Miscible Cyclic Time-Dependent Displacements in Porous Media
Creators: name: Yuan, Qingwang
Publisher: name: Graduate Studies
Year: 2014
Subjects: subject: Engineering--Chemical
subject: Engineering--Mining
subject: Engineering--Petroleum
subject: Miscible Displacements
subject: Cyclic Time-Dependent
subject: Porous Media
subject: Viscous Fingering
subject: Oil Recovery
subject: Inertial Effects

description: Miscible displacements in porous media are widely encountered in many industrial applications like enhanced oil recovery processes as well as environmental issues. When a low-viscosity fluid is used to displace a high-viscosity one, hydrodynamic instabilities, commonly referred to as viscous fingering, are often observed. This fingering phenomenon usually results in a displacement efficiency lower than that based on theoretical expectations. Therefore, the study and understanding on the fingering instability mechanisms are of significant relevance to industrial applications. This dissertation investigates the flow dynamics and instabilities of reactive and non-reactive miscible displacements in homogenous porous media with time-dependent injection velocities. Miscible displacements where inertial effects can be safely neglected and those where inertia is non-negligible are also considered. The non-reactive miscible displacements consisting of periodic cycles that involve alternating stages of constant injection and production or of injection and soaking are first examined without considering inertial effects. Both linear stability analysis (LSA) and nonlinear simulations are conducted. Results of LSA revealed that the growth rate of concentration disturbances follows the overall trends of the velocity but with noticeable differences. Nonlinear simulations revealed that the flow dynamics can be drastically changed from those of the constant injection velocity and the changes depend on the period of the cycles, the amplitude of the velocity and on whether the displacement is initiated through an injection or a soaking stage. The second part of the thesis is devoted to the effects of inertia on the viscous fingering for constant injection velocity. A modified Darcy's equation is used to include inertial corrections to the classic Darcy's law. LSA based on the quasi-steady-state-approximation (QSSA) showed that the inertial forces tend to stabilize the displacements at the initial time. Initial value calculations allowed to extend the analysis to longer times. In the third part, cyclic time-dependent displacements when inertial effects are non-negligible are investigated numerically. It is found that the effects of velocity models, cycle period, and amplitude greatly depend on whether inertia is considered or not. Furthermore, regardless of inertial influences, the cyclic extraction-injection (E/I) process is always less unstable than constant injection and its injection-extraction (I/E) counterpart. The period and amplitude have a monotonic attenuating effect on the instabilities for E/I process. However, for its I/E counterpart, their effects are strongly affected by inertia and have non-monotonic influences. A period-stabilizing range is found, in which the displacements of the cyclic time-dependent injection velocities are less unstable than those of the constant injection. Moreover, it was found that the velocity amplitude can attenuate or enhance the instabilities depending on whether the period is within a period-stabilizing or period-destabilizing range. Furthermore, the inertial influences are also found to greatly reduce the instabilities compared to non-inertial cases. Finally, the reactive displacements for time-dependent velocities without considering the inertial effects were examined. This reactive process is based on a generic bimolecular chemical reaction (BCR), A+B-&gt;C. Compared with constant velocity flows with the same overall amount of injected fluid, time-dependent displacements showed drastically different flow structures and chemical productivity. These differences are strongly affected by the period of the velocity cycles, the velocity scenarios, and the initial viscosity profiles.