APPROXIMATE SOLUTION FOR PRESSURE BUILD-UP DURING CO2 GEO- SEQUESTRATION IN BRINE AQUIFERS

Over the past 20 years, the concept of permanently storing (i.e. sequestering) carbon dioxide (CO2) in geologic media (e.g. brine aquifers) has gained increasing attention as part of important technology option of carbon capture and storing (CCS) within a portfolio of options aimed at reducing anthropogenic emissions of greenhouse gases to the earth’s atmosphere.

Although high injection rates can minimize the cost of injection, it can result in huge formation damage as well. Optimal injection rate has to remain within the safe pressure limits. Accordingly, a robust monitoring of the transient pressure build up characteristics resulting from CO2 geo-sequestration in brine aquifers is necessary.

While numerical simulations can provide reliable pressure buildup predictions, they require extensive knowledge about the formation, which is not available at the start of the injection process. There have been simple analytical and semi-analytical techniques to support monitoring the pressure buildup, however they are all assuming constant injection rate. Geo-sequestration injection more commonly occurs at a constant wellbore CO2 pressure, with the input rate decreasing as the CO2 front penetrates into the formation. Therefore, a new model predicting pressure build up that result from CO2 geo-sequestration under constant injection pressure is needed.

In this article, a new analytical solution with transient injection rate is derived using the method of matched asymptotic expansions. Also, both Darcyian and non-Darcyian flow have been accounted for within the solution, by using Forchheimer equation. The solution is extended to include both infinite and closed domains.