The Thermal Conductivity and Diffusivity Of Green River Oil Shales

Abstract

Thermal conductivities of Green River oil shales vary fourfold, decreasing with increasing oil yield and temperature. Values also decrease as the kerogen decomposes, but these changes are small after about 9 hours. Mineral composition, geographic location, depth of burial, axial stress, and pressure have no significant erect. The thermal properties, which are transversely isotropic, are applicable to the calculation of heat losses from in-situ recovery operations. Introduction Thermal decomposition of the essentially insoluble organic matter in oil shales is the easiest way to obtain shale oil. Proper planning of both surface and sub-surface thermal oil-shale recovery operations requires values of the thermal conductivity and diffusivity of oil shales.There are few publications reporting thermal conductivities of oil shale from the Green River formation. Gavin and Sharp reported three values for the thermal conductivity of an oil-shale sample assaying 42.7 gal/ton. Their reported values were obtained over the temperature range from 77 degrees to 167 degrees F, but the direction with respect to the bedding plane in which the measurements were taken was not indicated. Thomas presented thermal conductivity data of an oil shale assaying 30 gal/ ton and at a mean temperature of 104 degrees F, finding values parallel to the bedding plane to be 30 percent higher than those normal to it and finding essentially no effect of stress levels of 1,000 psi and above.Tihen et al. report on the thermal conductivity and diffusivity at room temperature of unconfined raw, retorted, and burned oil shales assaying from 8.6 to 58.6 gal/ton. Correlations for thermal conductivity are given for temperatures as high as 1,100 degrees F while considering the anisotropic character of the oil shales. Though bolted, samples developed cracks during heating, suggesting those results may be more applicable to rubbled pieces in subsurface cavities or large surface retorts than to the calculation of heat losses from a process zone in subsurface thermal operations.This report presents thermal conductivity data of confined Green River oil shales over a wide range of temperature, fluid pressure, axial stress, and kerogen content. The bulk of our measurements were carried out on oil shales as they are found in nature; that is, they were not previously retorted. At the higher temperatures, however, our reported values include the effects of at least some decomposition of the organic matter. Thermal conductivities of burned (organic-free) oil shales were measured on only two samples.The effects of kerogen content, fluid pressure, axial stress, temperature, orientation, heating time, and mineral composition on the thermal conductivities of oil shales were investigated. These basic results were then used together with specific gravity and a correlation of specific heat with oil yield by Fischer assay and temperature to obtain calculated thermal diffusivities for each sample. Instrumentation The transient line heat-source (probe) method, whose application is not particularly complicated by the addition of means for stressing the sample, was used in our investigation. JPT P. 97