AQUEOUS AND MINERALOGICAL CHANGES DURING HYDROUS OIL SHALE RETORTING

Heating of oil shale converts the kerogen in the rock to extractable hydrocarbons that can be brought to the surface and converted to value-added products. However, during this heating process, there are concomitant changes in the mineralogical makeup of the rock matrix and chemical composition of subsurface waters that may ultimately alter reservoir permeability or affect the subsurface migration of contaminants. Hydrous pyrolysis experiments were conducted over the temperature range of 25 to 350ºC. Quantitative powder x-ray diffraction suggests that ankerite and aragonite are converted to calcite. The Mg and Fe from this conversion combine with Si and Al from analcime and quartz to form smectite (saponite). Retort water is primarily a Na-HCO₃ type water. Dissolved F, B, N, P, Ca, K, Cl and Br increase with retort temperature. Arsenic concentrations were very high in some experiments but the concentrations are not correlated with retort temperature. Geochemical modeling was conducted to provide further insight to the geochemical reactions occurring during retorting. The experimental results are combined with heat-flow calculations to conceptualize the potential spatial extent of geochemical alterations in the native rock and subsurface waters.