Thermal Properties of Green River Oil Shales

The goal of the study was to characterize the temperature ranges and intensities of transitions associated with release of hydrocarbons from shale. Samples were obtained from core at three different depths: 74, 138 and 163 m. Their richness (by Fischer assay) was 31, 41 and 17.5 GPT, respectively. Samples were cut as cylinders oriented in three mutually perpendicular directions x, y and z. The techniques involved in this research were Thermogravimetry (TGA), differential scanning calorimetry (DSC), and thermomechanical analysis (TMA).  Thermal analysis was performed by heating the materials from 25 to 750 ºC in a nitrogen atmosphere at 2ºC/min. Some DSC measurements were also performed in air. TGA results obtained in nitrogen indicated two mass losses around 350 and 600 ºC due to evaporation. Each step was accompanied by an endotherm.  Heating in air caused extensive exothermic reaction between 300-600 ºC with the heat of transition in the range 1600-3000 J/g.  Thermomechanical analysis showed significant differences in thermal expansion between samples obtained from different depths as well as between samples oriented in different directions. TMA curves show sharp peaks for the 74 and 163 m samples in x and y directions while all the other samples demonstrate less dramatic behavior. The biggest expansion was recorded for samples from 74m (22% in y direction) and the smallest for samples from the 163 m level (0.6% in x and y directions). The coefficient of thermal expansion varied from initial ~20-100 x 10^-6/ ºC recorded before the first transition to ~3500 x 10^-6/ ºC during the transition. These observations clearly indicate anisotropy present in each layer of shale.  The results may prove useful in engineering of the in situ recovery process of hydrocarbons from oil shales.