ABSTRACT
The maximum temperature reached in a reservoir is an important experimental parameter when evaluating the results of field or laboratory studies of oil production by in situ combustion methods. Minerological changes often occur in reservoir rocks on heating, and these may serve as indicators of combustion-zone temperatures. The feasibility of using the method in tests involving the Alberta oil sands was investigated in the present study. Samples of oil sand were exposed to simulated in situ combustion by using a firetube apparatus, and temperatures estimated by the mineralogical analysis of postburn samples were compared with those recorded by using thermocouples. It is shown that a number of minerals commonly occur in the Alberta oil sands that undergo potentially useful transformations. Those investigated experimentally include: calcite, chlorite, dolomite, kaolinite, illite and smectite, the transformations of which allowed temperatures to be estimated over the range 350-700°C. Agreement between observed and estimated temperatures was normally good, provided that certain interfering factors were taken into account. These factors include the production of acids during in situ combustion, the effects of combustion-gas concentrations on some of the transformation temperatures, and the reaction of certain minerals under hydrothermal conditions. The last was not significant in the present work, but its effect in longer-term experiments and in the field requires further study.
