Analytical Failure Surfaces for Oil Shales of Varying Kerogen Content

Abstract

A subject of current national interest is the fracture of oil shale and other rock for energy and mineral resource recovery. Successful prediction of the nature of explosive rock breakage depends significantly on the completeness of understanding the material constitutive relations that are used. That is, all of the important physical properties related in any way to fracture must be included in the material description; shear strength is obviously one of these quantities. Since it is impractical to measure all material properties as functions of position every few feet in regions that are to be rubblized, it would be quite advantageous to be able to express the shear yield strength in terms of some easily measurable quantity, such as density. Correlation of other material properties with density has already been done for kerogen (the organic material) content [1], sonic velocities [2,3], and high-pressure Hugoniot response [4]. In the past there has been a considerable number of experimental measurements of compressive strength of oil shale as a function of sample orientation, confining pressure, and kerogen content [5,6]. Theoretical representations of the failure surfaces for these materials have been obtained [7,8], but no correlation with material density has been attempted over a significant range of confining pressures.