Pressure Loss at the Bit While Drilling with Foam

Ozbayoglu, E. M.
Foam is one of the most frequently used drilling fluids at underbalanced drilling operations. As foam flows, due to the pressure drop, a volumetric expansion is observed, which causes the foam quality to increase in the same direction with flow. Flow of foams through circular pipes and annular geometries are well studied. Interestingly, although one of the major sources of pressure drop is at the bit, there have been few studies of this subject for foams. Many drilling parameters including hole cleaning capacity, volumetric requirements of liquid and gas phase, and backpressure are out of control if the pressure drop at the bit is not accurately determined, even though pressure drops inside the pipes and wellbore are properly determined. This article introduces a more accurate model for estimating the pressure drop of foam flowing through the bit. The major difference between the proposed and the existing models is that the proposed model includes the effect of foam expansion and velocity change as a function of pressure. Pressure drop has been observed to increase significantly as the upstream pressure and foam average velocity increases when compared with the existing models. For the same flow conditions, pressure drop decreases as the foam quality increases, and as the upstream pressure increases, pressure drop also increases. The existing models cannot detect this event at all. In some cases, the pressure drop at the bit can be 10 times greater than the pressure drop predicted from existing models.


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Underbalanced drilling achieved by gasified fluids is a very commonly used technique in many petroleum-engineering applications. This study estimates the flow patterns and frictional pressure losses of two-phase fluids flowing through horizontal annular geometries using artificial neural networks rather than using conventional mechanistic models. Experimental data is collected from experiments conducted at METU-PETE Flow Loop as well as data from literature in order to train the artificial neural networks. ...
Citation Formats
E. M. Ozbayoglu, “Pressure Loss at the Bit While Drilling with Foam,” PETROLEUM SCIENCE AND TECHNOLOGY, pp. 687–698, 2009, Accessed: 00, 2020. [Online]. Available: