A computational strategy to evaluate the occurrence and characteristics of gas migration in wellbore cement using the lattice Boltzmann method

This paper presents a numerical approach that employs the multi-component/multi-phase (MCMP) lattice Boltzmann method (LBM) to model gas migration in wellbore cement after it has been placed. In particular, this approach can be used to investigate how the properties of the cement slurry and the conditions within the wellbore impact the potential occurrence and characteristics of gas migration. The MCMP LBM model proposed by Shan & Chen Shan and Chen (1993) was chosen for simulating the fluid-gas interactions during gas migration due to its flexibility in modeling complex multi-component/multi-phase systems and its computational efficiency. The capability of this LBM approach is evaluated by comparing with gas migration test results from a wellbore simulation chamber (WSC) that experimentally simulates gas migration in downhole conditions. The numerical approach is first calibrated by replicating the hydrostatic pressure change throughout the hydration process of a cement slurry estimated with the WSC. The calibrated numerical system is then validated by estimating the vulnerability period of the cement slurry, again compared to the experimental estimate from the WSC. The LBM approach is then used to examine how variations in overburden pressure potentially affect the vulnerability period, and then how the rheological properties of the cement slurry affect the gas migration process. The analyses show that the LBM can replicate the change in hydrostatic pressure transfer during cement slurry hydration, from fluid-like hydrostatic transfer to nearly solid behavior. The LBM can also accurately represent the vulnerability period of wellbore cement slurry consistently with that estimated by the WSC. The overburden pressure is shown to significantly affect the initial time of this vulnerability period, but the end time depends on the mechanical properties of the cement slurry and is relatively unaffected by the overburden pressure independently of those properties. Both yield stress and viscosity of the cement slurry have a significant effect on the form of gas migration during the vulnerability period, altering the rate of migration and the size and continuity of migrating gas channels.