Summary
A comprehensive semianalytical model has been built to investigate the
effects of drilling and perforating damage and high-velocity flow on the
performance of perforated horizontal wells. The model incorporates the
additional pressure drop caused by formation damage and high-velocity flow into
a semianalytical coupled wellbore/reservoir model. The reservoir model
considers the details of flow in the vicinity of the wellbore, including 3D
convergent flow into individual perforations, flow through the damaged zone
around the wellbore and the crushed zone around the perforation tunnels, and
non-Darcy flow in the near-wellbore region. The wellbore flow model includes
the effect of frictional pressure drop. Both oil and gas wells are
considered.
The expressions provided in this paper for additional pressure losses caused
by perforating damage, drilling damage, and high-velocity flow can be used to
optimize perforating parameters and decompose the total skin into its
components (perforation pseudoskin, damage skin, and non-Darcy skin).
Introduction
The performance of oil and gas wells may be influenced by the simultaneous
effect of mechanical skin, high-velocity (non-Darcy) skin, and completion
pseudoskin factors. The skin factors caused by formation damage and perforating
damage constitute the mechanical-skin factor. The extra pressure drop caused by
high-velocity flow is known as the rate-dependent or non-Darcy flow factor.
Compared to an ideal open hole, the wells with completions and other geometries
such as perforations, slotted liner, or partial penetration may experience
additional pressure loss or gain. The additional pressure change caused by well
completion and geometry is quantified in terms of pseudoskin factor. The
combined effects of all the skin factors lead to a total skin factor that may
be estimated from pressure-transient data. The total skin factor, however, is
not simply the sum of the individual skin components, and the computation of
the individual skin components is not straightforward (the interaction between
the individual components of total skin is nonlinear).
Many studies have concentrated on the effects of formation damage and
high-velocity (non-Darcy) flow on well performance. For perforated vertical
wells, McLeod’s analytical model has been a widely accepted approximation to
account for the additional pressure drop caused by formation damage and
high-velocity flow. Karakas and Tariq presented a semianalytical model to
predict the pseudoskin and productivity of perforated vertical wells with
formation damage. The models suggested by McLeod and Tariq, however, may not
work for selectively completed wells in which the flux distribution may be
nonuniform. An example of this case is selectively perforated horizontal
wells.
Tang et al. presented models for horizontal wells completed with slotted
liners or perforations. The additional pressure drop in the vicinity of the
wellbore because of formation damage, perforating, flow convergence, and
high-velocity flow was included in their models in the form of a total-skin
term. The existing horizontal-well models are not capable of explicitly
relating the skin factor to the physical parameters controlling the additional
pressure drop around the wellbore. In addition, the interplay between the skin
and flux distribution and its impact on the productivity of perforated
horizontal wells have not been discussed, especially for selectively perforated
horizontal wells. Non-Darcy flow effect in perforated horizontal wells is
another topic that has not been addressed adequately in the literature.
In this study, we present a semianalytical model to predict the productivity
of perforated horizontal wells under the influence of formation damage,
perforating damage, and high-velocity flow. The nonlinear interaction between
the individual skin components is accurately represented in the model. The
model is applicable to both single-phase oil and gas wells (the pseudopressure
concept is used to extend the oil-flow model to the gas wells). Using the
model, the combined effects of formation damage, the crushed zone around the
perforation tunnels, and the high-velocity flow on the horizontal-well
performance have been investigated in detail. The completion and damage
parameters controlling the well productivity were identified through
sensitivity studies.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
14 December 2002
- Revised manuscript received:
21 April 2005
- Manuscript approved:
24 May 2005
- Version of record:
15 August 2005
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