Previous Talks

Wednesday June 10th, 2015

Estimating the Influence of Stress State on Compaction Behavior – Models and Field Results

Matt R. Hauser, Alvin Chan, and Brent Couzens-Schultz, Shell

Abstract

Relationships between compaction state and effective stresses are the basis for most quantitative pore pressure and stress estimates.  Common practice uses only a single element of the stress tensor – the vertical stress – for these calculations;  mean stress formulations also exist, though they are less widely applied.  Using simple models and field data from two distinct stress regimes we examine the validity and limitations of the vertical-stress approach as well as a mean-stress approach, showing that in complex stress settings both can perform very poorly.  We propose a method for incorporating shear stresses into compaction relations by using state boundary surface formulations from soil mechanics and demonstrate how the resulting model may be calibrated and applied to field data.  This approach is found to perform much better in the complex stress environment, providing more stable calibration behavior and extrapolating more reliably to stress states beyond those present in the calibration data.  While vertical and mean stress compaction models may work well in simple stress environments, we conclude that incorporation of shear stress is necessary for models in complex stress settings.  While the addition of shear stress significantly improves agreement with field data, it also increases the complexity of the model as well as the requirements for calibration data.  We therefore conclude with a brief discussion of the settings in which each of these three approaches – vertical stress, mean stress and state boundary surface – may be most appropriate.

Speaker Biography

Matt Hauser joined Shell in 1995 after completing a Ph.D. in physics at the University of Illinois at Urbana-Champaign.  While at Shell he has worked on acoustic log analysis and interpretation, operational petrophysics and most recently pore pressure and fracture gradient modeling and real-time support.  He is currently a team lead and focal point for PPFG in the Americas.