UCS Estimation through Uniaxial Compressive Test, Scratch Test and Based Log Empirical Correlation

In Petroleum, Civil and Mining Engineering, designing structures dealing with rock mass is a day-to-day activity. In order to execute such projects, it is essential to know the strength and deformability of rocks, as well as their in situ stress state. In Petroleum Engineering, especially, obtaining rock samples from a well and carrying out lab mechanical tests is costly and time-consuming. Thus, Petroleum Engineers have been attempting to determine rock mechanical properties through index tests or log-based correlations as to expedite this process and reduce the global cost of the activity. I order to be confident about results obtained via index tests or correlations, though, it is necessary to carry out a calibration of such outcomes against results from standard mechanical tests. In this article, a procedure used to determine the unconfined compressive strength is proposed. The data from that process supports the planning of two pilot projects to be developed by Petrobras in an on-shore oil field. In order to estimate the UCS for this oil field, three methods were applied: the standard uniaxial test, the scratch test and a log-based correlation. Due to the excellent agreement among results of all three methods, it was possible to extrapolate the data regarding UCS for the entire interval to be analyzed. The set of logs available, mainly transit-time and density log, was used as a guide in the UCS extrapolation process.