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

Abstract

Abstract Foam has proven 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 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 specially designed a flow-through rotational viscometer and pipe viscometers with different hydroxyethylcellulose (HEC) polymer concentrations. Correlations have been developed for rheological parameters of aqueous and polymer-based drilling foams. Based on the experimental results of foam rheology and steady-state momentum balance equation, a foam flow hydraulics model was developed to predict pressure profile, ECD, foam velocity and quality along a vertical-inclined-horizontal wellbore. For practical applications, a simulator has been developed and validated by experimental/flowloop data obtained from the Advanced Cuttings Transport Facility of Tulsa University Drilling Research Project (TUDRP). The effects of polymer concentration, back pressure and wellbore trajectory on foam hydraulics were studied extensively using the simulator. Results show significant impact of polymer on foam hydraulics. When 0.5% v/v HEC polymer is added to aqueous foam, Bottom Hole Pressure (BHP) and foam density are significantly increased, while foam quality and velocity are greatly decreased. The polymer effects in vertical wells are more pronounced 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 MPD/UBO where foam is used will find this paper useful for practical design applications.