Geoscience

The Gas Hydrate Resources in the China Seas

YAO Bo-chu,YANG Mu-zhuang,WU Shi-guo，WANG Hong-bin

2008, 22(3): 333-341.

Asbtract ( 9329 )

PDF (5511KB) ( 2712 )

References | Related Articles | Metrics

The forming conditions of gas hydrate in the China seas according to the physical oceanography, palaeo-climate, sedimentary environment,and tectonic environment are discussed in this paper.The researching results show that the organism producibility is high and there are rich organic matters in sediments of the period 2，4，6 of oxygen-isotope in the South China Sea. In these periods the sedimentary velocity was very high, and there are very good material conditions for the formation of gas hydrate. In addition, since Pliocene, the Philippine Sea plate has collided with Asian plate in Taiwan area, extruding the northeast part of the South China Sea along northwest direction. Owning to the extruding force in the sediments the fluid is very active and it is benefit for the formation of the gas hydrate. We have collected the sedimentary samples containing the gas hydrates through the drilling on the northern slope of the South China Sea in 2007. In the Okinawa Trough of the East China Sea, some mud volcanoes or mud diapir structures and the active faults were found in the west slope of the trough. The sedimentary rates are high in Quaternary in the trough,from 10 cm/ka to 40 cm/ka. The BSRs in the seismic profiles show that there should exist the gas hydrates in the Okinawa Trough. For above reasons, we infer that gas hydrates are rich in the China seas.

Geological Factors for the Development and Newly Advances in Exploration of Gas Hydrate in East China Sea Slope and Okinawa Trough

LUAN Xi-wu, LU Yin-tao，ZHAO Ke-bin, SUN Dong-sheng, LI Jun

2008, 22(3): 342-355.

Asbtract ( 2087 )

PDF (1781KB) ( 485 )

References | Related Articles | Metrics

Up to now, East China Sea is the only marginal sea in which gas hydrate samples haven’t been revealed in the West Pacific. Based on the geological and geophysical data obtained both from our past several cruises and from other publications, geological factors including sedimentary sources, sedimentary thickness, source rock, sedimentation rate, temperature and pressure distribution that control gas hydrate development have been analysed. The paper points out that East China Sea has abundant sedimentary sources supplied mainly by Changjiang River and partly by Huanghe River which have the capability of transporting 1,498×10⁶ t of sediment each year from mainland China to East China Sea, Bohai Sea and Huanghai Sea. Several sedimentary centers have been clearly revealed along East China Sea Slope and west part of Okinawa Trough by our seismic data. Sediment thicknesses of those centers are all over 5 km with the earliest sediment layer since around Eocene or even Oligocene time. We believe that source rock is existing among the deeper part of the sediment center either Eocene layer or Oligocene layer which have already been confirmed as good quality source rock in East China Shelf Basin by drilling works, and hydrocarbons might be generated earlier from the source rock in those centers than in shelf basin due to higher temperature gradient in slope and trough area as comparing with that of the shelf area. Sedimentation rate along the slope and trough varies from several cm/ka to 400 cm/ka, with higher values mainly constraining in the sediment centers and delta area which is connecting to the end of slope canyons and distributing at the most west part of trough basin. Based on our measured sea floor temperature data, gas hydrates can only developed in the slope and trough area with water depth over than 600 m. Gas hydrates-stability-zone can be as thick as 650 m when take temperature gradient as 30 ℃/km, but thinning to northeast along the axis of Okinawa Trough and to northwest up to the slope as the water depth changing shallower and sea floor temperature changing warmer. Local geological structures like mud diapir, anticline, fracture system are quite common in the study area, and they mainly control the fluid migration forming a favorable environment for the gas hydrate development and preservation in the study area. Based on our analysis, and BSRs found on some seismic profiles, we believe that the reason for gas hydrates unrevealling in East China Sea as comparing with other marginal seas is mainly due to the relatively lower exploration level.

Marine Gas Hydrate System: State of the Art

2008, 22(3): 356-362.

Asbtract ( 2502 )

PDF (782KB) ( 1584 )

References | Related Articles | Metrics

Based on the summary of research progress on gas sources and formation mechanisms, geophysical and geochemical proxies, formation environments and geological models, distribution of marine gas hydrate, this paper points out and discusses the direction and scientific issues for formation mechanism research of marine gas hydrate in China.Many scientific data and samples such as the wire-line logging, in-situ temperature, properties, geochemical data and sediment cores, pore water, head space and void gas, microbiology samples, etc,were obtained through the gas hydrate drilling expedition in Shenhu area of the north slope of South China Sea in April-June 2007. So,Shenhu area is an ideal area for the research on formation mechanism and distribution pattern of marine gas hydrate. Focusing on the material basis, formation environment and process, responding index and formation system of gas hydrate, a series of research in the light of the interaction between gas, water, sediment and gas hydrate, geophysical and geochemical responding mechanism, coupling control of different conditions for gas hydrate formation should be carried out on the north slope of South China Sea.

Preliminary Discussion on Gas Hydrate Geological System

LU Zhen-quan, WU Neng-you, CHEN Jian-wen,GONG Jian-ming, WU Bi-hao

2008, 22(3): 363-375.

Asbtract ( 2294 )

PDF (2500KB) ( 1141 )

References | Related Articles | Metrics

In consideration of the discrepancy between gas hydrate theoretical prediction and its real occurrence, the inconsistent relationship between gas hydrate indicator and its existence, the irregular gas hydrate distribution law(vertically and horizontally)indicated by drilling and indirect evidence such as BSR around the world, how to strengthen studies on gas hydrate formation process and its distribution law seems practically significant in geological view. This paper attempts to bring forward the concept of gas hydrate geological system，which contains three components of gaseous hydrocarbon source subsystem, gas-bearing fluid migration sub-system and gas hydrate reservoir accumulation sub-system. In the meanwhile,some key gas hydrate geological systems are preliminarily summarized based on worldwide typical gas hydrate occurrences.

Micro-textures of Methane Seep Carbonates from the Northern South China Sea in Correlation with Fluid Flow

SU Xin, CHEN Fang, LU Hong-feng, HUANG Yong-Yang

2008, 22(3): 376-381.

Asbtract ( 3158 )

PDF (2163KB) ( 1015 )

References | Related Articles | Metrics

A small piece of carbonate concretion collected by research vessel “Haiyang 4” from about 3,000 m seafloor of northern South China Sea was analyzed. The piece of carbonates was identified as methane seep carbonate with 17% magnesium calcites andδ¹³C value of -61.403‰ and δ¹⁸O value of 3.560,6‰. The carbonate shows four micro-textures derived by methane degassing, fluid flow and organisms activities. Calcite rings occur commonly along the walls of vesicles. Inner walls of burrow(worm tubes)are also coated by carbonate rims. Bacterial filaments were found in the fractures or conduits of carbonate, which depended on the methane-rich fluid to survive. Fluid conduits and fractures were often filled by coarser sands, which resulted from fluid flow escaping along these conduits.

Diagenetic Environment and Implication of Seep Carbona-te Precipitations from theSouthwestern Dongsha Area，South China Sea

CHEN Zhong，YANG Hua-ping，HUANG Chi-yue，YAN Wen, LU Jun

2008, 22(3): 382-389.

Asbtract ( 2570 )

PDF (1881KB) ( 1226 )

References | Related Articles | Metrics

Cold fluids and authigenic carbonate precipitations at the seafloor are closely associated with gas hydrate dissociation, thus the identification and study on authigenic carbonates at cold fluids can be a key in the investigation for gas hydrates and seep communities. In this paper a comprehensive comparison has been performed on the lithology, chemical composition, isotope geochemistry and evaluation of seep carbonate precipitations collected from the Dongsha Islands area, Shenhu area and deepsea core of Site 1146, ODP Leg 184, South China Sea. Those seep precipitations are different in lithology, stable isotopes of carbon and oxygen, possibly reflecting their different diagenetic environments. Chemical compositions of TFe, AlAl₂O₃、TiO₂、K₂O、Na₂O、MnO and P₂O₅ are different in seep precipitations from the Dongsha Islands area and Shenhu area, implying they were influenced possibly by clay minerals and was micro Fe-, Mn-nodules or crusts, respectively. Cold fluid activity occurred once at the Shenhu area which was formed in early and later stages of seep precipitations. At least three times of cold fluid activities and several stages of carbonate precipitations were identified at the Dongsha Islands area, reflecting the difference in carbon sources and tectonics systems in two areas. It is concluded that gas hydrates could exist in the area of southern Dongsha Island, which were associated with thermogenic methane from deep sediments, and seep communities could also occur at that seafloor. This is a new access to investigate for gas hydrates and seep communities at the Southwestern Dongsha area.

Petrographic Characterization and Rare Earth Elements as Geochemical Tracers for Redox Condition of Seep Carbonates from Northwestern Black Sea

FENG Dong, CHEN Duo-fu

2008, 22(3): 390-396.

Asbtract ( 11463 )

PDF (3074KB) ( 2556 )

References | Related Articles | Metrics

Seep carbonate crusts described here were collected on the Romanian (RO)shelf(120 m water depth)and Ukrainian(UKR)slope(190 m water depth)of the Black Sea. X-ray diffraction investigations show that high-Mg-calcite and aragonite are the dominant minerals. Peloids and botryoidal aragonite in the carbonate crust suggest a genesis induced by bacterial metabolism at the seep sites. The content of rare earth elements(REE)of the 5% HNO_³treated solution of the carbonates are very low(0.068×10-6 to 2.817×10-6).The shale-normalized REE patterns of RO carbonate show significantly negative Ce anomalies, while that of UKR carbonate shows no Ce anomalies, indicating that RO and UKR seep carbonates were deposited in oxic and anoxic environments, respectively. The contents of REE and trace elements(e.g.V, Cd and U)are highest in microcrystalline, lowest in sparite, and intermediate in microspar, suggesting that the elements concentration of seep carbonate is a function of diagenesis. 

Stable Carbon and Oxygen Isotopes Characteristics of the Authigenic Carbonates in Recovered Sediments during IODP 311 Expedition

WANG Xiao-qin, WANG Jia-sheng, WEI Qing, CHEN Qi, LI Qing,HU Gao-wei, GAO Yu-ya

2008, 22(3): 397-401.

Asbtract ( 9433 )

PDF (979KB) ( 1143 )

References | Related Articles | Metrics

To understand better the responses of authigenic minerals in sediments of the gas hydrate geosystem, some authigenic carbonates in sediments from IODP 311 Expedition were analyzed for the purposes of studying their mineral components, textures, and stable carbon and oxygen isotopes. XRD and SEM results show that Fe-dolomites and calcites are the dominant minerals in the authigenic carbonates, which occurred mainly in porerich spheroids and unregular aggregations. The δ¹³C_PDBof collected authigenic carbonates recorded the typical extreme negative values is low to -41.50‰ , indicating the involvement of methane in the anaerobic oxidation of methane(AOM)under the methane seepage in gas hydrate geo-system. The δ¹⁸O_PDBof the authigenic carbonates generally decreased with depth, possibly implying a decreasing environment temperature during carbonate precipitation from lower(old) to upper(new) part of sediment column. This study thus has a significant meaning in exploring the potential marine gas hydrate in China and in deciphering the ancient methane hydrateassociated sedimentary records in the Earth history.

Study on the Authigenic Pyrites and Their Sulfur Stable Isotopes in Recovered Sediments during IODP 311 Expedition

CHEN Qi, WANG Jia-sheng, WEI Qing, WANG Xiao-qin, LI Qing, HU Gao-wei，GAO Yu-ya

2008, 22(3): 402-406.

Asbtract ( 3507 )

PDF (1911KB) ( 1792 )

References | Related Articles | Metrics

To understand better the response of authigenic minerals in sediments of the gas hydrate system, total 652 sediment samples recovered from IODP 311 Expedition were washed and all authigenic pyrites were picked up. SEM photographs show that pyrites occurred in forms of both microspheroids and cubic crystal aggregations,caused by microbial fossilization and inorganic processes,respectively. The stable sulfur isotopic compositions seem to have a wide range of δ³⁴S_CDT values from -35.4‰ to +53.6‰ for the processes of anaerobic oxidation of methane(AOM).Sea salt sulfate in the upper part of sediment column was dominantly reduced by AOM, and the remained sulfate involving reduction would probably cause positive sulfur isotopic excursion of pyrites. In the cold vent theδ³⁴S_CDT values increase gradually with depth from-35.83‰ near the top sediment to 32.49‰ in deep, indicating that more remained sulfates once involved in reduction under higher methane flux and more intensive AOM. This study will have important impact on exploring the potential marine gas hydrate in China and on deciphering the ancient methane derived sedimentary records in the Earth history.

Geochemical Characteristics of Hydrocarbon Gases and Their Origin from the Sediments of the South China Sea

ZHU You-hai, WU Bi-hao, LUO Xu-rong, ZHANG Guang-xue

2008, 22(3): 407-414.

Asbtract ( 9687 )

PDF (1883KB) ( 1053 )

References | Related Articles | Metrics

Hydrocarbon gases from sediments are the resources to form natural gas and gas hydrate, which could be measured by headspace gas, absorbed gas, and “extraction” gas(which released by acid treatment of the sediments). Total 767 samples of sediments from 473 stations were collected from the South China Sea, and were treated with acid to determine the concentrations of hydrocarbon gases. The methane concentrations range from 0.8 to 22,153.6 μl/kg with averagely 335.8 μl/kg, and six anomalous areas of higher methane concentrations are subdivided in the South China Sea, including the Taixinan Basin and the Dongsha Islands, the Bijianan Basin, the Qiongdongnan Basin and the Xisha Trough, the Zhongjiannan Basin and Zhongyebei Basin, the Wan'an Basin and Nanweixi Basin, and the Nansha Trough. However, the Nansha Trough is of the highest methane concentrations, and the Taixinan Basin is the secondly, respectively. Total 154 samples were been determined for carbon isotopic composition, whose δ¹³Cvalues of methane range from-101.7‰ to -24.4‰ with averagely -44.5‰(PDB).Furthermore, lower δ¹³Cvalues of methane(from -101.7‰ to -71.4‰)are observed in the Nansha Trough, which seem to be mainly microbial gas or mixed gas, whereas there are much 〖JP4〗more thermogenic gas in the other areas of the South China Sea, whose higher δ¹³C values(from -51.0‰ to -24.4‰)are discovered, respectively.

Gas Sources Genesis in the Gas Hydrate Discoveries and Potential Areas

GONG Jian-ming, ZHANG Min, CHEN Jian-wen, LI Jin, CHEN Li-ying，CHENG Hai-yan

2008, 22(3): 415-419.

Asbtract ( 3272 )

PDF (1013KB) ( 1306 )

References | Related Articles | Metrics

In order to study the gas sources genesis in gas hydrate discoveries and potential areas, gas-generating amounts of 58 sediment samples from 4 sites of ODP 204 Expedition have been modeled by 5 temperature points, gas chromatography is used to test the isotope from different temperature points. The test results show that methane carbon isotope(δ¹³C)is evidently heavier among the lower temperature modeling points, commonly larger than -40‰, displaying the isotopic feature of thermogenic gas; while the lighter δ¹³Ccould reach to -75.5‰ when the modeling temperature is higher than 55℃,showing the isotopic feature of biogenic gas. Integrated with the discussion of gas genesis of Dongsha potential area, the conclusions could be drawn as follows, gas genesis could be controlled by many factors, and correct gas genesis could be got through the combination of other factors besides the methane carbon isotope. 

Sea Floor Topography of Shallow Gas Hydrate Area:Data from Okhotsk Sea

LUAN Xi-wu,YUE Bao-jing

2008, 22(3): 420-429.

Asbtract ( 1253 )

PDF (4384KB) ( 1458 )

References | Related Articles | Metrics

Shallow gas hydrates had already been retrieved by gravity corer, busyness fishing net, and submersible machine on the sea floor and in the sediment near to the sea floor. However the formation mechanism of shallow gas hydrate, distribution of shallow gas hydrate, and also the relationship between shallow gas hydrate and sea floor topography still remain unclear. Based on the side scan sonar and sub-bottom profile data from 2006 gas hydrate cruise in the area of Okhotsk Sea, the paper found that shallow gas hydrates closely related to the dome structures. The dome structures were commonly found on the slope, especially along the Middle and Lower Sakhalin Slope which were about several hundred meters wide and several ten meters high. Different from sea floor sand waves and sand ridges, the dome structures were isolated structures but with a slightly longer and lower wing than that of the upper wing. Sub-bottom profile recorder also showed that buried dome structures also very well developed on the slope beneath a 30 cm modern sediment layer. A joint compress stress field from Deryugin basin to the Sakhalin Slope and also from north Sakhalin Slope to the South Sakhalin Slope along the strike slip fault along Sakhalin Slope was the main cause of the formation of the dome structures, and also the main cause of the diapir structures among the dome structures. Acoustic turbidity beneath the diapir structures clearly show the migration of free gases from deep to the gas hydrate stability zone and to the sea water body from the mini crater on top of the dome structure. Gas hydrates were formed due to the availability of free gas within the diapir structures from the bottom of gas hydrate stability zone up to the sea floor.

Submarine Landslide and Risk Evaluation on Its Instability in the Deepwater Continental Margin

WU Shi-guo, CHEN Shan-shan, WANG Zhi-jun,LI Qing-ping

2008, 22(3): 430-437.

Asbtract ( 5471 )

PDF (3936KB) ( 1515 )

References | Related Articles | Metrics

Submarine landslide is usually a kind of sedimentary process, which includes landslide and debris flow, and can transport sediment over several hundred kilometers. Therefore it leads to large scale slope instability,and makes great threats to deepwater oil platform, pipeline and seafloor cable and so on. Moreover, slope instability can probably cause destructive tsunami. Although various factors can trigger submarine slide, but earthquake and dissolution of gas hydrate have close relationship with formation of submarine slide. With the exploitation of deepwater oil field and the increasing development of abysmal sea project, more and more emphases are laid on the geologic process by people of the academia and industry circles. In this paper, we introduce the slide structure, identification criteria, triggering mechanism of landslide in the deepwater continental margin, and put forward the risk evaluation methods of submarine landslide.

Study on Recognizing Technology of Gas Hydrates Zone

SHA Zhi-bin，WANG Hong-bin，YANG Mu-zhuang，LIANG Jin-qiang，ZHANG Guang-xue，

2008, 22(3): 438-446.

Asbtract ( 2305 )

PDF (2863KB) ( 1110 )

References | Related Articles | Metrics

It is very difficult to distinguish gas hydrate zones from the normal profiles of stack or migration during interpretation of natural gas hydrates based on the seismic data,whereas the abnormal geophysical characteristic of gas hydrate zones can be shown preferably in the profiles of wavelet,inversions of velocity,model of velocity,fluid factor,inversions of wave impedance,instantaneous amplitude,apparent polarity and halftime energy.Some recognition technology of gas hydrate zones are collected from domestic and overseas,whilst some new ideas including the recognition of gas hydrate zones using the information of wavelet,velocity and other attributes,which can be applicable in the areas with no well,are put forward in this paper.The ideas and the methods mentioned in this paper might provide some valuable reference for the resource assessment of gas hydrates.

Well Logging Evaluation of Gas Hydrates in Shenhu Area，South China Sea

LU Jing-an,YANG Sheng-xiong,WU Neng-you,ZHANG Guang-xue,ZHANG Ming，LIANG Jin-qia

2008, 22(3): 447-451.

Asbtract ( 2484 )

PDF (2062KB) ( 1154 )

References | Related Articles | Metrics

The wireline logging was applied for recognizing the gas hydrate bearing zone in the drilling of Shenhu area, northern part of South China Sea. Altogether seven instruments which were natural gamma, resistivity, density, full wave sonic, temperature, caliper and neutron logging tools were employed. The main output parameters include GR, Rd(Rs),Den,Vp, temperature, Cali, Neutron counter and borehole orientation. These parameters play a very important role in identifying the depth of gas hydrate reservoir. This paper presented the operating approaches and procedures of logging in Shenhu area in detail. The preliminary evaluation and analysis were also made with the logging data from a drillhole ZK1 in a certain site.The results show good consistent between the porosity derived from density and that from resistivity,while the gas hydrate saturation determined from resistivity is higher than that from pore water analysis, the evaluation may be improved by combining with core data analysis. This study gives a good instruction for future formation evaluation of gas hydrates in China.

Characteristics of Thermoluminescence from Sediments and Its Implications in the Qiangtang Basin, Qinghai-Tibet Plateau

ZHANG Zhi-pan，ZHU You-hai, SU Xin

2008, 22(3): 452-456.

Asbtract ( 4932 )

PDF (2327KB) ( 986 )

References | Related Articles | Metrics

Thermoluminescences of sediments have been used in exploring oil and gas both on land and on marine，which has achieved great success. Owning to similarity between oil/gas and gas hydrate in origin and mechanism of migration, thermoluminescences could be used in exploration and exploitation of gas hydrate. 147 samples of sediments were collected from the Qiangtang Basin, Qinghai-Tibet Plateau for thermoluminescence survey. The results of thermoluminescence show that it is charactered by logarithm normal distribution and distinct abnormity. By integrating scientists’ achievement and our survey results, we concluded that the above thermoluminescence abnormities should be a high value abnormity of hydrate mineral resources. The thermoluminescence abnormities are concentrated in two areas, which indicates the approximate position of deep oil/gas or gas hydrate reservoirs, and has a great significance for the further research. 

Experiment of Simulation Natural Gas Migration Accompanying Hydrate Formation in Seepage System

GUAN Jin-an,FAN Shuan-shi,LIANG De-qing,ZHOU Xi-tang,WANG Wu-chang

2008, 22(3): 457-464.

Asbtract ( 2031 )

PDF (2094KB) ( 972 )

References | Related Articles | Metrics

Hydrate formation is a typical phenomenon of the interface transfer, and the nature of gas migration is the decisive factor for this transfer process. Some experiments have been done by simulating in-situ hydrate formation system by gas migrating in seepage system in a glass bubble cell. The phenomena in experiments indicate that gas migration can change the quality of mass and heat transfer of the interface between gas and liguid when hydrate is forming, and it’s a moving process of equilibrium curve. There will exist a “pseudo” buffer layer which has some distance of thickness in the interface between gas and liquid, and for gas migration, as long as gas reaches its saturation in solution in this buffer layer, the hydrate can form. The overburden stress in sediments capillary will gradually breed because of continuously hydrate formation in the course of gas migration, and will cause faults or fractures of the stratum matrix. Therefore,a new hydrate phase diagram must be built up in order to adapt the new characteristic of natural hydrate system brought by gas migration.

Study on Gas Hydrate Formation-dissociation and Its Acoustic Responses in Unconsolidated Sands

HU Gao-wei, YE Yu-guang,ZHANG Jian

2008, 22(3): 465-474.

Asbtract ( 2685 )

PDF (2761KB) ( 1056 )

References | Related Articles | Metrics

To improve our understanding of the evolvement of gas hydrate in sediments and its acoustic impact on unconsolidated sediments, methane gas hydrate was formed and then dissociated in 0.18-0.28 mm sands, and subsequent testing was conducted to enable acoustic properties and water contents to be measured with ultrasonic detection and time domain reflectometry(TDR). The results of testing on several runs of experiments show that both of gas hydrate formation and dissociation could be divided into three periods according to formation speed and dissociation speed, respectively. Based on the analysis of temperature and pressure data, it comes to the conclusion that hydrate forms at the surface of sediments first and dissociates gradually fast during the three periods of dissociation. Moreover, acoustic properties shows that methane gas hydrates have the ability to cement sand grains at hydrate contents around 0-1% leading to a sharp increase in compression velocity and wave attenuation in specimens with no hydrate in the pore space. Whilst hydrates form as a part of the pore fluid and cause the blanking of ultrasonic signal appearing at the period of saturation 1%-90% during gas hydrate formation and dissociation. Consequently, this study reveals the contact mechanism between gas hydrate and sediment grains and provides a new idea to explain seismic signals in oceanic geophysical exploration. 

Experimental Research of Methane Hydrate Dissociation

CHEN Qiang, YE Yu-guang, MENG Qing-guo, LIU Chang-ling

2008, 22(3): 475-479.

Asbtract ( 6210 )

PDF (1055KB) ( 1274 )

References | Related Articles | Metrics

Gas hydrates are considered to be a new kind of resources, it is critical to know the hydrate dissociation process to make good use of this resource. In this paper, simulation experiment is used to investigate the methane hydrate dissociation. There are two kinds of dissociation methods, one is isovolumetric dissociation and the other is normal pressure dissociation. The isovolumetric dissociation experiment is carried out at p=4.5 MPa, and the dissociation speed is fast during 5.18-8 ℃, and the reaction cell pressure has good relation with temperature. In the normal pressure dissociation, we use five different porous media to investigate the porous media effect during hydrate dissociation. The study is carried out at T=1 ℃ and we find that the dissociation speed is among 1.11×10^-5-2.41×10^-5 mol/s when the porous media radius are among 0.063-0.35 mm, but the speed is not proportional to the radius.

Formation and Raman Spectroscopic Characteristics of Nitrogen,Oxygen and Air Hydrates

LIU Chang-ling, YE Yu-guang, LU Hai-long, Ripmesster A John

2008, 22(3): 480-484.

Asbtract ( 5218 )

PDF (633KB) ( 2273 )

References | Related Articles | Metrics

The nitrogen hydrate, oxygen hydrate and air hydrate samples were synthesized at 16 MPa, 13 MPa and 15 MPa, respectively, at-20 ℃ in laboratory. The Laser Raman spectroscopy was used to investigate the characteristics of N—N and O—O stretching vibration in these samples. The results show that Raman shifts of N—N and O—O in the synthesized samples are very similar to those in natural samples. The Raman peak of N₂ is observed at 2,322.4 cm^-1 both in nitrogen hydrate and in air hydrate, while the Raman peak of O₂ at 1，547.8 cm^-1 in oxygen hydrate and air hydrate. The Raman spectroscopic observations on air hydrate dissociation suggest that air hydrate is a unit clathrate with N₂ and O₂ as guest molecules, rather than mixture of pure nitrogen hydrate and oxygen hydrate. The N₂ and O₂ molecules seem to occupy both the large and small cages of air hydrate together. Compared with the N/O ratio in air, O₂molecule is significantly enriched in the synthesized air hydrate with N₂/O₂ ratio of 2.4：1.

The Study on Effects of SDS and THF on Methane Hydrate Formation

TU Yun-zhong, JIANG Guo-sheng, ZHANG Ling, NING Fu-long, DOU Bi,WU Xiang

2008, 22(3): 485-488.

Asbtract ( 6653 )

PDF (801KB) ( 1183 )

References | Related Articles | Metrics

The artificial formation of methane gas hydrate is a critical stage for the experimental study on drilling in simulated gas hydrate bearing sediment. A natural gas hydrate formation and mini drilling experimental system was built to conduct methane hydrate formation experiments with addition of small quantity of dodecyl sodium sulfate(SDS)and tetrahydrofuran(THF). According to the results of the comparative experiment and an analysis of temperature and pressure data acquired during the experiment, the paper investigated the effects of SDS and THF on the formation rate and amount of methane hydrate. The author drew the conclusion that with the micro-scale use of these two additives, the formation of methane hydrate is significantly accelerated, and more methane hydrate is obtained. Thus, a great deal of time needed for experiment is saved，and spontaneously, it may be greatly convenient for further study on drilling fluid design of hydrate bearing sediment and mini drilling test on simulated gas hydrate strata. 

Table of Content