Yihuai Zhang

Swelling‐induced changes in coal microstructure due to supercritical CO2 injection

Enhanced coalbed methane recovery and CO2 geo-storage in coal seams are severely limited by permeability decrease caused by CO2 injection and associated coal matrix swelling. Typically it is assumed that matrix swelling leads to coal cleat closure and as a consequence, permeability is reduced. However, this assumption has not yet been directly observed. Using a novel in-situ reservoir condition x-ray micro computed tomography flooding apparatus, for the first time we observed such micro cleat closure induced by supercritical CO2 flooding in-situ. Furthermore, fracturing of the mineral phase (embedded in the coal) was observed; this fracturing was induced by the internal swelling stress. We conclude that coal permeability is drastically reduced by cleat closure, which again is caused by coal matrix swelling; which again is caused by flooding with supercritical CO2.

Microstructural effects on mechanical properties of shaly sandstone

AbstractUnderstanding the mechanical properties of shaly sandstone is of great importance in reservoir geomechanics. Because of the lack of core data, measurements based on acoustic wave velocities...