Determination of microstructural changes in a porous matrix under high-temperature impact on carbonate rocks

Heat treatment methods are the most widely used in the development of high-viscosity oil fields. The cyclic steam stimulation technology with injection of a high-temperature fluid has proven its efficiency in terrigenous formations and low efficiency for carbonate reservoirs of high-viscosity oil with small thicknesses. By means of experiments on real core samples, the authors have established that with an increase in temperature above 100 °C, an abnormal increase in filtration resistance occurs in samples, the mineralogical composition of rocks of which is mainly represented by calcites. Studies of the structure of the porous medium during filtration of a high-temperature fluid on microfluidic chips have shown that the cause of the abnormal drop in permeability, among other things, is thermal destruction of the oil itself, accompanied by precipitation of asphaltenes. This phenomenon significantly reduces the permeability of the porous skeleton, but is not as critical as with thermal destruction of calcites and the formation of new minerals with an increase in temperature above 300 °C, discovered during the study of the carbonate core. The growth of technogenic crystals inside porous channels was confirmed on a microfluidic chip simulating high-temperature exposure to a carbonate reservoir saturated with high-viscosity oil at temperatures of 250-300 °C.