Chan, Alvin W.1, Mark D Zoback1
(1) Stanford University, Stanford, CA
ABSTRACTS: The Effect of Stress Path on Reservoir Compaction and Permeability
The evolution of the stress state in a depleting reservoir has a significant influence
on the changes in physical properties within the reservoir. Utilizing a formalism we refer
to as Deformation Analysis in Reservoir Space (DARS) that combines laboratory rock physics
experiments with in-situ stress measurements, production-induced porosity and permeability
changes can be estimated. Empirical bounds of permeability reductions with compaction have
been derived from a number of laboratory studies on Gulf of Mexico sands. The
Kozeny-Carman relationship can match the empirical lower bound of permeability reduction
with an assumed percolation porosity close to 0% (corresponding to samples with an
extremely well-connected pore space). However, the Kozeny-Carman relationship generally
underestimates the effect of compaction on permeability changes. Using the empirical
porosity change/permeability change relationships, we examine the effects of
production-induced deformation on permeability reduction in a Gulf of Mexico reservoir,
Field Z, and compare them with in-situ measurements. The DARS analysis indicates that 25
MPa of depletion (~3600psi) will result in a change in porosity from 24% to 21%. The
predicted permeability changes range between 40% and 70%, depending on the initial
permeability. These predictions correspond reasonably well with measured permeability
changes in 3 wells in the field. As most of the porosity and permeability loss associated
with depletion are irreversible, stress management may become critical in uncemented sand
reservoirs in which inelastic compaction is the dominant mode of reservoir deformation.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.