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1.
天然气水合物的重要特征与评价及其在中国海域的勘探前景 总被引：1，自引：0，他引：1
从勘探技术和资源评价的角度综述了甲烷水合物生成和聚集的重要特征, 如地震反射剖面、测井曲线资料、地球化学特点等以及对未知区的地质勘探和选区评价 .甲烷水合物在地震剖面上主要表现为BSR(似海底反射)、振幅变形(空白反射)、速度倒置、速度-振幅结构(VAMPS)等,大规模的甲烷水合物聚集可以通过高电阻率(＞100欧姆.米)声波速度、低体积密度等号数进行直接判读.此项研究实例表明,沉积物中典型甲烷水合物具有低渗透性和高毛细管孔隙压力特点,地层孔隙水矿化度也呈异常值,并具有各自独特的地质特征.现场计算巨型甲烷水合物储层中甲烷资源量的方法可分为:测井资料计算法公式为:SW＝(abRw/φm.Rt)1/n;地震资料计算法公式为:ρp＝(1-φ)ρm+(1-s)φρw+sφρh、VH＝λ.φ.S.对全球甲烷水合物总资源量预测的统计达20×1015m3以上.甲烷水合物形成需满足高压、低温条件,要求海水深度＞300 m.因此,甲烷水合物的分布严格地局限于两极地区和陆坡以下的深水地区,并具有3种聚集类型:1.永久性冻土带;2.浅水环境;3.深水环境.深海钻探计划(DSDP)和大洋钻探计划(ODP)已在下述10个地区发现大规模的甲烷水合物聚集,他们是:秘鲁、哥斯达黎加、危地马拉、墨西哥、美国东南大西洋海域、美国西部太平洋海域、日本海域的两个地区、阿拉斯加和墨西哥湾地区.在较浅水沉积物岩心样中发现甲烷水合物的地区,包括黑海、里海、加拿大北部、美国加里福尼亚岸外、墨西哥湾北部、鄂霍茨克海的两个地区.在垂向上,甲烷水合物主要分布于海底以下2 000 m以浅的沉积层中.最新统计表明又主要分布于二个深度区间:200～450 m和700～920 m,前者是由ODP995～997站位发现的;后者在加拿大麦肯齐河三角洲马立克2L-38号井中897～922 m处发现.中国海域已发现多处甲烷水合物可能赋存地区,包括东沙群岛南部、西沙海槽北部、西沙群岛南部以及东海海域地区.姚伯初报道了南海地区9处地震剖面速度异常值的发现,海水深度为420～3 920 m,海洋地质研究所则在东海海域解释了典型BSR反射的剖面,具有速度异常、弱振幅、空白反射、与下伏反射波组具不整合接触关系(VAMPS)等,大致圈定了它们的分布范围,表明在中国海域寻找甲烷水合物具有光明的前景. 相似文献
2.
《Marine and Petroleum Geology》2003,20(2):163-175
Considerable attention has focussed on methane hydrates as a potential energy resource but much less on the potential environmental problems of exploiting these deposits. In fact, methane hydrate deposits represent a dynamic system formed as a result of the continuous migration of methane gas along fracture systems. Any exploitation of methane hydrates offshore will perforce take place in these unstable systems and could lead to the large-scale release of CH4 under unfavourable circumstances. However, most of this CH4 would be oxidized to CO2 within the water column under steady-state conditions. Only under exceptional circumstances would large-scale release of CH4 into the atmosphere take place. The impact of exploiting these deposits offshore on global climate may therefore be limited provided serious efforts are made to minimize environmental impacts. At present, prospects for the commercial exploitation of methane hydrates are in their infancy. Considerable ingenuity will be required to satisfy the requirements of safe operating conditions, mitigation of environmental hazards and commercial viability. The need to exercise caution before attempting to exploit these deposits is emphasized. 相似文献
3.
Evidence of shallow- and deep-water gas hydrate destabilizations in North Atlantic polar continental margin sediments 总被引：1，自引：0，他引：1
Destabilization of gas hydrates from the North Atlantic polar continental margins is geophysically detectable within hydrate
stability zones (HSZ). High-frequency seismic surveys of structures and propagation velocities of compressional waves have
changed the classic conception of a consistently stable hydrate zone. The results are important in two respects: (1) unstable
shallow-water gas hydrates can substantially contribute to the transfer of methane into the atmosphere, and (2) deep-water
gas hydrates also indicate destabilization, which results in slope instability with probably only a secondary role in the
transfer of methane to the atmosphere and thus in the greenhouse effect.
Received: 6 August 1997 / Revision received: 26 January 1998 相似文献
4.
To what extent methane liberated from marine hydrate will enter the ocean during a warmer world is unknown. Although methane release due to hydrate dissociation has been modelled, it is unclear whether or not methane will reach the seafloor during a warmer world and therefore contribute to oceanic and atmospheric budgets. Here we show, using a new three-dimensional (3-D) seismic dataset, that some hydrate deposits surround the gas chimneys passing through the HSZ. Bottom water warming since the last glacial maximum (LGM) is interpreted to cause hydrate dissociation but critically some of the released methane was not vented to the ocean. The released gas caused seal failure and free gas entered the hydrate stability zone (HSZ) through vertical gas chimneys to where new hydrate accumulations formed. This process is a new evidence for methane recycling and could account in part for the lack of methane in ice core records that cover warming events during the late Quaternary. This research provides new insight into how methane could be recycled rather than vented during a warmer world. 相似文献
5.
用地球化学方法勘查中国南海的天然气水合物 总被引：7，自引：0，他引：7
天然气水合物是一种未来新型能源,赋存于低温高压环境下的海洋沉积物中,但也可形成于大陆永久冻土带中。天然气水合物资源量巨大,具有经济和环境上的研究意义。近年来,国际上己对天然气水合物的产况、分布和形成机理开展了大量研究,但国内这方面的工作还刚刚开展。对中国南海的调查表明该区存在天然气水合物赋存的有利地质条件、温压条件和富含有机质的沉积条件。在南海的许多海区还发现了指示天然气水合物存在的地震标志(BSR)。介绍了在南海天然气水合物勘查中的地球化学异常标志。这些地球化学异常的产生可能与天然气水合物的形成或分解过程有关。研究内容包括沉积物中气体含量(主要为甲烷和乙烷),甲烷的碳同位素,孔隙水中阴离子(Cl^-、SO4^2-等)、阳离子(Ca^2 、Mg^2 、Ba^2 、Sr^2 ,B^3 和NH4^ 等)浓度和δ^18,δD,δ^11B,及^87Sr／^86Sr等同位素组成,此外还对海底沉积物的热释光特征和紫外、可见、近红外反射光谱特征开展了探索性研究。通过进一步加强理论和实验研究,结合地球物理和地球化学资料,在不远的将来将会在南海发现和圈定天然气水合物矿藏。 相似文献
6.
A Raman spectrometer extensively modified for deep ocean use was used to measure synthetic hydrates formed in an ocean environment. This was the first time hydrates formed in the ocean have been measured in situ using Raman spectroscopy. Gas hydrates were formed in situ in the Monterey Bay by pressurizing a Pyrex cell with various gas mixtures. Raman spectra were obtained for sI methane hydrate and sII methane + ethane hydrate. Gas occlusion resulting from rapid gas growth of methane hydrate was measured immediately after formation. The Raman shift for methane free gas was coincident with that of methane in the small 512 hydrate cage. The methane Raman peak widths were used to discriminate between methane in the free gas and hydrate phase. Methane + ethane sII hydrate was formed for 43 days on the seafloor. In this case, gas occlusion was not measured when the gas hydrates were allowed to form over an extended time period. Equivalent Raman spectra were obtained for the in situ and laboratory-formed sII methane + ethane hydrates, under similar p, T, and x conditions. With the Raman spectrometer operating in the ocean, seawater contributes to the Raman spectra obtained. Both the Raman bands for the sulfate ion and water were used to qualitatively determine the distribution of water phases measured (hydrate, seawater) in the Raman spectra. 相似文献
7.
There has been much interest in detecting the presence of methane gas in the ocean. Although methane exists predominantly as methane hydrate (a buoyant compound) in the deep ocean, recent computer simulations and anecdotal evidence have reported that these hydrates will decompose to produce methane bubbles in shallower waters. This paper describes how the quality factor Q of oscillating bubbles can be used to distinguish methane bubbles (Q=24) from the air bubbles (Q=34) which are ubiquitous near the ocean surface. Values of Q are reported for bubbles in water at atmospheric pressure containing air, carbon dioxide, argon, helium, methane and butane. Possible acoustic techniques for detecting and sizing methane bubbles in the ocean are discussed briefly. 相似文献
8.
U. von Rad U. Berner G. Delisle H. Doose-Rolinski N. Fechner P. Linke A. Lückge H. A. Roeser R. Schmaljohann M. Wiedicke SONNE / Scientific Parties M. Block V. Damm J. Erbacher J. Fritsch B. Harazim J. Poggenburg G. Scheeder B. Schreckenberger N. von Mirbach M. Drews S. Walter A. Ali Khan A. Inam M. Tahir A. R. Tabrez A. H. Cheema M. Pervaz M. Ashraf 《Geo-Marine Letters》2000,20(1):10-19
The Makran accretionary complex shows a distinct bottom-simulating reflector, indicating a thick gas-hydrate-bearing horizon
between the deformational front and about 1350 m water depth which seals off the upward flow of gas-charged fluids. A field
of presently inactive mud diapirs with elevations up to 65 m was discovered in the abyssal plain seawards of the deformation
front, suggesting that in the past conditions were favorable for periodic but localized vigorous mud diapirism. Regional destabilization
of the gas hydrate leading to focused flow was observed where deep-penetrating, active faults reach the base of the gas-hydrate
layer, as in a deeply incised submarine canyon (2100–2500 m water depth). At this location we discovered seeps of methane
and H2S-rich fluids associated with chemoautotrophic vent faunas (e.g., Calyptogena sp.). Driven by the accretionary wedge dynamics, the landward part of the gas-hydrate layer below the Makran margin is being
progressively uplifted. Due to reduced hydrostatic pressure and rising ocean bottom-water temperatures, gas hydrates are progressively
destabilized and dissociated into hydrate water, methane and H2S. Sediment temperatures lie outside the methane stability field wherever water depth is less than 800 m. Above this depth,
upward migration of fluids to the seafloor is unimpeded, thus explaining the abundance of randomly distributed gas seeps observed
at water depths of 350 to 800 m.
Received: 14 June 1999 / Revision accepted: 6 February 2000 相似文献
9.
N. Vedachalam S. Ramesh P. Udaya Prasanth G. A. Ramadass 《Marine Georesources & Geotechnology》2018,36(8):966-973
Natural gas hydrates is considered as a strategic unconventional clean hydrocarbon resource in the energy sector. Understanding the behavior of the rising methane gas bubbles during production leaks from the deep marine gas hydrate reservoirs well head is essential for environmental impact studies and to design environmental monitoring systems. Numerical model for quantitatively characterizing the vertical dissolution pattern of the wellhead released methane gas bubbles is analyzed for three potential gas hydrate locations in India. Simulation results indicate that the methane bubbles with diameter of 10?mm can transport methane gas till 650, 800, and 750?m from the seabed in the Krishna–Godavari(KG), Mahanadi and Andaman basins respectively. Results brought out that potential well head damage during methane hydrate production at 1050?m water depth could release up to 28?m3 of methane gas, in which 50% of the molar mass shall get dissolved within 40?m of water column from the seafloor. 相似文献
10.
We demonstrate the importance of investigation of the behavior of methane as a source of energy and an element of the Black-Sea
ecosystem affecting the global behavior of the climate. We describe the genesis of methane and the processes of its aerobic
and anaerobic oxidation. An especially important biogeochemical and ecological role is played by the anaerobic oxidation of
methane guaranteeing the formation of its effective sink inside the anaerobic zone and preventing its penetration into the
atmosphere as a greenhouse gas. On the basis of the analysis of the experimental data available from the literature, we also
discuss the principal regularities of the distribution of concentration of methane and its flows. It is shown that the formation
of methane hydrates at the bottom in the abyssal part of the Black Sea and the events of jet gas release on the periphery
of the basin can be regarded as the components of a single global process of gas release from the bottom of the Black Sea.
We present estimates of the components of methane budget in the Black Sea. The results of simulation of the dynamics of methane
bubbles and the processes of their gas exchange with the medium are analyzed. The data of hydroacoustic measurements are used
to evaluate the distribution of methane bubbles in sizes and the mass transfer of methane through the ocean–atmosphere interface.
Finally, we consider the methods of mathematical simulation of the distribution of methane in the ecosystem of the Black Sea.
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 40–56, September–October, 2008. 相似文献
11.
Preliminary studies of Caspian Sea have shown the possibility of gas hydrate accumulations, because of suitable physicochemical conditions, existence of clayey deposits, and high concentrations of organic matter. Studies have indicated that gas hydrates are mainly composed of methane. Therefore, based on physicochemical equations for methane hydrate stability in different pressure, temperature, and salinity, this study was designed to calculate the potential of gas hydrate formation in the Caspian Sea basin. For this, data of more than 600 locations were analyzed and in each location, upper and lower limits of methane hydrate formation zone were calculated. Then, the zoning maps of upper and lower limits were prepared which can be useful for exploring the gas hydrate as an energy source or predicting gas hydrate hazards. According to the calculations and maps, methane hydrate formation in Caspian Sea, theoretically, can take place from near the seabed to 4000 and 2500 m beneath the sea surface when low and high geothermal gradient are supposed, respectively. By comparing the results with gas hydrate zones revealed in geophysical profiles, it has been shown that, in Caspian Sea, gas hydrates probably accumulate near the lower limit when a high geothermal gradient is assumed. 相似文献
12.
Gas hydrates along continental margins are commonly inferred from the presence of bottom simulating reflectors (BSRs) on reflection seismic records. Shale and mud diapirs are often observed in the proximity of BSR-inferred gas hydrates. Analysis of data from documented gas-hydrate occurrences suggests that the areas where mud volcanoes exist on the seafloor are promising locations for sediments with high gas-hydrate concentration. Along the western continental margin of India (WCMI), we have identified several anomalous reflections on single-channel, analogue seismic records in the proximity of BSRs, from which the presence of gas-charged sediments and gas seepages was inferred. These features characterize both the shelf-slope region of the WCMI and the adjoining deep-sea areas. The seismic records also reveal mud/shale diapiric activity and pockmarks near the gas hydrates. 相似文献
13.
Microbial communities flourish at gas hydrate occurrences in ocean sediments. Studies are reported in this paper on the laboratory production, separation, characterization and hydrate catalysis of biosurfactants from cultures of the Bacillus subtilis bacterium associated with Gulf of Mexico gas-hydrate accumulations. The B. subtilis bacterium from ATCC 21332 species was cultured anaerobically with glucose as carbon-source to produce surfactin, one of the more potent surface active agents known. The surface-active agent was removed from the broth in foam created by bubbling inert gas through the mixture, and biosurfactant was then recovered from the collapsed-foam distilled water solution by acid precipitation and dichloromethane extraction. According to HPLC spectra, five surfactin isomers were identified in the sample of laboratory-generated biosurfactant. Recovered surfactin was then used to perform gas-hydrate formation studies in porous media saturated with the surfactin-water solution. Gas-hydrate induction time and formation rate determinations showed that the anaerobically-produced biosurfactants catalyzed hydrate formation markedly. The tests suggest prolific surfactin production by the B. subtilis bacterium and of other species under prevailing anaerobic conditions around seafloor gas hydrates that promotes hydrate formation and the propensity of the bioproduct to be dispersed in the porous media by natural gas vents. 相似文献
14.
A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits. The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system. 相似文献
15.
Methane can be released from the vast marine hydrate reservoirs that surround continents into oceans and perhaps the atmosphere. But how these pathways work within the global carbon cycle now and during a warmer world is only partially understood. Here we use 3-D seismic data to identify what we interpret to be a gas venting system that bypasses the hydrate stability zone (HSZ) offshore of Mauritania. This venting is manifested by the presence of the acoustic wipe-out (AWO) across a densely faulted succession above a salt diapir and a set of morphological features including a substantial, ∼260 m wide and ∼32 m deep, pockmark at the seabed. The base of the HSZ is marked by a bottom simulating reflector (BSR) which deflects upwards above the diapir, rather than mimicking the seabed. We use a numerical modelling to show that this deflection is caused by the underlying salt diapir. It creates a trapping geometry for gas sealed by hydrate-clogged sediment. After entering the HSZ, some methane accumulated as hydrate in the levees of a buried canyon. Venting in this locality probably reduces the flux of gas to the landward limit of feather edge of hydrate, reducing the volume of gas that would be susceptible for release during a warmer world. 相似文献
16.
17.
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
18.
Tove Nielsen Troels Laier Antoon Kuijpers Tine L. Rasmussen Naja E. Mikkelsen Niels Nørgård-Pedersen 《Geo-Marine Letters》2014,34(6):511-523
The present study is the first to directly address the issue of gas hydrates offshore West Greenland, where numerous occurrences of shallow hydrocarbons have been documented in the vicinity of Disko Bugt (Bay). Furthermore, decomposing gas hydrate has been implied to explain seabed features in this climate-sensitive area. The study is based on archive data and new (2011, 2012) shallow seismic and sediment core data. Archive seismic records crossing an elongated depression (20×35 km large, 575 m deep) on the inner shelf west of Disko Bugt (Bay) show a bottom simulating reflector (BSR) within faulted Mesozoic strata, consistent with the occurrence of gas hydrates. Moreover, the more recently acquired shallow seismic data reveal gas/fluid-related features in the overlying sediments, and geochemical data point to methane migration from a deeper-lying petroleum system. By contrast, hydrocarbon signatures within faulted Mesozoic strata below the strait known as the Vaigat can be inferred on archive seismics, but no BSR was visible. New seismic data provide evidence of various gas/fluid-releasing features in the overlying sediments. Flares were detected by the echo-sounder in July 2012, and cores contained ikaite and showed gas-releasing cracks and bubbles, all pointing to ongoing methane seepage in the strait. Observed seabed mounds also sustain gas seepages. For areas where crystalline bedrock is covered only by Pleistocene–Holocene deposits, methane was found only in the Egedesminde Dyb (Trough). There was a strong increase in methane concentration with depth, but no free gas. This is likely due to the formation of gas hydrate and the limited thickness of the sediment infill. Seabed depressions off Ilulissat Isfjord (Icefjord) previously inferred to express ongoing gas release from decomposing gas hydrate show no evidence of gas seepage, and are more likely a result of neo-tectonism. 相似文献
19.
The amount of methane leaked from deep sea cold seeps is enormous and potentially affects the global warming,ocean acidification and global carbon cycle. It is of great significance to study the methane bubble movement and dissolution process in the water column and its output to the atmosphere. Methane bubbles produce strong acoustic impedance in water bodies, and bubble strings released from deep sea cold seeps are called "gas flares"which expressed as flame-like strong backscatter in the water column. We characterized the morphology and movement of methane bubbles released into the water using multibeam water column data at two cold seeps. The result shows that methane at site I reached 920 m water depth without passing through the top of the gas hydrate stability zone(GHSZ, 850 m), while methane bubbles at site II passed through the top of the GHSZ(597 m) and entered the non-GHSZ(above 550 m). By applying two methods on the multibeam data, the bubble rising velocity in the water column at sites I and II were estimated to be 9.6 cm/s and 24 cm/s, respectively. Bubble velocity is positively associated with water depth which is inferred to be resulted from decrease of bubble size during methane ascending in the water. Combined with numerical simulation, we concluded that formation of gas hydrate shells plays an important role in helping methane bubbles entering the upper water bodies, while other factors, including water depth, bubble velocity, initial kinetic energy and bubble size, also influence the bubble residence time in the water and the possibility of methane entering the atmosphere. We estimate that methane gas flux at these two sites is 0.4×10~6–87.6×10~6 mol/a which is extremely small compared to the total amount of methane in the ocean body, however, methane leakage might exert significant impact on the ocean acidification considering the widespread distributed cold seeps. In addition, although methane entering the atmosphere is not observed, further research is still needed to understand its potential impact on increasing methane concentration in the surface seawater and gas-water interface methane exchange rate, which consequently increase the greenhouse effect. 相似文献
20.
The overall stability of marine strata holding gas hydrates is dependent on their shear strength characteristics. These characteristics, in turn, are dependent on thermal flux that is imposed for dissociation of the hydrates for the safe and efficient extraction of methane gas from the hydrate bearing sediments. Due to the imposition of thermal flux on these sediments, their fabric structure and pore space hydrate saturation changes, which impacts the overall stability of the sea bed. Estimating stability conditions in such a ‘multiphase and dynamic system’ necessitates collection of undisturbed samples without compromising their in-situ thermodynamic conditions. This is a daunting task given the huge cost of procuring samples and the challenge of maintaining an undisturbed sample with in-situ thermodynamic conditions till it is brought to the laboratory. Synthesizing hydrate bearing sample sediments in laboratory for conducting studies to identify heat migration mechanisms and thermal property measurements and linking them to the shear strength characteristics provides an affordable solution to this problem. With this in view, a critical review of the available literature, dealing with laboratory synthesis of hydrate bearing sediments, their thermal and strength characteristics, the coupled phenomenon of heat and fluid migration, and its impact on the overall stability of marine sediments, has been conducted and presented in this paper. This will facilitate understanding the factors governing and the mechanism of heat transfer in a multiphase system, the changes in the system brought about by the hydrate dissociation front, and the overall impact on the stability of seabed. 相似文献