We present a study of proppant embedment in shales and its effect on hydraulic fracture conductivity. We present an analytical model to predict the stress-dependent conductivity of hydraulic fractures based on simple laboratory measurements of proppant embedment. We also study the relations between rock mineralogy, mechanical properties, fluid composition and proppant embedment. Initial results show a close correlation between the amount of proppant embedment at a given stress and the rock stiffness which, in turn, is affected by the mineral content, mainly the amount and type of clay minerals present in the rock. These correlations are being utilized to predict the amount of conductivity loss due to proppant embedment in a variety of unconventional resource plays worldwide.
Production of hydrocarbons from tight formations, such as shales, requires stimulation by creating massive hydraulic fractures to expose large surface areas within the formation and facilitate the transport of hydrocarbons to the wellbore. Economic production requires sustaining sufficient conductivity in hydraulic fractures through the lifetime of the wells, however, maintaining such conductivity could be challenging in some cases, especially in soft, clay rich formations. Different mechanisms could contribute to the impairment of hydraulic fracture conductivity including fines migration , proppant diagenesis , proppant crushing , and reduction in fracture aperture due to the embedment of proppant particles into the surface of the hydraulic fracture [3,4]. The relative contribution of each of the impairment mechanisms varies from one formation to the other depending upon numerous variables including mechanical properties, mineral content, temperature, proppant type, fracture fluid type and closure pressure. In this paper, we study the embedment of proppants into shale fracture surfaces. The paper also presents an analytical model used to predict the reduction of the conductivity of hydraulic fractures resulting from proppant embedment at different closure pressure values.