Reservoir rock suitability for <i>in situ</i> 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 the 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 petrographical framework for reservoir screening aimed at optimizing the selection of lithologies for geothermal energy recovery and related low-carbon strategies.