@article {Nagel2013,
	title = {{Coupled Numerical Evaluations of the Geomechanical Interactions Between a Hydraulic Fracture Stimulation and a Natural Fracture System in Shale Formations}},
	journal = {Rock Mechanics and Rock Engineering},
	volume = {46},
	number = {3},
	year = {2013},
	month = {mar},
	pages = {581{\textendash}609},
	abstract = {Due to the low permeability of many shale reservoirs, multi-stage hydraulic fracturing in horizontal wells is used to increase the productive, stimulated reservoir volume. However, each created hydraulic fracture alters the stress field around it, and subsequent fractures are affected by the stress field from previous fractures. The results of a numerical evaluation of the effect of stress field changes (stress shadowing), as a function of natural fracture and geomechanical properties, are presented, including a detailed evaluation of natural fracture shear failure (and, by analogy, the generated microseismicity) due to a created hydraulic fracture. The numerical simulations were performed using continuum and discrete element modeling approaches in both mechanical-only and fully coupled, hydro-mechanical modes. The results show the critical impacts that the stress field changes from a created hydraulic fracture have on the shear of the natural fracture system, which in-turn, significantly affects the success of the hydraulic fracture stimulation. Furthermore, the results provide important insight into: the role of completion design (stage spacing) and operational parameters (rate, viscosity, etc.) on the possibility of enhancing the stimulation of the natural fracture network ({\textquoteright}complexity{\textquoteright}); the mechanisms that generate the microseismicity that occurs during a hydraulic fracture stimulation; and the interpretation of the generated microseismicity in relation to the volume of stimulated reservoir formation. {\textcopyright} 2013 Springer-Verlag Wien.},
	keywords = {Discrete element modeling, Horizontal well, Hydraulic fracturing, Multi-stage fracturing, Natural fractures, Numerical simulation, Stimulation, Stimulation optimization, Well completion},
	issn = {0723-2632},
	doi = {10.1007/s00603-013-0391-x},
	url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84877873776\&partnerID=tZOtx3y1},
	author = {Nagel, N. B. and Sanchez-Nagel, M. A. and Zhang, F. and Garcia, X. and Lee, B.}
}
@article {GARCIA2009,
	title = {{A clustered overlapping sphere algorithm to represent real particles in discrete element modelling}},
	journal = {G{\'e}otechnique},
	volume = {59},
	number = {9},
	year = {2009},
	month = {jan},
	pages = {779{\textendash}784},
	abstract = {An algorithm is presented for representing irregular particles as clusters of overlapping spheres, for use within discrete element method (DEM) simulations of particulates. The algorithm is sufficiently fast to be implemented on desktop computers. Although volume and moment of inertia comparisons of resulting clusters with prototypical geometric data show that in the region of 50 to 100 spheres may be needed to represent a particle, actual DEM simulations of an unstable pile of simulated particles show that only 10 or so spheres may be sufficient to capture the mechanics of the system.},
	keywords = {Numerical modelling},
	issn = {0016-8505},
	doi = {10.1680/geot.8.T.037},
	url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-77949702642\&partnerID=tZOtx3y1},
	author = {Garcia, X. and XIANG, J. and LATHAM, J.-P. and HARRISON, J.P.}
}
