A measure of drilling efficiency. Mechanical specific energy (MSE) is the energy required to remove a unit volume of rock. For optimum drilling efficiency, the objective is to minimize the MSE and to maximize the rate of penetration (ROP). To control the MSE, drillers can control the weight on bit (WOB), torque, ROP and drillbit revolutions per minute (rpm).
Reference: Teale R: "The Concept of Specific Energy in Rock Drilling," International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 2, no. 1 (March 1965): 57–73.