The system featured a slightly oversized outer tube, with milled fluted channels for enhanced fluid circulation and cuttings removal. Both the core bit and wireline coring system were run using controlled drilling parameters, that is, increased rod rotation speed with reduced weight on the bit. This is especially significant when drilling through concrete embedded with steel reinforcement. The Accu-dril directional drilling motor is powered by circulating drilling fluid to provide rotation and torque to the bit without rotating the drill string. Simply, the motor operates on the reverse application of the Moineau progressive cavity pump principle.
Directional d rilling with a downhole motor requires a deflection device to change hole direction.
Downhole orientation is achieved with a wireline survey instrument and an orientation collar aligned in the direction the motor will drill. As the motor advances the hole, the alignment angle increases or decreases along a continuous smooth arc, the radius of which is predetermined by the angle of the bent housing. This close alignment tolerance was necessary for a proposed future drill collar. Statistically, the higher the number of surveys recorded, the greater the degree of confidence in the accuracy of the hole orientation data. As drilling advanced the hole, overlapping survey stations provided a quality control check of the data for the preceding survey.