The combination of 7 to 10ft chops and a critical wavelength made drilling and steering from a semi-submersible in the South Caribbean difficult.
A 9 ½” XB-AST tool was made up in the BHA in order to stabilize the erratic drilling torque produced by the fluctuating weight on bit as a result of the fast rig motions. The change was made in the midst of a batch drilling campaign that gave a good basis for evaluating the effect.
The AST was entered in the 16 inch hole-section. The tool gave an immediate improvement in the torque response. The AST service was therefore continued in the 12 ¼ and 8 ½ inch hole sections and then throughout the drilling campaign.
The AST saved at least on day on each section drilled compared to previous wells having the same sea conditions. The reason for the improvement was that the drilling could commence with no restriction or hold-backs to prevent torque spikes and risk to the drilling equipment.