Evaluation of rock mechanical properties via scratch testing and its impact on energy production: comprehensive review

Bob L. Herd Department of Petroleum Engineering, Texas Tech University, Lubbock, TX 79409, USA

^* Corresponding author: doyin.kolawole@ttu.edu

Abstract

The scratch test is a non-destructive method made up of pushing a tool across the surface of a weaker rock at a given penetration depth. The uniaxial rock strength (UCS), fracture toughness (K_IC), and other geomechanical parameters influences how fracture nucleates, but fracture sizes and geometry adopted in hydraulic fracture design and modeling are most often overestimated. Although several researchers have attempted to evaluate UCS, K_IC and other geomechanical properties in conventional and unconventional formations through scratch testing method, but there remain differing opinions on the fundamental approach and principles to be adopted in estimating those properties. Therefore, the evaluation of geomechanical parameters and their effect on hydrocarbon exploration, energy storage, and hydrocarbon exploitation remain an important issue for energy industry. In this paper, we present a comprehensive review of the methods of approach, applications, and the mechanics of rock scratching. We show the merits of scratch test over other methods of estimating rock mechanical properties. Our review focuses on over 50 previous experimental studies using scratch tests in the past few decades to investigate UCS, K_IC and other geomechanical properties, including their impact on rock failure, fracture initiation and propagation. Finally, we highlight the fundamental research questions that are yet to be addressed. We envisage that advancement in our knowledge will improve optimization of hydrocarbon exploitation, energy storage, and field-scale modeling for energy production operations.