共查询到20条相似文献，搜索用时 31 毫秒
1.
Carl Jörg Petersen Stefan Bünz Steinar Hustoft Jürgen Mienert Dirk Klaeschen 《Marine and Petroleum Geology》2010
The newly developed P-Cable 3D seismic system allows for high-resolution seismic imaging to characterize upper geosphere geological features focusing on geofluid expressions (gas chimneys), shallow gas and gas hydrate reservoirs. Seismic imaging of a geofluid system of an Arctic sediment drift at the Vestnesa Ridge, offshore western Svalbard, provides significantly improved details of internal chimney structures from the seafloor to ∼500 m bsf (below seafloor). The chimneys connect to pockmarks at the seafloor and indicate focused fluid flow through gas hydrated sediments. The pockmarks are not buried and align at the ridge-crest pointing to recent, topography-controlled fluid discharge. Chimneys are fuelled by sources beneath the base of gas hydrate stability zone (GHSZ) that is evident at ∼160–170 m bsf as indicated by a bottom-simulating reflector (BSR). Conduit centres that are not vertically straight but shift laterally by up to 200 m as well as discontinuous internal chimney reflections indicate heterogeneous hydraulic fracturing of the sediments. Episodically active, pressure-driven focused fluid flow could explain the hydro-fracturing processes that control the plumbing system and lead to extensive pockmark formation at crest of the Vestnesa Ridge. High-amplitude anomalies in the upper 50 m of the chimney structures suggest formations of near-surface gas hydrates and/or authigenic carbonate precipitation. Acoustic anomalies, expressed as high amplitudes and amplitude blanking, are irregularly distributed throughout the deeper parts of the chimneys and provide evidence for the variability of hydrate and/or carbonate formation in space and time. 相似文献
2.
《Marine Geology》2004,203(1-2):119-140
The results of a combined geophysical and geochemical research programme on Deception Island, an active volcano at 62°43′S, 60°57′W in Bransfield Strait (Antarctica), are presented. Ultrahigh-resolution acoustic data obtained with a TOPAS (TOpographic PArameter Sonar) system and multibeam bathymetry (Simrad EM1000) allow a detailed analysis of submarine vents in Port Foster, the submerged caldera of Deception Island. The data show three different types of seafloor structures: low-relief mounds, high-relief mounds (‘wasp nest’-like) and spire-like structures. We interpret these structures as products of sediment volcanism and seeps caused by heating and boiling of pore fluids in gas-charged sediments, and related to recent short-lived volcanic events, possibly those that occurred in 1967, 1969 and 1970. In addition, subsurface vertical disturbed zones, formed by increased amplitude and phase-inverse reflectors beneath the mounds, suggest the presence of fluidised and brecciated sediments within hydrofracture systems. A key finding of this study is that there appears to be a close relationship between the submarine mounds detected by our ultrahigh-resolution seismic study, geochemical haloes, fault-pathways and present-day thermal anomalies in surface waters. We suggest that seafloor hydrofracture systems and subsurface pipes can be re-used as fluid migration pathways, resulting in hydrothermal seeps and vents on the seafloor, possibly up to decades after coeval volcanic eruptions. 相似文献
3.
为研究小尺度海底沉积物样品的声衰减特性,作者提出了用声学探针测量海底沉积物声波幅值的新方法,对沉积物样品扰动小,两个测量点的距离可小于波长,为海底沉积物微观声衰减测量提供了新手段。作者用小于波长的间隔逐点测量了沉积物的压缩波幅值,数据分析表明沿沉积物柱状样全长的声衰减满足指数衰减模型。目前主要用同轴差距衰减测量法获得海底沉积物声衰减数据,但该方法不能辨识声衰减模型,因此不同海区的测量结果难以建立联系。对此作者又提出用声吸收系数反演的幅值比与声衰减系数反演的R值(两种幅值比的比值)作评价依据,分析了垂直轴差距衰减测量法获得的南海海底沉积物声衰减测量数据,发现部分沉积物样品声衰减的R值远大于1,其声衰减不满足指数衰减模型。在声衰减满足指数衰减模型的条件下,用Hamilton的声衰减和频率经验公式预报的南海沉积物声衰减比与作者用声学探针测量海底沉积物所得的声衰减比对比,通过对R值分析得出Hamilton的声衰减和频率经验公式可以预报南海沉积物声衰减比的范围。作者提出的声学探针测量海底沉积物声衰减的方法的优点是既能获得声衰减数据又能辨识声衰减模型,不同海区测量的沉积物声衰减比可用R值建立联系。 相似文献
4.
Distribution and expression of gas seeps in a gas hydrate province of the northeastern Sakhalin continental slope, Sea of Okhotsk 总被引：1，自引：0，他引：1
Young Keun Jin Young-Gyun Kim Boris Baranov Hitoshi Shoji Anatoly Obzhirov 《Marine and Petroleum Geology》2011,28(10):1844-1855
Multidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the northeastern Sakhalin continental slope (NESS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2007 (CHAOS and SSGH projects). One hundred sixty-one gas seeps were detected in a 2000 km2 area of the NESS (between 53°45′N and 54°45′N). Active gas seeps in a gas hydrate province on the NESS were evident from features in the water column, on the seafloor, and in the subsurface: well-defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater, and gas hydrates in sediment near the seafloor. These expressions were generally spatially related; a gas flare would be associated with a seepage structure (mound), below which a gas chimney was present. The spatial distribution of gas seeps on the NESS is controlled by four types of geological structures: faults, the shelf break, seafloor canyons, and submarine slides. Gas chimneys that produced enhanced reflection on high-resolution seismic profiles are interpreted as active pathways for upward gas migration to the seafloor. The chimneys and gas flares are good indicators of active seepage. 相似文献
5.
Pockmarks are observed worldwide along the continental margins and are inferred to be indicators of fluid expulsion. In the present study, we have analysed multibeam bathymetry and 2D/3D seismic data from the south-western Barents Sea, in relation to gas hydrate stability field and sediment type, to examine pockmark genesis. Seismic attributes of the sediments at and beneath the seafloor have been analysed to study the factors related to pockmark formation. The seabed depths in the study area are just outside the methane hydrate stability field, but the presence of higher order hydrocarbon gases such as ethane and/or propane in the expelled fluids may cause localised gas hydrate formation. The selective occurrence of pockmarks in regions of specific seabed sediment types indicates that their formation is more closely related to the type of seabed sediment than the source path of fluid venting such as faults. The presence of high acoustic backscatter amplitudes at the centre of the pockmarks indicates harder/coarser sediments, likely linked to removal of soft material. The pockmarks show high seismic reflection amplitudes along their fringes indicating deposition of carbonates precipitated from upwelling fluids. High seismic amplitude gas anomalies underlying the region away from the pockmarks indicate active fluid flow from hydrocarbon source rocks beneath, which is blocked by overlying less permeable formations. In areas of consolidated sediments, the upward flow is limited to open fault locations, while soft sediment areas allow diffused flow of fluids and hence formation of pockmarks over a wider region, through removal of fine-grained material. 相似文献
6.
This study presents seismic observation of pipe anomalies from offshore Nigeria, outcrops of blow-out pipes from Rhodes, Greece, and geophysical modelling of an acoustic pipe. The studies give insight into how pipes form, their internal structure, the seismic image and geophysical artefacts related to the pipes. Over one hundred seafloor craters, 100 m-700 m wide and up to 30 m deep, have been observed on the seafloor offshore Nigeria. They are underlain by interpreted cones and seismic pipe anomalies that can be traced down to reservoir zones at 1000 m-1300 m below the seafloor. The seismic pipe anomalies are 50 m-150 m wide and almost vertical. They are interpreted as up-scaled pipes found in outcrops on Rhodes, Greece. The outcrops show pipe-related structures at three levels. Lowest, the reservoir rock contains metre-sized cavities which are filled with a mixture of clay derived from the overlying cap rock. In the middle, several circular to oval structures in plane view of pipes are observed in the lowest part of the cap rock. Highest, 15 m into the clay cap rock, strongly sheared country rock forms circular structures with a core of structureless clay. Based on outcrop observation on Rhodes we constructed an acoustic model of a 50 m wide and 1000 m long pipe. Seismic modelling proves that such pipes would be expressed in seismic data, that they are similar to the seismic pipe anomalies offshore Nigeria but this study also revealed that prominent intra-pipe reflections are artefacts. A formation model for the pipes is suggested: High fluid overpressure in the reservoir generated hydro fractures from the reservoir to seafloor where a mixture of gas and fluid flowed at high speed to form pipes, cones and seafloor craters. After hours to weeks of gas and fluid flow through the pipe the pore pressure in the reservoir dropped and the blow-out terminated. Muddy slurry fell back and plugged the cavity in the reservoir and the pipe. 相似文献
7.
《Marine Geology》2005,216(4):265-274
Magnetic susceptibility measurements on near-surface sediment cores from the North Cascadia accretionary sedimentary prism show that seismic blanking or wipe-out zones in the upper few hundred metres of sediments are associated with a prominent low magnetic susceptibility signature. Seismic blanking and low magnetization are both attributed to high upward methane flux within a vent zone, as evidenced by the presence of massive gas hydrate within the cores. Sedimentological analysis of these cores also reveals the presence of authigenic pyrite within the areas of magnetic susceptibility lows. This phenomenon is suspected to be produced by the reducing environment associated with the high upward methane flux and increased bacterial activity within the topmost sediments, resulting in diagenesis of highly magnetic detrital minerals such as magnetite into nearly non-magnetic pyrite. These low magnetic susceptibility zones may produce magnetic anomalies with a magnitude of 10–35 nT near the seafloor. Such anomalies might be detected using high-resolution near-bottom magnetometers to provide a means of mapping zones of methane venting. 相似文献
8.
Ana García-García Daniel L. Orange Norman M. Maher Adam S. Heffernan Gary S. Fortier Andy Malone 《Marine and Petroleum Geology》2004,21(10):1255-1264
High-resolution seafloor and sub-surface data were acquired as part of a site survey in Iskenderun Bay, SE Turkey to characterize the geohazards at the location of the proposed drilling site. A 3 km×3 km geophysical study reveals a pockmark field which trends NE and NNE, similar to the trend of major fault systems in the area. The pockmarks, with an average diameter of 35 m, reach their highest density in the northern part of the detailed survey area, with 13 features/km2. Acoustic anomalies in the seismic records (acoustic turbidity, blanking, enhanced reflectors) below the proposed drilling site indicated potential shallow gas beneath it. The local seismic anomalies (amplitude and frequency) parallel to stratigraphy were assigned a low gas risk. As a result of the active neotectonics in the area, the pockmark field presented a potential hazard for drilling at the original location. The geohazard study resulted in moving the proposed drilling site eastward to an area of fewer pockmarks, less sub-surface seismic anomalies, and thus a location interpreted as a lower geohazard environment. 相似文献
9.
10.
《Marine and Petroleum Geology》2013,39(1):128-142
The northern Gulf of Mexico is dominated by salt tectonics, resulting fracturing and numerous seafloor seeps and vents. Woolsey Mound, site of the Gulf of Mexico Hydrates Research Consortium's seafloor observatory, has been investigated extensively via surveys, direct sampling and seafloor instrument systems. This study presents an innovative approach to seismic data interpretation, integrating three different resolution datasets and maximizing seismic coverage of the complex natural hydrocarbon plumbing system at Woolsey Mound.3D industry seismic data reveal the presence of a salt body at in the shallow subsurface that has generated an extended network of faults, some extending from the salt body to the seafloor (master faults). Higher resolution seismic data show acoustic wipe-out zones along the master faults with expulsion features – seafloor pockmarks and craters – located immediately above them and associated, in the subsurface, with high-amplitude, negative anomalies at constant depth of 0.2 s TWTT b.s.f., interpreted as free gas. Since pockmarks and craters provide pathways for hydrocarbons to escape from depth into the water column, related sub-surface seismic anomalies may indicate free gas at the base of the gas hydrates stability zone (GHSZ). Fluid flow and gas hydrates formation are segmented laterally along faults. Gas hydrates formation and dissociation vary temporally in the vicinity of active faults, and can temporarily seal them as conduits for thermogenic fluids. Periodic migrations of gases and other fluids may perturb the GHSZ in terms of temperature and pressure, producing the observed lack of classical BSRs. 相似文献
11.
Located on the West Iberian margin, between Cabo Carvoeiro and Cabo da Roca, the Estremadura Spur is a trapezoidal promontory elongated in an east-west direction, extending until the Tore seamount. Recently a field with more than 70 pockmarks was discovered in the NW region of the Estremadura Spur outer shelf (Lourinhã Monocline). Pockmarks are the seabed culminations of fluid migration through the sedimentary column and their characteristic seabed morphologies correspond to cone-shaped circular or elliptical depressions. The characterization of these features and the understanding of the associated fluid escape process are the main objectives of this work. Here we characterize these structures to understand their structural and stratigraphic control based on: 1) Seismic processing and interpretation of the high resolution 2D single-channel sparker seismic dataset, 2) Bathymetric and Backscatter interpretation and 3) ROV direct observation of the seafloor.The analysis of the seismic profiles allowed the identification of six seismic units, disturbed by the migration and accumulation of fluids. The Estremadura Spur outer shelf has been affected by several episodes of fluid migration and fluid escape during the Pliocene-Quaternary that are expressed by a vast number of seabed and buried pockmarks. At present, the pockmarks are mainly inactive, as the seabed pockmarks are covered by recent sediments. It is concluded that the migration of fluids to the seabed occurred over the Pliocene-Quaternary, as indicated by the buried pockmarks at different depths below the seabed. The vertical stacking of various pockmarks suggests a cyclical fluid flow activity that can possibly be the result of the eustatic sea level variations and the subsequent changes of the hydrostatic pressure. 相似文献
12.
Three-dimensional (3D) seismic data acquired for hydrocarbon exploration reveal that gas accumulations are common within the
2–3 km thick Plio-Pleistocene stratigraphic column of the south-western Barents Sea continental margin. The 3D seismic data
have relatively low-frequency content (<40 Hz) but, due to dense spatial sampling, long source-receiver offsets, 3D migration
and advanced interpretation techniques, they provide surprisingly detailed images of inferred gas accumulations and the sedimentary
environments in which they occur. The presence of gas is inferred from seismic reflection segments with anomalously high amplitude
and reversed phase, compared with the seafloor reflection, so-called bright spots. Fluid migration is inferred from vertical
zones of acoustic masking and acoustic pipes. The 3D seismic volume allows a spatial analysis of amplitude anomalies inferred to reflect the presence of gas and fluids. At several locations, seismic attribute
maps reveal detailed images of flat spots, inferred to represent gas–water interfaces. The data indicate a focused fluid migration
system, where sub-vertical faults and zones of highly fractured sediments are conduits for the migration of gas-bearing fluids
in Plio-Pleistocene sediments. Gas is interpreted to appear in high-porosity fan-shaped sediment lobes, channel and delta
deposits, glacigenic debris flows and sediment blocks, probably sealed by low-permeability, clayey till and/or (glacio)marine
sediments. Gas and fluid flow are here attributed mainly to rapid Plio-Pleistocene sedimentation that loaded large amounts
of sedimentary material over lower-density, fine-grained Eocene oozes. This probably caused pore-fluid dewatering of the high-fluid
content oozes through a network of polygonal faults. The study area is suggested to have experienced cycles of fluid expulsion
and hydrocarbon migration associated with glacial–interglacial cycles. 相似文献
13.
海底浅层地质灾害的高分辨率地震识别技术 总被引：1，自引：0，他引：1
将渤海某油田最新采集的二维高分辨率资料处理解释后,结合区域地球物理及地质概况,利用地震相分析、波阻抗反演、井(孔)震标定等深层油气勘探的成熟技术,系统研究了各类海底浅层地质灾害因素的成因、特征、危害及展布规律,总结了一套完整的利用高分辨率地震识别海底浅层地质灾害的技术方法。结果表明,浅层断裂、浅层气和埋藏古河道是研究区海底浅层发育的主要地质灾害因素,通过刻画不同期次地质灾害因素的类型及其分布范围,为今后该油田海上施工提供了可靠的工程地质调查成果。因此,高分辨率地震技术能够很好地应用于海底浅层地质灾害的识别。 相似文献
14.
由沉溺珊瑚礁、各类胶结砂以及胶结的珊瑚石或贝壳碎屑等组成的硬质薄层通常呈零散状分布,地质取样难以准确确定它们是如何分布的,这给海底管线施工带来极大的困难和风险。本文以南海北部为例,基于多种物探资料并结合正演模拟,分析、总结了海底以及海底之下硬质薄层的声学特征,在研究区综合识别出23个硬质薄层分布区。研究认为,硬质薄层与松散沉积物物理性质的差异可用于声学探测数据识别和定位。在浅地层剖面上,硬质薄层表现为强反射薄层,并对其下方地层的地震反射信号有一定的屏蔽作用,这一现象有助于确定硬质薄层是否存在以及其埋深和位置。在侧扫声呐影像和后向散射强度图上,硬质薄层通常表现为具有不规则形状的明暗变化阴影,阴影的边界指示了硬质薄层的分布范围。当硬质薄层出露于海底时,侧扫影像、反向散射强度结合浅地层剖面可以有效地识别并确定硬质薄层的范围;而当硬质薄层位于海床浅部（埋深数米到十几米）时,浅地层剖面可能是识别硬质薄层的唯一且最有效的方法。 相似文献
15.
N. Satyavani Kalachand Sain Malcolm Lall B. J. P. Kumar 《Marine Geophysical Researches》2008,29(3):167-175
Seismic data from the Andaman offshore region has been examined to investigate for the presence of gas hydrates. The seismic
data displays reflection characteristics such as blanking, enhanced reflection patterns, shadows in instantaneous frequency,
and increase in amplitude with the offset, which are indicative of gas hydrates and underlying free gas. A prominent bottom-simulating
reflection, BSR, coupled with reverse polarity is observed around 650–700 ms. Seismic attributes such as the reflection strength
and instantaneous frequency are computed along this reflector in order to probe for the presence of gas hydrates or free gas
in this region. The reflection plot shows a strong reflector paralleling the seafloor. In addition, attenuation of the high
frequency signal is noticed, indicating the presence of free gas below the BSR. 相似文献
16.
中国东南近海海底沉积物声学物理性质及其相关关系 总被引：17，自引：3，他引：17
在获得的数据资料基础上,发现了中国东南近海海底沉积物声学物理参数的平面分布规律,通过对这些参数的回归分析以及对声速和沉积物密度的估计,建立了经验公式。结果显示,中国东南近海海底沉积物的基本声学物理特性如下:沉积物类型多样而且复杂,从黏土到砂砾有13个颗粒组分组合;沉积物物理力学参数变化范围较大;沉积物声学性质相对于附近海域的数据变化范围更大。这些都与海底沉积环境、沉积物来源、沉积条件和沉积作用过程有关。该项研究有助于建立海底地声模型及开展应用。 相似文献
17.
南海北部陆坡东沙海域海底丘状体气体与水合物分布 总被引：1，自引：0，他引：1
海底丘状体在天然气水合物发育区是一种常见的微地貌,对丘状体的研究有助于理解海底流体渗漏模式以及水合物的赋存规律。本文研究南海北部陆坡东沙海域天然气水合物发育区海底丘状体的特征及其与水合物的关系。研究所用的数据包括准三维多道地震数据、多波束数据以及浅地层剖面数据。在多波束海底地形图上,丘状体表现为局部的正地形,直径大约为300 m,高出周围海底约50 m。浅地层剖面上存在明显的声空白以及同相轴下拉现象,指示了海底丘状体气体的分布以及流体运移的路径。丘状体周围明显的BSR表明局部区域可能发育有水合物,水合物钻探结果也证实了这一推测。三维多道地震剖面上,丘状体正下方存在空白反射区域,这与泥火山的地震反射特征类似。但空白反射区域内存在强振幅能量,而且丘状体正下方存在连续的反射层,这表明该丘状体并非泥火山成因。综合钻探结果以及三维地震成像结果,认为水合物形成过程引起的沉积物膨胀以及海底碳酸盐岩的沉淀是形成该丘状体的主要原因。 相似文献
18.
Mud volcanoes and gas vents in the Okhotsk Sea area 总被引：5，自引：0，他引：5
Shakirov Renat Obzhirov Anatoly Suess Erwin Salyuk Anatoly Biebow Nicole 《Geo-Marine Letters》2004,24(3):140-149
Gas emissions from mud volcanoes on Sakhalin Island and water-column gas flares arising from cold seeps in the Okhotsk Sea appear to be related. They are likely activated by tectonic movements along the transform plate boundary separating the Okhotsk Sea Plate from the Eurasian and Amur plates. Gas vents (flares) and methane anomalies occur in the waters offshore Sakhalin Island, along with NE-SW-trending mounds and fluid escape structures on the seafloor. The intersection of the NE-striking transverse faults on land with the Central Sakhalin and Hokkaido-Sakhalin shear zones apparently determines the sites of mud volcanoes, a pattern that continues offshore where the intersection with the East Sakhalin and West Derugin shear zones determines the sites of the submarine gas vents. 相似文献
19.
We have obtained improved images of a debris flow deposit through the reprocessing of multichannel seismic reflection data
between Drifts 6 and 7 of the continental rise of the Pacific margin of the Antarctic Peninsula. The reprocessing, primarily
aimed at the reduction of noise, relative to amplitude preservation, deconvolution, also included accurate velocity analyses.
The deposit is dated as upper Pliocene (nearly 3.0 Ma) via correlation to Sites 1095 and 1096 of the Ocean Drilling Program
(ODP) Leg 178. The estimated volume is about 1800 km3 and the inferred provenance from the continental slope implies a run out distance exceeding 250 km. The dramatic mass-wasting
event that produced this deposit, unique in the sedimentary history of this margin, is related to widespread late Pliocene
margin erosion. This was associated with a catastrophic continental margin collapse, following the Antarctic ice sheet expansion
in response to global cooling. The seismic data analysis also allowed us to identify diffractions and amplitude anomalies
interpreted as expressions of sedimentary mounds at the seafloor overlying narrow high-velocity zones that we interpret as
conduits of fluid expulsion hosting either methane hydrates or authigenic carbonates. Fluid expulsion was triggered by loading
of underlying sediments by the debris flow deposits and may have continued until today by input of fluids from sediment compaction
following the deep diagenesis of biogenic silica. 相似文献
20.
《Marine Geology》2001,172(1-2):57-73
Conical mounds, 1–1.5 km in diameter, and up to 65 m high were mapped at the foot of the active Makran continental margin. The mounds developed seaward of the accretionary front in a relatively planar zone where the beginning of build-up of tectonic pressure initiates deformation. Based on shallow high-resolution 4 kHz sediment echosounding, the sedimentary sequence in this area is generally well stratified, as indicated by closely spaced horizontal reflections. However, in the vicinity of the mounds the sediment is characterised by many acoustically transparent zones, which are 100–300 m in diameter and cut near-vertically through the horizontal reflectors.Two sediment cores from the top of the largest cone and a neighbouring acoustically transparent zone reveal small-scale post-depositional deformation in a stratified sequence and methane concentrations up to 40,000 ng/g. This deformation and disruption of potential reflectors provides a clue to explain the acoustic transparency: we interpret it as caused by the rise of charged fluids and mud, leading initially to the (slight) disturbance of the generally good acoustic reflectors and eventually to the formation of conical mud mounds (mud volcanoes). MCS data, showing a buried mound in an analogous structural position, support the idea of tectonically induced mud/fluid expulsion seaward of the accretionary front. 相似文献