Impact of mechanical tripping on cuttings transport in large-diameter horizontal directional drilling applications

Abstract In horizontal directional drilling (HDD), both drilling performance and drilling efficiency are affected by the downhole condition, i.e. the presence of cuttings. Previous research has focused on cuttings transport during drilling; however, less effort has gone into investigating the effect of the movement of the bottom hole assembly (BHA) for downhole cleaning, possibly due to the lack of downhole annular pressure data. In HDD, mechanical trips are the movement of the drillhead from the cutting face towards the borehole entry point, and back again. In the current work, any movement of the BHA of a length greater than ten drill stem segments (towards the entry point) during the drilling process is defined as mechanical tripping. Based on the downhole annular pressure data from a large-scale HDD project, an initial analysis of the pressure drop due to six trips was determined for drilling the pilot bore. The average pressure drop observed for these six mechanical trips is 69%. This difference in annular pressure before and after tripping indicates that, in practice, this is a potential method to remove cuttings from the borehole.