Cuttings Transport in Directional and Horizontal Wells While Aerated Mud Drilling

摘要

Cuttings transport in aerated mud drilling for inclined annuliwith inclination angles between 30° to horizontal wasinvestigated. Experiments were carried out for over 300 flowconditions using a 9-m long un-pressurized annular testsection with 5-in. CSG and 2-in. DP, concentric or eccentricannulus geometry. Two types of base liquids, water and PHPAsolution, were used for aerated muds. In the experiments,cuttings were fed into the test section at a constant ratecorresponding to a supposed ROP, and the volumetricconcentration of cuttings in the annulus under steady state wasmeasured. From the analysis on the variation of cuttingsconcentration with mud flow rates ranging from sub-critical tocritical regions, the critical flow rate (CFR) criterion avoidinga formation of cuttings bed was found to correspond to thecuttings concentration of about 4 vol%. The annular velocity(AV) equivalent to the CFR was as high as 2 m/s in highlyinclined eccentric annulus using non-Newtonian conventionalPHPA fluid. Air injection significantly reduced the CFR andimproved the cuttings transport efficiency in highly inclinedannulus except for the horizontal annulus in which muchhigher AV of about 1.5 m/s was still required to transportcuttings effectively. The result indicates that the flow patternbetween gas and liquid considerably affects the cuttingstransport performance.