to form gas hydrates, as proposed to be a major contributor for gas hydrates within the accretionary prism to the south, appears to be insufficient to produce the widespread gas hydrate occurrences in the Winona Basin. Potential reasons for the lack of sufficient in situ gas production may be that sedimentation rates are 5-100 times higher than those in the accretionary prism so that available organic carbon moves too quickly through the gas hydrate stability field. The confinement of BSRs to ridges and folds within the Winona Basin results in an areal extent of gas hydrate occurrences that is a factor of five less than what is expected from regional gas hydrate stability field mapping using water-depth (pressure) as the only controlling factor only. 相似文献
8.
Host sediments may exert a significant influence on the formation of gas hydrate reservoirs. However, this issue has been largely neglected in the literature. In this study, we investigated the types, characteristics and the depositional model of the fine-grained gas hydrate-bearing sediments in the northeastern margin of the South China Sea by integrating core visual observations and logging-while-drilling downhole logs. The gas hydrate-bearing sediments consist dominantly of muddy sediments formed in the inter-canyon ridges of the upper continental slope, including hemipelagites, debrites (mud with breccia) and fine-grained turbidites. Cold-seep carbonates and associated slumping talus, muddy breccia debrites, as well as coarse-grained turbidites, may locally occur. Four classes and six sub-classes of log facies were defined by cluster analysis. Core-log correlation indicates that gas hydrates are majorly distributed in fine-grained sediments with high resistivity and low acoustic transit time (AC) log responses, which are easily differentiated from the fine-grained background sediments of high gamma-ray (GR), high AC, and low resistivity log values, and the seep carbonates characterized by low GR, high resistivity, high density, low AC and low porosity log values. The primary host sediments consist of fine-grained hemipelagic sediments formed by deposition from the nepheloid layers of river material and from the microfossils in seawater column. Most of the hemipelagic sediments, however, might have been extensively modified by slumping and associated gravity flow processes and were re-deposited in the forms of debrites and turbidites. Locally developed seep carbonates associated with gas hydrate dissociation and leakage provided additional sources for the gravity flow sediments. 相似文献
9.
J. Joseph P. Kumar S. K. Dewri C. Tandi J. Singh 《Marine Georesources & Geotechnology》2016,34(5):450-464
The methane gas production potential from its hydrates, which are solid clathrates, with methane gas entrapped inside the water molecules, is primarily dependent on permeability characteristics of their bearing sediments. Moreover, the dissociation of gas hydrates, which results in a multi-phase fluid migration through these sediments, becomes mandatory to determine the relative permeability of both gaseous and aqueous fluids corresponding to different hydrate saturations. However, in this context, the major challenges are: (1) obtaining undisturbed in-situ samples bearing gas hydrates; and (2) maintenance of the thermodynamic conditions to counter hydrate dissociation. One of the ways to overcome this situation is synthesis of gas hydrates in laboratory conditions, followed by conducting permeability tests on them. In addition, empirical relationships that relate permeability of the gas hydrate bearing sediments to pore-structure characteristics (viz., pore size distribution and interconnectivity) can also be conceived. With this in view, a comprehensive review of the literature dealing with different techniques adopted by researchers for synthesis of gas hydrates, permeability tests conducted on the sediments bearing them, and analytical and empirical correlations employed for determination of permeability of these sediments was conducted and a brief account of the same is presented in this article. 相似文献
10.
11.
2015~2016年在神狐新钻探区钻遇大量水合物岩心，证实南海北部神狐新钻探区具有较好的水合物成藏环境和勘探前景。结合2008~2009年该区采集的地震资料，我们对晚中新世以来细粒峡谷的沉积特征及其相应的水合物成藏模式进行了分析。通过对大量地震剖面进行解释，发现该区峡谷两侧的隆起上发育大量的滑塌体。本文通过岩心粒度分析，地震相识别分析和水合物测井响应分析等手段综合识别出对水合物成藏有控制作用的三种类型的滑塌体：原生滑塌体、峡谷切割滑塌体、和同生断裂滑塌体。结合沉积速率、流体流速分析和峡谷迁移等沉积学要素对滑塌体成因进行分析，认为峡谷切割滑塌体由于后期峡谷迁移对前期滑塌体切割形成的、同生断裂滑塌体是由于隆起区基底不平引起差异性沉降而形成的。不同类型的滑塌体发育位置不同：原生滑塌体常发育在隆起中坡度较缓的区域、峡谷切割成因滑塌体常发育在不定向迁移的峡谷两侧、同生断裂滑塌体常发育在隆起中坡度起伏较大的区域。三种类型滑塌及其相应的水合物成藏模式不同，其中原生滑塌体有利于水合物成藏，而另外两种类型的滑塌体由于其不能对自由气进行有效封堵而不利于水合物成藏。根据三种滑塌体对水合物成藏的响应指出在粗粒的含有孔虫粉砂岩储层上，覆盖细粒的泥岩对自由气进行封堵有利于水合物成藏，并且多层的泥岩覆盖是造成水合物稳定带中水合物多个分层成矿现象出现的原因。 相似文献
12.
Nikolay G. Granin Sergey I. Muyakshin Mikhail M. Makarov Konstantin M. Kucher Il’ya A. Aslamov Liba Z. Granina Igor B. Mizandrontsev 《Geo-Marine Letters》2012,32(5-6):427-436
Methane bubble fluxes in gas flares from bottom sediments in Lake Baikal were estimated for the first time using hydroacoustic methods. Earlier work has demonstrated the occurrence of gas seeps both inside and outside of areas where bottom simulating reflectors were identified in seismic profiles. Fluxes ranged from 14 to 216 tons per year, with the flux for the entire area of the central and southern basins ranging from 1,400 to 2,800 tons per year. Comparison with other water bodies showed that fluxes from the most intensive Baikal flares were similar to those in the Norwegian and Okhotsk seas. Gas hydrates decompose at the lower boundary of the gas hydrate stability zone due to sedimentation. Calculation of the amount of methane produced due to sedimentation gave a total of between 2,600 and 14,000 tons per year for the central and southern basins of the lake. Based on rough estimation, the total flux from shallow- and deep-water gas seeps is similar to the amount of methane produced due to sedimentation. This suggests that gas hydrates possibly occupy much more than 10?% of the pore volume near the base of the gas hydrate stability zone, or that there are other reasons for gas hydrate dissociation and bubble flux from these bottom sediments. 相似文献
13.
We studied the microbial communities collected from hydrate-bearing sediments on the North Slope of Alaska to determine how abiotic variables (e.g., grain size, hydrate presence, formation fluid gases) may correspond to the type and distribution of microbes in the sediments. The cores were acquired from sub-permafrost, Eocene (46-55 million year old) sediments in the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well within which hydrates are believed to have formed 1.5 mya. Forty samples, eight of which originally contained hydrates, were acquired from depths of ca. 606-666 m below land surface. Five drilling fluid samples acquired from the same depth range were included in the analysis as a control for possible contamination by drilling fluid microbes during the drilling and handling of cores. DNA was extracted from 15 samples (typically <1 ng DNA/g sediment was recovered) and then amplified using polymerase chain reaction with primers specific for bacterial and archaeal 16S rDNA genes, which indicates the likelihood that microbes were present in all analyzed samples. Only bacterial DNA amplicons were detected. Terminal-restriction fragment length polymorphism (T-RFLP) was used to measure bacterial diversity in the respective samples. Non-metric multidimensional scaling (NMS) was used to determine the abiotic variables that may have influenced bacterial diversity. NMS analysis revealed that the microbial taxa present in the sediment were distinct from the taxa present in the drilling fluids suggesting that the sediments were not contaminated by the drilling fluids. Multi-response permutation procedures (MRPP) found no significant difference between three sample groups identified a priori as being from within a hydrate zone, outside of hydrate zone, or on the edge of a hydrate/non-hydrate zone according to downhole nuclear magnetic resonance spectroscopy logs. However, among the several other abiotic parameters that were evaluated mud gas methane concentration and variables related to hydrate presence (e.g., chloride concentration, salinity, and resistivity) appeared to define the arrangement of microbial community signatures in plots resulting from NMS analysis. Communities from hydrate and non-hydrate layers each contained unique taxa as determined by the T-RFLP assay. 相似文献
14.
Keith A. Kvenvolden 《Marine and Petroleum Geology》1985,2(1):65-71
Two sites of the Deep Sea Drilling Project in contrasting geologic settings provide a basis for comparison of the geochemical conditions associated with marine gas hydrates in continental margin sediments. Site 533 is located at 3191 m water depth on a spit-like extension of the continental rise on a passive margin in the Atlantic Ocean. Site 568, at 2031 m water depth, is in upper slope sediment of an active accretionary margin in the Pacific Ocean. Both sites are characterized by high rates of sedimentation, and the organic carbon contents of these sediments generally exceed 0.5%. Anomalous seismic reflections that transgress sedimentary structures and parallel the seafloor, suggested the presence of gas hydrates at both sites, and, during coring, small samples of gas hydrate were recovered at subbottom depths of 238m (Site 533) and 404 m (Site 568). The principal gaseous components of the gas hydrates wer methane, ethane, and CO2. Residual methane in sediments at both sites usually exceeded 10 mll?1 of wet sediment. Carbon isotopic compositions of methane, CO2, and ΣCO2 followed parallel trends with depth, suggesting that methane formed mainly as a result of biological reduction of oxidized carbon. Salinity of pore waters decreased with depth, a likely result of gas hydrate formation. These geochemical characteristics define some of the conditions associated with the occurrence of gas hydrates formed by in situ processes in continental margin sediments. 相似文献
15.
A marine controlled source electromagnetic (CSEM) campaign was carried out in the Gulf of Mexico to further develop marine electromagnetic techniques in order to aid the detection and mapping of gas hydrate deposits. Marine CSEM methods are used to obtain an electrical resistivity structure of the subsurface which can indicate the type of substance filling the pore space, such as gas hydrates which are more resistive. Results from the Walker Ridge 313 study (WR 313) are presented in this paper and compared with the Gulf of Mexico Gas Hydrate Joint Industry Project II (JIP2) logging while drilling (LWD) results and available seismic data. The hydrate, known to exist within sheeted sand deposits, is mapped as a resistive region in the two dimensional (2D) CSEM inversion models. This is consistent with the JIP2 LWD resistivity results. CSEM inversions that use seismic horizons provide more realistic results compared to the unconstrained inversions by providing sharp boundaries and architectural control on the location of the resistive and conductive regions in the CSEM model. The seismic horizons include: 1) the base of the gas hydrate stability zone (BGHSZ), 2) the top of salt, and 3) the top and bottom of a fine grained marine mud interval with near vertical hydrate filled fractures, to constrain the CSEM inversion model. The top of salt provides improved location for brines, water saturated salt, and resistive salt. Inversions of the CSEM data map the occurrence of a ‘halo’ of conductive brines above salt. The use of the BGHSZ as a constraint on the inversion helps distinguish between free gas and gas hydrate as well as gas hydrate and water saturated sediments. 相似文献
16.
南海神狐海域含水合物层粒度变化及与水合物饱和度的关系 总被引：12，自引：0，他引：12
为探讨沉积物粒度与水合物饱和度的关系,对南海神狐海域水合物钻探区2个获取水合物的钻孔岩心沉积物进行了粒度分析及粒度与水合物饱和度对比分析.结果表明,含水合物沉积物具有粉砂含量72％～82％、黏土含量小于30％、砂含量一般小于10％的基本特征,其中粉砂中以8～32和32～63 μm粒级的中细一粗粉砂占优势;该特征与上下不... 相似文献
17.
We investigate gas hydrate formation processes in compressional, extensional and un-faulted settings on New Zealand's Hikurangi margin using seismic reflection data. The compressional setting is characterized by a prominent subduction wedge thrust fault that terminates beneath the base of gas hydrate stability, as determined from a bottom-simulating reflection (BSR). The thrust is surrounded by steeply dipping strata that cross the BSR at a high angle. Above the BSR, these strata are associated with a high velocity anomaly that is likely indicative of relatively concentrated, and broadly distributed, gas hydrates. The un-faulted setting—sedimentary infill of a slope basin on the landward side of a prominent thrust ridge—is characterized by a strong BSR, a thick underlying free gas zone, and short positive polarity reflection segments that extend upward from the BSR. We interpret the short reflection segments as the manifestation of gas hydrates within relatively coarse-grained sediments. The extensional setting is a localized, shallow response to flexural bending of strata within an anticline. Gas has accumulated beneath the BSR in the apex of folding. A high-velocity zone directly above the BSR is probably mostly lithologically-derived, and only partly related to gas hydrates. Although each setting shows evidence for focused gas migration into the gas hydrate stability zone, we interpret that the compressional tectonic setting is most likely to contain concentrated gas hydrates over a broad region. Indeed, it is the only setting associated with a deep-reaching fault, meaning it is the most likely of the three settings to have thermogenic gas contributing to hydrate formation. Our results highlight the importance of anisotropic permeability in layered sediments and the role this plays in directing sub-surface fluid flow, and ultimately in the distribution of gas hydrate. Each of the three settings we describe would warrant further investigation in any future consideration of gas hydrates as an energy resource on the Hikurangi margin. 相似文献
18.
福建洛阳江河口湿地沉积物粒度特征及其沉积环境意义 总被引：4，自引：1，他引：3
沉积物粒度是反映湿地沉积环境的重要指标之一．利用Mastersizer2000型激光粒度仪对取自福建洛阳江河口不同类型湿地的6根短柱状沉积物样品进行了粒度分析．结果显示，该地区沉积物基本为粘土质粉砂，红树林湿地内的沉积物最细，分选程度最好；互花米草湿地圈闭了大量水流带来的粗、细颗粒物质，导致平均粒径相对较大，分选相对较差．粒度参数的相关分析结果显示，平均粒径与分选系数的显著正线性相关，揭示了该地区水动力作用弱、物质来源单一的沉积环境，显著增加了河口湿地沉积速率． 相似文献
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20.
Timothy S. Collett Myung W. LeeWarren F. Agena John J. MillerKristen A. Lewis Margarita V. ZyrianovaRay Boswell Tanya L. Inks 《Marine and Petroleum Geology》2011,28(2):279-294
In the 1960s Russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature. 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 portions of most continental margins worldwide. In 1995, the U.S. Geological Survey made the first systematic assessment of the in-place natural gas hydrate resources of the United States. That study suggested that the amount of gas in the gas hydrate accumulations of northern Alaska probably exceeds the volume of known conventional gas resources on the North Slope. Researchers have long speculated that gas hydrates could eventually become a producible energy resource, yet technical and economic hurdles have historically made gas hydrate development a distant goal. This view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology. One of the most significant developments was the completion of the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope, which along with the Mallik project in Canada, have for the first time allowed the rational assessment of gas hydrate production technology and concepts. Almost 40 years of gas hydrate research in northern Alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the North Slope. We have also seen in Alaska the first ever assessment of how much gas could be technically recovered from gas hydrates. However, significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern Alaska. 相似文献