S. Narayan et Mb. Dusseault, Subsurface-to-surface resistivity method for monitoring fluid progression in improved oil recovery projects, IN SITU, 23(1), 1999, pp. 75-106
Improved oil recovery (IOR) methods involve enhanced progression of fluids
through an oil reservoir because of changes in petrophysical properties (re
lative permeabilities, wettability, saturations) or applied boundary condit
ions (pressure, temperature). Remote monitoring of IOR processes is primari
ly based on an ability to map the changes in reservoir physical properties
(electrical, acoustic, gravimetric...) that may occur during recovery. The
time period of IOR processes is of the order of months to years. A repeated
geophysical survey using a method sensitive to the appropriate physical pr
operty changes can, in principle, be used to map the fluid front or the ext
ent of the swept zone that arises as the result of the IOR process. Methods
based on changes in strata resistivity comprise one family of geophysical
approaches that may be used to monitor progression of IOR processes.
Electrical resistivity measurements are, in principle, sensitive to IOR-ind
uced fluctuations in reservoir conductivity. Seismic, deformation, or gravi
ty methods alone cannot be used to detect these fluctuations if they arise
largely through pore-fluid ionic concentration changes. Electrical resistiv
ity methods for reservoir description and monitoring thus appear particular
ly promising in such cases.
We present herein several two-dimensional (2-D) numerical model studies add
ressing the application of the subsurface-to-surface resistivity method for
monitoring IOR processes involving hot-water and steam injection. The theo
retical basis for this method and concept of sensitivity has been derived f
rom previous work(1). Based on generic reservoir model studies for hot-wate
r and steam injection, we believe that the feasibility for the application
of resistivity methods to monitoring of IOR processes is clearly demonstrat
ed.