Reservoir rock suitability for in-situ combustion, based on coke deposition behaviour

This study investigates the mineralogical and textural controls on coke deposition during in-situ combustion in reservoir sandstones, with implications for low-carbon energy recovery applications. Experimental simulations using feldspar-bearing, quartz-cemented Penrith Sandstone demonstrate that coke formation, the key requirement of high temperature combustion, occurs heterogeneously, primarily at grain contacts, along dissolved feldspar cleavage planes, and on rough detrital surfaces, but is largely absent from the flat faces of quartz cement. Quantitative X-ray computed tomography and scanning electron microscopy reveal that feldspar-rich zones experience greater porosity reduction through coke deposition, which is influenced by local specific surface area and mineral–fluid interactions. These findings indicate that feldspathic, poorly cemented, and fine-grained sandstones are more favourable substrates for coke formation, enhancing the thermal output potential during in-situ combustion and supporting the stable propagation of combustion fronts. The results provide a petrographic framework for reservoir screening aimed at optimising the selection of lithologies for geothermal energy recovery and related low-carbon strategies.