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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.