Summary
Multiphase flow and transport phenomena within fractures are important
because fractures often represent primary flow conduits in otherwise
low-permeability rock. Flows within the fracture, between the fracture and the
adjacent matrix, and through the pore space within the matrix typically happen
on different length and time scales. Capturing these scales experimentally is
difficult. It is, therefore, useful to have a computational tool that
establishes the exact position and shape of fluid/fluid interfaces in realistic
fracture geometries. The level set method (LSM) is such a tool. Our progressive
quasistatic (PQS) algorithm based on the level set method finds detailed,
pore-level fluid configurations satisfying the Young-Laplace equation at a
series of prescribed capillary pressures. The fluid volumes, contact areas, and
interface curvatures are readily extracted from the configurations. The method
automatically handles topological changes of the fluid volumes as capillary
pressure varies. It also accommodates arbitrarily complicated shapes of
confining solid surfaces.
Here, we apply the PQS method to analytically defined fracture faces and
aperture distributions, to geometries of fractures obtained from
high-resolution images of real rocks, and to idealized fractures connected to a
porous matrix. We also explicitly model a fracture filled with proppant, using
a cooperative rearrangement algorithm to construct the proppant bed and the
surrounding matrix. We focus on interface movement between matrix and fracture,
and snap-off of nonwetting phase into the fracture during imbibition in
particular. The extent to which nonwetting phase is trapped in
fracture/enclosed gaps is very sensitive to the direction of the displacement.
Simulated drainage curves in matrix differ systematically from drainage curves
in fracture and matrix with transfer between them. In a reservoir simulation,
the latter might serve as an upscaled drainage curve input for a fractured
medium.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
7 July 2008
- Meeting paper published:
21 September 2008
- Revised manuscript received:
5 January 2009
- Manuscript approved:
29 April 2009
- Published online:
12 November 2009
- Version of record:
12 March 2010
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