南海白云凹陷东南部两种不同类型块体搬运沉积体系的地震响应及成因分析

文章利用三维地震数据揭示了南海白云凹陷东南部两种不同类型的块体搬运沉积体系的内部反射特征、外部形态及运动指示标志, 并且探讨了其成因机制。结果表明, 自晚中新世以来研究区共发育4种地震相: 弱振幅水平状连续地震相、强振幅波状连续地震相、弱振幅半透明杂乱反射地震相和中-强振幅丘状连续反射地震相。通过地震相分析可知, 研究区自晚中新世以来共发育两种不同类型的块体搬运沉积体系: 1) 多期块体搬运沉积复合体, 主要由弱振幅半透明杂乱反射地震相组成, 边界模糊; 2) 单期块体搬运沉积体, 主要由弱振幅半透明杂乱反射地震相和中-强振幅丘状连续反射地震相组成, 边界清晰明显。另外, 研究结果发现高沉积速率和地震活动使得研究区的块体搬运沉积体系表现出内部运动指示特征发育程度低的特征, 而东沙构造活动导致该块体搬运沉积体系具有频发性。     

Origin and anatomy of two different types of mass–transport complexes: A 3D seismic case study from the northern South China Sea margin

Integration of 2D and 3D seismic data from the Qiongdongnan Basin along the northwestern South China Sea margin has enabled the seismic stratigraphy, seismic geomorphology and emplacement mechanisms of eight separate, previously undocumented, mass–transport complexes (MTCs) to be characterized. These eight MTCs can be grouped into two types:(1) Localized detached MTCs, which are confined to submarine canyons and cover hundreds of km², consist of a few tens of km³ remobilized sediments and show long striations at their base. They resulted from small-scale mass-wasting processes induced by regional tectonic events and gravitational instabilities on canyon margins.(2) Regional attached MTCs, which occur within semi-confined or unconfined settings and are distributed roughly perpendicular to the strike of the regional slope. Attached MTCs occupy hundreds to thousands of km² and are composed of tens to hundreds of km³ of remobilized sediments. They contain headwall escarpments, translated blocks, remnant blocks, pressure ridges, and basal striations and cat-claw grooves. They were created by large-scale mass-wasting processes triggered by high sedimentation rates, slope oversteepening by shelf-edge deltas, and seismicity.Our results show that MTCs may act as both lateral and top seals for underlying hydrocarbon reservoirs and could create MTC-related stratigraphic traps that represent potential drilling targets on continental margins, helping to identify MTC-related hydrocarbon traps.     

Seismic geomorphological analysis of deepwater gravity-driven deposits on a slope system of the southern Colombian Caribbean margin

Gravity-driven processes are important agents for transporting sediments downslope into deep-marine environments. The Pliocene to Holocene offshore succession of the Colombian Caribbean margin and its stratigraphic distribution, have been affected by faulting and mud diapirism, and have been characterized using 3D seismic data. Nine stratigraphic intervals were characterized within the study, and are interpreted to consist of a range of seismic geomorphologies, including slumps and debrites. Nine gravity-driven deposits were defined within the study area, interpreted to have been transported to the north and northwest. Slumps display high-amplitude, high continuity, elongated, stratified, lobate and confined morphologies, while debrites have a reflection-free pattern or show discontinuous, low-amplitude and chaotic reflections. Mixed slumps-turbidites-debrites deposits are composed by a succession of laterally and vertically interfingered slumps, debrites and turbidites. These deposits are morphologically lobate and broadly scattered. In addition, erosional features such as basal small scours, megascours, linear scours and rafted blocks were used as kinematic indicators within the gravity-driven deposits. There are several candidates triggering mechanism, including over-steepening of slope (related to high sediment supply or slope tectonism). In the study area, confined slumps and debrites with a main transport direction from south to north have been observed, while transport direction of the mixed slumps-turbidites-debrites was toward northwest. Additionally, the fact that slumps and debrites are found in depocenters between periclines suggests a confined environment of deposition. Finally, mixed slumps-turbidites-debrites are unconfined without evident structural control. We suggest that local intraslope sub-basin margin become over-steepened as a result of mud diapirism in the subsurface. In this situation, the paleobathymetry was sufficient to trap the resultant gravity-driven deposits within the sub-basins, suggesting a local origin. Seismic evidence of BSR (Bottom Simulating Reflector) suggests the presence of gas hydrate in the study area, and is taken as an additional potential mechanism to provide instability of slope and generate gravity-driven deposits.     

The application of high-resolution 3D seismic data to model the distribution of mechanical and hydrogeological properties of a potential host rock for the deep storage of radioactive waste in France

In the context of a deep geological repository of high-level radioactive wastes, the French National Radioactive Waste Management Agency (Andra) has conducted an extensive characterization of the Callovo-Oxfordian argillaceous rock and surrounding formations in the Eastern Paris Basin. As part of this project, an accurate 3D seismic derived geological model is needed. The paper shows the procedure used for building the 3D seismic constrained geological model in depth by combining time-to-depth conversion of seismic horizons, consistent seismic velocity model and elastic impedance in time. It also shows how the 3D model is used for mechanical and hydrogeological studies. The 3D seismic field data example illustrates the potential of the proposed depth conversion procedure for estimating density and velocity distributions, which are consistent with the depth conversion of seismic horizons using the Bayesian Kriging method. The geological model shows good agreement with well log data obtained from a reference well, located closest to the 3D seismic survey area.Modeling of the mechanical parameters such as shear modulus, Young modulus, bulk modulus indicates low variability of parameters confirming the homogeneity of the target formation (Callovo-Oxfordian claystone). 3D modeling of a permeability index (Ik-Seis) computed from seismic attributes (instantaneous frequency, envelope, elastic impedance) and validated at the reference well shows promising potential for supporting hydrogeological simulation and decision making related to safety issues.     

Salt tectonics and Pliocene stratigraphic framework at MC-118, Gulf of Mexico: An integrated approach with application to deep-water confined structures in salt basins

Integrated tectono-stratigraphic interpretation at MC-118 using 3D seismic, well logs and biostratigraphy reveals an area dominated by allochthonous salt and its related structures. OCS-Block MC-118 is located 130 km southeast of New Orleans on the Gulf of Mexico middle slope in ∼2600 ft of water.The area is divided into three domains based on their structural styles: (1) a western domain consisting of a basinward-dipping normal fault family and associated strata; (2) a central domain composed of a landward-plunging diapiric salt tongue canopy and associated salt welds, two flanking NE–SW trending salt-withdrawal mini-basins, and a crestal fault family; and (3) an eastern domain comprised of basinward/landward-dipping normal and listric normal fault families with their associated rollovers. These structural domains are genetically-and-kinematically related to the salt structure and extend beyond MC-118 boundaries. The salt structure is postulated to have evolved mostly passive, with punctuated active episodes, and by lateral spreading. This is part of a larger regional structure, eastern Gulf of Mexico, which involves some amalgamation between small-scale salt canopies and salt diapirs although collectively they appear mostly disconnected.A Pliocene (3.13–4.95 Ma) third-order genetic stratigraphic sequence, the focus of this study, is as much as ∼3600 ft thick within the mini-basins and contains: muddy mass transport complexes; sandy slope fans; muddy turbidites and condensed sections; and transitional facies flanking the salt structure that collectively have ponded and wedged external geometries. Mass transport complexes and muddy turbidites and condensed sections make most of the studied genetic sequence in a mud-dominated deltaic setting eastern Gulf of Mexico.Facies kinematic indicators and a matching number of genetic sequences accounted on the sea level chart support a eustatically driven mini-basin sedimentation. Nonetheless salt still plays a role in sedimentation (secondary/minor) by slumping generated during passive/active salt diapiric evolution.     

Pockmark-like depressions near the Goliat hydrocarbon field,Barents Sea: Morphology and genesis

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.     

Architecture of lacustrine mass-transport complexes in the Mesozoic Songliao Basin,China

3-D seismic data and wireline log profiles of the Central Depression in the Songliao Basin exhibit four lacustrine mass-transport complexes (MTCs) in the second and the third members of the Upper Cretaceous Nenjiang Formation. The mass-transport complex named MTC-A lies in the north of the Daqing Anticline with an area of approximately 95 km² and a maximum thickness of 62 m. It consists of five laterally and vertically stacked blocks striking E-W and has a convex-downslope front. The mass-transport complex named MTC-C is located in the south of the Daqing Anticline consisting of seven blocks. This MTC strikes NNE-SSW and has an area of approximately 61.5 km² and a maximum thickness of 55 m. MTC-B, the mass-transport complex lying in the middle of the Daqing Anticline, consists of three vertically stacked blocks and has a semi-circular outline striking E-W. MTC-B has an area of approximately 24 km² and a maximum thickness of 92 m. Along the Daqing Anticline from north to south, the three MTCs distribute in lacustrine facies in the NNE direction. The mass-transport complex named MTC-D located in the southeast of the Daqing Anticline has an area of approximately 150 km² with a maximum thickness of 135 m striking E-W, which is rich in mudstones. MTC-D is characterized by the three-layer architecture vertically consisting of a dragged layer at the bottom, a slumped layer in the middle, and a stable layer at the top. Besides, in the plane view, MTC-D can be divided into three parts according to the sliding distance and stacking pattern of the slip blocks: the detaching area, the stacking area and the drifting area. The MTCs are characterized by thickening upslope and thin-out downslope. Siltstones and very fine sandstones occur in 2–4 beds that are cumulatively 0.8–7 m thick in the upslope and central parts of the MTCs. The edges of the blocks are composed of mudstone. Seismic amplitude slices reveal arcuate or straight ridges on the block surfaces with a spacing density of 4–10 per kilometer and a height ranging from 25 to 40 m. The arcuate ridge paleo-morphology on the MTC surfaces suggests that blocks are slump bodies. The estimated minimum water depth at the time of the MTC emplacement is 30–70 m, and the sliding distance is 2–10 km. From 3-D seismic amplitude slices, no feeding channel connected to the mass-transport complexes is found. Besides, coupled with the continuous ridges on blocks and the clear and flat lateral edges suggest that mass-transport complexes belong to the prodelta slump bodies. Thus, the triggering mechanism of the MTCs may be closely related to earthquakes caused by volcanic activities with the evidence of three cinerite layers shown in the well cores.     

Depositional elements associated with a basin floor channel-levee system: case study from the Gulf of Mexico

The seismic geomorphology and seismic stratigraphy of a deep-marine channel-levee system is described. A moderate to high-sinuosity channel trending southeastward across the northeastern Gulf of Mexico basin floor, and associated depositional elements are well imaged using conventional 3D multi-channel seismic reflection data. Depositional elements described include channels, associated levees, a channel belt, avulsion channels, levee crevasses, frontal splays, sediment waves, and mass transport complexes. Distinguishing morphologic and stratigraphic characteristics of each depositional element are discussed. These deposits are presumed to be associated with repeated deep-marine turbidity flows and other mass transport processes.     

Fine-grained Pleistocene deepwater turbidite channel system on the slope of Qiongdongnan Basin, northern South China Sea

Recently, as oil exploitation has become focused on deepwater slope areas, more multi-channel high resolution 2D and 3D seismic data were acquired in the deepwater part of the Qiongdongnan Basin, northern South China Sea. Based on 3D seismic data and coherence time slice, RMS and 3D visualization, a series of deepwater channels were recognized on the slope that probably developed in the late Quaternary period. These channels trend SW–NE to W–E and show bifurcations, levees, meander loops and avulsions. High Amplitude Reflections (HARs), typical for channel–levee complexes, are of only minor importance and were observed in one of the channel systems. Most of the detected channels are characterized by low-amplitude reflections, and so are different from the typical coarse-grained turbidite channels that had been discovered worldwide. The absence of well data in the study area made it difficult to determine the age and lithology of these channels. Using a neighboring drill hole and published data about such depositional systems worldwide, the lithology of these channels is likely to be dominated by mudstones with interbedded thin sandstones. These channels are formed by turbidity currents originated from the little scale mountain river of mid-Vietnam in SW direction and were probably accompanied by a relative sea level drop in the last glacial age. These channels discovered on the northern South China Sea slope are likely to be fine-grained, mud-dominant and low N:G deposits in a deepwater paleogeographic setting.     

Strike-slip systems as the main tectonic features in the Plio-Quaternary kinematics of the Calabrian Arc

The oblique and diachronous collision of the Apennine-Maghrebian Chain with the Apulian (in the north-east) and Pelagian (in the south) continental forelands, has determined the characteristic arcuate structure of this orogen. The effects of Plio-Pleistocene deformation of the Calabrian Arc have been analysed on the basis of available reflection seismic profiles and using local time-structural maps reconstructed along the main structures. During this period, internal sectors of the Tertiary chain migrated forward on the oceanic Ionian foreland, and were cut by important strike-slip systems. These last have an orientation approximately coincident with that of the migration of the front, allowing differential movement of the different sectors of the arc, towards the weakly buoyant Ionian oceanic domain. The dataset suggests a clear connection between the development of the strike-slip systems cutting the chain and the direction of tectonic transport, towards the East during Late Messinian/Early Pliocene time, to the ESE during Late Pliocene/Early Pleistocene time, finally to the SSE during the Middle/Late Pleistocene to Present, showing a clockwise rotation in well defined stages during the kinematic evolution of the chain. The origin of the Strait of Messina during the different phases is also interpreted in the context of the analysed regional tectonic setting.     

时频分析技术在储层分析中的应用

时频分析是对地震信号进行分解,可以在不同频带上显示不同级别的地质现象。采用连续小渡变换方法,对地震资料进行储层时频分析和分频属性提取,时频主极值频率曲线与伽马曲线有较好对应关系,尤其是其低频趋势线。对A区块周边的两口井井旁道进行了时频分析,揭示出该区15Hz低频数据体与储层及含油气相关性较好。针对这一特征,对该区三维地震体进行了运算及属性提取,描述其储层展布。     

三维AVO分析及在黄骅坳陷港186井区的应用

利用Hampson-Russell／Geoview／AVO软件研究含气砂岩的地震反射振幅随炮检距的变化关系及AVO属性的特征。并将AVO技术应用于大港油田黄骅坳陷港186井区的天然气藏研究。结果表明,在地质条件复杂的地区,三维AVO分析可区分真假天然气响应,准确确定已知气藏及异常区的空间展布范围。     

Geophysical fingerprints of hyper-extended,exhumed and embryonic oceanic domains: the example from the Iberia–Newfoundland rifted margins

This study investigates the magnetic and gravity signatures and associated seismic character of hyper-extended, exhumed and embryonic oceanic domains along the conjugate Iberia–Newfoundland rifted margins. As these margins have been drilled down to basement along their distal parts, it is possible to explore and test different geophysical techniques and interpretations. The aims of this work are twofold: (1) to investigate the location and nature of the two main marginal boundaries—the necking zone and the J Anomaly, which define the limits of major domains; and (2) to map the lateral variations of gravity and magnetic signatures and their detailed correlation with seismic data, from the proximal margin until the first unequivocal oceanic magnetic anomaly (e.g. C34 Anomaly). The results point out that the J Anomaly corresponds to a first-order tectono-magmatic boundary, with a basement formed by polyphase magmatism. It marks the boundary between the exhumed mantle domain, with little magmatic additions, from a domain oceanwards that reveals comparable trends, frequencies and a general magnetic pattern at both sides of the Atlantic, suggesting a coeval evolution. We propose that the domain between the J and the C34 Anomalies was formed by an embryonic spreading system, with intermittent budgets of magma, similar to those observed at very slow spreading systems. The J Anomaly may thus correspond to the location of lithospheric breakup though its origin and the nature of the domain oceanwards remains to be constrained.     

裂隙识别技术及其在油气和水合物勘探中的应用

裂隙是油气藏和天然气水合物成藏成矿的有利疏导体系, 但是受地震分辨率的影响, 微裂隙不易用常规手段识别。为研发一套实用的裂隙识别技术, 文章分析了裂隙的地震波运动学和动力学特征, 结合相关技术功能原理, 融合三维可视化技术、相干技术等方法, 在莺歌海盆地的底辟构造中成功刻画出裂隙通道, 并据此技术发现大气田。经实践及分析, 该技术亦可应用于琼东南盆地天然气水合物的疏导体系研究, 是一套行之有效的裂隙识别技术。     

Simulation of free surface flow around a VLCC hull using viscous and potential flow methods

Numerical simulations have been carried out to determine the incompressible free surface flow around a VLCC hull form for which experimental results are available. A commercial viscous flow finite volume code using the two-phase Eulerian–Eulerian fluid approach and a potential flow code based on the Rankine source method have been used in this study. The simulation conditions are the ones for which experimental results exist. The shear stress transport (SST) turbulence model has been used in the viscous flow code. A tetrahedral unstructured grid was used with the viscous flow code for meshing the computational domain, while quadrilateral structural patches were used with the potential flow code for meshing the VLCC hull surface and the water surface around it. The results compare well with the available experimental data and they allow an understanding of the differences that can be expected from viscous and potential flow methods as a result of their different mathematical formulations, which make their complementary application useful for determining the total ship resistance.     

The role of basement tectonic reactivation on the structural evolution of Campos Basin,offshore Brazil: Evidence from 3D seismic analysis and section restoration

The structural analysis of regional 3D seismic data shows evidence of long-term tectonic inheritance in Campos Basin, offshore Brazil. Main Lower Cretaceous rift structures controlled themselves by strike-slip deformation belts related to Proterozoic orogenic events, have been episodically reactivated during the divergent margin phase of Campos Basin, from the Albian to the Miocene. Balanced cross-sections of major salt structures indicate that such tectonic reactivations have been controlling thin-skinned salt tectonics, triggering pulses of gravitational gliding above the Aptian salt detachment. Additionally, major basin features like the Neogene progradation front and the salt tectonic domains are constrained by the main Proterozoic orogenic trends of the Ribeira Belt (NE–SW) and the Vitória-Colatina Belt (NNW–SSE). As the basement involved structures observed in Campos Basin can be attributed to general geodynamic processes, it is suggested that basement tectonic reactivation can be as relevant as isostatic adjustment and detached thin-skinned tectonics on the structural evolution of divergent margin settings.     

4D seismic time-lapse monitoring of an active cold vent,northern Cascadia margin

Two single-channel seismic (SCS) data sets collected in 2000 and 2005 were used for a four-dimensional (4D) time-lapse analysis of an active cold vent (Bullseye Vent). The data set acquired in 2000 serves as a reference in the applied processing sequence. The 4D processing sequence utilizes time- and phase-matching, gain adjustments and shaping filters to transform the 2005 data set so that it is most comparable to the conditions under which the 2000 data were acquired. The cold vent is characterized by seismic blanking, which is a result of the presence of gas hydrate in the subsurface either within coarser-grained turbidite sands or in fractures, as well as free gas trapped in these fracture systems. The area of blanking was defined using the seismic attributes instantaneous amplitude and similarity. Several areas were identified where blanking was reduced in 2005 relative to 2000. But most of the centre of Bullseye Vent and the area around it were seen to be characterized by intensified blanking in 2005. Tracing these areas of intensified blanking through the three-dimensional (3D) seismic volume defined several apparent new flow pathways that were not seen in the 2000 data, which are interpreted as newly generated fractures/faults for upward fluid migration. Intensified blanking is interpreted as a result of new formation of gas hydrate in the subsurface along new fracture pathways. Areas with reduced blanking may be zones where formerly plugged fractures that had trapped some free gas may have been opened and free gas was liberated.     

深水浊流形成过程的水动力学模拟:以南海北部琼东南盆地浊流形成过程为例

Turbidity currents represent a major agent for sediment transport in lakes, seas and oceans. In particu-lar, they formulate the most significant clastic accumulations in the deep sea, which become many of the world＇s most important hydrocarbon reservoirs. Several boreholes in the Qiongdongnan Basin, the north-western South China Sea, have recently revealed turbidity current deposits as significant hydrocarbon res-ervoirs. However, there are some arguments for the potential provenances. To solve this problem, it is es-sential to delineate their sedimentary processes as well as to evaluate their qualities as reservoir. Numerical simulations have been developed rapidly over the last several years, offering insights into turbidity current behaviors, as geologically significant turbidity currents are difficult to directly investigate due to their large scale and often destructive nature. Combined with the interpretation of the turbidity system based on high-resolution 3D seismic data, the paleotophography is acquired via a back-stripping seismic profile integrated with a borehole, i.e., Well A, in the western Qiongdongnan Basin; then a numerical model is built on the basis of this back-stripped profile. After defining the various turbidity current initial boundary conditions, includ-ing grain size, velocity and sediment concentration, the structures and behaviors of turbidity currents are investigated via numerical simulation software ANSYS FLUENT. Finally, the simulated turbidity deposits are compared with the interpreted sedimentary bodies based on 3D seismic data and the potential provenances of the revealed turbidites by Well A are discussed in details. The simulation results indicate that a sedimen-tary body develops far away from its source with an average grain size of 0.1 mm, i.e., sand-size sediment. Taking into account the location and orientation of the simulated seismic line, the consistence between normal forward simulation results and the revealed cores in Well A indicates that the turbidites should ha     

Shallow gas and fluid migration in the northern Arafura Sea (offshore Northern Australia)

A variety of shallow gas indicators and fluid migration pathways have been interpreted from new sub-bottom profiler, multibeam bathymetry, side-scan sonar, and echo-sounder data together with geochemical analyses of sampled sediments from the northern Arafura Sea, offshore Northern Australia. This study provides new geological data and a seismic stratigraphy of the youngest units in the Money Shoal Basin, in an area that has not been closely studied in over 30 years. The shallow gas indicators include pockmarks, low frequency enhanced reflectors and acoustic blanking. These indicators are supported by gas within shallow cores. Geochemistry indicates that this gas has a microbial origin but deeper fluid movement is also suggested by the presence of interpreted hydrocarbon slicks based on synthetic aperture radar data. A region of likely hydrocarbon seepage is indicated by the clear coincidence of shallow gas indicators with an area of increased faulting and a zone of poor quality seismic data (recognised on conventional seismic data), together with anomalies (interpreted on remote-sensing data) aligned with mapped deep structures.     

Seal rock deformation by polygonal faulting,offshore Uruguay

Due to a lack of borehole data, reservoir and seal rock presence in frontier basins is typically inferred from seismic reflection data. However, analysis of the geometry and kinematic development of polygonal fault systems (PFS), which almost exclusively form within very fine-grained strata, provides another, largely untested method to infer reservoir and seal rock presence. We here use very high-quality 3D seismic reflection data from offshore Uruguay and a range of quantitative GIS-based techniques to document the planform and cross-sectional characteristics of a basin-scale (>6400 km²) PFS, and to investigate the role that stratigraphic variations in the Tertiary deep-water host-rock have on its geometrical variability and kinematic development. We demonstrate that a series of likely sandstone-rich deep-water deposits occur at the base of and within the main PFS tier. The geometric characteristics and throw distribution on individual polygonal faults suggest these sandstone-rich deep-water deposits represent a mechanical barrier to fault propagation, thus influencing fault height and areal density and, in some cases, strike. We argue that in largely unexplored, deep-to ultra-deep water basins, such as those characterizing offshore Uruguay, the distribution and geometric attributes of PFS can be used to delineate sandstone-rich reservoir bodies. Furthermore, these characteristics may help exploration geoscientists better understand seal heterogeneity and quality in data-poor basins.