51st U.S. Rock Mechanics/Geomechanics Symposium,
San Francisco, California, USA
2017. American Rock Mechanics Association
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242 since 2007
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ABSTRACT: Stress Shadows, the colloquial term used to describe the stress field change associated with hydraulic fractures, is a fundamental part of hydraulic fracture optimization in horizontal wells. The authors, and others, have written extensively about Stress Shadows and their potential influence on breakdown pressures, ISIP increases from toe to heal in horizontal wellbores, on hydraulic fracture rotation and asymmetric propagation, on perforation cluster efficiency, and on their potential impact on multi-well completion schemes. However, as many of the current Unconventional Plays, like those in the Permian Basin in Texas, in the STACK/SCOOP in Oklahoma, and the Bakken in North Dakota, involve sufficient vertical thickness that stacked laterals are being used or considered, the impact of Stress Shadows needs to also be considered for these developments.
Within this paper, the authors present numerical hydraulic fracture simulation results for a Bakken-type stacked play considering the impact of Stress Shadows on fracture propagation (both height and length) as well as fracture rotation. The results show that, under certain field conditions, there may be a benefit to optimizing lateral landing location, job design, and the vertical completion sequencing of the laterals (i.e., stimulating from shallow to deep rather than deep to shallow).
The authors, and others (Nagel, et al., 2011; Nagel, et al., 2013 a; Nagel, et al., 2013b; Wong, et al., 2013; Peirce and Bunger, 2014; Dohmen, et al., 2015; Skomorowski, et al., 2015; and Zangeneh, et al., 2015), have written fairly extensively about Stress Shadows - the colloquial or common term used to describe the stress changes induced by hydraulic fractures. Furthermore, the topic of Stress Shadows has been included in a patent application (Patent WO2015069817A1, 2015) and as a Society of Petroleum Engineers Distinguished Lecturer topic (Nagel, 2016).
In an elastic formation, stress and deformation are coupled. That is, if the formation is stressed, it will deform and if the formation is deformed, it will alter the local stress field. This concept was known and applied to a crack (i.e., a hydraulic fracture) in an elastic medium by Sneddon (1946). This points to one of several key understandings about Stress Shadows: Stress Shadows are a result of hydraulic fracture-induced deformations (e.g., hydraulic fracture width or natural fracture width) and any temporal changes in these deformations (e.g., closure of the hydraulic fracture on proppant) will alter the Stress Shadows. Furthermore, this means that Stress Shadows occur from all hydraulic fractures, whether initiated from a horizontal or a vertical wellbore.
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