Summary
Horizontal wells with multiple fractures are now commonly used in
unconventional (low-permeability) gas reservoirs. The spacing between
perforations and the number and orientation of transverse fractures all have a
major impact on well production.
The opening of propped fractures results in the redistribution of local
Earth stresses. In this paper, the extent of stress reversal and reorientation
has been calculated for fractured horizontal wells using a 3D numerical model
of the stress interference induced by the creation of one or more propped
fractures. The results have been analyzed for their impact on simultaneous and
sequential fracturing of horizontal wells.
Our results demonstrate that a transverse fracture initiated from a
horizontal well may deviate away from the previous fracture. The effect of the
reservoir?s mechanical properties on the spatial extent of stress reorientation
caused by an opened crack has been quantified. The paper takes into account the
presence of layers that bound the pay zone but have mechanical properties
different from those of the pay zone. The fracture vertical growth into the
bounding layers is also examined.
It is shown that stress interference, or reorientation, increases with the
number of fractures created and depends on the sequence of fracturing. Three
fracturing sequences are investigated for a typical field case in the Barnett
shale: (a) consecutive fracturing, (b) alternative fracturing, and (c)
simultaneous fracturing of adjacent wells. The numerical calculation of the
fracture spacing required to avoid fracture deviation during propagation, for
all three fracturing techniques, demonstrates the potential advantages of
alternate fracture sequencing and zipper fracs to improve the performance of
stimulation treatments in horizontal wells.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
22 November 2009
- Meeting paper published:
11 February 2010
- Revised manuscript received:
9 September 2010
- Manuscript approved:
30 November 2010
- Published online:
17 March 2011
- Version of record:
16 May 2011
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