Underbalanced Drilling Dynamics: Two-Phase Flow Modeling and Experiments

Abstract

Summary A dynamic model based on the drift-flux formulation is presented for treating transient phenomena in underbalanced drilling (UBD) operations. A set of mechanistic steady-state procedures for dealing with the definition of flow patterns, pressure drops, gas volumetric fractions, and in-situ velocities completes the model. The iteration between those mechanistic laws and the conservation equations is discussed. The numerical solution uses a composite explicit scheme, which reduces false oscillations and numerical diffusion. In addition, details about the boundary treatment are also presented. Model predictions are validated through comparison to fullscale experimental data in two distinct transient situations: first, a typical liquid unloading, and second, the injection of a high-velocity single pulse and a sequence of two pulses of a gas/liquid mixture. The comparisons address model limitations and improve the understanding of the physics involved.