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Society of Petroleum Engineers Distinguished Lecturer
Stress Shadows: How and Why They Can Affect Hydraulic Fracturing in Both Conventional and Unconventional Plays
Neal B. Nagel
OilField Geomechanics LLC
Abstract:
Much is now made about “Stress Shadows” and their impact on hydraulic fracturing - particularly in multi-stage horizontal laterals commonly used in Unconventionals. Unfortunately, there is no standard definition of Stress Shadows and, as a result, there is much confusion over what they are and aren’t, and, most importantly, why they can have a significant impact on hydraulic fracturing operations. The goal of this presentation will be to address this confusion and more fully explain Stress Shadows and their impact.
The creation of hydraulic fracture width during a stimulation generates a change in the stress field, which alters all three principal stresses as well as tip shear stresses. These stress changes are the Stress Shadows.
As hydraulic fracture propagation is often controlled by the stress field, Stress Shadows may change the propagation path for subsequent hydraulic fractures or, as seen in cluster fracturing, propagation may be impeded completely. The presence of natural fractures and weakness planes can also affect, and be affected by, Stress Shadows. At the hydraulic fracture tip, shear stresses are generated that offer the potential to shear and open closed natural fractures and weak planes – and if opened, it may be possible to stimulate them. Equally important, behind the hydraulic fracture tip Stress Shadows increase the magnitude of all three principal stresses, which tends to close weakness planes making them more difficult to stimulate. Because of these effects and others, understanding and designing for the impact of Stress Shadows is often critical for stimulation optimization.
Biography:
Dr. Neal Nagel is currently Chief Engineer for OilField Geomechanics and has nearly 30 years of industry experience. He is a well-known expert in the geomechanics of Unconventionals and has given many invited SPE, AAPG, HGS, SEG, and SPWLA presentations. Nagel has also authored or coauthored more than 50 technical papers, with 20+ related to Unconventionals, including a keynote presentation at the 2014 SPE HFTC. He is a past SPE Distinguished Lecturer, was chief editor of the 2010 SPE Monograph on Solids Injection, has served on the SPE Drilling and Completions Committee, and also been a local SPE section officer.