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1.
Gas hydrate and free gas distribution from inversion of seismic data on the South Shetland margin (Antarctica) 总被引：2，自引：0，他引：2
Tinivella Umberta Accaino Flavio Camerlenghi Angelo 《Marine Geophysical Researches》2002,23(2):109-123
Travel-time inversion is applied to seismic data to produce acoustic velocity images of the upper 800 m of the South Shetland margin (Antarctic Peninsula) in three different geological domains: (i) the continental shelf; (ii) the accretionary prism; (iii) the trench. The velocity in the continental shelf sediments is remarkably higher, up to 1000 m/s at 600–700 m below seafloor, than that of the other two geological domains, due to the sediment overcompaction and erosion induced by the wax and waning of a grounded ice sheet. Pre-stack depth migration was applied to the data in order to improve the seismic image and to test the quality of the velocity fields. Where the Bottom Simulating Reflector (BSR) is present, positive and negative velocity anomalies were found with respect to a reference empirical velocity profile. The 2D-velocity section was translated in gas hydrate and free gas distribution by using a theoretical approach. The analysis revealed that the BSR is mainly related to the presence of free gas below it. The free gas is distributed in the area with variable concentration and thickness, while the gas hydrate is quite uniformly distributed across the margin. 相似文献
2.
Erika Barison Giuseppe Brancatelli Rinaldo Nicolich Flavio Accaino Michela Giustiniani Umberta Tinivella 《Journal of Applied Geophysics》2011,73(3):267-277
One key step in seismic data processing flows is the computation of static corrections, which relocate shots and receivers at the same datum plane and remove near surface weathering effects. We applied a standard static correction and a wave equation datuming and compared the obtained results in two case studies: 1) a sparse ocean bottom seismometers dataset for deep crustal prospecting; 2) a high resolution land reflection dataset for hydrogeological investigation. In both cases, a detailed velocity field, obtained by tomographic inversion of the first breaks, was adopted to relocate shots and receivers to the datum plane. The results emphasize the importance of wave equation datuming to properly handle complex near surface conditions. In the first dataset, the deployed ocean bottom seismometers were relocated to the sea level (shot positions) and a standard processing sequence was subsequently applied to the output. In the second dataset, the application of wave equation datuming allowed us to remove the coherent noise, such as ground roll, and to improve the image quality with respect to the application of static correction. The comparison of the two approaches evidences that the main reflecting markers are better resolved when the wave equation datuming procedure is adopted. 相似文献
3.
Gas hydrates and active mud volcanism on the South Shetland continental margin, Antarctic Peninsula 总被引：1，自引：0，他引：1
During the Antarctic summer of 2003–2004, new geophysical data were acquired from aboard the R/V OGS Explora in the BSR-rich area discovered in 1996–1997 along the South Shetland continental margin off the Antarctic Peninsula. The
objective of the research program, supported by the Italian National Antarctic Program (PNRA), was to verify the existence
of a potential gas hydrate reservoir and to reconstruct the tectonic setting of the margin, which probably controls the extent
and character of the diffused and discontinuous bottom simulating reflections. The new dataset, i.e. multibeam bathymetry,
seismic profiles (airgun and chirp), and two gravity cores analysed by computer-aided tomography as well as for gas composition
and content, clearly shows active mud volcanism sustained by hydrocarbon venting in the region: several vents, located mainly
close to mud volcanoes, were imaged during the cruise and their occurrence identified in the sediment samples. Mud volcanoes,
vents and recent slides border the gas hydrate reservoir discovered in 1996–1997. The cores are composed of stiff silty mud.
In core GC01, collected in the proximity of a mud volcano ridge, the following gases were identified (maximum contents in
brackets): methane (46 μg/kg), pentane (45), ethane (35), propane (34), hexane (29) and butane (28). In core GC02, collected
on the flank of the Vualt mud volcano, the corresponding data are methane (0 μg/kg), pentane (45), ethane (22), propane (0),
hexane (27) and butane (25). 相似文献
4.
The seismic response to overpressure: a modelling study based on laboratory, well and seismic data 总被引：1，自引：0，他引：1
We investigate the seismic detectability of an overpressured reservoir in the North Sea by computing synthetic seismograms for different pore-pressure conditions. The modelling procedure requires the construction of a geological model from seismic, well and laboratory data. Seismic inversion and AVO techniques are used to obtain the P-wave velocity with higher reliability than conventional velocity analysis. From laboratory experiments, we obtain the wave velocities of the reservoir units versus confining and pore pressures. Laboratory experiments yield an estimate of the relationship between wave velocities and effective pressure under in situ conditions. These measurements provide the basis for calibrating the pressure model. Overpressures are caused by different mechanisms. We do not consider processes such as gas generation and diagenesis, which imply changes in phase composition, but focus on the effects of pure pore-pressure variations. The results indicate that changes in pore pressure can be detected with seismic methods under circumstances such as those of moderately deep North Sea reservoirs. 相似文献
5.
Gualtiero Böhm Flavio Accaino Giuliana Rossi Umberta Tinivella 《Geophysical Prospecting》2006,54(6):721-730
A joint inversion of both first and refracted arrivals is applied on a seismic line, acquired onshore, in order to obtain a well‐resolved velocity field for the computation of static corrections. The use of different arrivals in the inversion involves exploiting the information derived from the different raypaths associated with each wave type, thus enhancing the reliability of the inversion. The data was gathered by Saudi Aramco in an area of the Arabian Peninsula characterized by strong lateral variations, both in topography and shallow velocity, and where therefore a well‐defined near‐surface velocity field is important. In addition to velocity, the depth distribution of the quality factor Q is computed from the tomographic inversion of the seismic‐signal frequency shift. Thus, the Q‐factor field is used to perform an inverse Q‐data filtering and improve the resolution of the final stacked section. 相似文献
6.
The southern Chilean convergent margin, between 50° and 57° S, is shaped by the interaction of the three main plates: Antarctic, South America and Scotia. North of 53° S, the convergence between Antarctic and South America plates is close to orthogonal to the continental margin strike. Here, the deformational style of the accretionary prism is mainly characterized by seaward-verging thrusts and locally by normal faults and fractures, a very limited lateral extension of prism, a very shallow dip ( 6°) décollement, and subduction of a thick and relatively undeformed trench sedimentary sequence. South of 53° S, convergence is oblique to the margin, locally, the trench sediments are proto-deformed by double vergence thrusting and the front of the prism grows through landward-verging thrusting. The décollement is sub-horizontal and deep, involving most of the sediment over the oceanic crust in the accretionary process, building a comparatively wide and thicker prism. A Bottom Simulating Reflector is present across the whole prism to the abyssal plan, suggesting the presence of gas in the sediments.The analysis of P- and S-wave velocity reflectivity sections, derived by amplitude versus offset technique (AVO), detailed velocity information and the velocity-derived sediment porosity have been integrated with the structural analysis of the accretionary prism of two selected pre-stack depth migrated seismic lines, aiming to explain the relation between fluid circulation and tectonics.Accretion along double vergence thrust faults may be associated with the presence of overpressured fluid, which decreases the effective shear stress coefficient along the main décollement and within the sediments, and modify the rheolgical properties of rocks. The presence of an adequate drainage network, represented by interconnected faults and fractures affecting the entire sedimentary sequence, can favour the escape of pore fluid toward the sea bottom, while, less permeable and not faulted sediments can favour fluid accumulations. Gravitational and tectonic dewatering, and stratigraphy could control the consolidation and the pore overpressure of sediments involved in subduction along the trench. The results of our analysis suggest the existence of a feedback between tectonic style and fluid circulation. 相似文献
7.
We present the results obtained by processing high-resolution seismic data acquired along the spring line located in the Friuli-Venezia Giulia plain (NE of Italy), in order to characterize an important multilayered aquifer. This system is made of an unconfined layer and, at increasing depths, of several confined aquifers of variable thickness and hydraulic permeability, mainly consisting of sand and gravel material. The main targets of this study are two shallow aquifers located at about 30 m and 200 m depth respectively. The seismic method is not frequently used for this type of study but in this case, it was considered a good tool due to the depth of the targets. The detailed velocity model we obtained reveals lateral velocity variations with a maximum value of 600 m/s. The higher velocities could be associated to layers that are confined aquifers; in fact, sand and gravel are characterized by higher seismic velocity compared to clay layers. Pre-stack depth migration using this velocity model gives a clear picture of the multilayered aquifer, highlighting lateral changes of seismic amplitude along the main reflectors. Finally, vertical variations of Poisson's ratio, computed by amplitude versus offset analysis, provide useful information about the petrophysical properties, such as the fluid content of the subsoil and lithologic changes. 相似文献
8.
Ivan de la Cruz Vargas Cordero Umberta Tinivella Flavio Accaino Maria Filomena Loreto Francesco Fanucci Christian Reichert 《Geo-Marine Letters》2010,30(3-4):271-281
Two seismic sections offshore Arauco and Coyhaique, Chile, have been analysed to better define the seismic character of hydrate-bearing sediments. The velocity analysis was used to estimate the gas-phase concentration, which can serve to correlate hydrate presence to the geological features. The velocity model allowed us to recognise the hydrate layer above the bottom simulating reflector (BSR), and the free gas layer below it. The velocity field is affected by strong lateral variation, showing maximum (above the BSR) and minimum (below the BSR) values in the southern sector. Here, highest gas hydrate and free gas concentrations were calculated (15% and 2.7% of total volume respectively). The estimated geothermal gradient ranges from 35 to 95°C/km. In the northern sector, the highest gas hydrate and free gas concentrations are 15% and 0.2% of total volume respectively, and the geothermal gradient is uniform and equal to about 30°C/km. 相似文献
9.
10.
R. C. Neagu U. Tinivella V. Volpi M. Rebesco A. Camerlenghi 《International Journal of Earth Sciences》2009,98(4):839-848
Petrophysical properties (wet bulk density, porosity, P-wave velocity) are used to predict biogenic silica contents along
a seismic reflection profile that ties two well sites, 1095 and 1096, drilled by Ocean Drilling Program (ODP) Leg 178 on sediment
drifts on the Pacific continental margin of the Antarctic Peninsula. The biogenic silica contents along the seismic reflection
profile were estimated on the basis of three hypotheses about petrophysical properties distributions in the two boreholes
and statistical relationships between biogenic silica and other petrophysical properties, which were established on various
sediment layers within the boreholes. Our study demonstrates the possibility to reliably predict the distribution of biogenic
silica in the sub-seabed sediments if seismic data processed with amplitude preservation are used and statistical relations
are considered. We conclude that the statistical extrapolation of biogenic silica content along seismic reflection profiles
tied to borehole data is an efficient tool to quantify the amounts of silica undergoing crystalline transformation, which
may have strong implications for submarine slope destabilisation. 相似文献