Critical Review, Calibration, and Ranking of Popular Velocity
-Based
Pressure Prediction Models
Mario A. Gutierrez, Neil Braunsdorf, and Brent Couzens
Shell International Exploration and Production Inc,
Houston, TX
The goal of this presentation is to conduct a critical review of the
major physical model-oriented and empirical velocity
-based models used in
pre-drill pore pressure prediction, and introduce a new approach for pore
pressure model calibration and analysis. Pore pressure prediction involves a
broad range of methodologies to estimate fluid pressures from porosity and
depth
based trends, seismic velocities, and multivariate regressions. Model building
is typically characterized by an iterative sequence including model
identification, calibration, selection, and diagnostic checking. To predict
effective stress and pore pressure, practitioners apply a diverse set of
functional forms that relate velocities and fluid pressures,
using
in addition
to seismic
velocity
, predictive variables like porosity,
depth
, temperature,
etc.
Velocity
-based methods, in particular power-law
functions
, are very popular
in pre-drill pore pressure prediction, because they are simple and generally
provide acceptable estimates. One effective way to prioritize the model
selection process is by measuring the accuracy of model predictions.
Using
a new
approach, multiple functional forms are calibrated by non-linear minimization of
the difference between model-predicted and actual measured pore pressures. With
this approach, the quality of the pressure estimation is quantified and ranked
using
prediction error statistics, including RMS error, standard deviation,
absolute mean, maximum and minimum error, and the number of non-physical
predictions. Residual plots provide additional model diagnostics, highlighting
systematic errors and the effective predictive range as a function of
potentially important independent variables. Examples highlighting the
calibration and ranking approach functionalities will be presented.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005