Samenvatting

Increasing oil and energy demand asks for higher efficiency when it comes to oil recovery. To increase
oil recovery efficiency, pore-scale mechanisms during waterflooding, a common recovery method, have to
be better understood. This provides knowledge on the dynamic process during imbibition, which is currently
lacking.
To gain insight on these pore-scale mechanisms, experiments were conducted to capture pore-scale events
during dynamic imbibition. The experimental setup consists of a transparent glass micromodel, a high speed
camera, and a transmission microscope. A high speed camera is used because it allows better mapping of the
dynamic process than conventional cameras. Imbibition is carried out with water as wetting phase and air as
non-wetting phase. The micromodel represents a porous rock and contains interconnected pores-bodies with a
diameter of 60μm. The pore-necks are 13μm wide and 20μm long. The depth of the model is
10μm. The model’s wetting state is water-wet.
The main point of the investigation is the dependency of interfacial dynamics on bulk flowrate. Flowrates
of 1nl/min up to 320µl/min were tested, corresponds to capillary numbers of 9,19∙10-10 to 2,94∙10-4.
Average front displacement is in range of 0,5m/day to 18km/day. Tests on front velocities in the order of 0,6m/day are field relevant, higher front velocities are only investigated for understanding of interfacial dynamics. Interfacial velocities were determined by measuring displacement of the three phase (air, water, and glass) contact point in the captured video images.
Immiscible displacement in porous media is characterized by capillary number and mobility ratio. Capillary number
stands for the competition between viscous and capillary forces. Viscous forces are induced by injection of fluid,
and capillary forces by the capillary effect. As long as interfacial velocity increases with injection flowrate,
viscous forces dominate displacement. As capillary forces dominate displacement, interfacial dynamics are
independent of injection.
No dependency of interracial velocity on the bulk flowrate was observed for flowrates in range of 1nl/min
to 10µl/min, indicating that the system is capillary dominated. For flowrates corresponding to front velocities
of 5,8 and 18km/day an increase in injection resulted in a higher interfacial velocity, indicating that viscous
forces start to play a role in the displacement. This conclusion is supported by the event flowrate, the rate at
which an interface displaces air. Again no dependency is found on injection flowrate. When the ratio of event
flowrate to injection flowrate is examined, it is found that viscous forces start to play role in displacement
as injection exceeds 10µl/min. This conclusion is supported by visual observation of the displacement front
To investigate influence of wettability on interfacial velocity, dynamic imbibition experiments were carried
out on an intermediate wet micromodel with a contact angle of (90 ± 4)° at an injection flowrate of 100nl/min.
Measurements indicate that a larger contact angle, compared to water-wet case, leads to lower interfacial velocity. An explanation is found by considering capillary pressure, which goes to 0 as the contact angle approaches 90°. With decreasing capillary pressure, displacement will be less capillary dominated and more viscous dominated.