Hydraulic Predictions for Polymer-Thickened Foam Flow in Horizontal and Directional Wells

Abstract

Summary Foam has proved to be effective and economical in underbalanced operations (UBO) and is gaining wider applications in many areas. It provides the desired flexibility in controlling pressure profile and equivalent circulating density (ECD). However, the knowledge of rheology and hydraulics of polymer-thickened foams is still limited. This paper summarizes the significant effects of polymer on foam rheology and presents a hydraulic model that simulates aqueous and polymer-based foam flow in directional and horizontal wellbores. Experimental studies on the rheology of polymer-enhanced foam were conducted using a specially designed flow-through rotational viscometer and pipe viscometers with different concentrations of hydroxyethylcellulose (HEC) polymer. Correlations have been developed for rheological parameters of aqueous- and polymer-based drilling foams. On the basis of the experimental results of foam rheology and a steady-state momentum balance equation, a foam-flow hydraulics model was developed to predict pressure profile, ECD, foam velocity, and foam quality along a vertical/inclined/horizontal wellbore. For practical applications, a simulator has been developed and validated by experimental flow-loop data obtained from the Advanced Cuttings Transport Facility of Tulsa University Drilling Research Project. The effects of polymer concentration, backpressure, and wellbore trajectory on foam hydraulics were studied extensively using the simulator. Results show significant impact of polymer on foam hydraulics. When 0.5% volume to volume (v/v) HEC polymer is added to aqueous foam, bottomhole pressure (BHP) and foam density are significantly increased, while foam quality and velocity are greatly decreased. The polymer effects are more pronounced in vertical wells than in horizontal wells. Simulation results also indicate that it is possible to use foam to create a pressure profile within the narrow window between continuously changing pore-pressure and facture pressure gradients, which is not possible with conventional fluids. Those responsible for hydraulic optimization and well control in managed-pressure drilling/UBO where foam is used will find this paper useful for practical design applications.