Summary
An experimental investigation on polymer-based drilling foams was carried
out. Rheology tests were performed with foams that have different
concentrations of hydroxylethylcellulose (HEC) and 1% commercial surfactant.
Experiments were conducted in a large-scale flow loop that permits foam flow
through 2-, 3-, and 4-in. pipe sections, and a 6×3.5-in. annular section.
During the experiments, frictional pressure losses across the pipe and annular
sections were measured for different gas/liquid flow rates, polymer
concentrations (0, 0.25, and 0.5%), and foam qualities (70, 80, and 90%).
Significant rheological variations were observed between aqueous foams
containing no polymers and polymer-thickened foams.
Experimental data show three distinct flow curves for the 2-, 3-, and 4-in.
pipe sections, which indicates the presence of wall slip. The
Oldroyd-Jastrzebski approach was used to calculate the wall slip velocity and
determine the true shear rate. It has been found that wall slip decreases as
the foam quality or polymer concentration increases. Two foam hydraulic models,
which use slip-corrected and slip-uncorrected rheological parameters, have been
proposed. These models are applicable for predicting pressure loss in pipes and
annuli. Model predictions for the annular test section are compared with the
measured data. A satisfactory agreement between the model predictions and
measured data is obtained. This paper will help to better design foam drilling
and cleanup operations.
Introduction
The use of drilling foams is increasing because foams exhibit properties
that are desirable in many drilling operations. In practice, aqueous and
polymer-based foams have been used with commercial success. However,
drilling-foam rheology and hydraulics are still not sufficiently understood to
minimize the risk and costs associated with foam drilling. It is generally
accepted that the addition of polymers to the liquid phase affects the
viscosity and stability of foams. However, the degree to which the bulk
properties of drilling foams are enhanced by polymers has not been well
understood and is difficult to predict. For safe and economical foam drilling,
accurate knowledge of bottomhole pressure is essential. However, foam rheology
and pressure drop predictions are not accurate enough to provide adequate
hydraulic design information such as equivalent circulation density. This
problem is more pronounced when polymers are added, because the apparent foam
viscosity of polymer-thickened foams can be significantly higher than aqueous
foams. It becomes apparent that there is a need for polymer foam rheological
characterization in order to improve the knowledge of foam rheology and
hydraulics.
Foam rheological characterization was carried out using large-scale,
single-pass pipe viscometers (composed of 2-, 3-, and 4-in. pipe sections).
Foam qualities were varied from 70 to 90%. Test pressure and temperature were
100 psig and 80°F.
Two foam hydraulic models were considered, assuming both no-slip condition
at the wall and slip condition at the wall. The first model assumes no-slip
boundary conditions in both pipes and annulus. By assuming no slip condition at
the wall, slip-uncorrected foam rheological parameters were obtained from the
pipe viscometer measurements. It has been found that if we plot friction
factors vs. Reynolds numbers for all test data, regardless of pipe diameters,
foam qualities, and flow rates, a single curve is obtained. This curve is
similar to that obtained for incompressible fluid flow. Pressure drop in the
annulus is calculated with the proposed model, and satisfactory predictions are
obtained. The second model is based on the assumption that there is wall slip
in both pipes and annulus. Rheological parameters and wall-slip coefficient
corrections were first obtained using Oldroyd-Jastrzebski approach. The annular
pressure losses are predicted based on slip-corrected rheological parameters
and wall-slip coefficient correlations.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
14 February 2005
- Meeting paper published:
17 April 2005
- Revised manuscript received:
26 September 2006
- Manuscript approved:
9 October 2006
- Version of record:
20 March 2007
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