Heat flow and gas hydrates of the Baikal Rift Zone

Multi-channel seismic studies (MCS), performed during a Russian expedition in 1989 and a joint Russian-American expedition in 1992, have for the first time revealed a “bottom simulating reflector” (BSR) in Lake Baikal. These data have shown that gas hydrates occur in the southern and central basins of Lake Baikal in those places where the water depth exceeds 500–700 m. Four types of tectonic influence on the distribution of the gas hydrate were revealed: (a) Modern faults displace the BSR as they do with normal seismic boundaries. (b) Older faults displace normal reflectors, whereas the BSR is not displaced. (c) Modern faults form zones, where the BSR has been totally destroyed. (4) Processes that occur within older fault zones situated close to the base of the hydrated sediment layer lead to undulations of the BSR. The thickness of the hydrate stability field (inferred from seismic data) ranges between 35 and 450 m. Heat-flow values determined from BSR data range from 48 to 119 mW/m². A comparison between heat-flow values from BSR data and values measured directly on the lake bottom shows an overall coincidence. Changes in water level and bottom-water temperature that occurred in the past have had no noticeable influence on the present BSR depths or heat-flow values. Determination of deep heat flow from BSR data is in this case more reliable than by direct measurements. Received: 10 December 1998 / Accepted: 15 November 1999     

西沙海槽研究区天然气水合物地球化学勘探及成藏模式研究

依据ODP204航次1250C站位钻井样品酸解烃数据结果,以及作者在南海西沙海槽研究区天然气水合物地球化学现场勘查中得到的多种烃类指标数据、异常点上微量甲烷碳同位素数值等资料,对海洋水合物地球化学勘探的依据和研究区气态烃异常特征、气体成因、天然气水合物成藏模式等相关问题进行了研究探讨。结果表明:气态烃指标地球化学异常主要分布在工区北部斜坡地带,并与BSR等地震标志及深部断裂关系密切;西沙海槽研究区海底沉积物气态烃甲烷以热解成因为主,但也有混合成因;推测该区天然气水合物为断层渗滤综合成藏模式。研究成果比较合理地解释了BSR分布和海底沉积物甲烷局部异常并非完全一致的原因;评价预测了该区天然气水合物有利勘探目标。成果为该区天然气水合物勘探、天然气水合物成因机制研究和天然气水合物远景预测,提供了地球化学方面的证据。     

冲绳海槽中段西陆坡下缘天然气水合物存在的可能性分析

海洋中的天然气水合物主要发育在有机质供应充分、沉积速率快、热流值较高、水深大于300m的大陆斜坡和活动边缘的增生楔发育区;沉积物类型主要以泥质砂岩、砂质泥岩和浊积岩为主。似海底反射层(BSR)和极性反转是识别天然气水合物层的关键标志。冲绳海槽中段西陆坡下缘水深大于1000m;沉积物类型主要为粉砂质泥和泥质粉砂,在部分层位见浊积层。与东海陆架相比,西陆坡下缘的有机质含量、沉积速率的热流值都较高,其范围分别为0.75%～1.25%、10～40cm/ka和70～437mw/m2;单道地震剖面具有明显的似海底反射层(BSR)和极性反转特征,因此,推断冲绳海槽中段西陆坡下缘可能存在天然气水合物层。     

Dissociation of gas hydrates by hydrocarbon migration and accumulation-derived slope failures: An example from the South China Sea

The mechanism of slope failure associated with overpressure that is caused by hydrocarbon migration and accumulation remains unclear. High-resolution seismic data and gas hydrate drilling data collected from the Shenhu gas hydrate field (site SH5) offer a valuable opportunity to study the relations between submarine slope failure and hydrocarbon accumulation and flow that is associated with a ～2 km-diameter gas chimney developed beneath site SH5 where none gas hydrates had been recovered by drilling and sampling despite the presence of distinct bottom simulating reflectors (BSRs) and favorable gas hydrate indication. The mechanism of submarine slope failure resulted from buoyancy extrusion and seepage-derived deformation which were caused by overpressure from a ～1100 m-high gas column in a gas chimney was studied via numerical simulation. The ～9.55 MPa overpressure caused by hydrocarbons that migrated through the gas chimney and then accumulated beneath subsurface gas hydrate-bearing impermeable sediments. This may have resulted in a submarine slope failure, which disequilibrated the gas hydrate-bearing zone and completely decomposed the gas hydrate once precipitated at site SH5. Before the gas hydrate decomposition, the largely impermeable sediments overlying the gas chimney may have undergone a major upward deformation due to the buoyancy extrusion of the overpressure in the gas chimney, and slope failure was initiated from plastic strain of the sediments and reduced internal strength. Slope failure subsequently resulted in partial gas hydrate decomposition and sediment permeability increase. The pressurized gas in the gas chimney may have diffused into the overlying sediments controlled by seepage-derived deformation, causing an effective stress reduction at the base of the sediments and significant plastic deformation. This may have formed a new cycle of submarine slope failure and finally the total gas hydrate dissociation. The modeling results of buoyancy extrusion and seepage-derived deformation of the overpressure in the gas chimney would provide new understanding in the development of submarine slope failure and the link between slope failure and gas hydrate accumulation and dissociation.     

浅表层天然气水合物区的海底地形特征——以鄂霍次克海为例

使用重力取样器、渔网、深潜器等手段已经在海底及以下浅表层区域采获天然气水合物样品。但关于浅表层水合物的发育机制、分布规律及与海底地形的关系等问题还缺乏基本认识。根据2006年鄂霍次克海天然气水合物调查航次的调查数据,介绍了浅表层天然气水合物区的海底地形特征。萨哈林东北陆坡区,特别是中、下陆坡区发育大量海底凸起,这些凸起一般呈不对称的丘形,宽几百米,高几十米。不同于海底沙波、沙脊,海底凸起为孤立海底地形,在南北方向上并不连续。海底凸起和浅表层天然气水合物的发育密切相关。在海底剖面仪测量结果剖面上清楚地显示古陆坡凸起的发育。普遍地,现今海底陆坡凸起的幅度要小于古陆坡凸起的幅度,个别地方古、今陆坡凸起的形态有所变化,但大部分古、今陆坡凸起是一一对应的,基本形态没有根本变化。在萨哈林陆坡地区存在两个方向的挤压应力场,分别是由德鲁根盆地向萨哈林陆坡方向的挤压应力场、萨哈林陆坡沿萨哈林走滑断裂向南的挤压应力场。海底陆坡凸起是这两大应力场复合作用的结果。浊反射区中的游离气是底辟构造中的超高压多相物质向上迁移形成的。浊反射区上方对应的海底凸起应该是宏观构造挤压和局部底辟发育叠合的结果。浊反射区上方的海底凸起,在形态等方面应该和其他仅由挤压构造原因形成的凸起有所区别,比如顶部发育裂口等。在底辟构造中,由于游离气体的向上迁移,在整个水合物稳定域中从下到上,直至海底都可能形成水合物,从而使我们有机会使用重力采样器这样的设备也能采获天然气水合物样品。     

东海与泥底辟构造有关的天然气水合物初探

根据所获得的高分辨率地震资料分析,发现冲绳海槽南部西侧槽坡附近以及海槽内部发育有一系列泥火山（底辟）构造,在地形上表现为泥火山地貌,在穿过泥火山的地震剖面上,表现出典型的泥底辟构造。对穿过泥底辟构造的DMS01-5地震剖面进一步的处理和解释发现,泥底辟构造顶部存在明显的似海底反射（BSR）,其与海底反射波组极性相反,在BSR之上存在振幅空白带,在速度谱上出现速度异常,指示存在与泥火山有关的天然气水合物。从世界广泛发现的与泥底辟构造有关的天然气水合物来看,天然气水合物既可以在泥底辟构造的丘状外围成藏,也可以在其外围的海底沉积物中产出。在泥底辟构造的丘状外围附近,天然气水合物的形成机制类似于传统的矿物低温热液的形成;在泥底辟构造外围海底沉积物中,其形成过程类似于传统的矿物交代形成机制。冲绳海槽泥底辟构造的发育与很高的沉积速率和槽坡的活动断层有关。在冰期期间,长江携带大量的陆源物质直接输送到大陆坡地区,沉积速率达300 m/Ma,产生异常高压,同时张性断层极为发育,为流体的迁移提供了良好的通道,在异常压力以及上覆地层压力作用下大量流体向上运移,从而发育大量的泥底辟构造。富含甲烷的流体易在其外围及外围海底沉积物中形成天然气水合物藏。     

基于连续小波变换的天然气水合物层地震数据多尺度分析——布莱克海台USGS95-1测线应用实例

似海底反射（BSR）是目前天然气水合物层识别的主要依据,但是当BSR不明显或者缺失的时候怎样识别水合物层,以及水合物层顶面和下伏游离气层底面如何确定,仍然是水合物识别中难以圆满解决的两大难题。以布莱克海台USGS95-1测线地震数据为例利用小波变换进行多尺度研究发现水合物层和游离气层表现出不同的尺度特征：水合物层表现出大尺度特征,而游离气层具有小尺度特征;在最佳尺度剖面上,水合物层表现为低尺度背景中的近似平行于海底的高尺度带。利用水合物层和游离气层的这种尺度差异不但可以识别水合物层,而且还可以推断水合物层的顶面和游离气层的底面。     

中国近海天然气水合物的研究进展

南海、东海具有形成天然气水合物的良好动力学环境和丰富的烃类气体来源。根据卫星对海面增温异常的观测、底水气体地球化学、标志矿物和流体组成的研究表明 ,南海、东海海底存在强烈的烃流体活动和排气作用 ;南海南北陆坡区海底气体主要由CH4组成 ,前者多为微生物成因气 ,后者多为热解气 ;冲绳海槽热液沉积区的气体 ,主要为CO2 (86 % ) ,其次为CH4、H2 、H2 S(14 % ) ,分别来自岩浆流体及陆源有机质的降解 ,也属热解成因气。地震地球物理的研究主要集中于南海东北部、北部、南部陆坡区和冲绳海槽中南部 ,测线长度还很有限 ,虽然都有BSR标志的发现 ,但质量比较好 ,研究程度也比较高的还只有南海东北部主动陆缘和北部被动陆缘的一些海域。通过沉积物烃含量和热释光的研究 ,南海、东海共获得 6个地球化学异常区。在综合对比物化探、地热等项资料的基础上初步认为 :笔架南 (Ⅰ )、台西南—东沙 (Ⅱ )异常区是寻找水合物的最佳远景区 ;琼东南—西沙海槽(Ⅲ )、中建南—中业北 (Ⅳ )和冲绳海槽南部异常区是寻找水合物和常规油气藏的有利地区 ,但Ⅳ区更有利于寻找油气 ,其余 2区更有利于寻找水合物 ;南沙海域的研究程度总体上比较低 ,但在其中的南沙海槽 ,物化探异常标志均优 ,甲烷含量较其它地区高 2个数量级     

海洋天然气水合物的类型及特征

根据天然气水合物的产出条件,海洋环境水合物可以分为二类扩散系统水合物和渗漏系统水合物。扩散系统水合物分布广泛,在水合物稳定带内是水-水合物两相共存的热力学平衡体系,游离气仅发育于稳定带之下,在地震剖面上发育有指示水合物底界的强反射面(BSR)。该类水合物含量低,埋藏深。除温度和压力外,水合物的沉淀受甲烷溶解度和扩散速度的控制,并与气体组分、孔隙水盐度、天然气供应和有机碳转化等有关。渗漏系统与断层等通道相伴生,水合物发育于渗漏系统整个水合物稳定带,是水-水合物-游离气三相共存的热力学非平衡体系,水合物的沉淀受动力学控制。该类水合物含量高,埋藏浅,但一般不发育BSR。而且,天然气渗漏活动在海底沉积物和上覆水体中形成了一系列特殊的地质、地球物理、地球化学和特异生物群异常。     

Fluid migration and fluid seepage in the Connemara Field,Porcupine Basin interpreted from industrial 3D seismic and well data combined with high-resolution site survey data

This study documents the suite of processes associated with source-to-seafloor fluid migration in the Connemara field area on the basis of 3D seismic data, well logs, 2D high-resolution seismic profiles, subbottom profiles, short cores and sidescan sonar data. The combination of datasets yields details about fluid migration pathways in the deep subsurface, in the unlithified shallow subsurface and about the distribution of fluid and gas seeps (pockmarks) at the sea floor. The Connemara field area is characterized by vertical fluid migration pathways (“seismic chimneys” or “gas chimneys”) that extend from the top of the Jurassic sequence, cross-cutting the entire Cretaceous sequence to the Upper Tertiary deposits over a vertical distance of up to 1.5 km. Their localization is mainly structurally controlled to the crest of tilted fault blocks along the main hydrocarbon migration pathways. These chimneys are important conduits for focused vertical fluid/gas flow from the deep to the shallow subsurface. However, gas seeps (pockmarks) at the sea floor are almost randomly distributed, which indicates a change from focused to diffuse fluid/gas migration in shallow, unconsolidated sediment. Where the vertical chimneys reach up to unlithified Eocene to Miocene sands, widespread deformation, interpreted as fluidization, occurs around the main conduit. This deformation affects about 32% of the entire unconsolidated Tertiary section (Late Eocene – Miocene). A Plio-Pleistocene glaciomarine drift with up to five horizons with iceberg ploughmarks seals the Tertiary sands. In the near surface sediments it is observed that gas accumulation occurs preferentially at iceberg ploughmarks. It is inferred that lateral migration at five levels of randomly oriented ploughmarks dispersed gas over larger areas and caused random pockmark distribution at the sea floor, independent from the underlying focused migration pathways. This study demonstrates that fluid flow migration changes from structurally controlled focused flow in the deep consolidated subsurface to diffuse flow, controlled by sediment variability, in the shallow subsurface. This result is relevant to a better understanding of the distribution of seepage-induced features at the seafloor related to focused hydrocarbon migration pathways known from industry data and fluid flow modeling.     

Distribution and accumulation rate of Hg in the upper quaternary sediments of the Deryugin Basin,Sea of Okhotsk

The Hg distribution and some mineralogical-geochemical features of bottom sediments up to a depth of 10 m in the Deryugin Basin showed that the high and anomalous Hg contents in the Holocene deposits are confined to a spreading riftogenic structure and separate fluid vents within it. The accumulations of Hg in the the sediments were caused by its fluxes from gas and low-temperature hydrothermal vents under favorable oceanological conditions in the Holocene. The two mainly responsible for the high and anomalous Hg contents are infiltration (fluxes of hydrothermal or gas fluids from the sedimentary cover) and plume (Hg precipitation from water plumes with certain hydrochemical conditions forming above endogenous sources). The infiltration anomalies of Hg were revealed in the following environments: (1) near gas vents on the northeastern Sakhalin slope, where high Hg contents are associated only with Se and were caused by the accumulation of gases ascending from beneath the gas hydrate layer; (2) in the area of inferred occasionally operating low-temperature hydrothermal seeps in the central part of the Deryugin Basin, in which massive barite chimneys, hydrothermal Fe-Mn crusts, and anomalous contents of Mn, Ba, Zn, and Ni in sediments develop.     

Seismic attenuation for characterization of gas hydrate reservoir in Krishna-Godavari basin,eastern Indian margin

Gas hydrates have received global attention as a possible alternative non-conventional energy resource. Hence, the detection, characterization and quantification of gas hydrates are very important for evaluating the resource potential. Presence of gas hydrates in sediments above the bottom simulating reflector or BSR is associated with low attenuation or high quality factor (Q), whereas, free gas bearing sediments below the BSR exhibit high attenuation or low seismic Q. Here the logarithm spectral ratio (LSR) method is applied to marine seismic reflection data along two cross lines (18 and 46) in the Krishna-Godavari (KG) basin in eastern Indian margin, where gas hydrates have already been established by drilling/coring. The interval Qs is calculated for three sedimentary layers (A, B, and C) bounded by the seafloor, BSR, one reflector above and another reflector below the BSR at some common depth points (CDPs) to study the attenuation characteristics of sediments across the BSR. The estimated average interval Q (160) for the hydrate bearing sediments (layer B) is much higher than the average interval Q (80) for both the loose clayey sediments (Layer A) and underlying free gas saturated sediments (layer C). This demonstrates that estimation of seismic quality factor Q can be used for characterization of gas hydrate reservoir.     

中国近海天然气水合物找矿前景

天然气水合物是一种新型能源，在海底沉积物和陆上永远冻土带中均有广泛分布。西太平洋是全球三大天然气水合物成矿带之一，在其中已发现许多水合物矿床或矿点。中国近海，包括南海、东海和台湾东部海域，具备良好的天然气水合物成矿条件和找矿前景，并已在这些海域中发现了一系列的找矿标志。南海的西沙海槽、台湾西南陆坡和台西南盆地、笔架南盆地及其东缘增生楔、东沙群岛东南坡、南部陆坡区，东海的冲绳海槽和台湾东北部海域是中国近海最有利的天然气水合物找矿远景区。     

Bottom Simulating Reflector and Gas Seepage in Okinawa Trough： Evidence of Gas Hydrate in an Active Back-Arc Basin

To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural "anomalies" are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation:to help gather enough methane into a small area and to modulate the thermal regime.     

天然气水合物地震似海底反射现象AVO正演模型研究

似海底反射(BSR)现象是用人工地震方法识别含天然气水合物沉积地层的重要标志之一。针对水合物沉积物的悬浮、颗粒接触和胶结3种微观模式,进行了似海底反射现象正演模型的研究,考查了BSR现象产生的地震地质原因和运用AVO判断游离气的适用性。研究结果表明:在地震合成记录的帮助下,结合AVO变化曲线,可以认为BSR的成因有两种情况。实际工作中需要运用多种信息的综合分析而不是一种简单固定的模式来解释BSR的复杂成因。水合物沉积的3种微观模式都存在水合物的临界饱和度,当介质中水合物饱和度小于临界饱和度时,可以通过AVO曲线的变化形态来判断水合物沉积层下伏介质中是否含有游离气;而大于临界饱和度时,AVO技术则难以适用。AVO曲线形态、BSR现象与游离气三者之间存在复杂的关系,同样需要通过多种信息的综合分析来解释。     

南海北部陆坡高饱和度天然气水合物气源运聚通道控藏作用

气源运聚通道与天然气水合物富集成藏关系密切。利用准三维地震资料并结合钻探成果,深入研究了神狐海域GMGS3钻探区高饱和度水合物站位气源运移疏导通道地质地球物理特征及其控藏作用。结果表明:高饱和度水合物产出站位发育多种类型运移疏导通道,且与BSR空间耦合关系较好;紧邻BSR之下为强振幅反射,强振幅下部游离气体充注现象明显,表明水合物稳定域下部存在气体运移的通道,且深部气体向浅层发生了运移。深大断裂、底辟及气烟囱构成了沟通深部热解气及浅层生物气与浅层温压稳定域的垂向通道,在这些通道上方可以直接形成水合物;浅部滑塌面、水道砂及海底扇构成的高孔渗连续性砂体为浅层生物气及深部运移而来的部分热成因气横向运移通道,气体的侧向运移扩大了气体供给范围,增加了矿体横向展布规模。文章认为,天然气运移疏导系统与其他成藏要素匹配良好的构造和区域是勘探高饱和度水合物的有利目标。     

Bottom-simulating reflections and geothermal gradients across the western Svalbard margin

Seismic reflection data reveal prominent bottom-simulating reflections (BSRs) within the relatively young (<0.78 Ma) sediments along the West Svalbard continental margin. The potential hydrate occurrence zone covers an area of c. 1600 km². The hydrate accumulation zone is bound by structural/tectonic features (Knipovich Ridge, Molloy Transform Fault, Vestnesa Ridge) and the presence of glacigenic debris lobes inhibiting hydrate formation upslope. The thickness of the gas-zone underneath the BSR varies laterally, and reaches a maximum of c. 150 ms. Using the BSR as an in-situ temperature proxy, geothermal gradients increase gradually from 70 to 115 °C km⁻¹ towards the Molloy Transform Fault. Anomalies only occur in the immediate vicinity of normal faults, where the BSR shoals, indicating near-vertical heat/fluid flow within the fault zones. Amplitude analyses suggest that sub-horizontal fluid migration also takes place along the stratigraphy. As the faults are related to the northwards propagation of the Knipovich Ridge, long-term disturbance of hydrate stability appears related to incipient rifting processes.     

南海北部陆坡构造坡折带中的天然气水合物

构造坡折带是由同沉积构造长期活动引起的沉积斜坡明显突变的地带,对盆地充填的可容纳空间和沉积作用可产生重要的影响,构造坡折带和油气资源分布有着较为密切的关系。本文首次把“构造坡折带”概念引入到天然气水合物调查研究中,认为:构造坡折带是天然气水合物发育和赋存的重要构造单元。论文从海底坡降、断层发育以及温压场环境等角度讨论了构造坡折带对天然气水合物的控制作用,发现BSR发育位置的海底坡降一般在10×10-2～30×10-2之间;利用论文中设计的相对构造强度的算法计算了南海北部陆坡D区的相对构造强度,发现相对构造强度的次高值区有利于水合物赋存;根据高分辨率地震数据计算的构造坡折带的温压场环境,发现构造坡折带中连续变化的温压场环境能够使游离气运移到适宜的温压场中并形成水合物。在对上述研究进行总结归纳的基础上,初步提出了南海北部陆坡构造坡折带中天然气水合物的成藏模式。     

Geochemical characteristics of sediment pore water from Site XS-01 in the Xisha trough of South China Sea and their significance for gas hydrate occurrence

Gas hydrate is a recently-found new source of energy that mostly exists in marine sediments. In recent years, we have conducted gas hydrate exploration in the South China Sea. The Xisha trough, one of the promising target areas for gas hydrate, is located in the northern margin of the South China Sea, adjacent to several large oil and gas fields. The Xisha trough extends 420 km long with the water depth of 1 500 m in the west part and 3 400 m in the east part and deposits thick sediments with organic matter content of 0.41%–1.02%. Previous studies on topographical features, geological P-T conditions, structural geology, sedimentary geology and geophysical bottom simulating reflectors (BSR) in the Xisha trough suggest that this area is favorable for the formation and accumulation of gas hydrate. In this paper, we present geochemical analyses for the sediment and pore water from a piston core at Site XS-01 in the Xisha trough. Seven pore water samples were analyzed for their anion (Cl⁻, SO₄ ²⁻, Br⁻, I⁻) contents, cation (Na, K, Ca, Mg) contents and trace element (Li, B, Sr, Ba, Rb, Mn) contents. Eight sediment samples were analyzed for stable carbon and oxygen isotopic compositions. A number of geochemical anomalies such as anions (e.g. Cl⁻, SO₄ ²⁻), cations (e.g. Ca, Mg) and trace elements (e.g. Sr, Ba, B) were found in this study. For example, the concentrations of Cl⁻ and SO₄ ²⁻ in pore water show a decreasing trend with depth. The estimated sulfate/methane interface (SMI) is only 18 m, which is quite similar to the SMI value of 23 m in the ODP164 Leg 997 at Blake Ridge. The Ca, Mg and Sr concentrations of pore water also decrease with depth, but concentrations of Ba, and Mg/Ca and Sr/Ca ratios increase with depth. These geochemical anomalies are quite similar to those found in gas hydrate locations in the world such as the Blake Ridge and may be related to the formation and dissociation of gas hydrates. The salt exclusion effect during the gas hydrate formation will cause an increase in major ion concentrations in the pore waters that diffused upward such as Cl. The anaerobic methane oxidation (AMO) may lead to the change of SO₄ ²⁻ and other cations such as Ca, Mg, Sr and Ba in pore water. Low δ ¹³C value of authigenic carbonates is a good indicator for gas hydrate occurrence. However, the bulk sediment samples we analyzed all show normal δ ¹³C values similar to biogenic marine carbonates, and this may also suggest that no gas hydrate-related authigenic carbonates exist or their amount is so small that they are not detectable by using this bulk analytical method. In conclusion, we suggest that the Site XS-01 in the Xisha trough of the northern margin of the South China Sea is a potential target for further gas hydrate exploration. Translated from Quaternary Sciences, 2006, 26(3): 442–448 [译自: 第四纪研究]     

南海北部天然气水合物富集特征及定量评价

为寻找有资源前景的高富集天然气水合物及水合物储层的精细刻画方法,利用南海6次钻探发现的高饱和度水合物层的测井、岩心和三维地震数据,分析水合物富集层测井与地震异常特征.发现:（1）不同饱和度的孔隙与裂隙充填型水合物层的测井和地震异常不同,裂隙充填型水合物层具有各向异性;（2）受高通量流体运移的影响,在粉砂沉积物的水合物稳定带底界附近能形成中等饱和度的水合物层,识别标志为稳定带内极性与海底一致的强振幅反射,而非BSR和振幅空白;（3）裂隙充填型中等饱和度水合物层在地震剖面上表现为地层上拱和弱-中等强度振幅反射.储层-疏导-气源的耦合控制着水合物的富集特征和分布,断层与流体运移控制着细粒粉砂质沉积物中水合物的富集与厚度.基于饱和度岩相的统计学反演,能识别3 m非水合物和低饱和度水合物层及空间分布.