Summary
This paper investigates the effect of selective perforating on
horizontal-well performance. Theoretical investigation is based on a general 3D
analytical model that was published previously. For a given perforation design,
the changes in flow rate, pseudosteady-state productivity, and cumulative
production can be computed using the solution. The investigation shows that the
ratio of total-perforated length to the drilled-well length is the most
dominant parameter controlling the long-term performance of the selectively
perforated horizontal wells. The other important parameters are the degree of
formation and perforating damage.
We additionally examined the effect of the so-called “oriented perforating”
on the horizontal-well performance in isotropic and anisotropic formations. Our
research shows that accurately oriented perforating could significantly improve
the well productivity in anisotropic formations.
Introduction
Selective Perforating. Horizontal wells may be perforated in selected
intervals for several reasons. The most common reasons for selective completion
are reducing the cost, delaying premature water/gas breakthrough, preventing
wellbore collapse in unstable formations, and effectively producing multiple
zones with large productivity contrast.
Selective perforating with blank sections provides flexibility for future
intervention and workover options and for shutting off the sections subject to
excessive water/gas intrusion. On the other hand, selective completion could
hurt the well productivity.
Oriented Perforating. The orientation of perforations is also a
concern in optimizing well productivity. Perforations aligned with minimum
stress direction produce more sand. To reduce the risk of sand production, it
may be better to orient the perforations vertically. Additionally, subsurface
rocks exhibit horizontal permeabilities that are higher than vertical
permeabilities. Therefore, perforation tunnels perpendicular to higher
permeability would possess better flow efficiency.
On the other hand, debris resulting from the perforation process has to be
surged out of the tunnels to improve the productivity of the perforated
completions. It is more difficult to clean the perforations on the low side of
the horizontal wells. Liner and solids debris in the low-side perforation
tunnels may not be removed under the typical underbalance pressures
applied.
Vertically oriented perforation tunnels at the top side of the horizontal
wellbore are preferred for better perforation stability and cleanup efficiency.
However, if the perforations are to be packed, it is difficult to transport the
gravel into vertically oriented tunnels at the top side.
Field observations and sand-production models have shown that the stability
of the perforation cavity may be weakened if all the perforations are oriented
vertically with a phasing angle of zero. Therefore, to minimize the sand
production and to create more stable perforations, it may be better to orient
the perforations ±10 to 20° from the vertical. This type of perforating design
has been referred to as oriented perforating.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
8 June 2004
- Manuscript approved:
28 April 2005
- Version of record:
20 February 2006
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