塔里木盆地玉北地区奥陶系成岩作用研究

玉北地区奥陶系是塔里木盆地海相碳酸盐岩油气勘探的重要目的层和产层。通过观察岩石薄片和铸体薄片,结合岩心观察、扫描电镜、阴极发光,辅以地化资料等,对玉北地区奥陶系成岩作用进行研究,认为:玉北地区奥陶系的主要建设性成岩作用有岩溶、白云化、重结晶和溶蚀作用等,破坏性成岩作用有压实-压溶、胶结、硅化和充填作用等,此外,还有去白云化、褐铁矿化、泥晶化等对储集性能影响极小的成岩作用,可划分为同生成岩阶段、早—晚成岩阶段和表生成岩阶段。     

同位素方法对西八千地下热水的成因分析

辽宁凌海西八千地热田位于下辽河盆地的西部边缘地带,属新生代沉积盆地热传导型地热。为取得相对高温地下热水,确定开采热储层为古近系沙河街组三段、四段的砂岩和砂砾岩含水层。采取1组地热水样进行了稳定同位素(18O、2H、)和放射性同位素(14C、3H)的检测。应用HO、3H、14C等同位素方法对地下热水成因进行分析,得出其地下热水是由早期的沉积水和近期大气降水经迳流补给的水混合而成的。     

Brittle failure of shale under uniaxial compression

Shale gas reservoirs are characterized by tight matrix, well-developed micro-fissures, and laminations. The study about the failure of shale under compression is of great significance to safe drilling operation and the subsequent reservoir stimulation. The variation of rock mechanical properties with the angle between the axial stress and bedding plane normal (coring angle) is analyzed based on laboratory tests. A failure criterion is applied and verified to describe the strength of shale. Moreover, ultrasonic technology is used to study the damage characteristics of shale during the uniaxial compression process. The experimental results show that shale strength decreases initially and then increases with the increase of the coring angle. The Young’s modulus and Poisson’s ratio increase with the increase of coring angle. In a compression process, damage is essentially the development of new micro-cracks induced by the compression. Shale failure is the microscopical reflection of the process of the generation and expansion of axial micro-cracks, so it is the result of damage accumulation. The variation of the lateral p wave velocity can function as a monitor of the development process of shale damage. The damage factor will increase in the linear elastic stage and then enlarge rapidly after entering the stage of unstable micro-crack expansion.     

黔西北下寒武统牛蹄塘组页岩气成藏条件与有利勘探区预测

以野外露头调查、老井复查和岩心样品测试等为基础,通过现场解吸实验和等温吸附模拟的含气性分析,认为黔西北下寒武统牛蹄塘组岩性主要为深水陆棚黑色碳质页岩和浅水陆棚粉砂质页岩,其中富有机质页岩段为牛蹄塘组底部的碳质页岩。页岩沉积厚度大(大于39m)、分布稳定。有机质类型主要为Ⅰ型干酪根,有机碳含量较高(富有机质页岩段平均大于5%),有机质热演化程度处于高—过成熟阶段;页岩储层中微裂缝、微孔隙发育,具较好的孔隙度(平均5.14%)和渗透率(0.011 4×10-3μm2),含气量大(平均1.3 m3/t),具有良好的气资源潜力。预测金沙—息烽以及仁怀两个地区为页岩气勘探有利区。     

Trace and rare earth element geochemistry of the Upper Triassic mudstones in the southern Ordos Basin,Central China

Oil‐source correlation studies have demonstrated that the crude oils in the Ordos Basin were mainly derived from organic‐rich lacustrine mudstones of the Yanchang Formation. The sedimentology, petrology and organic geochemistry of these mudstones have been studied intensively, but their trace and rare earth element (REE) characteristics have received little attention. In this paper, we present trace and rare earth element data of the Upper Triassic Yanchang Formation mudstones in the southern Ordos Basin to constrain the palaeoenvironment, provenance and depositional setting. Our results show that the REE and trace element concentrations of the Yanchang Formation mudstones are higher than those of the upper continental crust (UCC). The Sr contents and Sr/Ba and Y/Ho ratios of these mudstones indicate the absence of a marine transgression during the sedimentation of the Upper Triassic mudstones. The depositional environment of the Upper Triassic mudstones was slightly oxic as evidenced by the values of Eu/Eu*, Ce/Ce*, Ce_anom, δU, U/Th, V/Cr and Ni/Co. The UCC‐normalized distribution pattern of REEs, spider diagrams, the ratios of related elements, the bivariate diagrams of Th/Sc–Zr/Sc and La/Th–Hf and the ternary plots of La–Th–Sc and Th–Sc–Zr/10 signify that the provenances of the Chang9–7 mudstones were mainly derived from a continental island arc, whereas the provenances of the Chang6–3 mudstones were mainly derived from a mixture of continental island arc and active continental margin, and the latter contain less recycled materials. Combined with the previous studies of detrital zircon dating and petrography of the Yanchang Formation sandstones in the southern Ordos basin, we propose that the Qinling orogenic belt served as one of the primary source regions occurring between the Chang7 and Chang6 periods, corresponding to the initial uplift of the west Qinling Mountains due to the collision between the Yangtze and North China blocks. Copyright © 2014 John Wiley & Sons, Ltd.     

Impacts of extreme precipitation on tree plantation carbon cycle

Extreme precipitation events are expected to increase in frequency and magnitude in future due to global warming, but relevant impacts on tree plantation ecosystem carbon cycle are unknown. In this study, we use an atmosphere–vegetation interaction model (AVIM2) to estimate the likely impacts of extreme precipitation events on carbon fluxes and carbon stocks of a tree plantation in south China. Our results indicate that shifting from moderate precipitation events to extreme precipitation events whilst keeping monthly precipitation unchanged could decrease the tree plantation carbon accumulation. Tree plantation net primary productivity, net ecosystem productivity, soil carbon stock and vegetation carbon stock could decrease by 4.2, 28, 4.3 and 1.4 % during the studying period of 1962–2004, respectively. Though reductions in net primary productivity and net ecosystem productivity are relatively smaller than their annual variations, our sensitivity test shows that the tree plantation carbon stock could decrease by 3.3 % if the assumed extreme precipitation regime lasts for 500 years. Observed and simulated gross primary productivity, ecosystem respiration and net ecosystem productivity have significant positive correlation with soil water content (SWC), especially the deep SWC. The mechanism for the extreme precipitation effect is that the increase in extreme precipitation events will cause SWC to decrease, consequently, reducing carbon fluxes and stocks.     

A synoptic and dynamical characterization of wave-train and blocking cold surge over East Asia

Through an agglomerative hierarchical clustering method, cold surges over East Asia are classified into two distinct types based on the spatial pattern of the geopotential height anomalies at 300 hPa. One is the wave-train type that is associated with developing large-scale waves across the Eurasian continent. The other is the blocking type whose occurrence accompanies subarctic blocking. During the wave-train cold surge, growing baroclinic waves induce a southeastward expansion of the Siberian High and strong northerly winds over East Asia. Blocking cold surge, on the other hand, is associated with a southward expansion of the Siberian High and northeasterly winds inherent to a height dipole consisting of the subarctic blocking and the East Asian coastal trough. The blocking cold surge tends to be more intense and last longer compared to the wave-train type. The wave-train cold surge is associated with the formation of a negative upper tropospheric height anomaly southeast of Greenland approximately 12 days before the surge occurrence. Further analysis of isentropic potential vorticity reveals that this height anomaly could originate from the lower stratosphere over the North Atlantic. Cold surge of the blocking type occurs with an amplifying positive geopotential and a negative potential vorticity anomaly over the Arctic and the northern Eurasia in stratosphere. These anomalies resemble the stratospheric signature of a negative phase of the Arctic Oscillation. This stratospheric feature is further demonstrated by the observation that the blocking type cold surge occurs more often when the Arctic Oscillation is in its negative phase.     

Production of dimethylsulfide and acrylic acid from dimethylsulfoniopropionate during growth of three marine microalgae

We measured the concentrations of dimethylsulfide （DMS）, acrylic acid （AA）, and dimethylsulfoniopropionate （DMSP） during growth of three microalgae： Prorocentrum micans, Gephyrocapsa oceanica, and Platymonas subcordiformis. The DMSP, AA, and DMS concentrations in culture media varied significantly among algal growth stages, with the highest concentrations in the late stationary growth stage or the senescent stage. In the stationary growth stage, the average DMSP concentration per cell in P. micans （0.066 5 pmol/cell） was 1.3 times that in G. oceanica （0.049 5 pmol/ cell） and 20.2 times that in P. subcordiformis （0.003 29 pmol/cell）. The average concentrations of AA were 0.044 6, 0.026 9, and 0.003 05 pmol/cell in P. micans, G. oceanica, and P. subcordiformis, respectively, higher than the concentrations of DMS （0.272, 0.497, and 0.086 2 fmol/cell, respectively）. There were significant positive correlations between cell density and AA, DMSP, and DMS concentrations. The ratios of DMS/AA and AA/（DMSP＋AA） in the three algae differed significantly over the growth cycle. In all three microalgae, the DMS/AA ratios were less than 25% during the growth period, suggesting that the enzymatic cleavage pathway, which generates DMS, was not the main DMSP degradation pathway. The changes in the DMS/AA ratio indicated that there was a higher rate of enzymatic breakdown of DMSP in the early growth period and a lower rate during senescence. In all three microalgae, the AA/（DMSP＋AA） ratio （degradation ratio of DMSP） decreased during the exponential growth phase, and then increased. The variations in these ratios can approximately indicate the cleavage mechanism of DMSP at different stages of algal growth.     

Seasonal dynamics of crustacean zooplankton community structure in Erhai Lake,a plateau lake,with reference to phytoplankton and environmental factors

The seasonal dynamics of a crustacean zooplankton community in Erhai Lake was investigated from May 2010 to April 2011. In total, 11 species were recorded, including six （6 genera） cladoceran and five （5 genera） copepod species. The crustacean zooplankton densities ranged from 24.3 to 155.4 ind./L. In winter and spring, the large-bodied cladoceran Daphnia galeata dominated the crustacean plankton community. In summer and autumn, when the colonial or filamentous algae dominated the phytoplankton communities, the small-bodied species （e.g. Bosminafatalis, Ceriodaphnia quadrangular, and Mesocyclops leuckarti） replaced the large-bodied ones. One-way ANOVA and redundancy analysis revealed that community structure was dependent upon total nitrogen, total phosphorus, water temperature, transparency, and the biomass of small algae. The variation in both phytoplankton structure and environmental variables were important factors in the seasonal succession of crustacean zooplankton structure in Erhai Lake.