Lubrication Process at the Wall in Foam Flow-Application to Pressure Drop Estimation While Drilling UBD Wells

摘要

When drilling underbalanced, the pressure of the drilling fluid is maintained at a value below the formation pressure. In order to lower well pressure, specific low density fluids are needed i.e. gas, aerated mud or foam. Foam is particularly beneficial for drilling mainly due to its low density coupled with good carrying capability, but its use remains hazardous due to the incomplete knowledge of its bottom-hole properties and especially of its flowing properties. Pressure drop estimation is crucial for UBD operations, in order to be able to keep in real time the bottom hole pressure in the adequate range. In this study, we analyze the pressure drop variation with the flow rate in a circular pipe for different foam qualities and formulations. Experimental investigations are realized in a pressure and temperature circular conduct flow. We show that lubrication at the wall plays a crucial role. Indeed, the intrinsic viscosity of the foam can be very high leading to the development of a water layer at the wall responsible for the lubrication of the flow. A two-phase description of the system allows the analytical estimation of the pressure drop. The size of the lubricated layer is then deduced and discussion of its range of existence is discussed. Main parameters of its formation are also discussed. We show that this lubrication effect can be significant in pressure drop estimation for Underbalanced operations.