Creep Properties of Shale and Predicted Impact on Proppant Embedment for the Caney Shale, Oklahoma

The Caney shale is an emerging hydrocarbon play located in southwest Oklahoma, USA. Within the Caney shale exist facies which were initially dubbed “reservoir” and “ductile” based on evaluation of well logging data. While past work has shown the distinction of “brittle” and “ductile” is not mechanically justifiable according to formal definitions, the current work shows some important differences between nominally ductile and reservoir zones. First, the “ductile” zones are more clay rich and have textural differences which can be expected to lead to differences in mechanical properties. One important impact of these differences is observed in triaxial creep experiments showing the “ductile” zones are more prone to creep deformation. Numerical simulations predict the “reservoir” zones will experience very little proppant embedment due to creep deformation of hydraulic fractures around proppant particles. On the other hand, “ductile” zones can be expected to undergo creep-driven proppant embedment leading to loss of fracture aperture ranging up to 100% loss, depending upon the spatial density of the proppant distribution. Hence, this research shows the identification of nominally “ductile” zones from well logs, while a misnomer, can be useful in finding clay-rich, creep-prone zones which will be the most prone to proppant embedment and hence vulnerable to greater production decline over time. Highlights The Caney shale has previously been identified as a ductile formation which would be difficult to produce. The terms “ductile” and “brittle” are not sufficient to describe the behavior of the Caney shale and this is supported through laboratory characterization. “Brittle” reservoir zones contain less clay and are mechanically stronger than “ductile” zones. “Ductile” zones are more prone to creep and proppant embedment than the “brittle” reservoir zones. While not sufficient to describe the mechanical behavior of formations, “ductile” and “brittle” identification can be used to identify zones which are more or less prone to long-term deformation and which are mechanically weaker.