This paper provides a detailed description of conditions in the
hydraulically damaged fracture environment after closure and how to integrate
them into a reservoir-simulation model.
A special model-initialization algorithm was developed and realized in a
support tool to make possible the computing of a post-fracture performance in
tight gas formations by a reservoir simulator. The input represents the
treatment schedule of the fracturing process and some results produced by
commercial fracturing packages or geophysical measurements.
To represent the fracture geometry and properties, the information about the
distribution of the proppant concentration in the fracture as well as the
fracture-width variation is translated into the permeabilities and porosities
of the fracture gridblocks. To determine the fracturing-fluid saturation in the
invaded zone, a new approach was derived to imitate the fracture propagation at
a fracturing period under consideration of the leakoff processes. The
penetration of the fracturing fluid into the matrix was modeled by the
Buckley-Leverett equations for two-phase nonmiscible displacement, with
boundary conditions provided by a classical leakoff theory.
The approach is illustrated with a simulation model prepared for the
analysis of the cleanup process in a damaged fractured well within a
Rotliegende tight gas formation in north Germany.
The fluid that leaked off into the tight gas formation during the fracturing
treatment may significantly suppress gas production because of the two-phase
flow effects and the capillary end effect between the reservoir and fracture
(Holditch 1979). Therefore, for more plausible evaluation of hydraulic fracture
stimulation, an accurate representation of the flow in the immediate fracture
environment becomes a necessity. In terms of numerical simulation of
post-fracture well performance, the problem can be addressed by (1) an adequate
representation of the fracture in a reservoir simulator and (2) a reasonably
accurate picture of the initial fluid distribution around the fracture.
© 2006. Society of Petroleum Engineers
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- Original manuscript received:
8 November 2003
- Revised manuscript received:
1 July 2005
- Manuscript approved:
9 July 2005
- Version of record:
20 May 2006