Estimating unconfined compressive strength and Young’s modulus of carbonate rocks from petrophysical properties

Abstract

Geomechanical studies in carbonate rocks often require the use of log relations to obtain mechanical properties when laboratory measurements are not available. This study presents a new set of equations to predict the unconfined compressive strength (UCS) and Young’s modulus (E) for three carbonate lithologies: limestone, dolomite, and chalk. The equations are developed based on more than 700 mechanical-physical tests of carbonate rocks across different geological settings and geographical locations. The obtained results confirmed that petrophysical properties are consistent in determining the carbonate mechanical properties. The relations are developed based on either a single parameter or multiple parameters where coefficient of determination was improved for the multiple parameter relations. Scattering in the prediction of UCS and E is expected due to the carbonate heterogeneity in mineralogy, porosity, fabric as well as testing conditions. Thus, the applicable range of each relation is investigated. To test whether improved fits are achieved in this study, the relations are compared with the literature, and they showed a higher coefficient of determination. The proposed relations can be generally used as a starting point for UCS and E estimate when carbonate mechanical properties from laboratory tests are not available.