Experimental and numerical investigation of wormholing during CO2 storage and water alternating gas injection

Carbon dioxide (CO2) injection into geological formations is gaining global interest. Examples include CO2 storage to mitigate greenhouse gas emissions and water alternating gas (WAG) injection for enhanced oil recovery (EOR) and storage. Injected CO2 inevitably dissolves in water (injected or formation), which results in acidic conditions that can dissolve the rock matrix in carbonate reservoirs. Depending on the dissolution's location and pattern in the reservoir, this may benefit well injectivity and/or threaten well integrity. Fine-gridded models with detailed physics and chemistry capture the relevant effects but are not suitable for the application to the field scale where instead correlations are used. The correlations that exist, however, are so far not sufficiently constrained to be of practical use. We report new experimental and modelling work that provides the means for qualitative to quantitative field-scale predictions of these effects for all the different combinations of CO2-water injection of interest. These show that, for conventional injection strategies (dry CO2 injection and WAG), there are no material concerns, but there are potential well integrity issues that need more detailed investigation for the proposed alternative strategies of carbonated water injection or co-injection.