Characterisation of likelihood of gas hydrates occurrence in the South China Sea based on Bonferroni mean-based TOPSIS and fuzzy set theory

The efficiency of gas hydrate production depends on the success of gas exploration and occurrence evaluation. The existing evaluation models are generally univariate and only applicable to certain geological settings. This study presents a holistic approach to evaluate the likelihood of gas hydrate occurrence by supplying an index for mapping gas hydrate levels with depth. The approach integrates a generalised TOPSIS method with the fuzzy set theory. An expedition of gas hydrate conducted in the Shenhu area of the South China Sea was adopted as a case study to assess the reliability of the proposed index. As a multivariate model, the proposed approach enables the capture of non-linearity associated with gas hydrates in its entirety. The magnitude of the strength of the influential factor varies substantially from one site to another across the Shenhu area. The results also show that no site achieves the highest likelihood ‘Level V’. These results are consistent with the gas saturation values obtained using Archie’s relationship. For example, at SH4 and SH7, the values of the likelihood index are the highest between 170–185 m and 150–165 m, respectively, and the observed saturation at these locations varies from 20% (SH4) to 43% (SH7). The proposed likelihood index yields a prominent ability to quantify the level of occurrence of gas hydrates with depth at different sites. It appears to be an efficient multicriteria system bound to improve the management of the gas production trial stage.     

中国海相油气田勘探实例之八四川盆地磨溪气田嘉二气藏的勘探与发现

磨溪气田位于四川盆地川中古隆中斜平缓构造带南部,其嘉二气藏为一中型海相气藏,含气面积为179.45km2,主力产层为三叠系嘉陵江组嘉二2亚段。气藏勘探始于1979年,于2004年勘探取得突破,至2005年底探明地质储量为326.59×108m3,年产天然气4×108m3。气藏储层为局限海—蒸发海台地碳酸盐岩微相,储层的发育分布主要受沉积作用和成岩作用控制,气藏类型为岩性—构造复合圈闭,气藏气水关系复杂。论述了气藏的发现和勘探开发历程及气藏的基本地质特征,总结了取得勘探突破的实践、认识与启示。     

Coupled use of carbon isotopes and noble gas isotopes in the Potiguar basin (Brazil): Fluids migration and mantle influence

We used the carbon isotope ratios of hydrocarbons and CO₂, and the proportions of noble gas isotopes of associated gases from several geological provinces of the Potiguar Basin (Brazil) for gas/source rock correlation, and to determine maturity, post-genetic processes (migration, leakage, biodegradation), and to assess the possible interactions between hydrocarbons and surrounding waters. Barriers of permeability at the basin scale, the amount of water interacting with the accumulated hydrocarbons, proportion of meteoric water, and contamination of the fluids by the mantle were quantified for the distinct petroleum systems defined in this basin.     

The potential benefits to the basin modeling enterprise of modularization and incorporating organic and inorganic chemical change

Mineral and hydrocarbon resources in basins are produced by fluid movements whose nature is not fully understood. Flow models in realistically defined basins that predict chemical change are needed to make progress, but these models will be difficult to develop and keep vital. Two simple examples are given to illustrate what is required, and the challenges to basin modeling are then outlined. It is argued that the best strategy is to modularize existing physical and chemical codes and place as many of these modules as possible in the public domain. This will keep the modeling enterprise open to the new entry and continuing invigoration.     

Gas-hydrate promotion by smectite–bioproduct interactions

Gas hydrates accumulate on the Gulf of Mexico seafloor around hydrocarbon seeps in waters sufficiently deep to provide adequate pressure/temperature combinations. High microbial activities occur around the hydrate accumulations. To understand apparent catalytic effects of bioproducts on hydrate formation, the mechanism of sII hydrate nucleation in unconsolidated porous media was investigated in our laboratory. Because smectite clays interacting with biopolymers had been shown to promote laboratory hydrates by decreasing induction times, increasing formation rates and altering morphology, these materials commonly found in near-surface sediments were selected for study as possible nucleating agents. Dynamic light scattering (DLS) with a helium–neon laser was used to measure particle diameters down to about 2 nm. Scanning electron microscopy (SEM) was utilized to verify particle sizes and to give additional information on biopolymer–clay associations. This paper presents evidence that nanometer-sized particles of mineral–bioproduct associations of about 80 nm–450 nm diameter may act as nucleation sites for hydrate crystal initiations in sediments and then remain dispersed throughout the accumulated hydrate mass. Emulsan biopolymer was shown by SEM to apparently unfold and associate with the smectite (nontronite) in a backbone arrangement and to give multiple hydrate nucleation sites along a linear network. SEM and DLS measurements were in agreement on particle sizes and shapes. X-ray diffraction suggested that biopolymer intercalates the smectite interlayer, probably driven by clay associations with biopolymer hydrophilic groups. It is hypothesized that hydrocarbon gases attach to biopolymer hydrophobic fatty-acid branches protruding from clay interlayers and subsequently facilitate hydrate structure formation by interacting with nearby water associated with the hydrophilic segments of the biopolymer.     

龙须菜(Gracilaria lemaneiformis)多糖的分离纯化及其组成研究

以龙须菜粗多糖为原料,利用离子交换层析分离纯化,紫外光谱、醋酸纤维薄膜电泳和凝胶过滤层析法鉴定多糖的纯度及其分子量,同时进一步采用气相色谱分析龙须菜多糖的单糖组成.结果表明,利用蒸馏水、0.3mol/L NaCl和1.2mol/L NaCl溶液分步洗脱,DEAE-Sephadex A-25离子交换层析纯化得到龙须菜多糖的三个组分G1、G2和G3,得率分别为3.61%、69.26%、18.70%:G1、G2和G3均显示为单一电泳谱带和单一洗脱峰,无蛋白、核酸杂质,分子量依次为21993、48460、61031U;G2和G3的单糖组成主要为半乳糖、3.6-内醚半乳糖及少量葡萄糖;G2糖链通过1→2键与1→6键方式连接,存在非还原末端基及连三羟基,G3糖链则通过1→3键与1→2键方式连接.     

Sweden and the Baltic Sea pipeline: Between ecology and economy

Building a submarine pipeline in the Baltic Sea to transport natural gas from Russia to Germany contradicts targets to reduce fossil fuel dependency and seems to ignore a long history of environmental challenges in the area. This article examines the tensions between the environmental, economic, and national security arguments framing the Swedish government decision to allow the pipeline to be laid on the Baltic seabed passing through the Swedish economic zone. At first sight, the decision seems to run contrary to Sweden's ambitious environmental policy. However, by framing the issue within a broader understanding of the country's tradition of consensual decision-making, and considering the tensions and contradictions inherent in policies for sustainable development, the permission fits well with the logic that, in case of conflict, economic growth is given priority even when the environment is at stake.     

吹扫捕集-气相色谱/质谱法测定地下水中1,4-二噁烷

1,4-二噁烷有毒,极易进入生态系统对人体及环境造成危害,在自然环境中对水的亲和性较强,且不易为生物所降解,是地下水中一种新型有机污染物,已被世界卫生组织(WHO)定为一种受控物质。但仅有少数国家对地下水中1,4-二噁烷含量作出限量规定,如日本为50μg/L;我国在此方面尚未作出规定,有关检测方法也未见文献报道。吹扫捕集-气相色谱-质谱法(PT-GC/MS)具有分析快捷、方法简便、检出限低等优点,近年来被广泛应用于水样分析,本文应用该方法测定地下水中的痕量1,4-二噁烷。通过添加硫酸铵作为样品保护剂,提高了样品的保存时间及防止样品因微生物降解等因素产生变质的问题,同时改善了1,4-二噁烷吹扫脱附效果,仪器响应值提升了1倍。在优化的实验条件下,方法精密度为5.9%~6.6%;检出限为1.02μg/L,已经达到了WHO饮用水质量标准限量(0.05 mg/L)要求,且低于同位素稀释-GC-MS的检出限(3.2μg/L)。本方法可以满足地质调查及环境评价的需求。