A study on factors affecting pullback forces in Horizontal Directional Drilling

Abstract

This thesis aims to explore the influence of borehole alignment accuracy and other soil and pipe parameters on the pullback forces during the pullback phase in Hor- izontal Directional Drilling (HDD) operations. To that end a model inspired by PipeForce V1 was implemented and expanded upon in Python. The model was used to calculate the pullback forces based on the measured product pipe naviga- tional coordinates obtained from actual HDD projects. Calculated pullback force data was compared to actual measurements. It was found that pullback forces tend to decrease with increasing borehole alignment accuracy. The extent of the influ- ence depends on the length of the installation under consideration. Furthermore, through analysing ballasting and specific gravity of slurry, it was found that a bal- ance between those factors resulted in a decrease in the maximal pullback forces, through optimising the effective vertical force on the product pipe. Lastly, it was found that the originally proposed model PipeForce V1 should not be applied to longer installations due to an almost quadratic growth in one of the calculated fac- tors, which was not checked for in the original publication.