环渤海地区前新生代油气资源的综合地质、地球物理研究

本文介绍了中国科学院知识创新工程重大项目“环渤海（湾）地区前新生代海相油气资源研究”的综合地质地球物理研究思路和取得的一些认识.环渤海地区前新生代油气的探测目标以古潜山油气藏为主,主要存在拉张、挤压、走滑、负反转与重力滑动等五种构造样式,不同地区的构造样式及其组合特点并不相同.利用重磁数据结合其它地质地球物理资料圈绘出研究区前新生界残留盆地和残余厚度的宏观分布.研究区中生界（包括上古生界）残余厚度存在两条增厚带,厚度超过5 km.其他为一些特点不一的增厚中心.渤中地区为残余厚度的缺失区,向四周残余厚度逐渐加大.下古生界（包括部分元古界）残余厚度的增厚中心多数成块、带状分布,很多地区已遭受剥蚀.这些残余厚度的增厚中心往往与前新生代油气藏的位置吻合较好.本文介绍了地震三维高精度叠加技术和最佳偏移孔径技术等方法在前新生代残留盆地油气研究中的发展,提高了古潜山地区地震资料的信噪比和分辨率,保证三维叠前偏移的振幅保真.在储层预测研究方面,本文在储层多种参数提取的基础上,实现了反假频储层预测方法.它主要应用于研究区中深层低渗透油藏裂缝密集带研究,实例表明其厚度预测和预测精度都有明显改善.最后,在钻井、地球物理资料基础上,结合研究区石油地质特征等,给出了环渤海地区8个前新生代油气潜力有利区.     

Undrained behaviour of two silica sands and practical implications for modelling SSI in liquefiable soils

The aim of the present study is twofold. Firstly, the paper investigates the undrained cyclic and post-cyclic behaviour of two silica sands by means of multi-stage cyclic triaxial tests. Secondly, based on the post-cyclic response observed in the element test, the authors formulate a simplified stress–strain relationship that can be conveniently used for the construction of p–y curves for liquefiable soils. The multi-stage loading condition consists of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading that aimed to investigate the post-cyclic response of the liquefied sample. It was found that due to the tendency of the liquefied soil to dilate upon undrained shearing, the post-liquefaction strain–stress response was characterised by a distinct strain–hardening behaviour. The latter is idealized by means of a bi-linear stress–strain model, which can be conveniently formulated in terms of three parameters, i.e.: (i) take-off shear strain, γ_to, i.e. shear strain required to mobilize 1 kPa of shear strength; (b) initial secant shear modulus, G₁, defined as 1/γ_to; (c) post-liquefied shear modulus at large strain, G₂ (γ⪢γ_to). Based on the experimental results, it is concluded that these parameters are strongly influenced by the initial relative density of the sample, whereby γ_to decreases with increasing relative density. Differently both shear moduli (G₁ and G₂) increases with increasing relative density. Lastly, the construction of new p–y curves for liquefiable soils based on the idealized bi-linear model is described.     

Formation of conical fractures in sedimentary basins: Experiments involving pore fluids and implications for sandstone intrusion mechanisms

Large sand intrusions often exhibit conical morphologies analogous to magmatic intrusions such as saucer-shaped or cup-shaped sills. Whereas some physical processes may be similar, we show with scaled experiments that the formation of conical sand intrusions may be favoured by the pore-pressure gradients prevailing in the host rock before sand injection. Our experiments involve injecting air into a permeable and cohesive analogue material to produce hydraulic fractures while controlling the pore pressure field. We control the state of overpressure in the overburden by applying homogeneous basal pore pressure, and then adding a second local pore pressure field by injecting air via a central injector to initiate hydraulic fractures near the injection point. In experiments involving small vertical effective stresses (small overburden, or high pore fluid overpressure), the fracturing pressure (λ_fract) is supralithostatic and two dipping fractures are initiated at the injection point forming a conical structure. From theoretical considerations, we predict that high values of λ_fract are due to strong cohesion or high pore fluid overpressure distributed in the overburden. Such conditions are favoured by the pore pressure/stress coupling induced by both pore pressure fields. The dips of cones can be accounted for elastic-stress rotation occurring around the source. Contrary to magmatic chamber models, the aqueous fluid overpressure developed in a parent sandbody (and prevailing before the formation of injectites) may diffuse into the surrounding overburden, thus favouring stress rotation and the formation of inclined sheets far from the parent source. For experiments involving higher vertical effective stresses (thick overburden or low pore fluid overpressure), the fracturing pressure is lower than the lithostatic stress, and a single fracture is opened in mode I which then grows vertically. At a critical depth, the fracture separates into two dilatant branches forming a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetry) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks.     

煤矿井巷间地质构造及其异常多波联合探测技术与应用

影响煤矿层安全高效开采的最主要的地质因素是断层构造及其异常,特别是落差在3~5m的中小断层构造对生产影响最大.为了保证开采工作的顺利进行,通常需在工作面回采前对面内地质条件进行探测与评价.利用地震波CT多波联合探测反演与解释,可精确确定工作面内的地质构造及异常范围.其弯曲射线追踪SIRT法反演可获得收敛性好的探测区域波速结果,以纵波波速结果为主,高速区代表断层构造迹线,低速区代表煤层增厚,同时结合其它参量成图,可有效识别各种地质构造及其特征.3241工作面的探测与回采实例有效地说明了,多波联合探测技术可为面内生产解决大量的实际地质问题.     

Ductile deformation and its geological implications for retrograded eclogites from the Hongqiyingzi Complex in Chicheng,northern Hebei,China

The rheology of rocks at depth remains a key point in earth sciences. Deformation of high-temperature–highpressure rocks from the subduction zone has not been fully studied; in particular, the deformation behavior of eclogites remains poorly understood. This research is focused on the microstructure and fabric of retrograded eclogites from the Hongqiyingzi Complex in Chicheng, north Hebei, China, based on photomicrography, scanning electron microscopy(SEM) and electron backscattered diffraction(EBSD) analysis. The analytical results show that plastic deformation occurred in the garnets during exhumation, but they do not show an obvious lattice preferred orientation(LPO). This can be interpreted as being caused by the simultaneous activation of multiple slip systems in the garnets during deformation by dislocation creep. The plagioclases have a special fabric; the(001) LPO presents a maximum in Z direction which can be correlated with a new [100](001) slip system. The misorientation angle distribution(MAD) of the plagioclases in the deformed retrograded garnet augens shows a special bimodal distribution with peaks in both a low-angle range(40?) and a high-angle range(140?). In the retrograded garnet augens(i.e. "white eye socket" garnets) the maximum peak moves from a high-angle range to a low-angle range when we analyze only those plagioclases surrounding the residual garnet porphyroclast. Deformation behavior is controlled by the crystallographic orientation of the host grain and the grain boundary sliding process. Hornblendes in different layers and the retrograded garnet augens show almost the same strong LPO patterns, which are correlated with the [001](010) slip system; and MAD diagrams show a peak in a low-angle range(40?). Integrating recent studies on metamorphism and geochronology, we argue that ductile deformation occurred during the exhumation periods together with retrograded metamorphism.     

南海北部深水盆地流体活动系统及其成藏意义

根据高精度的3D和2D地震资料,对南海北部深水盆地的流体活动系统的类型、影响因素和它们之间的演化关系进行了研究.南海北部深水区存在着包括:泥火山、泥底辟、气烟囱、管状通道、多边形断层和构造断层等多种类型的流体活动系统.根据地震反射特征,可以把它们划分为断层有关的流体活动系统和柱状流体活动系统两大类.研究发现研究区内的流体活动系统主要受构造和沉积两方面的影响.并且,气烟囱、泥底辟和泥火山存在着单向演化的关系,可以从是否有沉积物参与运移及是否喷出海底将它们区分开来.最后,本文探讨了流体活动系统对深水油气和天然气水合物成藏的重要影响,建立了南海北部流体活动系统的存在模式.     

Organic geochemistry of the Lower Permian Tak Fa Formation in Phetchabun Province,Thailand:implications for its paleoenvironment and hydrocarbon generation potential

The outcrop samples of the Tak Fa Formation(Lower Permian) in Phetchabun Province have been studied to determine their organic geochemical characteristic,depositional paleoenvironment,and hydrocarbon generation potential.The total organic carbon(TOC) values ranging from 1.42 to 4.58 wt% and extractable organic matter values ranging from 76.84 to 197.65 ppm of the Tak Fa Formation were generally low and associated with low S2 values(0.00-0.50 mg HC/g rock) and hydrogen index values in range of 0-32 mg/g TOC,although this could reflect highly thermal maturity and complex tectonic history.Thus,kerogen classification can be based on a nonbiomarker study for these outcrop samples instead.The non-biomarker plot,Pr/n-C_(17) and Ph/n-C_(18) from this study indicates that organic matter originally comes from type Ⅱ/III kerogen.The samples were also investigated and indicated that the organic matter inputs were derived from mixed marine and terrigenous sources and deposited under suboxic to oxic conditions.The depositional environment of the Tak Fa Formation in this study is interpreted to be an estuarine environment or restricted lagoonal carbonate platforms.This has been achieved from normal alkane and isoprenoids distributions,terpane,and sterane biomarkers.Thus,the Tak Fa Formation is considered to be a hydrocarbon source rock during the time of the deposition.Although the geochemical data in this study indicate that the Tak Fa Formation has experienced high maturation,one or more locations could meet a condition that places this formation to be an active source rock.The approach and concepts presented in this study can be applied to similar evaporite-carbonate deposits in Thailand to find more petroleum plays.     

Seasonal variation in albedo and radiation exchange between a burned and unburned forested peatland: implications for peatland evaporation

Forested boreal peatlands represent a precipitation‐dependent ecosystem that is prone to wildfire disturbance. Solar radiation exchange in forested peatlands is modified by the growth of a heterogeneous, open‐crown tree canopy, as well as by likely disturbance from wildfire. Radiation exchange at the peat surface is important in peatlands, as evaporation from the peat surface is the dominant pathway of water loss in peatlands of continental western North America. We examined shortwave and longwave radiation exchange in two forested ombrotrophic peatlands of central Alberta, Canada: one with (>75 years since wildfire; unburned) and another without a living spruce canopy (1–4 years since wildfire; burned) between the autumn of 2007 and 2010. Above‐canopy winter albedo was nearly two times greater in the recently burned peatland than the unburned peatland. Incoming shortwave radiation at the peat surface was much higher at the burned peatland, which increases the amount of energy available for evaporation. This is especially true for hollow microforms that are generally shaded by the tree canopy in unburned peatlands. Snow‐free albedo was similar between peatlands, although an increase in longwave losses at the burned site resulted in slightly greater net radiation at the unburned site. Copyright © 2015 John Wiley & Sons, Ltd.     

Differences in leaf construction cost between alien and native mangrove species in Futian, Shenzhen, China: implications for invasiveness of alien species

Construction cost (CC) is a quantifiable measure of energy demand for biomass production, and low CC is hypothesized to give an alien plant growth advantages and increase its potential to be an invader. Comparison of leaf CC and growth traits between alien and native mangroves in Shenzhen Futian Nature Reserve showed CC per unit mass (CC_mass), carbon concentration and gross and ash-free caloric values of alien mangroves were significantly lower than those of native species, while the height and chest circumference were just the opposite. Alien species Sonneratia apetala had the lowest CC_mass while Sonneratia caseolaris had the lowest CC_area, and were 8.99% and 32.17% lower than those of native species, respectively. Conversely, specific leaf area (SLA) of these two Sonneratia species was significantly higher than native species. Lower CC and higher SLA make the two Sonneratia species grow and spread faster than other mangroves and enhance their invasive potential.     

龙门山与四川盆地过渡带构造变形几何学、运动学及其对地震风险评估的影响

龙门山前至龙泉山构造带是理解青藏高原东南缘向东南扩展及其与四川地块相互作用的关键地带,也是探讨2008年5.12汶川MW8.0级地震的构造变形机制及开展地震风险评估的关键部位。     

Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids: implications for the δS variations of dissolved bisulfate and elemental sulfur from active crater lakes

Sulfur isotope effects during the SO₂ disproportionation reaction to form elemental sulfur (3SO₂+3H₂O→2HSO₄⁻+S+2H⁺) at 200–330°C and saturated water vapor pressures were experimentally determined. Initially, a large kinetic isotopic fractionation takes place between HSO₄⁻ and S, followed by a slow approach to equilibrium. The equilibrium fractionation factors, estimated from the longest run results, are expressed by 1000 ln α_HSO4⁻–S=6.21×10⁶/T²+3.62. The rates at which the initial kinetic fractionation factors approach the equilibrium ones were evaluated at the experimental conditions.δ³⁴S values of HSO₄⁻ and elemental sulfur were examined for active crater lakes including Noboribetsu and Niseko, (Hokkaido, Japan), Khloridnoe, Bannoe and Maly Semiachik (Kamchatka), Poás (Costa Rica), Ruapehu (New Zealand) and Kawah Ijen and Keli Mutu (Indonesia). Δ_HSO4⁻–S values are 28‰ for Keli Mutu, 26‰ for Kawah Ijen, 24‰ for Ruapehu, 23‰ for Poás, 22‰ for Maly Semiachik, 21‰ for Yugama, 13‰ for Bannoe, 9‰ for Niseko, 4‰ for Khloridonoe, and 0‰ for Noboribetsu, in the decreasing order. The SO₂ disproportionation reaction in the magmatic hydrothermal system below crater lakes where magmatic gases condense is responsible for high Δ_HSO4⁻–S values, whereas contribution of HSO₄⁻ produced through bacterial oxidation of reduced sulfur becomes progressively dominant for lakes with lower Δ_HSO4⁻–S values. Currently, Noboribetsu crater lake contains no HSO₄⁻ of magmatic origin. A 40-year period observation of δ³⁴S_HSO4⁻ and δ³⁴S_S values at Yugama indicated that the isotopic variations reflect changes in the supply rate of SO₂ to the magmatic hydrothermal system. This implies a possibility of volcano monitoring by continuous observation of δ³⁴S_HSO4⁻ values. The δ¹⁸O values of HSO₄⁻ and lake water from the studied lakes covary, indicating oxygen isotopic equilibration between them. The covariance gives strong evidence that lake water circulates through the sublimnic zone at temperatures of 140±30°C.     

Contrasting styles of Mount Vesuvius activity in the period between the Avellino and Pompeii Plinian eruptions,and some implications for assessment of future hazards

Intense explosive activity occurred repeatedly at Vesuvius during the nearly 1,600-year period between the two Plinian eruptions of Avellino (3.5 ka) and Pompeii (79 A.D.). By correlating stratigraphic sections from more than 40 sites around the volcano, we identify the deposits of six main eruptions (AP1-AP6) and of some minor intervening events. Several deposits can be traced up to 20 km from the vent. Their stratigraphic and dispersal features suggest the prevalence of two main contrasting eruptive styles, each involving a complex relationship between magmatic and phreatomagmatic phases. The two main eruption styles are (1) sub-Plinian to phreato-Plinian events (AP1 and AP2 members), where deposits consist of pumice and scoria fall layers alternating with fine-grained, vesiculated, accretionary lapilli-bearing ashes; and (2) mixed, violent Strombolian to Vulcanian events (AP3-AP6 members), which deposited a complex sequence of fallout, massive to thinly stratified, scoria-bearing lapilli layers and fine ash beds. Morphology and density variations of the juvenile fragments confirm the important role played by magma-water interaction in the eruptive dynamics. The mean composition of the ejected material changes with time, and shows a strong correlation with vent position and eruption style. The ranges of intensity and magnitude of these events, derived by estimations of peak column height and volume of the ejecta, are significantly smaller than the values for the better known Plinian and sub-Plinian eruptions of Vesuvius, enlarging the spectrum of the possible eruptive scenarios at Vesuvius, useful in the assessment of its potential hazard.     

Fluids in the lithosphere, 1. Experimentally-determined wetting characteristics of CO2H2O fluids and their implications for fluid transport, host-rock physical properties, and fluid inclusion formation

The equilibrium distribution of CO₂H₂O fluids in synthetic rock samples (principally dunite and quartzite) has been characterized by measurements of the dihedral wetting angle, θ, resulting from 5-day annealing periods at 950–1150°C and 1 GPa. For fluids in equilibrium with polycrystalline quartz, θ varies systematically from 57° for pure H₂O to 90° at X_CO2 0.9. Similarly, for San Carlos olivine, θ varies from 65° for pure H₂O to 90° at X_CO2 0.9. The addition of solutes (NaCl, KCl, CaF₂, Na₂CO₃) to H₂O causes a major decrease in θ in the quartz/fluid system (to values as low as 40°), but has no effect on fluid wetting in dunite. Reconnaissance experiments on other mono- and polymineralic aggregates indicate universally high wetting angles (θ 60°) in upper mantle assemblages and for CO₂ in felsic compositions. For diopside + H₂O, θ 80°, with large variation due to crystalline anisotropy. In no case does θ approach 0°, the condition necessary for fluid to be present along all grain boundaries.Because a value of θ greater than 60° precludes the existence of an interconnected fluid phase in a rock, our results have important implications not only for fluid transport but also for the physical properties of the bulk fluid/rock system. Any static fluid present in the upper mantle must exist as isolated pores located primarily at grain corners, and transport can occur only by hydrofracture. In the continental crust, aqueous fluids (especially saline ones) are likely to form an interconnected network along grain edges, thus contributing to high electrical conductivity and allowing the possibility of fluid transport by porous flow or surface energy-driven infiltration.