EFFECT OF HYDRATION ON THE THERMAL STABILITY OF ENZYME

The thermal stability of New Zealand culture rabbit muscle aldolase was investigated by differential scanning calorimetry in the water content range 0.23-3.70 g water per g protein.The experimental results showed that at water contents below 0.47g/g,an endothermic peak was observed and at water contents above 0.57g/g,an endothermic and an exothermic peak were both observed on DSC thermogram.Thermal denaturation result of the enzyme and the relationship between two transition temperatures and water contents were first reported in this paper.Up to now we have not seen any similar reports concerning the exothermic transition.

Characteristics of Gas Hydrate Stability Zone and Resource Evaluation in Okinawa Trough

According to the processing and interpretation of multichannel seismic reflection data in the area of Okinawa Trough, the BSR （bottom simulating reflector） was identified in 16 seismic profiles. By means of special processing technologies such as AVO and waveform inversion, the authors, for the first time, directly used the BSR to outline the distribution tendency of thickness of gas hydrate stability zone in the Trough and thought that the largest stability zone thickness was in the south and the smallest in the north. Then through calculation the authors got the thickness of hydrate stability zone and resource of the hydrate. This would be useful to the future hydrate exploration and resource evaluation in the Okinawa Trough.

Methane hydrate stability in the presence of water-soluble hydroxyalkyl cellulose

The effect of low-dosage water-soluble hydroxyethyl cellulose （approximate MW～90,000 and 250,000） as a member of hydroxyalkyl cellulosic polymer group on methane hydrate stability was investigated by monitoring hydrate dissociation at pressures greater than atmospheric pressure in a closed vessel. In particular, the influence of molecular weight and mass concentration of hydroxyethyl cellulose （HEC） was studied with respect to hydrate formation and dissociation. Methane hydrate formation was performed at 2℃ and at a pressure greater than 100 bar. Afterwards, hydrate dissociation was initiated by step heating from -10℃ at a mild pressure of 13 bar to 3℃, 0℃ and 2℃. With respect to the results obtained for methane hydrate formation/dissociation and the amount of gas uptake, we concluded that HEC 90,000 at 5000 ppm is suitable for long-term gas storage and transportation under a mild pressure of 13 bar and at temperatures below the freezing point.

Heat flow pattern,base of methane hydrates stability zones and BSRs in Shenhu Area,northern South China Sea

Using the collected 433 heat flow values, we estimated the bases of methane hydrate stability zone （BHSZ）, in northern South China Sea （NSCS）. Through comparing BHSZs with the depths of bottom simulating reflectors （BSRs）, in Shenhu Area （SA）, we found that there are big differences between them. In the north of SA, where the water depth is shallow, many slumps developed and the sedimentation rate is high, it appears great negative difference （as large as -192%）. However, to the southeast of SA, where the water depth is deeper, sedimentation rate is relatively low and uplift basement topography exists, it changes to positive difference （as large as ＋45%）. The differences change so great, which haven＇t been observed in other places of the world. After considering the errors from the process of heat flow measurement, the BSR depth, the relationship of thermal conductivity with the sediments depth, and the fluid flow activities, we conclude that the difference should be not caused by these errors. Such big disagreement may be due to the misunderstanding of BSR. The deviant ＂BSRs＂ could represent the paleo-BSRs or just gas-bearing sediment layers, such as unconformities or the specific strata where have different permeability, which are not hydraterelated BSRs.

Geothermal investigation of the thickness of gas hydrate stability zone in the north continental margin of the South China Sea

The exploration of unconventional and/or new energy resources has become the focus of energy research worldwide,given the shortage of fossil fuels.As a potential energy resource,gas hydrate exists only in the environment of high pressure and low temperature,mainly distributing in the sediments of the seafloor in the continental margins and the permafrost zones in land.The accurate determination of the thickness of gas hydrate stability zone is essential yet challenging in the assessment of the exploitation potential.The majority of previous studies obtain this thickness by detecting the bottom simulating reflectors（BSRs） layer on the seismic profiles.The phase equilibrium between gas hydrate stable state with its temperature and pressure provides an opportunity to derive the thickness with the geothermal method.Based on the latest geothermal dataset,we calculated the thickness of the gas hydrate stability zone（GHSZ） in the north continental margin of the South China Sea.Our results indicate that the thicknesses of gas hydrate stability zone vary greatly in different areas of the northern margin of the South China Sea.The thickness mainly concentrates on 200–300 m and distributes in the southwestern and eastern areas with belt-like shape.We further confirmed a certain relationship between the GHSZ thickness and factors such as heat flow and water depth.The thickness of gas hydrate stability zone is found to be large where the heat flow is relatively low.The GHSZ thickness increases with the increase of the water depth,but it tends to stay steady when the water depth deeper than 3 000 m.The findings would improve the assessment of gas hydrate resource potential in the South China Sea.

Spatial distribution and inventory of natural gas hydrate in the Qiongdongnan Basin,northern South China Sea

Natural gas hydrate is a potential clean energy source and is related to submarine geohazard,climate change,and global carbon cycle.Multidisciplinary investigations have revealed the occurrence of hydrate in the Qiongdongnan Basin,northern South China Sea.However,the spatial distribution,controlling factors,and favorable areas are not well defined.Here we use the available high-resolution seismic lines,well logging,and heat flow data to explore the issues by calculating the thickness of gas hydrate stability zone(GHSZ)and estimating the inventory.Results show that the GHSZ thickness ranges between mostly~200 and 400 m at water depths>500 m.The gas hydrate inventory is~6.5×109-t carbon over an area of~6×104 km2.Three areas including the lower uplift to the south of the Lingshui sub-basin,the Songnan and Baodao sub-basins,and the Changchang sub-basin have a thick GHSZ of~250-310 m,250-330 m,and 350-400 m,respectively,where water depths are~1000-1600 m,1000-2000 m,and2400-3000 m,respectively.In these deep waters,bottom water temperatures vary slightly from~4 to 2℃.However,heat flow increases significantly with water depth and reaches the highest value of~80-100 mW/m2 in the deepest water area of Changchang sub-basin.High heat flow tends to reduce GHSZ thickness,but the thickest GHSZ still occurs in the Changchang sub-basin,highlighting the role of water depth in controlling GHSZ.The lower uplift to the south of the Lingshui sub-basin has high deposition rate(~270-830 m/Ma in 1.8-0 Ma);the thick Cenozoic sediment,rich biogenic and thermogenic gas supplies,and excellent transport systems(faults,diapirs,and gas chimneys)enables it a promising area of hydrate accumulation,from which hydrate-related bottom simulating reflectors,gas chimneys,and active cold seeps were widely revealed.

Acidolysis hydrocarbon characteristics and significance of sediment samples from the ODP drilling legs of gas hydrate

To study on the significance and basis of acidolysis index to China marine gas hydrate exploring, since 2006, 111 samples derived from Leg 164 and 204 of the Ocean Drilling Program （ODP） were analyzed in the experiment center of China Petroleum Exploration Research Institute to obtain data on acidolysis hydrocarbon index and methane carbon isotopes by the gas chromatography （GC） of PE AutoSystem XL and isotope mass spectrometer （IRMS） of Finnigan MAT25 I. Through these, we study the reliability of the acidolysis method and characterize the gas hydrate potential. The results show that the acidolysis hydrocarbon index has a stable correspondence with the Gas Hydrate Stability Zone （GHSZ） in the ODE and that there are clear abnormal signs in shallow samples that might reliably reflect the existence of authigenic carbonate caused by hydrocarbon migration from bottom hydrate. We therefore propose that the ability to characterize the acidolysis hydrocarbon is crucial to submarine gas hydrate exploration in China.

Comment on "Estimation of potential distribution of gas hydrate in the northern South China Sea" by Chunjuan Wang et al.

Herein we would like to comment on the paper ＂Estimation of potential distribution of gas hydrate in the northern South China Sea＂ by Wang et al. 2010 in Chinese Journal of Oceanology and Lirnnology, 28（3）： 693-699. The purpose of this comment is to point out that the given probabilities of gas hydrate occtwrence in the northern Zhujiang Mouth Basin and the Yinggehai Basin in the figure of Wang et al. （2010） are improper. After introducing our work of estimation of gas hydrate stability distribution in the northern South China Sea, we suggest that Wang et al. （2010） dismissed the basic P-T rule for the existence of gas hydrate. They should consider more the variables of water depth, seabed temperature and geothermal gradient in their gas hydrate distribution model in future studies.

Effects of salinity on methane gas hydrate system

Using an approximately analytical formation, we extend the steady state model of the pure methane hydrate system to include the salinity based on the dynamic model of the methane hydrate system. The top and bottom boundaries of the methane hydrate stability zone (MHSZ) and the actual methane hy-drate zone (MHZ), and the top of free gas occurrence are determined by using numerical methods and the new steady state model developed in this paper. Numerical results show that the MHZ thickness becomes thinner with increasing the salinity, and the stability is lowered and the base of the MHSZ is shifted toward the seafloor in the presence of salts. As a result, the thickness of actual hydrate occur-rence becomes thinner compared with that of the pure water case. On the other hand, since lower solubility reduces the amount of gas needed to form methane hydrate, the existence of salts in sea-water can actually promote methane gas hydrate formation in the hydrate stability zone. Numerical modeling also demonstrates that for the salt-water case the presence of methane within the field of methane hydrate stability is not sufficient to ensure the occurrence of gas hydrate, which can only form when the methane concentration dissolved in solution with salts exceeds the local methane solubility in salt water and if the methane flux exceeds a critical value corresponding to the rate of diffusive methane transport. In order to maintain gas hydrate or to form methane gas hydrate in marine sedi-ments, a persistent supplied methane probably from biogenic or thermogenic processes, is required to overcome losses due to diffusion and advection.