A kind of coccoid dinoflagellates-like fossils gives a new explanation of source of dinosterane in the Early-Middle Cambrian

The coccoid fossils covered with thick gelatinous envelop containing several gametes are discovered in gyps and salt deposits of Cambrian, H₄ well and chert bed of the base of Yuertus Formation (∈¹₁) of Xiaoerbulake Section. The fossils are described and compared with coccoid dinoflagellates. These fossils may be a coccoid life-cycle stage (vegetative cyst) of coccoid dinoflagellates. If this identification is correct, the coccoid dinoflagellates-like fossils could give a reasonable explanation of the dinoflagellate-specific biomarkers from Cambrian, H₄ well, Tarim Basin.     

The migration fractionation: an important mechanism in the formation of condensate and waxy oil

Fault-initiated pressure release within reservoirs and the injection of external excessive dry gas may result in occurrence of oil and gas phases. Because of different partitioning coefficients of compounds in two phase flow, lower-molecular-weight components are easier to dissolve in gas phase, yielding condensates, while higher-molecular-weight components are retained in the oil phase, yielding waxy oil cumulations. The fractionation process causes extensive compositional variability in aliphatic/aromatic hydrocarbon ratios, molecular compound distributions and carbon isotope ratios that are traditionally considered to be related to the source organic matter or the thermal maturity.     

尾部特征参数对气动阻力交互影响与全局优化研究

汽车尾部结构气动减阻优化时,各几何特征参数间往往存在此消彼长的现象,使得优化变得盲目而复杂.对此,为探明关键几何参数的交互影响规律,以Ahmed类车体为研究对象,在HD-2风洞试验对标验证基础上,对后背3个主要特征参数进行了CFD仿真研究,并在此基础上,为克服盲目性,应用集成优化平台对尾部特征参数进行优化设计.结果表明,后背倾角角度对减阻的贡献量最大,背部两侧圆角半径次之,后背顶部圆角半径最小;三者的改变对气动阻力的影响都具有非单调性;当后背倾角角度、后背顶部圆角半径和背部两侧圆角半径分别为13°、283 mm、58 mm时,能有效减小气动阻力,减阻率达到11.76%,为具体车型减阻优化研究提供借鉴.     

Study on sterols from brown algae （Sargassum muticum）

Significance of sterol compounds in studying bio- logical precursors, evolution and application of bio- markers in geological bodies and fossil fuels such as oil and coal resulted in a research upsurge during the 1970s―1980s, and a lot of papers were the…     

Influences of marine floor hydrothermal activity on organic matter abundance in marine carbonate rocks——A case study of middle-upper Proterozoic in the northern part of North China

FOR A LONG TIME, RESEARCHERS HAVE BEEN REGARDING THE BIOLOGICAL PRODUCTIVITY, THE SEDIMENTATION RATE, THE DEPOSITION ENVIRONMENT, AND THE PRESERVATION CONDITION OF THE DEPOSITIONAL ORGANIC MATTER AS THE CONTROLLING FACTORS OF ORGANIC MATTER ABUNDANCE IN T…     

Hydrocarbon sources and stages of reservoir formation in Kuqa depression, Tarim Basin

 Kuqa depression bears not only plenty ofnatural gas, but also a large amount of condensate and smallquantity of crude oil. Based on the geochemical correlationbetween the Jurassic and Triassic terrestrial hydrocarbonsource rock, this paper confirms that the natural gas in Kuqadepression belongs to coal-type gas and the main gas sourcerock is attributed to the middle to lower Jurassic coal seriesformation, while the main oil source rock is the upper Tri-assic lacustrine mudstone. The authors indicated that Kuqadepression was slowly subsided in Mesozoic, but rapidlywent down in Late Tertiary, which made the Jurassic andTriassic source rock suddenly deep-buried and rapidlyevolved to high and over-mature phase since 5 Ma. TheTriassic source rock is postponed to the Early Miocene dur-ing 23-12 Ma when entering the oil-generating peak, whilethe Jurassic is suspended to the latest 5 Ma, especially since2.5 Ma to the dry gas-generating period, which is one of thecharacteristics of the source rock thermal evolution in Kuqadepression. This paper presents a two-stage trapping andlate gas trapping model in Kuqa depression whose charac-teristics are: The main oil and gas reservoirs have differentsources. The oil reservoir is formed early while the gas res-ervoir is formed lately. During the early stage, it, mainly asoil, takes long distance lateral migration, while in the laterstage, it, mainly as gas, takes the vertical migration and alsohas lateral migration. The trap formed in different time onthe south and north sides of the depression and evolved intoa distributional pattern with oil in the south part and gas inthe north, also oil on the outer ring and gas on the inner ring.This paper points out that the late trapping of the naturalgas in Kuqa depression is favorable for the preservation oflarge gas fields.     

Molecular fossils and oil-source rock correlations in Tarim Basin, NW China

The distribution of "molecular fossils" (bio-markers) of steroid compounds in extracts from some spe-cific geologic age in the Tarim Basin have been analyzed andare used as the fingerprints for the oil-source rock correla-tion. Having been affected by maturation, migration, phasefractionation and biodegradation, not any molecular fossilsrelated to source and environment can be used as the finger-prints for oil-source rock correlation. Some special bio-markers widely existed in the extracts from Cambrian andOrdovician rocks in the Tarim Basin and showed obviousdifference in each stratum, including dinosteranes (C₃₀),4-methyl-24-ethyl-cholestanes (C₃₀) and their aromatizedsteroids, C₂₄-norcholestanes and C₂₈ steranes originated fromdinoflagellates and diatom. Few oils such as the heavy oildrilled in the Cambrian reservoir from Tadong 2 well (TD2)correlated well with the extracts from the Cambrian. Theamazing similarity of the relative contents of these com-pounds between the marine oils produced in Tazhong andTabei uplifts and the extracts from the Upper Ordoviciansuggests that the Middle-Upper Ordovician is the very likelymain source for the marine oils.     

Oil cracking： An important way for highly efficient generation of gas from marine source rock kitchen

The potentials of gas generation by kerogen in the late period and by crude oil cracking are closely related to the origin of natural gas in the high- to over mature marine area and their exploration perspectives. The carbon structure of kerogens, with different types and at different evolution stages, have been experimentally studied using the high magnetic field solid ^13C nuclear magnetic resonance technique in order to determine the oil and gas potential of kerogens. Results show that the contents of gas potential carbon（GPC） of types Ⅰ, Ⅱ, Ⅲ kerogens at the high- to over mature stage are very low, indicating their weak gas-generating capacity and limited gas production; however, the content of oil potential carbon（OPC） of the low mature type Ⅰ kerogen is much higher, implying that a large amount of crude oil generated during the oil-generating period will be the material for later gas generation by oil cracking. The kinetic experiment of gas generation by crude oil cracking shows that, when the temperature is about 160℃（R0=1.6%）, the crude oil will start to produce large amounts of gas; the temperature range for major gas generation of crude oil is higher than that of the kerogens, and the gas production is 2 to 4 times higher than that of kerogens. The natural gas derived from oil cracking （called oil-cracked gas） is much abundant in methyl hexamethylene, which is quite different from the natural gas produced by thermal degradation of kerogens （named kerogen degradation gas） at high- to over mature stage.