Simulation Study Comparing Offshore Versus Onshore CO2 Well Blowouts

Abstract

We have simulated onshore and offshore blowouts of an idealized CO2 injection well using T2Well, a state-of-the-art coupled well-reservoir simulator. The purpose of the study is to understand dynamic multi-phase non-isothermal flow phenomena in CO2 wells to inform risk assessment studies for offshore geologic carbon sequestration sites. The scenario we chose consists of a vertical well of 3050 m length completed in a mature geologic carbon sequestration reservoir filled with CO2 connected to a horizontal surface pipe. At time zero, we assume the surface pipe was breached producing a 2-inch diameter hole. In the onshore scenario, the pipe blowout causes CO2 to enter the ambient air at 0.101325 MPa and 22.78 °C, whereas in the offshore scenario the blowout is into the water column at a depth of 50 m where pressure and temperature are 0.598 MPa and 22.78 °C, respectively. The simulations show that the overall CO2 leakage rates are very similar for the onshore and offshore scenarios, with subtle differences in flow rates of various phases likely arising from differences in pressure at the leakage point. Overall, the main differences between onshore and offshore CO2 blowouts are expected to arise mostly after discharge due to differences between how CO2 disperses in ambient air versus in the water column.