Success of high-resolution volumetric Q-tomography in the automatic detection of gas anomalies on offshore Brunei data

Gamar, Fatiha; Carotti, D.; Guillaume, P.; Gacha, A.; Lopes, L.

doi:10.1190/segam2015-5865727.1

Cited by 9 publications

(3 citation statements)

References 9 publications

(9 reference statements)

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“…To mitigate this problem, the amplitude spectra can be smoothed before the peak frequencies for different source-receiver pairs are estimated. Gamar et al (2015) propose a robust way of estimating the peak frequencies in the observed and the predicted signals by taking the autocorrelation of the signal in short-time windows and finding the peak frequency only at the part of the signal around the maximum peak of the autocorrelation function. We expect the inverted Q tomogram obtained from such a robust estimation of the peak frequencies and from their shifts to be more accurate.…”

Section: Discussionmentioning

confidence: 99%

Wave-equation Q tomography

Dutta

Schuster

2016

GEOPHYSICS

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Strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth. The amplitude and the dispersion losses from attenuation are often compensated for during prestack depth migration. However, most attenuation compensation or Qcompensation migration algorithms require an estimate of the background Q model. We have developed a wave-equation gradient optimization method that inverts for the subsurface Q distribution by minimizing a skeletonized misfit function ϵ, where ϵ is the sum of the squared differences between the observed and the predicted peak/centroid-frequency shifts of the early arrivals. The gradient is computed by migrating the observed traces weighted by the frequency shift residuals. The background Q model is perturbed until the predicted and the observed traces have the same peak frequencies or the same centroid frequencies. Numerical tests determined that an improved accuracy of the Q model by wave-equation Q tomography leads to a noticeable improvement in migration image quality.

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Section: Discussionmentioning

confidence: 99%

Wave-equation Q tomography

Dutta

Schuster

2016

GEOPHYSICS

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“…8 Jing Li, et al For real data, since the peak-frequency is very sensitive to noise, Gamar et al (2015) used an auto-correlated trace windowed about the zero-time lag to pick the peak frequency. This increases the robustness of the peak-frequency estimation.…”

Section: Work Flow For Wqs Inversionmentioning

confidence: 99%

Wave-equation Qs inversion of skeletonized surface waves

Dutta

Schuster

2017

Geophysical Journal International

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We present a skeletonized inversion method that inverts surface-wave data for the Q s quality factor. Similar to the inversion of dispersion curves for the S-wave velocity model, the complicated surface-wave arrivals are skeletonized as simpler data, namely the amplitude spectra of the windowed Rayleigh-wave arrivals. The optimal Q s model is the one that minimizes the difference in the peak frequencies of the predicted and observed Rayleigh wave arrivals using a gradient-based wave-equation optimization method. Solutions to the viscoelastic waveequation are used to compute the predicted Rayleigh-wave arrivals and the misfit gradient at every iteration. This procedure, denoted as wave-equation Q s inversion (WQ s), does not require the assumption of a layered model and tends to have fast and robust convergence compared to full waveform inversion (FWI). Numerical examples with synthetic and field data demonstrate that the WQ s method can accurately invert for a smoothed approximation to the subsurface Q s distribution as long as the V s model is known with sufficient accuracy.

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“…The authors of [13] use the concept of attenuated travel time tomography to estimate the interval Q and successfully delineate a known zone of low Q along the 3D survey offshore Australia. In [14], the high-resolution Q tomography technique is used to automatically detect shallow gas pockets in Brunei. In reference [15], the authors apply an improved peak frequency shift to estimate the Q factor using time migration data in a 2D seismic line in the Sichuan Basin (China) and conclude that the quality factor can be used to detect hydrocarbons.…”

Section: Introductionmentioning

confidence: 99%

Geophysical Characterization and Attenuation Correction Applied for Hydrate Bearing Sediments in Japan Sea

et al. 2023

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Estimation of rock properties from seismic data is important for exploration and production activities in the petroleum industry. Considering the compressional velocity—the speed of propagating body waves in formations—and the quality factor (Q)—a measure of the frequency-selective energy losses of waves propagating through formations—both properties are usually estimated from multichannel seismic data. Velocity is estimated during multichannel processing of seismic reflection data in either the time or depth domain. In marine seismic acquisition, Q can be estimated from the following sources: Vertical Seismic Profile (VSP) surveys, where sources are located near the sea surface and geophones are distributed at depth along a borehole; and multichannel reflection data, where sources are also located near the sea surface and receivers are distributed either at the sea surface (conventional seismic survey with streamers) or on the sea floor (use of nodes or Ocean Bottom Cables (OBC)). The aforementioned acquisition devices, VSP, conventional streamers, nodes, and OBCs are much more expensive than single-channel acquisition with one receiver per shot due to the cost of operation. There are numerous old and new datasets from academia and the oil industry that have been acquired with single-channel acquisition devices. However, there is a paucity of work addressing the estimation of velocity and Q from this type of equipment. We investigate the estimation of Q and velocity from single-channel seismic data. Using the windowed discrete Fourier transform for a single seismic trace, we calculate the peak and dominant frequency that changes with time. In the geologic environment, higher frequencies are attenuated at shallow depths (time), while lower frequencies remain at deeper positions. From the rate at which higher frequencies are attenuated with time, we estimate the effective quality factor (Qeff). However, when using Kirchhoff migration to process single-channel seismic data, events far from the vertical projection of the receiver contribute to the trace at a given time. Then, an underestimation of the effective quality factor occurs. To compensate for the effects of more distant events with lower-frequency content contaminating the shorter events, we propose a linear equation to correct the effective quality factor estimated from migrated seismic data. Effective Q and its correction are estimated in five single-channel seismic lines surveyed along the Joetsu Knoll, a SW-NE anticline structure on the eastern margin of the Sea of Japan. These results are linked to geomorphological and geological features and the velocity field. Joetsu Knoll is a known site of massive gas hydrates (GH), which occur in the first hundred metres of Neogene sediments and, together with gas chimneys, play an important role in seismic wave absorption. Qeff estimated from migrated seismic data maintains the spatial relationship between high and low Q regions. The region of low Q, which is below 124 and has an average value of 57, occurs near the anticlinal hinge and tends to coincide with the region in which the Bottom Simulating Reflector (BSR) resides. The coexistence of GH and free gas coincides with the very low P velocity gradient of 0.225 s−1. BSR occurrence, Qeff and the geometry of the Joetsu anticline testify to progressive gas hydrate depletion northward along the dome.

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Success of high-resolution volumetric Q-tomography in the automatic detection of gas anomalies on offshore Brunei data

Cited by 9 publications

References 9 publications

Wave-equation Q tomography

Wave-equation Q tomography

Wave-equation Qs inversion of skeletonized surface waves

Geophysical Characterization and Attenuation Correction Applied for Hydrate Bearing Sediments in Japan Sea

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