Cuttings Transport with Foam in Horizontal Highly-Inclined Wellbores

摘要

Foams are of considerable interest for annular pressuremanagement in many drilling applications. While foamrheology and hydraulics have been studied in the past,knowledge of cuttings transport with foam is very limited forvertical wells, and even less well understood for horizontaland inclined-well configurations. In this paper, cuttingstransport with foam in horizontal and highly-inclined wellsis analyzed.Using the principles of mass and linear momentumconservation, a model consisting of three layers (motionlessbed – observed in most experiments, moving foam-cuttingsmixture and foam free of cuttings) is presented. The modelincludes seven independent equations and seven unknowns. Acomputer simulator was developed to solve simultaneously thesystem of equations for flow velocities, cuttings bed height,slip velocity, the in-situ concentration of flowing cuttings andpressure drop.An extensive experimental program on cuttings transportwas conducted using The University of Tulsa DrillingResearch Projects’ full-scale (8” by 4 ?”) flow loop at 70° to90° inclinations (from vertical). A broad range of annularvelocities and cuttings injection rates was investigated usingfoam qualities of 70% to 90%. Results from the experimentsare presented in the form of graphs showing the cuttings bedcross-sectional area and pressure losses vs. foam flow rate. Inall experiments, the foam behaved as a pseudo-plastic fluid;foam qualities of 80% and 90% exhibited noticeable wall slip.At a given flow rate and rate of penetration, bed thicknessincreases with an increase in foam quality. There is little effectof inclination angles in the range of 70°-90°.The experimental data were used to verify results from thesimulator. The simulator is capable of estimating bedthickness and pressure drop with an error of less than 20% inmost cases.