Least Principal Stress Prediction Using a Viscoplastic Stress Relaxation Model Applied to Stacked Pay in the Permian Basin

Abstract

The height of propagating hydraulic fractures is largely controlled by the variation of the least principal stress with depth. Thus, prediction of the least principal stress would be extremely helpful when designing hydraulic fracturing operations so that vertical propagation of hydraulic fractures is contained to the production horizon or extending to multiple producing horizons as required. We are utilizing a viscoplastic stress relaxation model following Sone and Zoback (2014) developed in our research group over the past several years. A basic element of the model is that stress magnitudes become more isotropic in more viscoplastic formations as time evolves (causing the least principal stress, or frac gradient, to increase) whereas in less viscoplastic formations, the frac gradient will be lower. We attempt to apply this model quantitatively, to a case study conducted in the Permian Basin where multiple horizontal wells were drilled and hydraulically fractured to produce from three adjacent producing horizons. The least principal stress has been measured at different depths and core samples were available for laboratory testing from multiple depths. Laboratory creep tests were done to quantify the degree of stress relaxation in the different formations and obtain the constitutive parameters of a time dependent power law that describes the viscoplastic behavior in the various formations. We show that the viscoplastic model is helpful for explaining vertical hydraulic fracture growth as inferred from the distribution of microseismic events recorded during hydraulic fracturing at different producing horizons.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017