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Q Factor: From VSP to Seismic Line
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
Q factor of geological formations can be obtained from VSP data. Attenuation introduces dissipative dispersion which can be measured from the frequency-dependent phase velocity of the VSP down-going wave. Between 2 geophone positions, the variation of velocity AV due to the variation of frequency is estimated from a residual variation dΔt of the arrival times of the down-going wave. A scan procedure in dΔt, equivalent to a velocity scan, has been implemented to estimate the quantity ΔV and the Q factor, the search being done in realistic domain of Q values, as example between 20 and 100. The frequencies are given by instantaneous frequencies. The methodology has been extended from well data to surface seismic data. The procedure can be used to build a geo-model in depth defined by mechanical parameters: velocities, density, and Q factor.
The methodology has been applied to estimate Q factors of the Callovo-Oxfordian argillaceous rock (Cox) and the Oxfordian and Dogger limestone directly located above and below, using both VSP’s and seismic lines. The Q factor of the Cox varies between 35 and 50 while the Q factors of the Oxfordian and Dogger limestone are higher, ranging between 65 to 100.