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Schiemenz A.,Geophysics | Schiemenz A.,Schlumberger | Igel H.,Geophysics
Geophysical Journal International | Year: 2013

We use the method of simultaneously encoded sources to performcomputationally inexpensive full-waveform inversion (FWI) on fixed-spread, marine seismic data. A workflow is proposed whereby both data- and model-based preconditioning strategies are enforced to mitigate the non-linearity of the seismic inverse problem. Artificial crosstalk, introduced by the false correlation of forward and adjoint wavefields of simultaneously simulated sources, is minimized by simulating supershots of random linear combinations of data with iteration-varying encoding. Using encoded sources with partial-source assembly, crosstalk is furthermore suppressed by randomizing the locations of encoded subsources. Synthetic case studies verify our basic workflow approach, demonstrating accurate model reconstruction in the most extreme case of a single supershot. Application to real data from the Valhall oilfield in the North Sea demonstrates reconstruction of near-surface features with one to two orders of magnitude speedup per FWI iteration. Such an efficiency gain can be incorporated into a seismic data processing workflow both for tomographic inversion and for quality control measures. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Maheshwari B.K.,Indian Institute of Technology Roorkee | Mahajan A.K.,Wadia Institute of Himalayan Geology | Sharma M.L.,Indian Institute of Technology Roorkee | Paul D.K.,Indian Institute of Technology Roorkee | And 2 more authors.
International Journal of Geotechnical Engineering | Year: 2013

The correlation between shear wave velocity Vs and standard penetration test resistance N is investigated in Northwest Himalaya. The study focuses primarily on two sites: Dhanauri and Roshnabad in the Ganga foreland basin. The Dhanauri site comprises a mixture of clay, silt and sand, and the Roshnabad site comprises predominantly gravelly soil. A new empirical formula is suggested to correlate shear wave velocity and standard penetration resistance, based on a dataset collected as part of an earthquake risk evaluation study in the Northwest Himalayan region, India. The formula is based on geotechnical exploration (standard penetration test) and seismic experiments (multichannel analysis of surface wave). The relationship derived was compared with existing correlations in the literature. © 2013 W. S. Maney & Son Ltd

Esmaeilpour S.,Geophysics | Riahi M.A.,University of Tehran | Emamzadeh A.,Petroleum University of Technology of Iran | Sokooti R.,National Iranian Oil Company
Journal of the Earth and Space Physics | Year: 2010

Distinguishable amplitude phenomena on surface seismic data often resulted from contrasts in the elastic parameters of subsurface layers. Various techniques have been involved to analyze and highlight such phenomena for their potential use as "Direct Hydrocarbon Indicator (DHI)". More recently, other techniques have been developed based on the variation of reflection coefficient with angle of incidence, conventionally called Amplitude-Versus- Offset (AVO). During the last twenty years the significance of AVO analysis for studying seismic reflection in oil exploration has been considered more importantly. In this work, first, a seismic line from a gas field and also a well are selected to indicate the results of the application of AVO analysis for detection of hydrocarbon reservoir in this field. In this project, using well logs and information obtained by core analysis, a synthetic seismogram has been built applying Zoeppritz equation. And Using Hampson-Russell software, AVO attributes have been extracted from synthetic seismogram. Then anomalies of these attributes have been investigated and compared with the anomalies from AVO attributes which were extracted from real seismic data to characterize the reservoir. It has been seen that the extracted attributes of the synthetic seismogram confirm the anomalies from real seismic data. Finally according to the obtained result, observed anomalies can be interpreted as a Gas Cap for this reservoir. This study is useful to identify reservoir and nonreservoirs and the results of this study are considered as input for detailed reservoir studies. In particular, knowing the reservoir physical and saturating fluid properties is of great importance in making plans for developing the reservoir.

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