System and method for determing soil characteristics and drilling instability during horizontal directional drilling

A method for detecting instability within a borehole made via horizontal directional drilling, the method employing a drilling rig, a drillstring, and a drilling head, the method comprising the following steps:

• determining the thrust applied to the drilling head (Th) and the torque applied to the drilling head (Qh) by way of a load cell positioned proximate to the drilling head;
• determining the thrust applied to the drillstring (Ts) and torque applied to the drillstring (Qs) by way of a load cell positioned proximate to the drilling rig;
• determining the length of the borehole (s) by way of an odometer positioned proximate to the drilling rig;
• determining the angle of rotation of the drillstring φh and φs the windup of the drillstring (w=φh−φs) by the way of navigational sensors located at the a proximal and distal ends;
• generating a plot of thrust efficiency (Th/Ts) as a function of borehole length, a plot of torque efficiency (Th/Ts) as a function of borehole length and a plot was a borehole length;
• and
• predicting instability within the borehole upon a simultaneous decline in Th/Ts and Th/Ts plots and an increase in w plot.