Modeling and simulation of under-balanced drilling operation using two-fluid model of two-phase flow

Modeling and simulation of gas-liquid two-phase flow in under-balanced drilling (UBD) operation is very important in order to accurately predict the bottom-hole pressure (BHP) and other parameters of two-phase flow. In this paper one-dimensional form of steady-state two-fluid model in the Eulerian frame of reference is used to simulate the two-phase flow in the UBD operation. Simulation is performed to calculate the parameters such as pressure, volume fraction and velocities of two phases at different flow regimes, namely bubbly, slug and churn turbulent flow. The governing equations along with appropriate constitutive relations form a system of coupled ordinary differential equations (ODEs) which are solved using the well-known iterative Newton method. The effect of gas and liquid injection flow rates and also the choke pressure on the wellbore pressures, particularly on the BHP are investigated numerically. In order to validate the results of the current two-fluid model, they are compared with the actual field data and also with the results of the WELLFLO software using different mechanistic models. The comparisons show that the two-fluid model can accurately predict the BHP and other two-phase flow parameters.