Methods and systems for controlling a drilling operation based on an MSE value calculated for a depth increment are disclosed herein. In an exemplary method, drilling parameters characterizing a drilling operation in a subterranean formation are received in a control system. The drilling parameters are used by the control system to calculate a depth-based mechanical specific energy (MSE) based on some amount of energy expended by at least a portion of a drilling assembly while drilling at least one identified depth sub-interval of a depth interval of a subterranean formation. The control system uses the calculated depth-based MSE to control the drilling operation.