Correlations of Mud Rheological Properties With Cuttings-Transport Performance in Directional Drilling

Abstract

Summary An experimental study comparing the effects of mud rheological parameters on annular drill-cuttings buildup was conducted in a large-scale flow section. Rheological parameters examined were mud yield point (YP); plastic viscosity (PV); YP/PV ratio; power-law exponent; consistency index; Fann™ V-G Meter dial readings at 600, 300, 200, 100, 6, and 3 rev/min; effective viscosity (calculated by the power-law derivation); and initial and 10-minute gel strengths. Fifteen bentonite/polymer water-based muds were used, ranging from water to a mud with YP and PV values of 20 lbf/100 ft2 and 40 cp [19.6 Pa and 0.04 Pa·s], respectively. For each mud, flow tests were run at annular velocities from 120 to 240 ft/min [37 to 73 m/min] and hole angles from 30 to 90° from vertical. The effective drilling rate for all tests was 50 ft/hr [15 m/h]. Altogether, 180 tests are analyzed. When data were correlated with annular cuttings volume in steady-state flow, the best fit was obtained with low-shear-rate parameters. These parameters include the 6- and 3-rev/min dial readings and initial gel strength. Correlation coefficients for these were often from 0.9 to 0.95. For hole angles ≤45° (from vertical), increasing values of these parameters improved cuttings removal (i.e., reduced cuttings volume). The same was observed at angles near horizontal, but only in the laminar flow regime. Cuttings volumes were always smaller in the turbulent regime during near-horizontal flow.