Estimation of UCS of Carbonate Formation for an Iraqi Oil Field

Abstract

The unconfined compressive strength (UCS) is a crucial factor of rock strength parameters for estimating the in situ stresses of the rock, designing the most effective fracture design, predicting the best mud weight, and mitigating drilling issues. UCS is commonly determined by subjecting rock samples to uniaxial or triaxial strains until they fail. Laboratory tests provide a direct and more precise estimation of UCS. However, it is unable to generate a continuous profile along the well (i.e., limited to specific depth intervals) due to the presence of specimens, expense, and time consumption. Consequently, other approaches were devised to overcome the gaps in the UCS prediction by utilizing wire-line log data. Several empirical correlations for predicting UCS are derived from well-log data, particularly the porosity, density, and sonic logs. In this paper, the previous correlations for predicting the UCS of carbonate formation have been evaluated using measured data of UCS. The results show that the compressional wave velocity (VP) is the best well log parameter for estimating carbonate formation’s unconfined compressive strength, and Yasar and Erdogan correlation best predicts the UCS that fit the measured data for carbonate formations. Thus, Yasar and Erdogan correlation has been chosen to estimate a continuous profile of UCS across the entire depth of carbonate formation in the Rumaila oil field.