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1.
High-resolution seismic reflection profiles (3·5 kHz) have revealed the presence of extensive interstitial gas accumulation within the sedimentary sequences of Loch Tay, Scotland, as identified by acoustic turbidity masking the seismic stratigraphy. Within the central section of the loch, in the deepest water area directly above the zone of the seismically active Loch Tay Fault, focused flows of gas through the sediment pile to the loch bed via chimneys and pockmarks, together with gas seeps within the water column, have been identified. Microbiological observations indicate that the gas is biogenic CH4 , produced by both chemoautotrophic (which use CO2 as a source of carbon and H2 as a source of energy) and aceticlastic species (which use acetate as a source of carbon and energy) of methanogens in the fine-grained, organic rich deposits that have been focused into the zone of accumulation in the deep central part of the loch. The spatial distribution of the gas escape features suggests that earthquake movements along the Loch Tay Fault are responsible for facilitating focused gas escape in this part of the loch, by the creation of new pathways and conduits through the sediment pile, along which gas can migrate upwards and exit into the water column. Relict pockmarks and associated chimneys identified in the seismic records indicate that gas escape has been taking place since Pleistocene times though the precise timings cannot be ascertained. This is the first time that such features have been reported from a lake in the UK. 相似文献
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3.
Detailed reviews of multichannel seismic reflection, sparker, chirp and multibeam data that were collected on the southern Marmara Sea shelf revealed various shallow gas indicators and related sedimentary structures, including enhanced reflections, seismic chimneys, acoustic blanking, bright spots, pockmarks, mound-like features and seeps. Seismic attribute analyses were applied to characterise the existence of gas-bearing sediments. The distribution of shallow gas indicators provides important insights into their origin and the geological factors that control them. Prominent gas accumulations and seeps are observed along the profiles that cross the branches of the central segment of the North Anatolian Fault Zone, which indicates that the gas seeps are controlled by active faulting. This indicates that the faults act as conduits through the sedimentary column. The dense occurrences of gas directly off the river mouths along the shallow bays provide clues about the organic-rich carbon content of the sediments and biogenic methane generation. In some areas, the gas-related acoustic anomalies are mostly located in the upper sediments below the marine unit, which indicates that the gas emissions in these areas were terminated as a result of the increased overburden pressure after the Holocene sea level rise and the deposition of the marine unit. 相似文献
4.
This paper represents an attempt of analysing the amplitude versus offset (AVO) behaviour and specific seismic attributes
of sedimentary structures from the Porcupine Basin, SW of Ireland. During the last decade, a huge number of carbonate mounds
were investigated in this region in water depths of 600–1,000 m, but the genesis and growth of these mounds are still not
clearly identified. The aim of this paper is to give a better understanding of the connection between fluid migration pathways
in the deeper underground and surface expressions of their fluid expulsions like gas chimneys and pockmarks through which
the mounds may generate themselves. The data used in this study to determine boundary conditions for the physical properties
of the underlaying strata were gathered from the northern flank of the Porcupine Basin, where a huge amount of fluid and/or
gas chimneys covers the seabed. Marine seismic reflection data contain information about the elastic properties of the underlying
earth, mainly based on the observed variations in the seismic reflection amplitude at different shot–receiver offsets. To
extract elastic parameters from the data, inversion techniques were used, which presume that input amplitudes are proportional
to reflection coefficients for plane wave reflection. To calibrate the AVO analyses with the existing stratigraphy in the
working area we have used the well logs from several bore holes in the region. The results of this study show clearly that
the investigated and identified pockmarks on the seafloor are the surface expression of hydrocarbon seepage in the deeper
sedimentary underground. 相似文献
5.
在调研了国内外气烟囱研究成果与思路的基础上,通过全新的地震解决方案——OpendTect平台提供的基于属性多层感知器(MLP)的人工神经网络(ANN)的方法预测气烟囱的发生概率体,并利用倾角导向体对算法进行改进,提出倾角控制下的地震气烟囱识别技术,很好地补充并发展了模式识别技术在地震勘探领域的应用。通常该技术一方面可以解释运移通道和浅层气成藏的原因;另一方面,形成的气烟囱地震数据体还可以预测源岩的发育情况;此外,对于判别断层封闭性也非常适用。最后应用这一技术对海拉尔盆地贝尔凹陷一含油区块的运移通道和成藏规律进行研究,分析该研究区的断裂发育特征和运移通道类型,总结了油源、通道、储层和盖层的空间配置关系,并建立相应的成藏模式。 相似文献
6.
ABSTRACT The Black Sea contains immense gas accumulations. Exploration of gas accumulations is geologically and economically important because migration of methane in sediments may cause massive slope failures and the methane seeps may indicate deeper hydrocarbon reservoirs. Human activity both in and on the seafloor (oil industry) and natural activity (earthquakes, cyclones) trigger mechanisms for seafloor failure and gas release that may have a local and possibly global environmental impact. Recently, sonar and high‐resolution seismic surveys were carried out to obtain information about the effects of gas and gas‐filled sediments throughout the Turkish margin of the Eastern Black Sea, and shallow gas was detected on the subbottom profiler records. It continues about 25–65 m below the sea floor and is marked by bright and cloudy spots, sometimes pockmarks and acoustic voids. The lower section of the Turkish shelf is an extensive pockmarked plateau. The pockmarks are seen as circular structures with high backscattering on the sonar records. 相似文献
7.
Lijie Wang Jitian Zhu Haiteng Zhuo Zhipeng Sun Aixue Song 《International Geology Review》2020,62(7-8):1108-1130
ABSTRACT Understanding fluid flow structures in a rifted basin may enhance our knowledge of their origination and evolution. Through geochemical analysis and seismic interpretation, different fluid flow features are identified in the central depression of Qiongdongnan basin, northern South China Sea. These structures include mud diapir, gas chimney, hydrothermal pipes, faults, blowout pipes, and associated extrusions. Mud diapirs are primarily located on the slope belts, whereas gas chimneys are on the basement highs in the southwest of the study area. Their distribution appears closely controlled by tectonic stress field and overpressure, the later is caused by hydrocarbon generation and compaction disequilibrium. High sediment overloading, weak post-rift tectonic activity, and high average geothermal gradient may contribute to the compaction disequilibrium. The occurrence of gas chimneys on the basement high suggests that lateral transportation and relief of overpressure is a significant factor. Distribution of broad hydrothermal pipes is related with the thinning continental crust and pre-existing boundary faults in the central depression. They are probably attributed to intruded sills dissolution and were caused by hydrothermal fluids vertically. Geochemical data from gas reservoirs analysis indicates that mud diapirs and gas chimneys are critical pathways for thermogenic gases, whereas hydrothermal pipes and part of the faults may act as pathways of both thermogenic and inorganic gases. The blowout pipes mainly occur in the northwestern central depression near the continental slope, where fluid flows ascend gradually from a series of Pliocene-current prograding wedge-formed units with a hydraulic fracture in shallow. Hundreds of seafloor pockmarks and mounds associated with blowout pipes located above the NE-SW elongated Pliocene-Quaternary slope-break belts. These extrusive structures indicate that fluids ascend through blowout pipes and were expelled at the present seabed. Our results indicate that fluid flow structures are probably responsible for fluid activities and must be taken into account when assessing the hydrocarbon potential, geologic hazard, and benthic ecosystem. 相似文献
8.
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。 相似文献
9.
L. Zühlsdorff V. Spieß C. Hübscher H. Villinger A. Rosenberger 《International Journal of Earth Sciences》2000,88(4):655-667
A high-resolution seismic survey was carried out at the accretionary prism on the continental slope off Vancouver Island,
Canada. Two GI-Gun data sets with different source frequency ranges of 50–150 and 100–500 Hz were combined with 4 kHz narrow-beam
echosounding data (Parasound). The data allow spatial correlation between a gas hydrate bottom simulating reflector (BSR)
and distinct areas of high near-sea-floor reflectivity. An integrated interpretation of the multi-frequency data set provides
insight into the regional distribution of tectonically induced fluid migration and gas hydrate formation in the vicinity of
ODP Leg 146 Sites 889 and 890. The BSR at the base of the gas hydrate stability field is observed within accreted and deformed
sediments, but appears to be absent within bedded slope basin deposits. It is suggested that these basin deposits inhibit
vertical fluid flow and prevent the formation of a BSR, whereas the hydraulic conductivity of the accreted sediments is sufficiently
high to allow for pervasive gas migration. An elevation of the BSR beneath the flanks of a topographic high is interpreted
as an indicator for local upflow of warm fluids along permeable pathways within outcropping accreted sediments. Parasound
data reveal discontinuous zones of high reflectivity at or directly beneath the sea floor, which may indicate local cementation
of surface sediments. In combination with GI-Gun data, the occurrence of these reflective areas can be related to the location
of slope sedimentary basins acting as hydraulic seals. It is proposed that the seals sometimes fail along faults extending
beneath the BSR, leading to focused upflow of methane-bearing fluid and the formation of carbonate pavements at the sea floor.
Received: 9 November 1998 / Accepted: 6 April 1999 相似文献
10.
ABSTRACT Mud diapirs and gas chimneys are widely developed in continental slope areas, which can provide sufficient gas for hydrate formation, and they are important for finding natural gas hydrates. Based on the interpretation and analysis of high-resolution 2D and 3D seismic data covering the deep-water area in the Qiongdongnan Basin (QDNB), northern South China Sea, we studied the formation mechanism of mud diapirs and gas chimneys and their relationship with natural gas hydrates. Mud diapirs and gas chimneys are columnar and domelike in shape and the internal regions of these bodies have abnormal reflections characterized by fuzzy, chaotic, and blanking zones. The reflection events terminate at the rims of mud diapirs and gas chimneys with pull-up reflections and pull-down reflections, respectively. In addition, ‘bright spots’ and diapiric-associated faults occur adjacent to mud diapirs and gas chimneys. The rapidly deposited and deeply buried fine sediments filling in the Tertiary in deep-water areas of the QDNB and overpressure potential derived from undercompacted mudstones, as well as from the pressurization of organic matter and hydrocarbon generation, provide abundant materials and intensive driving forces for the formation of mud diapirs and gas chimneys. Bottom simulating reflectors (BSRs) with strong amplitude and high or poor continuity were recognized atop the mud diapirs and gas chimneys and in the structural highs within the same region, indicating that they have a close relationship with each other. The mud diapirs and gas chimneys and associated high-angle faults provide favourable vertical pathways for the hydrocarbons migrating from deep strata to shallow natural gas hydrate stability zones where natural gas hydrates accumulate; however, some BSRs are characterized by weak amplitude and poor continuity, which can be affected by high temperature and overpressure in the process of the mud diapir and gas chimney activities. This mutually restricting relationship must be taken into consideration in the process of gas hydrate exploration in QDNB. 相似文献
11.
More than 100 new heat flow measurements have been collected in recent years (2002–2004) in different tectonic environments
of the northern Black Sea. The northern periphery of the Black Sea is characterized by strong geodynamic and seismic activity,
high sedimentation rates, diapiric structures, mud volcanism, and fluid and gas escape at the sea floor. We present new thermal
data from the shelf, continental slope and deep-water basin, measured off-shore using a marine thermo-probe and on-shore in
drill holes. Heat flow density ranges from 20 to more than 2,000 mW/m2. For two local areas (the Dnieper gas seeps and the Dvurechenski mud volcano area), we discuss the relation between heat
flow variability and the geological and physical processes in the near-bottom sediment layer. The Dnieper gas seeps area is
characterized by strong small-scale heat flow variability and is controlled by fluid and gas migration. In the Dvurechenski
active mud volcano, the near-bottom temperature in sediments is anomalously elevated because additional heat is carried out
by mass flows of fluids and clay minerals. Away from the mud volcano heat flow quickly decreases to background values. 相似文献
12.
Long‐term pockmark maintenance by fluid seepage and subsurface sediment mobilization – sedimentological investigations in Lake Neuchâtel 
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下载免费PDF全文 Pockmarks and mud volcanoes from marine and lacustrine environments are thought to be the surface expression of focused fluid flow (gas and/or water). However, the control fluid flow exerts on the sediment dynamics and rates of activity of such features, especially the maintenance and growth of pockmarks, is not well understood. This study suggests that variable fluid flow is the driving process that has maintained two lacustrine pockmarks over thousands of years. In Lake Neuchâtel (western Switzerland), the currently active Chez‐le‐Bart Pockmark (diameter ca 160 m, depth ca 10 m) and the Treytel Pockmark (diameter ca 100 m, depth ca 4 m) indicate ‘quiescent’ fluid flow as well as past, ‘eruptive’, events of subsurface sediment mobilization. This study aims to test the hypothesis that phases of increased fluid flow through the pockmarks have led to the remobilization and spilling of sediment over the pockmark rims, and that different modes of activity phases are responsible for their maintenance and growth. So termed ‘subsurface sediment mobilization deposits’ are visible in seismic profiles and correlate to specific, sedimentary intervals in Kullenberg‐type long piston cores. In a detailed analysis, different modes of transport are recognized, which are attributed to high‐density flows that correspond to multiple pulses of activity. The pockmark morphology, seismic stratigraphy and core correlation with pre‐existing data reveals that the two pockmarks have been maintained throughout the Holocene and underwent several switches between ‘quiescent’ and ‘eruptive’ mode activity. 相似文献
13.
This study, based on 3.5 kHz SBP, 3D seismic data and long piston cores obtained during MD179 cruise, elucidated the timing and causes of pockmark and submarine canyon formation on the Joetsu Knoll in the eastern margin of the Sea of Japan. Gas hydrate mounds and pockmarks aligned parallel to the axis on the top of the Joetsu Knoll are associated with gas chimneys, pull-up structures, faults, and multiple bottom-simulating reflectors (BSRs), suggesting that thermogenic gas migrated upward through gas chimneys and faults from deep hydrocarbon sources and reservoirs. Seismic and core data suggest that submarine canyons on the western slope of the Joetsu Knoll were formed by turbidity currents generated by sand and mud ejection from pockmarks on the knoll. The pockmark and canyon formation probably commenced during the sea-level fall, lasting until transgression stages. Subsequently, hydropressure release during the sea level lowering might have instigated dissociation of the gas hydrate around the base of the gas hydrate, leading to generation and migration of large volumes of methane gas to the seafloor. Accumulation of hydrate caps below mounds eventually caused the collapse of the mounds and the formation of large depressions (pockmarks) along with ejection of sand and mud out of the pockmarks, thereby generating turbidity currents. Prolonged pockmark and submarine canyon activities might have persisted until the transgression stage because of time lags from gas hydrate dissociation around the base of the gas hydrate until upward migration to the seafloor. This study revealed the possibility that submarine canyons were formed by pockmark activities. If that process occurred, it would present important implications for reconstructing the long-term history of shallow gas hydrate activity based on submarine canyon development. 相似文献
14.
南海北部陆坡区神狐海域构造特征及对水合物的控制 总被引：5，自引：0，他引：5
通过对南海北部陆坡区神狐海域高精度2D和3D地震资料的精细解释,在研究区共识别出4种构造类型,分别为气烟囱(流体底辟)、区域大尺度断层、深水扇中的正断层和滑移体中的滑脱断层。气烟囱具有直立的通道形态,其内部结构可划分为杂乱反射带、模糊反射带和顶部强振幅区域。大尺度断层位于水合物钻探区的西北部和东北部,断层规模大,对深部地层表现出明显的控制作用。深水扇中的正断层广泛发育于上新世的深水扇中,特别是在水合物钻探区西部进积特征明显的深水扇中,正断层的数量更多。滑移体中的滑脱断层在神狐海域的第四纪地层中非常常见,在剖面上呈雁列式分布。研究结果表明,大尺度断层由于和水合物钻探区的距离较远,对于水合物的成藏可能不起控制作用。气烟囱和规模小数量多的断裂体系为含气流体的运移提供了垂向和侧向的输送通道,构成了水合物的流体运移体系。当富含甲烷气体的流体通过这些垂向-侧向的运移通道时,在合适的温压条件下,被适于水合物聚集的沉积体所捕获,就有可能形成水合物。水合物钻探区内东西部构造特征的差异,使得研究区内形成了不同的流体运移体系,这可能是控制钻探区水合物不均匀性分布的一个关键因素。 相似文献
15.
The eastern offshore of India covers a vast stretch of sedimentary tract fed by major rivers like Ganges, Brahmaputra and
Mahanadi in the north, Krishna and Godavari in the center, and Cauvery and Palar in the south, which led to variations in
shelf-slope characteristics, degree of slope and hence slope instability. The structure as well as seismic attribute maps
prepared from multibeam bathymetry and high-resolution 3D seismic data set has been analyzed to identify various geohazards
in the deep water offshore regions of the east coast of India. These can be categorized as slope instability, slope canyons,
shallow gas, mass transport complexes, sediment waves, gas hydrates, gas chimney, mud volcanoes and shallow faults. The slope
instability is primarily related to rapid sedimentation by the active river systems while the other geohazards are often developed
in association with shallow gas flows and leakages. The bottom simulating reflectors (BSRs) identified in the seismic sections
indicate the presence of gas hydrates. Rapid sedimentation, BSR formation, dissolution and expulsion of water as well as gas
and their subsequent vertical migration are responsible for the formation of shallow gas-related hazards. The results from
the above analysis are of immense help in minimizing the risk of shallow hazards during exploration, drilling and subsurface
installation activities along the eastern Indian offshore. 相似文献
16.
继我国在神狐海域两次天然气水合物试采成功之后,近几年来在琼东南盆地的勘探证实了天然气水合物的存在,而且钻探表明其与浅层气具有复杂的共生关系.为揭示琼东南盆地深水区天然气水合物与浅层气共生体系成藏特征,结合岩心、测井及三维地震数据,阐明了天然气水合物与浅层气的空间分布特征,研究结果表明,天然气水合物主要赋存在海底以下200 m范围内的沙质沉积物中,且其形成过程与浅层气的垂向运移有关.对天然气水合物与浅层气共生体系成藏特征的深入分析表明,深部热成因气和浅部生物成因气是其重要的气体来源,第四系未固结沙层是良好的储层,且天然气水合物和浅层气共生体系的分布主要受深部气烟囱和断层的控制.浅层气藏为天然气水合物提供稳定的气源条件;第四系块体流沉积与含天然气水合物地层能有效地封堵浅层气的纵向运移,进一步促进浅层气的成藏.因此,天然气水合物的形成与浅层气的发育具有正反馈的相互作用关系,有利于形成更大规模的天然气水合物矿体和浅层气藏,具有良好的商业开发潜力. 相似文献
17.
Christian Hermanrud Jon Marius Venstad Joe Cartwright Lars Rennan Kristine Hermanrud Hege M. Nordgård Bolås 《Mathematical Geosciences》2013,45(1):1-30
Both water level drops and erosion have previously been suggested as causes of fluid overpressures in the subsurface. Quantification of the relevance of these processes to supra-lithostatic fluid pressure formation with a wide selection of input parameters is lacking, and thus desired. The magnitudes and drop times that are required for water level drops to result in supra-lithostatic pore pressures in a variety of situations are calculated. Situations with pore fluids consisting of water, water with dissolved methane, water with a gas hydrate layer and dissolved methane in the underlying sediments, and water with dissolved methane, a gas hydrate layer, and free gas accumulation below the hydrate layer are separately addressed. The overpressure formation from reservoir gas expansion is also simulated. The simulation results demonstrate that high fluid overpressures can develop in a rock as a response to a water level drop without the presence of gas, provided that the rock has a sufficiently low compressibility. The contribution to fluid overpressuring is however dramatically increased if the pore water is saturated with methane prior to the water level drop, and is further amplified by the presence of gas hydrates and free gas accumulations beneath such hydrates. Gas expansion in reservoirs should be expected to significantly increase the fluid overpressures in shallow, sealed pressure compartments that experience erosion or water level drops, even if the water level drop duration exceeds one million years. Enough relationships between the calculated overpressure formation and the main controlling factors are provided in order to enable readers to make inferences about a variety of geological settings. Analyses of simulation results prompt us to suggest that pockmarks are likely to be triggered by gas expansion in vertical fluid migration pathways, that the giant craters at the seabed west of Albatross South in the Barents Sea result from hydrate dissociation, and that overpressure build-up due to gas expansion has contributed to reservoir overpressuring in many eroded basins, including the Hammerfest Basin in the Barents Sea. 相似文献
18.
Active hydrate destabilization in Lake Baikal,Siberia? 总被引：1，自引：0，他引：1
Marc De Batist Jan Klerkx Pieter Van Rensbergen Maarten Vanneste Jeffrey Poort Alexander Y. Golmshtok rei A. Kremlev Oleg M. Khlystov Petr Krinitsky 《地学学报》2002,14(6):436-442
ABSTRACT In this paper, we present new seismic and heat-flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper-than-normal and regions of shallower-than-normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift-basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre-existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present-day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature. 相似文献
19.
ABSTRACT Bubble plumes from hydrocarbon seeps drive upwelling flows in the water column that can disappear if the bubbles dissolve. This may lead to formation of a layer enriched in gases and substances transported by the bubbles, a process we term bubble deposition. A review of observed dissolved methane layers in the North Sea showed their existence in an area of active seeping pockmarks at a height of ∼ 20–30 m above the sea bed, well below the thermocline. To test the bubble deposition hypothesis, rising seep bubbles were simulated numerically. The model predicted a dissolution depth consistent with the observed methane layer for ∼ 2700-µm-radius bubbles. The model also predicted that bubbles smaller than 3400 µm dissolved subsurface, decreasing to 2000 µm for a 10-cm s−1 upwelling flow. We speculate that this layer may be attractive to marine organisms. Although North Sea seeps are not oily, this mechanism also applies to oily bubbles from hydrocarbon seeps or a leaking undersea gas/oil pipeline. Thus bubble deposition can create a subsurface oil layer which rises far slower than either the bubble stream or droplets entrained in the stream. 相似文献
20.
Fluid migration within the sedimentary column contributes significantly to slope failure and pockmark formation and can be an effective triggering mechanism to generate submarine landslides. Pockmarks are thus commonly listed among geohazards. Contrary to these accepted notions, we propose here an alternative view of pockmarks with an example from the Eastern Niger Submarine Delta: Pockmarks and associated chimneys may increase or modify the shear strength of sedimentary layers and locally enhance seafloor stability. The analysis of two 3D seismic volumes shows that a landslide deposit divides into two branches around a cluster of three pockmark chimneys, interpreted to impede its further development. The morphological characteristics of a slide constrained by fluid seepage features show the potential role of fluid escape in marine sediment strengthening. 相似文献