Summary
A transient-mechanistic model of cuttings transport with foam has been
recently developed and solved numerically. In this study, the new model has
been used to revisit the classical theory of hydraulic optimization (i.e.,
maximum bit-hydraulic-horsepower/jet-impact-force criteria).
A new methodology has been suggested to determine the optimum
gas-/liquid-injection rates for maximizing drilling rates when drilling with
foam in vertical wells while keeping the bottomhole pressure at minimum.
The new method can be easily used in the field to determine the best
combination of gas-/liquid-injection rates and total-bit flow area (i.e.,
jet-nozzle sizes), such that the maximum drilling rate is
achieved.
Introduction
Foam is often used as a circulating fluid in underbalanced drilling
operations because of its high viscosity and variable density. Applications of
foam as a drilling fluid in many drilling operations, and the results from
various field cases, are well documented.1–6
Drilling hydraulics has long been recognized as one of the most important
considerations for maximizing drilling efficiency and minimizing drilling
cost.7–10 The concept of hydraulics optimization for
drilling with incompressible fluids has been well investigated.11–17
Optimization of drilling hydraulics requires calculation of frictional
pressure losses in the system and the minimum fluid velocity to carry the
cuttings in the annulus. Finding satisfactory answers for both of these
problems has been a challenge for engineers, even for incompressible drilling
fluids.
The hydraulic-optimization problem becomes more complicated when drilling
with foam because of the compressible nature of the foam. Determining the
optimum backpressure and
gas-/liquid-injection rates for effective cuttings transport, while
achieving the maximum drilling rate, are some of the major questions needing to
be answered.
In this paper, a new methodology is presented for determining the optimum
combination of backpressure, gas/liquid ratio, and total flow area to maximize
the drilling rate when drilling with foam.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
7 March 2005
- Revised manuscript received:
1 September 2005
- Manuscript approved:
4 September 2005
- Version of record:
15 December 2005
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