Thermomechanical properties of the Garden Gulch Member of the Green River Formation

Extensive well logging and laboratory rock mechanics experiments gathered within the context of in-situ retorting are used to derive an anisotropic thermomechanical model for deformation of oil shale from the Garden Gulch Member of the Green River Formation in the Piceance Basin of Colorado. Elastic moduli determined from sonic velocities are shown to be consistent with but about twice as high as those from static measurements at small strain. Porosity correlates inversely with organic content, and the relative contributions of kerogen, minerals, and porosity to sonic velocities are determined from a combination of new and literature data. Young's modulus of kerogen derived by extrapolation to high kerogen volume fraction is consistent with measurements from previous workers. The temperature dependence and anisotropy of the triaxial tests can be described fairly well by Reuss and Voigt averages for a laminar material. The intrinsic (end-member) static Young's moduli of the kerogen and mineral components are 1 and 7 GPa, respectively, with thermal softening of each described by apparent activation energies of 17 and 9 kJ/mol, respectively. Isostatic compression creep tests are used to further constrain the temperature dependence of the plastic deformation viscosity. The apparent activation energy for creep is about 35 kJ/mol. The thermochemical properties of the clay-rich Garden Gulch Member are compared to those of the dolomite-rich Parachute Creek Member. At low organic content, the Young's modulus of the Garden Gulch Member is about four times lower, and the properties of the two members approach each other for high organic content.