Samuel Jackson, Sam Krevor

Unpredicted, rapid plume elongation has been observed at subsurface CO2 storage projects worldwide, exemplified by the Sleipner project. We show that conventionally ignored centimetre-metre scale heterogeneity in capillary pressure characteristics can manifest as rapid field-scale, decametre-kilometre, plume migration. We analyse the effect in the Goldeneye Field, UK, a proposed storage site with a unique combination of sample/data accessibility and generality as an archetype sandstone reservoir. We overcome previous barriers by characterising in greater detail over larger scales - the 65m reservoir height at cm-m resolution - and through use of an upscaling scheme which resolves small-scale heterogeneity impacts in field-scale simulations. These models reveal that significant early time retardation of buoyantly rising CO2 plumes is followed by rapid migration under the caprock in the presence of anisotropic, layered heterogeneities. Lateral migration speeds can be enhanced by 200%, placing first order controls on fluid flow and providing a mechanistic explanation for field observations.