Standardization of Mechanical Specific Energy Equations and Nomenclature

Summary This paper recommends standardized names and equations for the two most common uses of mechanical specific energy (MSE) concepts: “total MSE” and “downhole MSE.” These names and their equations should be used uniformly in all applications, including electronic drilling recorder (EDR) picklists, rigsite surveillance, engineering surveillance, data analytics, research, and technical publications. MSE, used as a metric for drilling efficiency, is a mathematical calculation of the energy used per volume of rock drilled. The downhole MSE equation calculates the efficiency of the bit alone, while the total MSE equation includes both the bit and drillstring. Those who use MSE in surveillance or analytics know the negative effects created by the lack of standardization over the years; it is certainly not a new problem. The lack of standardized nomenclature has resulted in the use of the same name for different equations, or different names are given for two equations that are identical. This affects the ability of drill teams to engage vendors in the redesigning of performance limitations or to communicate new operational practices between teams and rigs. In addition to standardizing nomenclature, this document corrects a mathematical error that is common in calculating the total MSE. The concern with the inconsistencies has increased as MSE has become a key element in many automated optimization schemes. Inconsistencies or uncertainties in the basis of MSE values calculated in real time or shared in large data sets will affect the industry’s ability to develop useful analytics or to automate rig control platforms and data-driven decisions. This paper also includes a discussion of the MSE measurement errors and their effect on calculated values, which is of particular interest to controls engineers and those involved in data analytics. Examples are provided to illustrate how the two different MSE values are used in field operations. Also, a substantial list of current and potential future uses of MSE is included to encourage better MSE-based practices to potentially lead to the development of new uses in the future, including automation. This ad hoc MSE Standardization Committee is a volunteer group with representation from operators, rig contractors, service companies, and data acquisition vendors. The guidance given reflects their shared experience in utilizing MSE in surveillance and analytics, and the recommended equations are technically correct.