@conference {Nagel2012a,
	title = {{Hydraulic fracturing optimization for unconventional reservoirs - The critical role of the mechanical properties of the natural fracture network}},
	booktitle = {Society of Petroleum Engineers - SPE Canadian Unconventional Resources Conference 2012, CURC 2012},
	volume = {1},
	year = {2012},
	pages = {227{\textendash}237},
	abstract = {The success of many shale plays depends on the optimal stimulation of natural fractures, and the characterization of the natural fracture systems is a key issue often leading to the construction of a discrete fracture network (DFN). The DFN chiefly consists of fracture spacing, fracture dip, and dip direction from numerous sources, and, in some cases, is matched to well test data allowing for the determination of hydraulic properties. However, a commonly missing component of natural fracture characterization, and the component most important to evaluating the coupled hydro-mechanical behavior of the fractures during a hydraulic fracture stimulation, is the evaluation of the mechanical behavior of the fractures. The important mechanical parameters of the fractures include: a) elastic properties such as shear and normal stiffness, which relate changes in pore pressure to changes in aperture; b) strength parameters such as cohesion and friction angle, which define when a fracture may shear and open; c) dilational properties, which relate fracture opening to shear slippage; d) fracture toughness, which determines the pressure required to extend a fracture; and e) initial aperture. In this paper, using a new, state-of-the-art, fully-coupled, 3D distinct element hydraulic fracturing simulator, mechanical fracture parameters were evaluated in a parametric study in order to determine their impact on the effectiveness of hydraulic fracture stimulations. Copyright 2012, Society of Petroleum Engineers.},
	isbn = {9781622764884},
	url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84875645702\&partnerID=tZOtx3y1},
	author = {Nagel, Neal B. and Garcia, Xavier and Lee, Byungtark and Sanchez-Nagel, Marisela}
}
@conference {Nagel2012,
	title = {{Understanding "SRV": A numerical investigation of "wet" vs. "dry" microseismicity during hydraulic fracturing}},
	booktitle = {Proceedings - SPE Annual Technical Conference and Exhibition},
	volume = {4},
	year = {2012},
	pages = {3375{\textendash}3386},
	abstract = {Effective monitoring of hydraulic fracturing stimulations is critical to their optimization, and the evaluation of field microseismic data is now commonly used in many of the active shale plays for this purpose. The concept of Stimulated Reservoir Volume (SRV), for example, is a common technique wherein the extent of the microseismic data is used to represent the size of the fluid drainage area for a fracture or well. A principal challenge with the interpretation of microseismic data - and its use to determine drainage area or some other metric for the success of the stimulation - is the understanding of the actual cause of the microseismicity itself. Basic geomechanics principles show that rock failure - the cause of microseismicity - is a result of changes in the in-situ effective stresses relative to a given rock strength. Effective stress - which is the stress acting on the rock matrix - may change either through a change in pore pressure (leading to {\textquoteright}wet{\textquoteright} microseismicity) or through a change in the total stress (leading to {\textquoteright}dry{\textquoteright} microseismicity). Dry microseismicity may occur well beyond the pressure field and be hydraulically disconnected from the wellbore. In this paper, we present the results of a numerical study of hydraulic fracturing-induced microseismicity using a discrete element code, where the mechanical behavior of the natural fractures is modeled explicitly, which allows for the quantitative evaluation of {\textquoteright}wet{\textquoteright} versus {\textquoteright}dry{\textquoteright} microseismicity. Copyright 2012, Society of Petroleum Engineers.},
	isbn = {9781622764150},
	url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84874038119\&partnerID=tZOtx3y1},
	author = {Nagel, Neal B. and Garcia, Xavier and Nagel, Marisela Sanchez and Lee, Byungtark}
}
