Cyclic time-dependent reactive flow displacements in porous media

• This is the first study to analyze time-dependent velocity (t-d-v) reactive flows in porous media.
• T-d-v can destabilize flows that are stable under constant velocity and lead to more chemical production.
• Effects of the t-d-v depend on the viscosity distribution of the chemicals.
• The characteristics of the t-d-v can be used to control the flow and the rate of chemical production.
• Differences between t-d-v and constant velocity flows are discussed and explained.

Reactive miscible flow displacements in homogeneous porous media with time-dependent injection velocities are analyzed. The displacements consist of periodic cycles that involve alternating stages of injection and extraction. Nonlinear simulations are used and the dynamics of the flows are characterized qualitatively as well as quantitatively in terms of the amount of generated chemical product. The simulations revealed that, when compared with constant velocity flows with the same overall amount of injected fluid, time dependent displacements show drastically different flow structures and chemical productivity. These differences are strongly dependent on the period of the velocity cycles and the scenario of whether the displacement is initiated through an injection or an extraction process. In particular, for non-monotonic viscosity profiles, displacements with larger period result in stronger chemical production while the effects of the velocity scenarios depend on the nature of the instability at the initial front. Moreover, for monotonically decreasing viscosity profiles known to be stable under constant injection velocity, only displacements starting with extraction can trigger instabilities and increase the amount of chemical product. Finally for monotonically increasing viscosity profiles, displacements that start with injection tend to generate more chemical product than the constant velocity flow and its counterpart starting with an extraction instead.