A Coupled Well-Reservoir Model to Quantify CO2 Release Rates and Temperatures during Well Blowouts in Geologic Carbon Storage

Abstract

Modern wells are designed for safe and efficient transport of fluids. CO₂ injection wells are managed through engineering best practice such that acute releases of fluids are exceedingly rare. However, stakeholders have interest to understand the scale and dynamics of such low probability events to better inform investment and insurance decision making. Here we present a physics-based well-reservoir model to simulate transient acute release of CO₂ from injection wells through an unconfined bore-hole. The developed well model captures supercritical–liquid–gas–solid phase transitions of CO₂ during rapid depressurization. We applied this model to study the CO₂ flow rates and well-head cooling from an onshore injection well in a deep saline aquifer. For a hypothetical well undergoing two-week long release after 1 year of injection at a rate of $0.25$ MT/year, we observed up to $48000$ tons of total CO₂ released. A near-triple-point temperature of −58°C was observed at the wellhead. Our simulations show the CO₂ flow rate to be sensitive to the reservoir permeability. With the developed model as a reference, we investigate various simplifications to speed up computations. The heat transfer between the well-bore and surrounding rocks is shown to have insignificant impact on the flow rate over two weeks, and is therefore be neglected in the simplified model. We use simulations to demonstrate the validity of a quasi-steady flow assumption inside the well. The proposed simplifications are shown to significantly speed up computations of acute CO₂ release.