Direct seismic detection of methane hydrate on the Blake Ridge

Geophysics ◽  
2003 ◽  
Vol 68 (1) ◽  
pp. 92-100 ◽  
Author(s):  
Matthew J. Hornbach ◽  
W. Steven Holbrook ◽  
Andrew R. Gorman ◽  
Kara L. Hackwith ◽  
Daniel Lizarralde ◽  
...  
Keyword(s):  
Methane Hydrate ◽  
Thick Layer ◽  
P Wave ◽  
Upward Migration ◽  
Seismic Reflection Data ◽  
Bottom Simulating Reflector ◽  
Reflection Data ◽  
Bright Spots ◽  
Seismic Detection ◽  
Blake Ridge

Seismic detection of methane hydrate often relies on indirect or equivocal methods. New multichannel seismic reflection data from the Blake Ridge, located approximately 450 km east of Savannah, Georgia, show three direct seismic indicators of methane hydrate: (1) a paleo bottom‐simulating reflector (BSR) formed when methane gas froze into methane hydrate on the eroding eastern flank of the Blake Ridge, (2) a lens of reduced amplitudes and high P‐wave velocities found between the paleo‐BSR and BSR, and (3) bright spots within the hydrate stability zone that represent discrete layers of concentrated hydrate formed by upward migration of gas. Velocities within the lens (∼1910 m/s) are significantly higher than velocities in immediately adjacent strata (1820 and 1849 m/s). Conservative estimates show that the hydrate lens contains at least 13% bulk methane hydrate within a 2‐km3 volume, yielding 3.2 × 1010kg [1.5 TCF (4.2 × 1010 m3] of methane. Low seismic amplitudes coupled with high interval velocities within the lens offer evidence for possible methane hydrate “blanking.” Hydrate bright spots yield velocities as high as 2100 m/s, with bulk hydrate concentrations predicted as high as 42% in an approximately 15‐m thick layer. Our results show that, under certain circumstances, hydrate in marine sediments can be directly detected in seismic reflections but that quantification of hydrate concentrations requires accurate velocity information.

scholarly journals Seismic interferometry using multidimensional deconvolution and crosscorrelation for crosswell seismic reflection data without borehole sources

Geophysics ◽  
2011 ◽  
Vol 76 (1) ◽  
pp. SA19-SA34 ◽  
Author(s):  
Shohei Minato ◽  
Toshifumi Matsuoka ◽  
Takeshi Tsuji ◽  
Deyan Draganov ◽  
Jürg Hunziker ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Field Data ◽  
Time Lapse ◽  
P Wave ◽  
Source Distribution ◽  
Seismic Interferometry ◽  
Imaging Method ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Receiver Arrays

Crosswell reflection method is a high-resolution seismic imaging method that uses recordings between boreholes. The need for downhole sources is a restrictive factor in its application, for example, to time-lapse surveys. An alternative is to use surface sources in combination with seismic interferometry. Seismic interferometry (SI) could retrieve the reflection response at one of the boreholes as if from a source inside the other borehole. We investigate the applicability of SI for the retrieval of the reflection response between two boreholes using numerically modeled field data. We compare two SI approaches — crosscorrelation (CC) and multidimensional deconvolution (MDD). SI by MDD is less sensitive to underillumination from the source distribution, but requires inversion of the recordings at one of the receiver arrays from all the available sources. We find that the inversion problem is ill-posed, and propose to stabilize it using singular-value decomposition. The results show that the reflections from deep boundaries are retrieved very well using both the CC and MDD methods. Furthermore, the MDD results exhibit more realistic amplitudes than those from the CC method for downgoing reflections from shallow boundaries. We find that the results retrieved from the application of both methods to field data agree well with crosswell seismic-reflection data using borehole sources and with the logged P-wave velocity.

Petroleum Prospectivity of the Tasman Frontier

2014 ◽  
Vol 54 (2) ◽  
pp. 520
Author(s):  
Francois Bache ◽  
Vaughan Stagpoole ◽  
Rupert Sutherland ◽  
Julien Collot ◽  
Pierrick Rouillard ◽  
...  
Keyword(s):  
Source Rock ◽  
New Caledonia ◽  
Source Rocks ◽  
Rock Composition ◽  
Seismic Reflection Data ◽  
Bottom Simulating Reflector ◽  
Reflection Data ◽  
Stratigraphic Framework ◽  
Well Data ◽  
The One

The Fairway Basin lies between Australia and New Caledonia in the northern Tasman Frontier area with water depths ranging from less than 1,000–2,400 m. This basin was formed in the mid-to-late Cretaceous during the eastern Gondwana breakup and since then has received detrital and pelagic sediments. It is known for its 70,000 km2 bottom simulating reflector, interpreted as one of the world’s largest gas hydrate layers or as a regional diagenetic front. The seismic reflection data shows sedimentary thicknesses (up to 4 km) and geometries capable of trapping hydrocarbons. The authors interpreted the seismic stratigraphy and available well data in terms of paleogeography and tectonic evolution. This work allowed the discovery of a deeply buried delta, probably of the same type as the deep-water Taranaki Delta. This stratigraphic framework is used to constrain multi-1D generation modelling and to test three main hypotheses of source rocks. The most likely scenario, similar to the one accepted for the Taranaki petroleum province, are a type-III and type-II source rocks intercalated in a Cretaceous prograding series. Another possible scenario is a source rock equivalent to the east Australian Walloon Formation and the occurrence of the marine source rock in the pre-rift sequence. Although, the large modelled volumes at this stage are speculative due to limited data on source rock composition, richness and distribution, as well as on the presence and quality of reservoir and seal, this study confirms the prospectivity of the Fairway Basin and the need for more data to further assess this basin.

Application of waveform tomography to marine seismic reflection data from the Queen Charlotte Basin of western Canada

Geophysics ◽  
2011 ◽  
Vol 76 (2) ◽  
pp. B55-B70 ◽  
Author(s):  
E. M. Takam Takougang ◽  
A. J. Calvert
Keyword(s):  
Seismic Reflection ◽  
Field Data ◽  
Velocity Model ◽  
P Wave ◽  
Low Velocity ◽  
Seismic Line ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Sonic Log ◽  
Waveform Tomography

To obtain a higher resolution quantitative P-wave velocity model, 2D waveform tomography was applied to seismic reflection data from the Queen Charlotte sedimentary basin off the west coast of Canada. The forward modeling and inversion were implemented in the frequency domain using the visco-acoustic wave equation. Field data preconditioning consisted of f-k filtering, 2D amplitude scaling, shot-to-shot amplitude balancing, and time windowing. The field data were inverted between 7 and 13.66 Hz, with attenuation introduced for frequencies ≥ 10.5 Hz to improve the final velocity model; two different approaches to sampling the frequencies were evaluated. The limited maximum offset of the marine data (3770 m) and the relatively high starting frequency (7 Hz) were the main challenges encountered during the inversion. An inversion strategy that successively recovered shallow-to-deep structures was designed to mitigate these issues. The inclusion of later arrivals in the waveform tomography resulted in a velocity model that extends to a depth of approximately 1200 m, twice the maximum depth of ray coverage in the ray-based tomography. Overall, there is a good agreement between the velocity model and a sonic log from a well on the seismic line, as well as between modeled shot gathers and field data. Anomalous zones of low velocity in the model correspond to previously identified faults or their upward continuation into the shallow Pliocene section where they are not readily identifiable in the conventional migration.

Impedance‐type approximations of the P–P elastic reflection coefficient: Modeling and AVO inversion

Geophysics ◽  
2004 ◽  
Vol 69 (2) ◽  
pp. 592-598 ◽  
Author(s):  
Lúcio T. Santos ◽  
Martin Tygel
Keyword(s):  
Reflection Coefficient ◽  
Normal Incidence ◽  
Simple Expression ◽  
P Wave ◽  
Reflection Coefficients ◽  
Seismic Reflection Data ◽  
Acoustic Reflection ◽  
Reflection Data ◽  
Avo Inversion ◽  
Elastic Impedance

The normal‐incidence elastic compressional reflection coefficient admits an exact, simple expression in terms of the acoustic impedance, namely the product of the P‐wave velocity and density, at both sides of an interface. With slight modifications a similar expression can, also exactly, express the oblique‐incidence acoustic reflection coefficient. A severe limitation on the use of these two reflection coefficients in analyzing seismic reflection data is that they provide no information on shear‐wave velocities that refer to the interface. We address the natural question of whether a suitable impedance concept can be introduced for which arbitrary P–P reflection coefficients can be expressed in a form analogous to their acoustic counterparts. Although no closed‐form exact solution exists, our analysis provides a general framework for which, under suitable restrictions of the medium parameters, possible impedance functions can be derived. In particular, the well‐established concept of elastic impedance and the recently introduced concept of reflection impedance can be better understood. Concerning these two impedances, we examine their potential for modeling and for estimating the AVO indicators of intercept and gradient. For typical synthetic examples, we show that the reflection impedance formulation provides consistently better results than those obtained using the elastic impedance.

Petroleum implications of stacked deltas in the Fairway Basin, offshore New Caledonia, Northern Tasman Frontier

2014 ◽  
Vol 54 (2) ◽  
pp. 537
Author(s):  
Pierrick Rouillard ◽  
Julien Collot ◽  
Francois Bache ◽  
Rupert Sutherland ◽  
Karsten Kroeger ◽  
...  
Keyword(s):  
Source Rock ◽  
New Caledonia ◽  
Source Rocks ◽  
Rock Composition ◽  
Seismic Reflection Data ◽  
Bottom Simulating Reflector ◽  
Reflection Data ◽  
Stratigraphic Framework ◽  
Well Data ◽  
The One

The Fairway Basin lies between Australia and New Caledonia in the northern Tasman Frontier area with water depths ranging from less than 1,000–2,400 m. This basin formed in mid-to-Late Cretaceous during eastern Gondwana breakup and received detrital and pelagic sediments since that time. It is known for a 70,000 km2 bottom simulating reflector interpreted as either one of the world’s largest gas hydrate layers or as a regional diagenetic front. Seismic reflection data shows sedimentary thicknesses (up to 4 km) and geometries capable of trapping hydrocarbons. We interpret seismic stratigraphy and available well data in terms of paleogeography and tectonic evolution. This work allowed the discovery of a deeply buried delta probably of the same type as the deepwater Taranaki Delta. This stratigraphic framework is used to constrain multi-1D generation modelling and to test three main hypotheses of source rocks. The most likely scenario, similar to the one accepted for the Taranaki petroleum province, are a type-III and type-II source rocks intercalated in Cretaceous prograding series. Another possible scenario is a source rock equivalent to the East Australian Walloon Formation and occurrence of marine source rock in the pre-rift sequence. Although large modelled volumes at this stage are speculative due to limited data on source rock composition, richness and distribution, as well as on the presence and quality of reservoir and seal, this study confirms the prospectivity of the Fairway Basin and the need for more data to further assess this basin.

SCALE AND ANGLE DEPENDENT REFLECTION PROPERTIES OF SELF-SIMILAR INTERFACES

2001 ◽  
Vol 09 (03) ◽  
pp. 1015-1023 ◽  
Author(s):  
JEROEN GOUDSWAARD ◽  
KEES WAPENAAR
Keyword(s):  
P Wave ◽  
Well Logs ◽  
Seismic Reflection Data ◽  
Multi Scale ◽  
Reflection Data ◽  
P Wave Velocity ◽  
Self Similar ◽  
Modulus Maxima ◽  
Seismic Reflectors ◽  
Scale Behavior

We propose an alternative parameterization of seismic reflectors in the subsurface, in terms of self-similar singularities, which are generalizations of stepfunctions. This parameterization captures the multi-scale behavior of real sonic P-wave velocity logs, as can be derived by performing modulus maxima analysis on wavelet-transformed well-logs. Results on synthetic seismic reflection data, modeled in real well-logs, show that a singularity parameter can be retrieved, that is consistent with the parameter derived directly from the well-log.

scholarly journals Characterization of shallow overpressure in consolidating submarine slopes via seismic full waveform inversion

2020 ◽  
Vol 53 (3) ◽  
pp. 366-377 ◽  
Author(s):  
Giuseppe Provenzano ◽  
Antonis Zervos ◽  
Mark E. Vardy ◽  
Timothy J. Henstock
Keyword(s):  
Pore Pressure ◽  
Seismic Reflection ◽  
Mass Movement ◽  
Waveform Inversion ◽  
P Wave ◽  
Excess Pore Pressure ◽  
Full Waveform Inversion ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Full Waveform

Pore pressures higher than hydrostatic correspond to localized reductions of the level of shear stress required to induce lateral mass movement in a slope, and therefore play a key role in preconditioning submarine landsliding. In this paper, we investigate whether multi-channel seismic reflection data can be used to infer potentially destabilizing pore-pressure levels at a resolution and sensitivity useful for in-situ slope stability characterization. We simulate the continuous deposition of sediment on consolidating slopes in two scenarios, with combinations of sedimentation rate and permeability distribution leading to disequilibrium compaction. Ultra-high-frequency (UHF; 0.2–2.5 kHz) seismic reflection data are computed for each model and a stochastic full waveform inversion (FWI) method is used to retrieve the sub-seabed properties from the computed seismograms. These are then interpreted as time–depth variations in the effective stress (σʹ) regime, and therefore local overpressure ratio and factor of safety, using a combination of p-wave velocity to σʹ transforms. The results demonstrate that multi-channel UHF seismic data can provide valuable constraints on the distribution of physical properties in the top 50 m below seabed at a sub-metric scale, and with a sensitivity useful to infer destabilizing excess pore pressure levels.Thematic collection: This article is part of the Measurement and monitoring collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring

A strategy for nonlinear elastic inversion of seismic reflection data

Geophysics ◽  
1986 ◽  
Vol 51 (10) ◽  
pp. 1893-1903 ◽  
Author(s):  
Albert Tarantola
Keyword(s):  
Wave Velocity ◽  
Seismic Reflection ◽  
Wave Impedance ◽  
P Wave ◽  
S Wave ◽  
Seismic Reflection Data ◽  
S Waves ◽  
Wave Velocities ◽  
Reflection Data ◽  
P Wave Velocity

The problem of interpretation of seismic reflection data can be posed with sufficient generality using the concepts of inverse theory. In its roughest formulation, the inverse problem consists of obtaining the Earth model for which the predicted data best fit the observed data. If an adequate forward model is used, this best model will give the best images of the Earth’s interior. Three parameters are needed for describing a perfectly elastic, isotropic, Earth: the density ρ(x) and the Lamé parameters λ(x) and μ(x), or the density ρ(x) and the P-wave and S-wave velocities α(x) and β(x). The choice of parameters is not neutral, in the sense that although theoretically equivalent, if they are not adequately chosen the numerical algorithms in the inversion can be inefficient. In the long (spatial) wavelengths of the model, adequate parameters are the P-wave and S-wave velocities, while in the short (spatial) wavelengths, P-wave impedance, S-wave impedance, and density are adequate. The problem of inversion of waveforms is highly nonlinear for the long wavelengths of the velocities, while it is reasonably linear for the short wavelengths of the impedances and density. Furthermore, this parameterization defines a highly hierarchical problem: the long wavelengths of the P-wave velocity and short wavelengths of the P-wave impedance are much more important parameters than their counterparts for S-waves (in terms of interpreting observed amplitudes), and the latter are much more important than the density. This suggests solving the general inverse problem (which must involve all the parameters) by first optimizing for the P-wave velocity and impedance, then optimizing for the S-wave velocity and impedance, and finally optimizing for density. The first part of the problem of obtaining the long wavelengths of the P-wave velocity and the short wavelengths of the P-wave impedance is similar to the problem solved by present industrial practice (for accurate data interpretation through velocity analysis and “prestack migration”). In fact, the method proposed here produces (as a byproduct) a generalization to the elastic case of the equations of “prestack acoustic migration.” Once an adequate model of the long wavelengths of the P-wave velocity and of the short wavelengths of the P-wave impedance has been obtained, the data residuals should essentially contain information on S-waves (essentially P-S and S-P converted waves). Once the corresponding model of S-wave velocity (long wavelengths) and S-wave impedance (short wavelengths) has been obtained, and if the remaining residuals still contain information, an optimization for density should be performed (the short wavelengths of impedances do not give independent information on density and velocity independently). Because the problem is nonlinear, the whole process should be iterated to convergence; however, the information from each parameter should be independent enough for an interesting first solution.

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