Experimental and analytical investigation on the normal contact behavior of natural proppant simulants

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Original languageEnglish
Article number107
Journal / PublicationGeomechanics and Geophysics for Geo-Energy and Geo-Resources
Issue number4
Online published2 Nov 2021
Publication statusPublished - Nov 2021


Granular materials are of interest in various fields of engineering and science and they commonly display rough morphologies which govern their constitutive behavior. One of the emerging applications of granular materials is their use as proppants in hydraulic fracturing and the present study provides an investigation into the normal contact behavior of three types of proppant simulants using micromechanical-based experiments. As the complex processes in hydraulic fracturing necessitate accurate modeling of the order of nano-to-micrometers of displacements, a micromechanical investigation of grain contact response accounting for extremely small ranges of deformations is necessary to provide insights with potential applications in contact mechanics modeling. The proppant simulants used in the present study are composed of quartz sand grains from different origins with variations of their local surface morphologies and nano-to-micro scale roughness. Based on their local radii, which govern the contact behavior of non-conforming surfaces, the proppant simulants would approximately correspond to mesh 16/30–20/40. In view of their global radii, these grains would be considered on the upper bound of potential sizes used in hydraulic fracturing. In terms of normal contact response, the data were fitted using two contact mechanics models and a discussion is elaborated on their applicability in simulating the normal load–displacement behavior of grains at their contacts. It is shown that surface asperities play an important role in the constitutive behavior of the grain contacts and control the different zones of response as observed from both experiments and analytical expressions. Natural grains used as proppants may display smoother surfaces compared with other geological materials, such as weathered rocks or crushed rocks. However, their roughness is still an important influencing factor that should be considered in the simulation of multi-scale problems, especially when micrometer-level displacements are important to be encountered. Based on differentiation of the normal force for a given range of displacements, tangent stiffness was derived and the data showed that tangent normal stiffness (KN) increases with normal displacement. Thus, the load (or stress) state of a given contact is important to provide appropriate values of the ratio (KT/KN), where the tangential stiffness (KT) decreases rapidly with the increase of the sliding displacement.

Research Area(s)

  • Micromechanics, Morphology, Normal contact stiffness, Proppant, Roughness