The effect of slight to minor biodegradation on C<Subscript>6</Subscript> to C<Subscript>7</Subscript> light hydrocarbons in crude oils: a case study from Dawanqi Oilfield in the Tarim Basin,NW China

Light hydrocarbons (LHs) are one of the main petroleum fractions in crude oils, and carry much information regarding the genetic origin and alteration of crude oils. But secondary alterations—especially biodegradation—have a significant effect on the composition of LHs in crude oils. Because most of the LHs affected in oils underwent only slight biodegradation (rank 1 on the biodegradation scale), the variation of LHs can be used to describe more the refined features of biodegradation. Here, 23 crude oils from the Dawanqi Oilfield in the Tarim Basin, NW China, eleven of which have been biodegraded to different extents, were analyzed in order to investigate the effect of slight to minor biodegradation on C₆–C₇ LHs. The study results showed that biodegradation resulted in the prior depletion of straight-chained alkanes, followed by branched alkanes. In slight and minor biodegraded oils, such biodegradation scale could not sufficiently affect C₆–C₇ cycloalkanes. For branched C₆–C₇ alkanes, generally, monomethylalkanes are biodegraded earlier than dimethylalkanes and trimethylalkanes, which indicates that branched alkanes are more resistant to biodegradation, with the increase of substituted methyl groups on parent rings. The degree of alkylation is one of the primary controlling factors on the biodegradation of C₆–C₇ LHs. There is a particular case: although 2,2,3-trimethylbutane has a relative higher alkylation degree, 2,2-dimethylpentane is more resistant to biodegradation than 2,2,3-trimethylbutane. 2,2-Dimethylpentane is the most resistant to biodegradation in branched C₆–C₇ alkanes. Furthermore, the 2-methylpentane/3-methylpentane and 2-methylhexane/3-methylhexane ratios decreased steadily with increasing biodegradation, which implies that isomers of bilateral methyl groups are more prone to bacterial attack relative to mid-chain isomers. The position of the alkyls on the carbon skeleton is also one of the critical factors controlling the rate of biodegradation. With increasing biodegradation, Mango’s LH parameters K1 values decrease and K2 values increase, the values of n-heptane and isoheptane decrease, and the indices of methylcyclohexane and cyclohexane increase. LH parameters should be applied cautiously for the biodegraded oils. Because biodegraded samples belong to slight or minor biodegraded oils, the values of n-heptane and isoheptane from Dawanqi Oilfield can better reflect and determine the “Biodegraded” zone. When the heptane value is 0–21 and the isoheptane value is 0–2.6, the crude oil in Dawanqi Oilfield is defined as the “Biodegraded” zone.     

Nuclear field shift effects on stable isotope fractionation: a review

An anomalous isotope effect exists in many heavy element isotope systems (e.g., Sr, Gd, Zn, U). This effect used to be called the “odd–even isotope effect” because the odd mass number isotopes behave differently from the even mass number isotopes. This mass-independent isotope fractionation driving force, which originates from the difference in the ground-state electronic energies caused by differences in nuclear size and shape, is currently denoted as the nuclear field shift effect (NFSE). It is found that the NFSE can drive isotope fractionation of some heavy elements (e.g., Hg, Tl, U) to an astonishing degree, far more than the magnitude caused by the conventional mass-dependent effect (MDE). For light elements, the MDE is the dominant factor in isotope fractionation, while the NFSE is neglectable. Furthermore, the MDE and the NFSE both decrease as temperatures increase, though at different rates. The MDE decreases rapidly with a factor of 1/T², while the NFSE decreases slowly with a factor of 1/T. As a result, even at high temperatures, the NFSE is still significant for many heavy element isotope systems. In this review paper, we begin with an introduction of the basic concept of the NSFE, including its history and recent progress, and follow with the potential implications of the inclusion of the NFSE into the kinetic isotope fractionation effect (KIE) and heavy isotope geochronology.     

Internal Microanatomy and Zoological Affinity of the Early Cambrian Olivooides

The early Cambrian pentamerous microfossil Olivooides/Punctatus in South China, which is characterized by a diagnostic stellate tubular apex, has been well-known for its almost complete development sequence that can be confidently traced from embryos and hatched juveniles, to conical adults. However, its zoological affinity remains highly controversial. Here we describe the internal microanatomic structures of the soft-body inside the peridermal theca of Olivooides multisulcatus Qian, 1977, including interradial pairs of tentacles, adradial and perradial frenula, perradial oral marginal lappets and twins of perradial gastric saccule-like humps as well as a circular velarium with striated coronal muscles. Particularly, one specimen shows bifurcated velarial canals along the bell aperture. Both the components of the soft-body and the external theca (or cyst) are arranged in perfect pentaradial symmetry. These characteristics are more compatible with those of living cubomedusans and co-occurring Cambrian athecate embryonic cubozoans. Concerning the presence of peridermal theca, Olivooides most likely represents an extinct thecate stem-group cubomedusae but devoid of both perradial eyes and specialized pedalia. The well-grown soft body inside the peridermal tube displays a set of mixed features of both polyp and medusa.     

Study on the Global Carbon Assimilation System Based on Multisource Remote Sensing Data

The Paris agreement signed in April, 2016 aims to balance global anthropogenic carbon emissions and terrestrial carbon sinks by the middle of the 21^st century. To fulfill this goal, it is necessary to calculate carbon fluxes of different regions reliably. The global carbon assimilation system is an effective technique for achieving this goal. The Ministry of Science and Technology of China supports the project entitled as study on the global carbon assimilation system based on multisource remote sensing data through the national key research and development programs for global change and adaptation during the thirteen-five period. This project will develop synergic inversion techniques for retrieving key parameters of biological and atmospheric cycles and for assimilating multisource remote sensing and ground based data. Then, the high resolution global carbon assimilation system coupled with an ecological model will be constructed. This system is able to assimilate jointly multisource observation data and to optimize key model parameters, photosynthesis and respiration carbon fluxes of global terrestrial ecosystems, and anthropogenic carbon emission fluxes of key regions. This system will be used to study quantitatively the spatial and temporal patterns of carbon fluxes of global terrestrial ecosystems and anthropogenic carbon emission fluxes of key regions and to identify the mechanisms driving the global terrestrial carbon sinks and sources. The outputs of this study will be helpful for the fulfillment of the key research and development programs for global change and adaptation and provide valuable data and technical support for the decision-making in China.     

Comparative Study of the Carbon Emission Situation and Goals between China and India

As the two large developing and populous countries, China and India face the dual challenges of economic development and climate change. Both of them are active in carbon emissions reduction, while India also bears the pressure of being “benchmarked” against China. With taking China and India as the sample of a comparative analysis, and the statistical value of a long sequence as the basic analysis data, based on the detailed analysis and comparison of carbon emissions history, the carbon emissions situation of the two countries from various dimensions including economic development, energy reserves and consumption, etc. were comparatively analyzed. The carbon intensity and energy structure after achieving the objectives were measured and compared by focusing on the carbon emissions reduction targets in China and India. The comparative results show that: China’s total carbon emissions are greater than India’s, but the growth rate of emissions, per capita emissions are significantly lower than India’s, while the carbon intensity decreases significantly faster than that of India. China has taken more efforts to make commitments to carbon reduction than India. With India’s energy structure adjustment, the situation will be gradually better than that in China.     

Comparative Analysis of International Energy Consumption Characteristics and China's Countermeasures

With the rise of low carbon economy and the deterioration of the international energy situation, most countries in the world pay more attention to energy issues. In this paper, based on a comparison with several countries of large energy consumption, we used long sequence statistics to analyze the energy consumption characteristics from the world and the history, including energy consumption, energy consumption structure and energy efficiency, and then summed up the characteristics of energy consumption in developed countries, analyzed China's energy consumption process and the current stage, and found out the main problems of energy consumption in China. At last, countermeasures for the healthy development of China's energy were proposed, including actively promoting scientific and technological progress, upgrading energy structure, developing low carbon economy, rationalizing energy prices, improving the proportion of clean energy consumption and emphasizing synergistic effect on environment protection.     

昭通示范区黄金坝气田五峰—龙马溪组页岩气储层地质特征

昭通国家级页岩气示范区黄金坝气田是继礁石坝和长宁—威远之后中国又一个在页岩气勘探、开发领域实现重大突破的地区,为了系统地展示黄金坝气田页岩气资源富集的储层条件,为未来的勘探工作提供参考,以五峰—龙马溪组页岩气储层为研究对象,从区域地质条件、储层岩石学、物性和地球化学4个方面对该页岩气储层进行了综合研究。结果表明稳定的区域构造和良好的顶底板条件是黄金坝地区页岩气资源富集的关键,良好的保存条件使储层维持了较高的压力(压力系数1);较高的孔隙度(平均4%)和TOC含量(目的层2%)提供了良好的储集空间,使储层具有较高的含气量(1.35~3.48 cm3/g,平均2.50 cm3/g);天然气地球化学数据表明,区内天然气主要成分为CH4(97%),其次还含有少量的C2H6、C3H8和CO2;天然气同位素数据表明烃类C同位素组成发生了倒转,表明储层具有良好的封闭性。但储层孔隙系统较为复杂,且非均质性极强,从而导致渗透率较低,在储层改造施工过程中应予以充分考虑。总体上,黄金坝气田具有较好的开发前景,生产测试表明,区内直井压裂产量为0.5×104~3.5×104m3/d/井,水平井压裂产量可达12×104~40×104m3/d/井。     

云南建水腊里河超基性岩地质特征及其构造意义

川滇黔等地在二叠世晚期发生峨眉山玄武岩短期内大规模溢流喷发。滇西地区发育的镁铁—超镁铁质岩均被认为是峨眉山大火成岩省的产物,但在滇东地区却一直缺少该类岩石组合的报道。本文在滇东建水地区首次发现了腊里河超基性岩体,通过LA-ICP-MS锆石UPb定年分析表明该超基性岩先期形成年龄为(246±5.2)Ma,为晚二叠-早三叠世的产物,后期中侏罗世晚期(169.6±2.0)Ma(MSWD=3.5)发生岩浆活化。该超基性岩Mg#值平均为78.73,稀土元素表现出略微右倾的平坦型特征,Rb、Sr、Ba、Pb等大离子亲石元素相对富集,高场强元素Zr、Hf相对亏损,Ta异常富集。其地化特征表现出富集型地幔源区特征,与峨眉山玄武岩成因关系密切。晚二叠世建水地区由于地幔柱活动形成地表溢流玄武岩,在深部岩浆房由玄武质岩浆结晶分异作用形成超基性侵入岩,到中侏罗世晚期,伴随着华南地区发生多期次构造运动,先前存在于岩浆房中的超镁铁质岩经过后期热液改造活化,沿着断层裂隙侵入地表。     

涉及埃达克岩实验的若干基本概念与问题辨析

根据热力学原理,部分熔融是相变的一种表现形式。当岩石沿p-T轨迹穿过固相线时即可发生熔融。自然界岩石常见的不一致熔融行为可以导致残留相具有不同于源岩的整体成分与矿物组合。残留相与源岩可以属于不同的变质相,岩性也可以不同。"C型埃达克岩"含有含水矿物,它们不是干体系熔融的产物。实验岩石学研究表明,基性成分(SiO_250%)体系较中性、酸性体系在1.0~2.0 GPa压力条件下失水熔融时更易于形成"榴辉岩质"的残留相。源岩除SiO_2以外的其它主要氧化物会影响残留相中各矿物的比例,进而影响熔体的Sr、Y及HREE含量。因此,"C型埃达克岩"高Sr低HREE特征的形成取决于熔融温压条件以及源岩的主量元素、微量元素组成等多重因素。高钾含量(K_2O≈1.0%)的基性、中基性源岩形成的熔体成分与"C型埃达克岩"相比过于富Al或富Na。中等富钾的基性源岩的低程度熔融可以形成高硅的"C型埃达克岩",但无法形成中性的"C型埃达克岩"。