A New Parameter to Predict Successful Oil Shale Retorting

Rock-Eval pyrolysis and Fischer assay are traditionally used to evaluate the oil potential of oil shales. However, these techniques only give information about the yield of volatile oil, not on the composition of the oil shale or the oil derived from it. Thus, molecular data is crucial for understanding the thermal behavior of the organic matter during retorting. The infrared spectra of kerogen, the insoluble organic fraction in oil shales, offer a picture of its macromolecular structure, and make it possible to determine the relative abundance of carboxyl, carbonyl, aliphatic CH, aromatic CH groups, and skeletal aliphatic hydrocarbons within the kerogen. The composition and relative abundance of these functional groups is important to consider when retorting an oil shale. It is well known that at any given temperature, the pyrolysis of organic material containing a large quantity of C-OR functional groups will yield a smaller amount of oil than the pyrolysis of organic material containing predominantly aliphatic hydrocarbons. This is due to the fact that C-O bonding is more unstable than C-H bonding, and consequently will be cleaved off the macromolecule first.

Thus, we have defined a new retorting factor parameter to account for oil shales that contain a high proportion of oxygenated functional groups within the macromolecular network of the kerogen. This parameter is defined as the ratio of the summation of the peak areas of oxygenated functional groups divided by the summation of the oxygenated functional groups and the aliphatic hydrocarbon functional groups. We applied this newly developed parameter to a series of Carboniferous, Permian, and Devonian oil shales to assess their oxygenated functional content and hence their retorting behavior, and compared the predictions from this new parameter with their historical mining records.