The Prévost group develops simulation tools that capture the effects of coupling between fluid flow, thermal, and geomechanical effects. Since the inception of CMI, the group’s Dynaflow model has been adapted to simulate aquifer geochemistry and multiphase flow as well as to predict physical stresses induced by CO2 injection. The model has recently been extended with new features, making it capable of simulating the flow and heat transfer for fluids with changing number of phases. The current implementation can simulate leaks of CO2 -brine mixture which can form one, two or three fluid phases.
Modeling the flow of boiling CO2-brine mixtures
Previous CMI research and particularly results of the Prévost group revealed possible risks of CO2 leakage from long-term storage in deep aquifers. At the depth of an aquifer, the temperature and pressure are high, so that CO2 is in a supercritical state and forms two almost immiscible phases with brine. However, if a leak causes upward migration of CO2 and brine to shallow depths, where the temperature and pressure are lower, CO2 becomes subcritical and starts boiling, forming an additional gas phase. Appearance of this third phase may change the characteristics of the flow dramatically.
The researchers have enhanced Dynaflow with a thermodynamic module based on an equation of state that is capable of predicting the number of phases and their composition based on temperature or energy of an element for every time step of the finite element simulation of the fluid flow. Modeling the flow with changing numbers of phases also required a new numerical procedure for solving the energy transport equation.
Basic test cases showed that, where the temperature substantially drops, there is the possibility of formation of a wide (about 100 meters) region of coexistence of three phases. Current and future work is focused on testing of the implemented algorithms for more complicated conditions representing realistic CO2 injection sites.