Anti Stick-slip Tool – AST
Modern drilling technology is characterized by an advanced suite of downhole tools, including PDC drill bits that are capable of drilling entire well sections in one run. In difficult formations, however, the PDC bits pose a risk of severe stick-slip vibrations that can make the drilling process inefficient and even destructive.
Although quite similar to a shock absorber in appearance, Tomax’s patented AST tool is, to continue the vehicle analogy, less of an absorber and more of an active traction control system. All weight and torque supplied to the bit goes through the AST, and the tool uses its internal mechanism to continuously control the weight fed to maintain a steady load and prevent stalls and the accumulation of excess torsional energy in the string.
The AST is an autonomous, “bolt-on ” solution with no need for added rig crew, and it requires minimum effort to deploy. The AST is typically placed above the MWD or non-magnetic portion of the BHA and is also often used with PDC-based reamer devices.
Just as the drillstring can stall and accumulate severe amounts of torsion in a stringer, the same happens when the bit is subjected to a rapid increase in weight from rig movement in rough seas offshore or a jerky forward motion in a lateral well onshore. In both cases, the AST will prevent the torque from shooting up and immediately seek to establish stable parameters.
With AST, the risk from the PDC cutters is eliminated, and this new technology is offering net benefits to a growing number of oilfield operators. What is now being explored is the potential for added value from increased drilling efficiency using sharper cutters with minimal loss of contact friction as the AST counteracts stick-slip-initiated drilling vibration.