Drill bit pressure drop during foam drilling operations

Foam is one of the most frequently used drilling fluids for underbalanced drilling operations. This paper introduces a more accurate model than the existing models for estimating the pressure drop of foam flowing through the drill bit. The major difference between the proposed and existing models is that the proposed model includes the effect of foam expansion and velocity change as a function of pressure. It has been observed that pressure drop increases significantly as the upstream pressure and foam average velocity increases. For the same flow conditions, pressure drop decreases as the foam quality increases, and as the upstream pressure increases, pressure drop also increases. These events cannot be detected by existing models. In some cases, the pressure drop at the bit can be 10 times greater than the pressure drop predicted by existing models.