Summary
For multistage hydraulic fracturing of horizontal wells with cased-hole
completion, multiple perforation clusters are used typically to create multiple
fractures in any single stage. How to place these perforation clusters is a
critical issue because the number of perforation clusters to be used and the
space between them significantly impact how effectively the fractures can be
created in the formation. To optimize the spacing of perforation clusters,
stress distributions and fracture mechanics need to be well understood.
In this study, the displacement-discontinuity method is used to construct a
boundary-element model, which is able to analyze the stress distributions
around multiple transverse fractures and the geometries of those fractures.
With the boundary-element model, multiple cases are investigated for a
different number of fractures and fracture spacings. Changes of both minimum
and maximum stresses and shear stress around these fractures are illustrated
first. It is found that for the cases with more than two parallel fractures,
there is a strong stress concentration around the center fractures. The
calculated displacements indicate that the created fractures are no longer
elliptic-like, and the widths of the center fractures are reduced significantly
compared with those of a single fracture. For the case of two parallel
fractures, the stress concentration between two fractures also results in
asymmetrical fracture shape, but the fracture widths are not reduced
significantly.
This study indicates that the number and spacing of the fractures need to be
selected carefully to create effective fractures with appropriate fracture
geometries. The boundary-element model provides a useful tool to relate rock
geomechanic properties to stress distribution and fracture geometries for
multiple fractures in hydraulic fracturing of horizontal wells, which can be
used as a guide to space the perforation clusters.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
2 November 2009
- Meeting paper published:
24 September 2009
- Revised manuscript received:
1 February 2012
- Manuscript approved:
24 April 2012
- Published online:
18 September 2012
- Version of record:
7 December 2012
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