Development and Application of a Fully Implicitly Coupled Wellbore/Reservoir Simulator To Characterize the Transient Liquid Loading in Horizontal Gas Wells

Abstract

Summary Liquid loading is a challenging issue in most mature gas fields. The dynamic interaction between wellbore and reservoir when liquid loading happens cannot be comprehensively simulated by a single wellbore simulator or a single reservoir simulator. In this paper, we develop a fully implicitly coupled wellbore/reservoir model to characterize the flow transients in liquid-loaded horizontal gas wells. We fully couple a wellbore model with an in-house reservoir simulator based on the control-volume finite-difference method. Wellbore transient material-balance equations and mixture momentum-balance equations are solved simultaneously with the reservoir equations to obtain pressure, mixture velocity, and phase holdup in each wellbore segment. Also, we propose a modified drift-flux model that is capable of predicting the flow-regime transition for different pipe inclinations from vertical to horizontal. The modified drift-flux model is integrated in the coupled wellbore/reservoir simulator to characterize the two-phase flow in horizontal wellbores. We validate the coupled wellbore/reservoir model with a commercial multisegment wellbore (MSW)/reservoir simulator. The revised drift-flux formulation not only matches a commercial simulator in production forecast and wellbore pressure, but also predicts the subsequent unstable liquid production caused by flow-regime transitions. For a synthetic field-scale case, the new model predicts gas production that lasts 23 days longer than the prediction of a commercial simulator. This paper extends the capability of a fully implicitly coupled wellbore/reservoir simulator to simulate the transient liquid-loading phenomenon. The model can serve as a promising tool for gasfield development.