Influencing factor analysis of shale micro-indentation measurement

Abstract

To address the difficulty in measuring mechanical properties within the reservoir formation during the process of drilling in shale formations, micro-indentation measurement technology is performed to determine the micro elastic modulus and the indentation hardness of a shale outcrop in the Longmaxi Formation in the Sichuan Basin (the Changning Area). Additionally, factors influencing the micro-indentation measurement are analyzed from aspects such as indenter defects, experimental parameter settings, shale surface properties, and shale composition. The results show that the elastic modulus and indentation hardness decrease with increasing indentation depth. The test is less affected by indenter passivation. The area function needs to be calibrated when the tip radius of the indenter is more than 10 μm. It is observed that the test is substantially influenced by the parameter settings, so reasonable parameters should be determined before conducting the test. The Oliver-Pharr method is applicable to shale outcrops of the Longmaxi Formation, which meet the general requirements of the method. The measured values increase with increasing packing density. Moreover, the fitting percentage of the unloading curve has an impact on the result, and the reasonable fitting percentage of the unloading curve for shale samples was determined to be from 45% to 75%.