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1.
A series of tests were conducted in order to investigate the shear strength and deformation behavior of methane hydrate-bearing sediments during dissociation using the thermal recovery method or depressurization method. An innovative temperature-controlled high pressure triaxial apparatus which can reproduce the in situ conditions of hydrate reservoirs was used. The results indicate that: (1) the failure strength of isotropically consolidated methane hydrate-bearing sediments which dissociated completely using the thermal recovery method is less than that of pure Toyoura sand. However, the initial stiffness and volumetric strain are higher than that of pure Toyoura sand. (2) The thermal recovery method will cause the failure of methane hydrate-bearing sediments when the axial load is higher than the strength of methane hydrate-bearing sediments after dissociation. (3) The depressurization method will not cause collapse of methane hydrate-bearing sediments during depressurization. However, water pressure recovery will lead to failure when the axial load is larger than the strength of the methane hydrate-bearing sediments after dissociation. (4) The depressurization rate shows little effect on the ultimate deformation of methane hydrate-bearing sediments, while the initial deformation rate increases with increasing depressurization rate. (5) The larger the reduction of pore pressure, the larger axial strain and volumetric strain.  相似文献   

2.
Systematic analyses have been carried out on two gas hydrate-bearing sediment core samples, HYPV4, which was preserved by CH4 gas pressurization, and HYLN7, which was preserved in liquid-nitrogen, recovered from the BPXA-DOE-USGS Mount Elbert Stratigraphic Test Well. Gas hydrate in the studied core samples was found by observation to have developed in sediment pores, and the distribution of hydrate saturation in the cores imply that gas hydrate had experienced stepwise dissociation before it was stabilized by either liquid nitrogen or pressurizing gas. The gas hydrates were determined to be structure Type I hydrate with hydration numbers of approximately 6.1 by instrumentation methods such as powder X-ray diffraction, Raman spectroscopy and solid state 13C NMR. The hydrate gas composition was predominantly methane, and isotopic analysis showed that the methane was of thermogenic origin (mean δ13C = −48.6‰ and δD = −248‰ for sample HYLN7). Isotopic analysis of methane from sample HYPV4 revealed secondary hydrate formation from the pressurizing methane gas during storage.  相似文献   

3.
Hydro-thermo-chemo and mechanically coupled processes determine hydrate morphology and control gas production from hydrate-bearing sediments. Force balance, together with mass and energy conservation analyses anchored in published data provide robust asymptotic solutions that reflect governing processes in hydrate systems. Results demonstrate that hydrate segregation in clayey sediments results in a two-material system whereby hydrate lenses are surrounded by hydrate-free water-saturated clay. Hydrate saturation can reach ≈2% by concentrating the excess dissolved gas in the pore water and ≈20% from metabolizable carbon. Higher hydrate saturations are often found in natural sediments and imply methane transport by advection or diffusion processes. Hydrate dissociation is a strongly endothermic event; the available latent heat in a reservoir can sustain significant hydrate dissociation without triggering ice formation during depressurization. The volume of hydrate expands 2-to-4 times upon dissociation or CO2CH4 replacement. Volume expansion can be controlled to maintain lenses open and to create new open mode discontinuities that favor gas recovery. Pore size is the most critical sediment parameter for hydrate formation and gas recovery and is controlled by the smallest grains in a sediment. Therefore any characterization must carefully consider the amount of fines and their associated mineralogy.  相似文献   

4.
Abstract

It is important to understand the deformation mechanism of methane-hydrate specimens (MHSs) to avoid deforming the seabed during methane-hydrate production. For this purpose, discrete-element method (DEM) modelling is advantageous because it requires much less cost and effort compared to artificial specimens and in situ sediments. In this study, a method for generating DEM numerical simulation models of MHSs is proposed to study the deformation mechanism of MHSs. First, numerical models that consider the saturation of methane hydrate (SMH), following which the bi-axial compression of these models is simulated. The mechanisms controlling the shear strength of MHSs are verified and modified by investigating the stress–strain response behavior, crack-development process, and evolution of the void change rate (Echange) of MHSs. The increases of the peak strength and secant elastic modulus of the MHS with the increment of confining pressure follow parabolic relationships. Under different loading rates, the peak strength tends to increase parabolically with the increment of loading rate, while the relationship between the secant elastic modulus and loading rate is linear. Based on the testing results, empirical formulas of peak stress and elastic modulus are proposed for different confining-pressure and strain-rate conditions.  相似文献   

5.
A triaxial system is designed with a temperature range from-20 ℃ to 25 ℃ and a pressure range from 0 MPa to 30 MPa in order to improve the understanding of the mechanical properties of gas hydrate-bearing sediments.The mechanical properties of synthetic gas hydrate-bearing sediments (gas hydrate-kaolin clay mixture) were measured by using current experimental apparatus.The results indicate that:(1) the failure strength of gas hydrate-bearing sediments strongly depends on the temperature.The sediment’s strength increases with the decreases of temperature.(2) The maximum deviator stress increases linearly with the confining pressure at a low-pressure stage.However,it fluctuates at a high-pressure stage.(3) Maximum deviator stress increases with increasing strain rate,whereas the strain-stress curve has no tremendous change until the axial strain reaches approximately 0.5%.(4) The internal friction angles of gas hydrate-bearing sediments are not sensitive to kaolin volume ratio.The cohesion shows a high kaolin volume ratio dependency.  相似文献   

6.
Gases were analyzed from well cuttings, core, gas hydrate, and formation tests at the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well, drilled within the Milne Point Unit, Alaska North Slope. The well penetrated a portion of the Eileen gas hydrate deposit, which overlies the more deeply buried Prudhoe Bay, Milne Point, West Sak, and Kuparuk River oil fields. Gas sources in the upper 200 m are predominantly from microbial sources (C1 isotopic compositions ranging from −86.4 to −80.6‰). The C1 isotopic composition becomes progressively enriched from 200 m to the top of the gas hydrate-bearing sands at 600 m. The tested gas hydrates occur in two primary intervals, units D and C, between 614.0 m and 664.7 m, containing a total of 29.3 m of gas hydrate-bearing sands. The hydrocarbon gases in cuttings and core samples from 604 to 914 m are composed of methane with very little ethane. The isotopic composition of the methane carbon ranges from −50.1 to −43.9‰ with several outliers, generally decreasing with depth. Gas samples collected by the Modular Formation Dynamics Testing (MDT) tool in the hydrate-bearing units were similarly composed mainly of methane, with up to 284 ppm ethane. The methane isotopic composition ranged from −48.2 to −48.0‰ in the C sand and from −48.4 to −46.6‰ in the D sand. Methane hydrogen isotopic composition ranged from −238 to −230‰, with slightly more depleted values in the deeper C sand. These results are consistent with the concept that the Eileen gas hydrates contain a mixture of deep-sourced, microbially biodegraded thermogenic gas, with lesser amounts of thermogenic oil-associated gas, and coal gas. Thermal gases are likely sourced from existing oil and gas accumulations that have migrated up-dip and/or up-fault and formed gas hydrate in response to climate cooling with permafrost formation.  相似文献   

7.
Gas hydrate has been recognized as a potential energy resource in South China Sea (SCS). Understanding the acoustic response of gas hydrate formation in the SCS sediments is essential for regional gas hydrate investigation and quantification. The sediments were obtained from gravity core sampling at E 115°12.52363′ N 19°48.40299′. Gas hydrate was formed within a “gas + water-saturated SCS sediments” system. Combination of a new bender element technique and coated time domain reflectometry (TDR) was carried out to study the acoustic response of hydrate occurrence in SCS sediments. The results show the acoustic signal becomes weak when hydrate saturation (Sh) is lower than 14%. The acoustic velocities (Vp, Vs) of the sediments increase with Sh during hydrate formation, and Vs increases relatively faster when Sh is higher than 14%. These results indicate that tiny hydrate particles may firstly float in the pore fluid, which causes a significant acoustic attenuation, but has little influence on shear modulus. As time lapses and Sh approaches 14%, numerous particles coalesce together and contact with sediment particles. As a result, Vs has a sharp increase when hydrate saturation exceeds 14%. Several velocity models were validated with the experimental data, which suggests a combination of the BGTL (Biot–Gassmann Theory modified by Lee) model and the Weighted Equation is suitable to estimate Sh in SCS.  相似文献   

8.
ABSTRACT

The purpose of this paper is to analyze the stability of submarine slope during the natural gas hydrate dissociation. A model is deduced to calculate the excess pore fluid pressure. In addition, a new method is proposed to define and calculate the factor of safety (FoS) of the submarine slope. Case study is also performed, results of which show that dissociation of hydrates would decrease the stability of submarine slope. If the cohesion of the hydrate-bearing sediments is small, the submarine slope would become unstable because of the shear failure. If the cohesion of the hydrate-bearing sediments is large enough, the tensile failure would happen in the hydrate-bearing sediments and the excess pore pressure may explode the submarine slope. Under the drained condition, the submarine slope may remain stable because the buildup of excess pore fluid pressure could not take place. Moreover, FoS would be underestimated by the assumption that natural gas hydrates dissociate in the horizontally confined space, but would be overestimated by only taking into account of the base of the natural gas hydrate-bearing sediments. The compressibility factor of natural gas should also be considered because treating natural gas as ideal gas would underestimate the stability of submarine slope.  相似文献   

9.
Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct–Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C1 through C5) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg− 1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH4. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH4 concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis.  相似文献   

10.
The Taixinan Basin is one of the most potential gas hydrate bearing areas in the South China Sea and abundant gas hydrates have been discovered during expedition in 2013. In this study, geochemical and microbial methods are combinedly used to characterize the sediments from a shallow piston Core DH_CL_11(gas hydrate free) and a gas hydrate-bearing drilling Core GMGS2-16 in this basin. Geochemical analyses indicate that anaerobic oxidation of methane(AOM) which is speculated to be linked to the ongoing gas hydrate dissociation is taking place in Core DH_CL_11 at deep. For Core GMGS2-16, AOM related to past episodes of methane seepage are suggested to dominate during its diagenetic process; while the relatively enriched δ18O bulk-sediment values indicate that methane involved in AOM might be released from the "episodic dissociation" of gas hydrate.Microbial analyses indicate that the predominant phyla in the bacterial communities are Firmicutes and Proteobacteria(Gammaproteobacteria and Epsilonproteobacteria), while the dominant taxa in the archaeal communities are Marine_Benthic_Group_B(MBGB), Halobacteria, Thermoplasmata, Methanobacteria,Methanomicrobia, Group C3 and MCG. Under parallel experimental operations, comparable dominant members(Firmicutes and MBGB) are found in the piston Core DH_CL_11 and the near surface layer of the long drilling Core GMGS2-16. Moreover, these members have been found predominant in other known gas hydrate bearing cores, and the dominant of MBGB has even been found significantly related to gas hydrate occurrence. Therefore,a high possibility for the existing of gas hydrate underlying Core DH_CL_11 is inferred, which is consistent with the geochemical analyses. In all, combined geochemical and microbiological analyses are more informative in characterizing sediments from gas hydrate-associated areas in the South China Sea.  相似文献   

11.
Gas hydrate stability conditions restrict the occurrence of gas hydrate to unconsolidated and high water-content sediments at shallow depths. Because of these host sediments properties, seismic and well log data acquired for the detection of free gas and associated gas hydrate-bearing sediments often require nonconventional analysis. For example, a conventional method of identifying free gas using the compressional/shear-wave velocity (Vp/Vs) ratio at the logging frequency will not work, unless the free-gas saturations are more than about 40%. The P-wave velocity dispersion of partially gas-saturated sediments causes a problem in interpreting well log velocities and seismic data. Using the White, J.E. [1975. Computed seismic speeds and attenuation in rocks with partial gas saturation. Geophysics 40, 224–232] model for partially gas-saturated sediments, the difference between well log and seismic velocities can be reconciled. The inclusion of P-wave velocity dispersion in interpreting well log data is, therefore, essential to identify free gas and to tie surface seismic data to synthetic seismograms.  相似文献   

12.
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   

13.
In natural gas hydrate marine settings, cold seepage of methane fluid is a widely observed phenomenon, where authigenic minerals serve as an indication of potential gas hydrate-bearing reservoirs at depth. In this study, based on the data from the site HD196 near Dongsha Island, northern continental slope of South China Sea, laboratory experiments and numerical simulation studies were conducted to investigate the biogeochemical processes of authigenic mineral formation induced by methane seepage. The bioreactor experimental results show that in response to methane flux, pH increased to 8.5 after 20 days of reaction, and Eh declined rapidly first and then remained unchanged at about 100 mV. The decrease in SO42−, HS− and HCO3− concentrations indicated the occurrence of anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR). The depletion of Fe2+ implied the formation of iron-bearing minerals, e.g., iron sulfides. Carbonate minerals were also identified in the experimental phase of this study. Most iron sulfides existed as massive pieces, and in some cases as spherical or rod-shape pieces. The calcium carbonates were observed as blocky pieces. Numerical simulations were also performed to reproduce the biogeochemical reactions that occurred in the reactor experiments. Based on experimental data, kinetic parameters associated with the observed reactions were calibrated. The model simulated results are general consistent with those obtained by the experiments conducted in this study. The combination of simulation and experimental studies provided a powerful tool to investigate the biogeochemical processes in the methane leakage environment at different temporal and spatial scales. This study gave a new perspective to understand the formation of cold seep authigenic minerals in marine sediments, and was significant for future investigations on the effects of hydrate decomposition.  相似文献   

14.
为评价水合物甲烷对底栖有孔虫群落结构和同位素的影响,对南海北部神狐海域获取天然气水合物的钻孔BY3岩心,进行底栖有孔虫群落结构和稳定同位素分析,发现含水合物层底栖有孔虫丰度、分异度下降,群落中以内生种占绝对优势,有孔虫破碎率增加;与不含水合物层中的底栖有孔虫相比,含水合物层的底栖有孔虫碳同位素值出现较明显的负偏移。含水合物层中的Uvigerinaspp.、Cibicidesspp.和Oridorsalisspp.的δ13C平均值分别为-1.61‰、-0.79‰和-1.80‰,而在不含水合物层它们的δ13C平均值分别为-0.88‰、-0.27‰和-1.04‰;其中Uvigerinaspp.和Oridorsalisspp.的δ13C最轻值均出现在含水合物层,分别为-1.83‰和-2.29‰。这些说明底栖有孔虫在生长和埋藏过程中可能受到沉积物中甲烷水合物形成和演化的影响。  相似文献   

15.
利用高压低温三轴仪对含水合物粉细砂进行剪切试验。分别用气饱和法与水饱和法制样，实现不同水合物饱和度和围压条件的三轴剪切，并分析含水合物砂的胶结作用对剪切特性的影响。试验结果表明：低饱和度时，气饱和与水饱和试样的偏应力差别不大；高饱和度时，制样方式对偏应力的影响较显著；水饱和试样的剪胀性大于气饱和试样，剪胀性随饱和度的升高和围压的降低而增大。峰值偏应力和稳态偏应力由黏聚力和摩擦力两部分组成，水合物的存在对稳态内摩擦角影响不大。  相似文献   

16.
The huge amount of methane hydrate deposits identified in deep marine sediments is considered as the new resource for future energy. Since carbonates are one of the major components of marine sediments, in the present study, an investigation has been made to study methane hydrate stability and kinetics in the presence of CaCO3 and MgCO3. Effect of the presence of carbonates on the solubility of methane in the system has also been examined as it directly affects the hydrate formation process. It has been observed that in presence of CaCO3 and MgCO3, the hydrate formation is inhibited. Comparative studies have also been done in the presence of artificial seawater to consider the effect of presence of different salts. Mole consumption of methane gas during hydrate formation in different carbonate samples was measured using real gas equation and found to be minimum in CaCO3 in seawater sample due to the combined effect of the presence of CaCO3 and different salts of seawater. An increase in nucleation and induction time was also observed demonstrating the inhibition of hydrate formation in the presence of these components. Further, the decrease in hydrate formation rate also confirmed the inhibition effect of CaCO3 and MgCO3 on hydrate formation.  相似文献   

17.
《Marine Geology》2001,172(1-2):1-21
In this paper we present and discuss the frequency-dependent behaviour of the acoustic characteristics of methane hydrate-bearing sediments in Lake Baikal, Siberia. Five different types of seismic sources (airgun-array, two types of single airguns, watergun and sparker) are used, encompassing a frequency bandwidth from 10 up to 1000 Hz. On low-frequency airgun-array data, the base of the hydrate stability zone (HSZ) is observed as a high-amplitude bottom-simulating reflection (BSR) with reversed polarity. The amplitude and continuity of the BSR decrease or even disappear on medium- to high-frequency data, a feature explained in terms of vertical and horizontal resolution. The increasing reflection amplitude of the BSR with increasing offset, the calculated reflection coefficient of the BSR and the occurrence of enhanced reflections below the BSR suggest the presence of free gas below the HSZ. The observation of some enhanced reflections extending above the BSR may be interpreted as an indication for free gas co-existing with hydrates within the HSZ. Amplitude blanking above the BSR is highly variable while the BSR itself appears to act as a low-pass frequency filter for medium- to high-frequency data.New single-channel airgun profiles provide the first seismic information across the Baikal Drilling Project (BDP-97) deep drilling site, at which hydrate-bearing sediments were retrieved at about 200 m above the base of the local HSZ. At the drilling site there are no seismic characteristics indicative of the presence of hydrates. Combination of the drilling and seismic information has allowed us to make a rough estimation of the volume of hydrates and carbon stored in the sediments of Lake Baikal, which lead us to conclude that the Lake Baikal gas hydrate reservoirs do not form a prospective energy resource.  相似文献   

18.
We studied specific lipid biomarkers of archaea and bacteria, that are associated with the anaerobic oxidation of methane (AOM) in a cold seep environment as well as the origin of sedimentary organic matter on the continental slope off NE Sakhalin in the Sea of Okhotsk. The organic geochemical parameters demonstrated that most of the sedimentary organic matter containing hydrate layers could be derived from marine phytoplankton and bacteria, except for a station (LV39-29H) which was remarkably affected by terrestrial vascular plant. Specific methanotrophic archaea biomarkers was vertically detected in hydrate-bearing cores (LV39-40H), coinciding with the negative excursion of the δ13Corg at core depths of 90–100 cm below the seafloor. These results suggest that methane provided from gas hydrates are already available substrates for microbes thriving in this sediment depth. In addition, the stable isotope mass balance method revealed that approximately 2.77–3.41% of the total organic carbon (or 0.036–0.044% dry weight sediment) was generated by the activity of the AOM consortium in the corresponding depth of core LV39-40H. On the other hand, the heavier δ13C values of archaeol in the gas hydrate stability zone may allow ongoing methanogenesis in deeper sediment depth.  相似文献   

19.
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   

20.
We report some main results of multidisciplinary investigations carried out within the framework of the Indian National Gas Hydrate Program in 2002–2003 in the Krishna–Godavari Basin offshore sector, east coast of India, to explore indicators of likely gas hydrate occurrence suggested by preliminary multi-channel seismic reflection data and estimates of gas hydrate stability zone thickness. Swath bathymetry data reveal new evidence of three distinct geomorphic units representing (1) a delta front incised by several narrow valleys and mass flows, (2) a deep fan in the east and (3) a WNW–ESE-trending sedimentary ridge in the south. Deep-tow digital side-scan sonar, multi-frequency chirp sonar, and sub-bottom profiler records indicate several surface and subsurface gas-escape features with a highly resolved stratification within the upper 50 m sedimentary strata. Multi-channel seismic reflection data show the presence of bottom simulating reflections of continuous to discrete character. Textural analyses of 76 gravity cores indicate that the sediments are mostly silty clay. Geochemical analyses reveal decreasing downcore pore water sulphate (SO4 2−) concentrations (28.7 to <4 mM), increasing downcore methane (CH4) concentrations (0–20 nM) and relatively high total organic carbon contents (1–2.5%), and microbial analyses a high abundance of microbes in top core sediments and a low abundance of sulphate-reducing bacteria in bottom core sediments. Methane-derived authigenic carbonates were identified in some cores. Combined with evidence of gas-escape features in association with bottom simulating reflections, the findings strongly suggest that the physicochemical conditions prevailing in the study area are highly conducive to methane generation and gas hydrate occurrence. Deep drilling from aboard the JOIDES Resolution during 2006 has indeed confirmed the presence of gas hydrate in the Krishna–Godavari Basin offshore.  相似文献   

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