Underground oil-shale retort monitoring using geotomography

Geophysical tomographs (geotomographs) were made of two underground oil-shale retorts: (1) the Occidental Oil Shale Inc. miniretort constructed for ignition tests at the demonstration mine at Logan Wash, Colorado; and (2) the Geokinetics Oil Shale Inc. Retort 25 near Vernal, Utah. These experiments demonstrate that geotomography may be a valuable diagnostic tool for underground oil-shale retorting process. At the Geokinetics in-situ retort, the technique delineated the zones of high permeability in a cross-section of the retort. At the Occidental modified in-situ miniretort, the technique imaged the high temperature zone of the retort with a spatial resolution of about 2 m, and showed its temporal development over a period of eleven days.