Experimental Examination of the Mathematical Model for Predicting the Borehole Pressure during Horizontal Directional Drilling

Abstract

Predicting the borehole pressure during Horizontal Directional Drilling (HDD) is a significant part of HDD. Borehole stability means that pressure on the bore-face must be less than formation fracture pressure and more than the collapse pressure to avoid fluid losses or borehole breakouts. The proposed research is aimed at an analysis comparison between the mud pressure data collected in the real field and the ones the mathematical model predicted. Then the optimal model will be applied to predict the allowable maximum borehole pressure during HDD. Borehole stability during drilling consists of evaluating the drilling fluid weight to maintain the borehole wall integrity. The tensile failure (hydraulic fracturing) and dog-ear shape breakout are two main failure modes around boreholes during HDD. The cavity expansion model was used to calculate maximum and minimum allowable drilling fluid pressure in a bore. Both 2D and 3D finite element (FE) models of maximum borehole pressure were developed by the Drucker-Prager and Mohr-Coulomb theories using ANSYS Parametric Design Language (APDL) to support the customized parametric study. The result showed the maximum mud pressure closely matched the estimation obtained using the Delft equation in this field experiment for shallow layers within clay. The FE modeling procedure used was able to capture the volumetric compressive behavior of the soil around the borehole.