Experimental Characterization of Long-Chain Polymer Drilling Fluids

Sophisticated new drilling technologies such as managed pressure drilling (MPD) and dual gradient drilling (DGD) rely critically on accurate hydraulics modeling. Current fluid measurement and characterization technology performs well under a variety of conditions, but long-chain polymer additives have been shown to introduce significant complexity into the process of predicting frictional pressure losses in drilling operations. Considering the frequent use of long-chain polymer additives as both viscosifiers and friction reducers in drilling, completions and well intervention operations, this work seeks to further investigate the behavior of fluids containing these materials and propose improvements to existing measurement and pressure loss prediction methods. A series of experiments was performed using a fully automated high temperature pipe viscometer to understand the effects of long chain polymer-based additives on fluid behavior in laminar, transitional and turbulent flow. Frictional pressure losses were measured in a cesium formate fluid viscosified with concentrations of xanthan gum up to 2.5 lb/bbl at temperatures ranging from 100 – 230°F. Results were compared with widely used theoretical models for frictional pressure losses, showing significant discrepancy between current theory and empirical results. In light of this discrepancy, a new method for determining frictional pressure losses in turbulent flow was proposed and evaluated. Direct measurement of pressure losses using a flow loop was shown to provide substantially improved pressure prediction in turbulent flow when compared to theoretical correlations commonly used in industry. A field-scale prototype was also developed to apply the pipe viscometer concept, providing the means to conduct future field trials of the technology. The field prototype’s ability to characterize complex drilling fluid behavior in both laminar and turbulent flow shows significant promise for future applications in the drilling fluids domain.