- 1581 - Governing Parameters for Approximation of Carbonates UCS M. R. Asef Assistant Professor in Engineering Geology, Tarbiat Moallem University, Iran e-mail: asef@tmu.ac.ir M. Farrokhrouz Senior Well Engineer, South Zagros Oil & Gas Production Co., Iran e-mail: mfarrokhrouz@gmail.com ABSTRACT Knowledge of uniaxial compressive strength (UCS) of carbonate rocks is essential in almost every engineering project. Since appropriate core sampling is sometimes extremely difficult (e.g. deep projects in petroleum industry), estimation of rock strength based on other rock properties has always been a demanding alternative. In this research, it was clarified that three parameters of Young’s modulus (E), porosity (φ), and the Biot’s coefficient (α) affect the uniaxial compressive strength (UCS) of carbonate rocks. Since porosity in carbonates is affected by particle size, degree of compaction, diagenesis process, and the solution history, it could vary at different geological formations and geographic locations. Contribution of the Biot’s coefficient, however, confirms the poroelastic behaviour of carbonate rocks. As a result, approximation equation of the UCS of carbonate rocks was suggested to be based on E, φ, and α. A significant advantage of this research is that suggested prediction equation is independent of the geological formation and/or the geographic location of carbonate rock. Furthermore, analysis of the data indicated that for low porosity carbonates, UCS is related to E, φ, and the Biot’s coefficient, while at highly porous carbonates UCS is dominantly influenced by E. This improvement would facilitate prediction of the UCS based on non-distractive parameters such as sound velocity and density. KEYWORDS: Carbonates, Limestone, Uniaxial Compressive Strength, UCS, Porosity, Young’s Modulus