Articles written in Journal of Earth System Science
Volume 129 All articles Published: 15 June 2020 Article ID 0136 Research Article
Super-virtual interferometry (SVI) is a technique in which cross-correlation between consecutive receiver responses is carried out to obtain the virtual head-wave arrivals, which are then convolved with the initially recorded traces to get the super-virtual trace. SVI can be used to enhance the refracted phases by stacking all the arrivals acquired using multiple shots at one position, leading to an improved SNR by a factor of $\surd n$, where $‘n’$ is the number of sources and receivers to generate the head-waves. In this study, we have generated few synthetic common shot gathers (CSGs) using forward modelling over a three-layer velocity–depth model with an embedded spherical anomaly, a complex five-layer velocity–depth model and the Marmousi model. Certain amount of noise is added on these gathers and then SVI technique is applied on the gathers which has resulted in an improved SNR of refracted phases at the far offset. We have further tested this technique on a field dataset acquired from the Kumaon Himalayan region using a 450 kg thumper as an energy source and 111 active channel remote acquisition unites (RAUs) with 5 Hz geophones as sensors. The resulting SVI gathers show the refracted arrivals more clearly. Continuity in the phases is increased after stacking and iterative SVI.
Volume 130 All articles Published: 18 February 2021 Article ID 0044 Brief Communication
The estimation of a reliable velocity–depth model from towed streamer marine seismic data recorded in deep water, especially with a complex seafloor environment, is challenging. The determination of interval velocities from the normal move-out (NMO) of the reflected seismic signals for shallow reflectors (<1 km below the seafloor) is compromised by the combination of a long wave path in the water column and the complex ray paths due to topography, leading to small move-out differences between reflectors. Furthermore, low sediment velocities and deep water produce refraction arrivals only at limited far offsets that contain information about deeper structures. Here, we present an innovative method where towed streamer seismic data are downward continued to the seafloor leading to the collapse of the seafloor reflection and the emergence of refraction events as first arrivals close to zero offset, which are used to determine a high-resolution near surface velocity–depth model using an efficient tomographic method. These velocities are then used to perform pre-stack depth migration. We found that the velocity–depth model derived from tomography of downward continued towed streamer data provides a far superior pre-stack depth migrated image than those produced from velocity–depth models derived from conventional velocity estimation techniques.
$\bullet$ A comparison in velocity from conventional NMO, sparsely spaced OBS tomography, and tomography of downward continue streamer data is carried out.
$\bullet$ Accuracy in velocities are proved from the prestack depth migration results.
Volume 131 All articles Published: 2 February 2022 Article ID 0043 BriefCommunication
The uncertainty associated with seismic interpretation poses a significant challenge to the hydrocarbon
industry in accurately identifying the potential hydrocarbon zones. Over the years several new techniques
have emerged to address this problem. Amplitude variation with offset analysis is one of the prominent
methods to estimate various subsurface properties from pre-stack gathers. Due to the presence of fluid in
reservoir pores, seismic velocity dispersion occurs within the seismic bandwidth, resulting in reflection
coefficient as a function of frequency. In this study, a prototype inversion scheme is developed for
Volume 131, 2022
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