Summary
Unconventional fracturing techniques, such as high-rate waterfracs,
waterflooding, or steam stimulation, produced water and cuttings reinjection,
CO2 sequestration, and coalbed methane stimulation, are difficult to
model because of strong interactions among the fracturing process,
geomechanical changes in the porous media, and reservoir fluid flow. The
resulting strong poroelastic/thermoelastic effects, permeability and porosity
changes, and possible rock failure make current conventional fracturing models
inadequate in such circumstances. Therefore, it is necessary to develop new
models that include all of these mechanisms and that are capable of conducting
integrated data analysis.
This paper presents a new fracturing model with all of these mechanisms
included. The model fully couples fracture mechanics with reservoir and
geomechanics simulation. This methodology allows us to model fracture
initiation and propagation, post-frac multiphase cleanup in the reservoir and
fracture and pre-frac and post-frac well performance in a changing stress and
pressure environment, all within the same system.
The model couples a 3D finite element geomechanics model with a conventional
3D finite difference reservoir flow simulator. The geomechanics module
implicitly models fracture propagation via displacements on the fracture face.
The flow and geomechanics/fracturing are coupled in an iterative manner that is
equivalent to full coupling of geomechanical and reservoir flow modeling. The
3D (planar) fracture geometry and the pressures in it are the common dynamic
boundary conditions for the flow and stress modules. The new iterative process
yields smooth fracture propagation, and the model has been tested on classical
fracturing problems.
A field example demonstrates the validity and advantages of the approach. To
illustrate the model capabilities, we model a waterfrac stimulation performed
in Bossier tight-gas sands. The model results show that the model is capable of
matching complex injection history and calibrating the stress-dependency of
formation permeability.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
1 August 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
1 July 2008
- Manuscript approved:
26 July 2008
- Published online:
16 July 2009
- Version of record:
28 September 2009
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