Incorporating the effects of elemental concentrations on rock tensile failure

Abstract

To bridge the gap between elemental concentrations and rock mechanics, this paper proposed to predict a tensile failure using the weight concentrations of various elements. In this research, the Brazilian test was used to measure the indirect tensile strength of sandstones under different environmental conditions, i.e., oven drying, water immersion, and mud filtration. According to the mechanical test results of 37 sandstone specimens, the fracture patterns can be quite complicated due to an interaction of tensile fracture with shear fracture or bending fracture. To improve the prediction accuracy of the statistical analysis, a digital image correlation (DIC) technique was used to capture the dynamic fracturing process and to verify the validity of the Brazilian tests. Finally, only 15 specimens met the principle of the Brazilian test with a valid tensile failure. Using the energy-dispersive system (EDS), a distinct disparity of elemental concentrations was identified between those two sides of a fracture, such as the content contrasts of C, Mg, Al, Si, Ca, Ti, Fe, and Zn. These key elements can be used to identify the fracture positions and predict the rock mechanical properties, e.g., Brazilian test strength, Young's modulus, and Poisson's ratio. The excellent correlation performance, between rock strength parameters and elemental concentrations, proved it applicable to provide another potential function of the Elemental Capture Spectroscopy log in the evaluation of wellbore integrity.