Analysis of Development Methods for Gravel Envelope Wells - 16
3.7 Conclusions
The preceding analysis and computations permit some conclusions to
be drawn regarding the efficacy of the five well development techniques. These are:
- 1. Unless filter pack material is carefully chosen to provide some, but
not excessive, loss through the well screen, high velocity jetting, even when
considered under the most favorable assumptions, is unlikely to provide effective
well development. Without some loss of particles to allow jet-induced motion of
the pack material, the rate of velocity decay of the jet within the filter pack is
extremely rapid. However, jetting can be an effective development technique
provided motion of the filter pack is induced.
- 2. Line swabbing provides relatively high tangential velocities at the
interface between the filter pack and the formation. At any given location the
velocities occur briefly during passage of the swab. Radial production flows out
of the formation, in addition to tangential scouring velocities, are developed.
The magnitude of the production flow is inversely proportional to the depth of
screen below the swab. For these reasons many passes of the swab are likely to be
necessary to develop the well.
- 3. Rocker beam swabbing effectiveness is limited by the head available to
produce flow through the filter pack. This may be compensated for by the pulsating
flow induced. The rocking mode, combined with slow hauling, is an effective method
provided that sufficient power is available to encourage transport through the
filter pack.
- 4. Single swab development with injection pumping below the swab produces
significant tangential velocities at the filter pack/ formation interface. Since
the entire well is under pressure which creates recharge flows, makeup water is
required. Hauling and dropping the drill pipe induces high tangential velocities
in the filter pack. It is not obvious ho this flow will be divided between
recharging the formation and flushing the filter pack.
- 5. Operation of double swab injection development depends markedly on
whether a bypass conduit is available to permit return flow from below the swabs.
Without this bypass the operation is virtually identical to a single swab, and flow
losses to recharge may be significant from pressurization of the lower well section.
With flow bypass the following comments are made:
- Efficiency is high since, depending on well depth, a reasonable fraction of
energy expended is within the filter pack.
- Tangential velocities within the filter pack can be controlled easily by
adjusting pumping rates.
- Leakage past swab clearances can be offset by increased pumping rates to
maintain the same flow through the filter pack.
• Abramowitz, M. and Stegun, I.A. Handbook of Mathematical Functions.
Dover Publications, New York, 1965.
• Bear, J. Hydraulics of Groundwater. McGraw-Hill, New York, 1979.
• Carslaw, H.S. and Jeager, J.C. Conduction of Heat in Solids. Oxford, London,
1959.
• Zdener, F.F. and Allred, R.E. "Correct methods are essential in well development."
The Johnson Driller's Journal, January-February, 1979.
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