Tomax has launched the Curve Drilling Anti Stick-Slip Tool (CD-AST) to accompany high-performance motor-powered, flexible rotary steerable systems. The company’s anti stick-slip technology (AST) is installed close to the drill bit and stabilizes the loading of the bit within 20 milliseconds. This is an improvement over traditional surface controls thousands of feet higher up.
With assistance from the AST at the bottom end of the string, the driller can push harder with less worry about the motor and the bit. The result is faster rates of penetration.
The AST regulator constantly pushes the system dynamics toward the optimal intersect between cut and friction. This is where the cutters remove the most rock with the least waste to heat and vibration.
With the CD-AST, the AST regulator provides faster corrections of the cutter interface than before. This is achieved by an architecture directly adapted to transmit the input energy from a motor, unaffected by the wellbore curvature.
The new tool combines the best of the proven tool design with an all-new progressive energy storage and deflection capability.
The tool is initially being produced in 7-in. OD for hole sizes from about 8 3/8 to 9 7/8 in. The inner diameter is the same as for existing tools and the operational range matches the relevant motors.
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.
NEW: XC-AST
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.
APPLICATIONS
THE PREVENTION OF TORSIONAL VIBRATIONS OR STICK-SLIP IS AN ESSENTIAL ASPECT OF THE PROCESS OF DRILLING EXPLORATION AND PRODUCTION WELLS FOR OIL AND GAS.
Through its patented Anti Stick-slip Tool (AST), Tomax provides a stable, safe drilling environment, free from stick-slip vibrations produced in the process of cutting through problematic underground formations. The suppression of stick-slip vibrations will also release energy for faster rates of penetration (ROP). As a result, the use of AST will always add significant value where the drilling operation faces risk from stick-slip vibrations.
- STRINGERS
- PERFORMANCE
- ENLARGEMENT
- ROUGH SEAS INT
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