Numerical modeling of real-time gas influx migration in vertical wellbores during drilling operation

In this work, a mathematical one-dimensional two-phase model (liquid + gas) has been developed to simulate the dynamic flow system in the event of a gas kick during vertical drilling. The flow system is a drift-flux model where the fluid properties are represented by averaged mixture properties rather than by two independent formulations. With this model, different flow scenarios and influx fluid propagation are investigated in vertical wells. The numerical solution is based on finite volume staggered discretization solved implicitly by a first-order upwind scheme. A sensitivity analysis of the influx model parameters, namely, the gas slip velocity, was performed and its impact on the bottom hole pressure and kick propagation is demonstrated. This model is further extended to predict the kick velocity and pressure in the annulus at the bit based on surface flow measurements in real-time drilling. This paper details on the model development of transient two-phase flow along with validation with experimental results. It is foUnd from the study that the developed light-weight simulation model could be employed in real-time drilling to model influx events, and the drift -flux simulation approach is comparable with the experimental and analytical results. © 2019 by Begell House, Inc.