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Deriving effects of pressure depletion on elastic framework moduli from sonic logs
- Source: Geophysical Prospecting, Volume 57, Issue 3, Apr 2009, p. 427 - 437
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- 17 Oct 2008
Abstract
We have developed a method to determine the effect of pore pressure depletion on elastic framework moduli, by utilizing sonic logs from wells drilled at different locations through a reservoir at varying depletion stages. This is done by first inverting the sonic logs for elastic framework bulk and shear moduli, thus carefully removing pressure dependent fluid effects. By crossplotting these elastic framework moduli against an increase in net stress (which is directly related to depletion), we derive the stress sensitivity of the elastic framework moduli. We found that the observed stress sensitivity was consistent with time‐lapse seismic results and that the sensitivity derived from the sonic logs was much smaller than predicted by hydrostatic measurements on core samples. This method is applicable to depletion scenarios in mature fields and can be used both for modelling and inverting time‐lapse seismic data for effects of pore pressure depletion on seismic data.