Cuttings Transport in Directional and Horizontal Wells While Aerated Mud Drilling

Abstract

Introduction Cuttings transport in underablanced drilling is critical especially while drilling highly inclined or horizontal sections. However, existing guidelines for cuttings transport in directional wells drilled underbalanced might be seldom established based on reliable experimental data because a few experimental studies1,2 has been conducted so far. In addition, most studies on cuttings transport or hole cleaning in underbalanced drilling found in literatures3–5 are covering only vertical wells. Even in drilling with conventional mud, it is reported6 that the prediction of critical flow rate (CFR) for cuttings transport in a ERW was inconsistency between the prediction models, though many studies have been done both experimentally7–11 and theoretically12–16. We made a comprehensive experimental study on cuttings transport in aerated mud drilling using a field scale flow loop apparatus. We have carried out 63 experimental runs to measure the cuttings concentration covering over 300 flow conditions with annular test section inclination angles from 30 to 90°. From the experimental results, the performance or efficiency of cuttings transport in inclined annulus is evaluated based on the quantitative data of cuttings concentration in the annulus. The critical fluid flow rate for cuttings transport is also discussed. Experiments Experimental Apparatus. Fig. 1 is a schematic drawing of the Cuttings Transport Flow Loop System (CTFLS). The 9-m long test section simulating a borehole annulus consists of a 5-in. (127.0 mm) ID transparent acrylic outer pipe (borehole or casing) and a 2.063-in. (52.4 mm) or 2.875-in. (73.0 mm) OD steel inner pipe (drillpipe). To make a visual observation and image analysis through the transparent section, CCD cameras and video recording system are equipped. The test section mounted on a movable frame can set its inclination angle from 0 to 90° in 15° increments. The test section can also simulate an eccentric annulus with drillpipe eccentricity of +0.8.