The counterforce assisted XC-AST solution from Tomax provides a new, economical method for drilling hard rock using PDC technology
The patented counterforce assisted XC-AST solution keeps the lower BHA and the drill-bit suspended in both axial and rotational directions at the critical moment when the first cutter touches the rock. As the load increases, the helix-telescope function of the AST (Anti Stick-Slip Tool) ensures a steady load within the capacity of the PDC cutters, regardless of how hard the rock is. This new and improved principle of operation will produce the first vital circles of cut free from chatter. As more of the cutters are engaged, a smooth bottom-hole pattern develops. When the full cutting face is engaged, the counterforce assisted XC-AST system is practically offloaded, while the main springs in the AST system take over to keep the system in tune. Now the Weight On Bit (WOB) can be brought beyond the compressive strength of the rock to produce a fast yet safe ROP (Rate Of Penetration).
Conventional drill-strings have high inertias in both rotational and axial directions. Therefore heavy-set and often quite blunt drill-bits are preferred to prevent damage in hard rock. The downside of the heavy-set approach is the difficulty of providing enough WOB to properly engage the cutters in the hardest layers. The result is often long periods of ineffective, slow grinding and unpredictable bit life. The counterforce assisted XC-AST makes it safe to run a drill-bit that is sharp enough to stay engaged even in the hardest layers. A continuous cut at moderate WOB produces less heat and makes the cutter last longer. The larger cuttings from a sharper edge are easily removed to leave the cutting surfaces clean at all times. Together these factors provide for great benefits and can make PDC a very economical alternative to diamond impregnated turbine bits.