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Why You Should Take Caution in Using Rock Physics Model Approximations for Time-lapse Analysis
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
Summary
Rock physics models are used as a method of modelling the influence of production-related stress change on seismic velocities. Many different models exist, however, almost all require either stress-velocity core data or complex laboratory techniques (e.g. X-ray diffraction) to calibrate. This becomes an issue when core data is not available, which is often the case for non-reservoir rocks. In these circumstances, approximate rock physics models may be applied, which use simplified formulae derived from best-fit parameters to constrained core datasets. However, in this study we show why you should take caution in using such relationships. Although they may provide good approximations of the absolute magnitude of the rock velocity, they are limited in predicting time-lapse changes in seismic velocity due to stress. This is because of the difficulty in relating parameters that govern the shape/curvature of the nonlinear relationship to best-fit constants or abundant rock properties. Although we use only simple isotropic relationships in this study, the conclusions remain applicable to all models, including anisotropic ones. This study also demonstrates the important of an accurate rock physics model in time-lapse monitoring scenarios. We show that just small discrepancies in model parameters can lead to large differences in predicted time-lapse velocities.
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