Society of Petroleum Engineers
|Document ID ||149274-MS||DOI
|Content Type||Conference Paper
|Title||Modeling the Effect of Permeability Anisotropy on the Steam-Assisted Gravity Drainage (SAGD) Process
Prince N. Azom and Sanjay Srinivasan, University of Texas at Austin
Canadian Unconventional Resources Conference,
15-17 November 2011,
2011. Society of Petroleum Engineers
|6.8 Fundamental Research in Reservoir Description and Dynamics
6.3.1 Flow in Porous Media
6.4.5 Thermal Methods (e.g.,Steamflood, Cyclic Steam, THAI, Combustion)
The SAGD process utilizes horizontal wells hence permeability anisotropy can
play a very strong role in recovery. In fact, it has been well documented that
poor vertical permeability kills the SAGD process because the steam chamber
will not grow properly. Several authors have attempted to model this phenomenom
by using time-independent averaging (e.g. harmonic, geometric averaging etc.)
methods only to discover the inadequacy of such an approach as several field
implementations reveal a definite time component to this effect. Consequently
most studies on the effect of anisotropy during SAGD have involved only
commercial simulators. However, there exists a need to describe this phenomenon
quantitatively prior to any numerical simulation and delineating conditions
where it can be considered important or not.
Isotropy of permeability can be geometrically represented as a sphere (or
circle in 2D) where the permeability radii are the same in all directions.
Anisotropy can be represented as an ellipsoid (or ellipse in 2D) with varying
permeability radii in different directions and the principal axes representing
principal permeability directions. In this work, we assume that the principal
axes point in the vertical and horizontal directions. We will show that the
SAGD process has a unique geometry that allows a meaningful mapping of the
steam chamber wall to the coordinate frame of such an ellipsoid. We will then
use this transformation to incorporate permeability anisotropy within the
framework of Butler type models. This will be done in dimensionless space and
the results obtained can be used as type curves for correcting any isotropic
SAGD model for anisotropic effects.
Our results show that the effect of anisotropy is time dependent (generally
obeying a sigmoid function) and there exists a given time for a given set of
reservoir and fluid properties, after the effect of anisotropy ceases to exist.
This is remarkable because it suggests a way to improve modeling efficiency for
reservoirs with strong anisotropic permeabilities.
Our results also explain why most other static averaging methods fail. The
analytical expression can be used as a fast SAGD predictive model suitable for
history matching purposes.
The SAGD process involves the injection of steam and production of heavy
oil/bitumen via pairs of horizontal wells that are usually separated 5 – 10 m
apart, with the producer well at the bottom. The basic physics of the SAGD
process is relatively simple and involves the growth of a steam chamber and the
drainage of lower viscosity oil along the chamber wall by gravity.
|File Size ||499 KB
||Number of Pages||12