Estimating hardness and Young's modulus of shale using drill cuttings: Implications for hydraulic fracturing in shale gas reservoir development

Shale formations are widely prevalent in the oil and gas industry as potential hydrocarbon reservoirs. The hardness and Young's modulus of shale significantly impact the success of hydraulic fracturing operations in shale gas reservoir development. The unavailability of standard-sized core samples (length to diameter ratio ∼2.5) makes it challenging to determine the mechanical properties of shale in the laboratory. This study investigates techniques for estimating hardness and Young's modulus using drill cuttings. The microhardness was measured on shale cuttings of ∼1 mm in size using a micro indenter. Young's modulus was measured at the macro-scale using a uniaxial compression test on a 25 mm diameter core sample. The relationship between microhardness and Young's modulus established for Longmaxi (China) and Ice-Box (Western Canada) shales was applied to another shale (e.g., Sembar Shale of Pakistan), for which no core samples were available. The measured mineralogy of the studied shales provides a common base for the comparison of microhardness and Young's modulus using isotropic and anisotropic theoretical models. A positive correlation was observed between Young's modulus and microhardness for the three shales tested in this study. Although the scale of measurement/assessment is different, the theoretical models show an insignificant impact of the scale range (micro (mm) to macro (cm)) on Young's modulus, microhardness, and brittleness.