1. INTRODUCTION The authors, and others (Nagel, et al., 2011; Nagel, et al., 2013a; 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. Another key understanding about Stress Shadows, as explained by Nagel, et al. (2013a), is that Stress Shadows include the alteration of not only the minimum horizontal stress (for vertical hydraulic fractures in a normal faulting stress environment) but also alterations of the maximum horizontal stress and the vertical stress (Figure 1) as well as the shear stresses associated with the hydraulic fracture tip (i.e., Stress Shadows affect the S1, S2, and S3 principal stresses as well as the xy, xz, yz shear stresses). Furthermore, Rios, et al. (2013) showed that the change in stress field due to Stress Shadows can be additive from hydraulic fracture to hydraulic fracture under certain conditions (predominantly the spacing between hydraulic fractures). As highlighted by the authors and others, Stress Shadows can create a myriad of effects associated with hydraulic fractures, particularly multi-stage hydraulic fractures along horizontal wellbore. These effects include an increase in the both the breakdown pressure and Instantaneous Shut-In Pressure (ISIP) from toe to heal along horizontal laterals, hydraulic fracture rotation and asymmetric wing length, perforation cluster efficiency, ARMA 17-884 Consideration of Stress Shadows in Stacked Plays Nagel, N.B. OilField Geomechanics LLC, Rosenberg, TX, USA Gokaraju, D. and Mitra, A. MetaRock Laboratories, Houston, TX, USA Sanchez-Nagel, M.A. OilField Geomechanics LLC, Rosenberg, TX, USA Copyright 2017 ARMA, American Rock Mechanics Association This paper was prepared for presentation at the 51 st US Rock Mechanics / Geomechanics Symposium held in San Francisco, California, USA, 25-28 June 2017. This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and critical review of the paper by a minimum of two technical reviewers. The material, as presented, does not necessarily reflect any position of ARMA, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of ARMA is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 200 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgement of where and by whom the paper was presented. 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).