Proceedings of the
Second International Energy 2030 Conference,
November 4-5, 2008, Abu Dhabi, U.A.E.
Hydrodynamic Transition Zone at OWC in Non-Darcy Flow
Louisiana State University, USA
Andrew K. Wojtanowicz
Louisiana State University, UAE
Worldwide, there are great numbers of oil reservoirs with un-recovered oil and thousands of marginal
wells that are idling, not because the resources have been depleted, but because they have become
unprofitable due to excessive water production. For most operators, produced water is a single most
important factor controlling economics of their business. Excessive water production makes the whole
economics of reservoir/well management vulnerable to ever-fluctuating crude oil prices.
There are many ways water finds its way to wells – due to wells’ integrity failure, or heterogeneity of
the oil bearing formation (natural fractures, high permeability channels, etc.). However, even in relatively
homogenous strata, after the water breaks through the oil into a well, it progressively dominates the inflow
thus leaving the oil behind (by-passed). This process is known as a progressive transition zone above the
oil water contact (OWC) and applies to well-reservoir systems with water coning, water cresting and water
channeling with crossflow. We postulate that one of the mechanisms contributing to transition zone
expansion is a transfer of water into the oil across moving OWC– transverse dispersion.
Transverse dispersion is a hydrodynamic mixing process caused by a concurrent segregated two-phase
flow [1=Ewing, 2000]. One reason for the mixing is loss of stability at the flowing fluids interface. In the
Hele-Shaw cell flow experiments, where the flow is constricted by solid surface, Gondret  showed that
the interface would be more stable for smaller gap of the cell plates. Later, Duan and Wojtanowicz 
used a Hele-Shaw cell to study the effect of shear stress on the interface stability. Their experiments
revealed cyclic perturbation of the interface in segregated flow. The size of the perturbation zone would
increase at higher shearing rate gradient resulting from the velocity difference of oil and water.
Using granular-packed cell experiments, Blackwell , Bijeljic and Blunt , and Jha et al. 
demonstrated the mechanisms and effect of factors controlling two dimensional transition zone in miscible
flow. Transverse dispersion was quite small comparing to the longitudinal diffusion or dispersion, which
would explain why transverse dispersion in miscible flow doesn’t attract enough attention. In immiscible
flow, on the other hand, Perkins  flow experiments with a sand packed model showed progressive
symmetric transition zone perpendicular to the direction of flow for two fluids having similar mobilities.
The objective of this study was to demonstrate the effects of fluid viscosities’ contrast and granular size
of the porous medium on the size and shape of the transition zone in linear segregated flow of oil and
water, at flow velocities beyond the validity of Darcy’s Law. It was also important to understand the
physical mechanisms contributing to the dispersion, develop mathematical models and formulate criteria
for the process, as well as relate the transverse dispersion process to the actual oil well inflow conditions.