Real-time estimation of reservoir influx rate and pore pressure using a simplified transient two-phase flow model

• A simplified two-phase model for real-time well control applications is presented.
• The two-phase model is validated on experimental data, showing very good agreement.
• A novel method to estimate influx rate and pore pressure during a gas kick is presented.
• The method uses the simplified two-phase model and a Recursive Least Squares algorithm.
• The method is successfully tested on a well control scenario from a commercial simulator.

The ability to perform accurate pore pressure and reservoir inflow estimation during a kick incident is necessary, particularly when drilling in formations with narrow pressure margins. Currently available techniques for pore pressure estimation and reservoir characterization either rely on empirical correlations requiring access to well logging data and other petrophysical information, or require downhole pressure sensing and advanced flow metering capabilities. This paper introduces a model-based estimation technique which uses surface measurements commonly available in a Managed Pressure Drilling (MPD) system, coupled with a simplified transient two-phase model. This model is capable of representing essential dynamics during a gas kick with reduced computational overhead, but without sacrificing significant modeling accuracy. First, the model is validated in a gas kick scenario against experimental data, showing good agreement between key measured parameters and the model predictions, and thereby justifying the model applicability to field operations. Next, data generated from a commercial simulator test case is used to evaluate the proposed estimation methodology. The estimated pore pressure and reservoir productivity are close to their respective values from the commercial simulator, and the flow out rate and surface back-pressure predicted by the simplified two-phase model yield very good match against the simulator results.