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Abstract

AAPG Memoir 76, Chapter 15: Forward Modeling of Log Response in Geopressured Formations Reveals Valuable Insights to the Various Pore-Pressure Prediction Techniques , by J. C. Rasmus, Pages 159 - 164
from:
AAPG Memoir 76: Pressure Regimes in Sedimentary Basins and Their Prediction, Edited by Alan Huffman and Glenn Bowers
Copyright © 2001 by The American Association of Petroleum Geologists. All rights reserved.

Chapter 15
Forward Modeling of Log Response in Geopressured Formations Reveals Valuable Insights to the Various Pore-Pressure Prediction Techniques

J. C. Rasmus
Schlumberger Product Center,
Sugar Land, Texas


ABSTRACT

A forward model for log response in a geopressured shale is developed. The state of compaction, lithology, water depths, salinity profiles, compaction coefficients, and clay characteristics are all user modifiable. Effective-stress relationships for geopressured shales that are currently widely practiced in the industry all assume constant log response is indicative of constant porosity and, therefore, constant effective stress. This modeling reveals that, although the porosity of a geopressured shale may remain constant for a constant effective stress, its log reponse does not. Therefore, this chapter illustrates that any effective-stress technique that uses the log response directly cannot be used to accurately compute the effective-stress state of the shale. Instead, the log response must first be characterized in terms of lithology, salinity profile, fluid moduli, water depth, and compaction coefficients. The modeling shows that this is much more critical for resistivity than velocity measurements.

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