Tech Bulletin – VertiTrak Bit Selection Page 1

Hughes Christensen - Company Confidential ©2003 Baker Hughes Incorporated

With the increasing popularity of the VertiTrak™ System, there has been an increased demand for PDC bit selection guidelines for VertiTrak. This proprietary document fills that need. It contains a brief overview of the tool, compares and contrasts the VertiTrak System to the AutoTrak® RCLS, and offers general PDC bit selection guidelines. VertiTrak Tool Overview The VertiTrak System is the industry’s first automated vertical drilling system. It delivers deviation control without compromising preferred drilling parameters to maintain wellbore verticality. The VertiTrak System is powered by the Mach1 X-treme™ power section, delivering high performance power and torque. It also utilizes pad steering technology which is similar to that used with AutoTrak RCLS. This combination of technology delivers improved wellbore stability, decreased tortuosity, reduced torque and drag, and minimized casing wear. The VertiTrak System improves penetration rates while maintaining directional control. The VertiTrak System has been deployed in a variety of applications, including highly-dipped formations and salt formations which are susceptible to deviation tendencies. It has also been applied in lean casing profile wells which require more precise wellbore placement. VertiTrak Modes of Operation The VertiTrak System is typically run in steering mode, where either one or two of the ribs on the steering head are constantly engaged with the borehole walls. The bit rotation is powered exclusively by the X-treme power section while near-bit sensors monitor the borehole inclination. When the sensors detect the wellbore deviating from vertical, the control sub activates internal hydraulic pumps which control the three steering pads. These steering pads will then counteract any deviation tendencies, bringing the wellbore back to 0.0° inclination. When the drilling operation has been completed, the steering ribs can be disengaged (ribs-off mode) via downlink to permit tripping out of the hole. With the steering ribs retracted, the tool

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PDC Bit Selection for VertiTrak

Tech Bulletin – VertiTrak Bit Selection Page 2

Hughes Christensen - Company Confidential ©2003 Baker Hughes Incorporated

can safely trip in and out of the hole while avoiding damage to the steering head. On occasion, reaming and/or backreaming may be necessary. In these situations surface rotation is necessary to get the system to bottom or back to surface. The assembly can be rotated at 40 rpm during the reaming/backreaming process. Once the assembly has made it through the “tight spots” another downlink can be sent to the tool to switch back to steer mode and drilling can continue. VertiTrak Bit Selection A common misconception is that the ideal bit for the VertiTrak system has the same features that are ideal for the AutoTrak RCLS. This is not the case. The VertiTrak System and AutoTrak RCLS operate very differently, so they require different bit features. The AutoTrak steering head is mounted on a non-rotating sleeve to isolate it from the rotating drillstring. Because the steering controls are not affected by erratic downhole RPM, it has no trouble maintaining direction, even when stick-slip is fairly severe. Conversely, the VertiTrak steering head is fixed to the X-treme motor immediately above the bit. Erratic downhole RPM can cause the tool to apply correction forces in the wrong direction. In a sense, tool face control for VertiTrak is just as important as it is when drilling with conventional steerable motor assemblies. The HCC recommendation is that all new VertiTrak applications are reviewed by a Design Application Review Team. This will help ensure that lessons learned are applied so the latest technology is introduced when and where it is needed. For occasions when a formal review is not possible, we offer the following guidelines based on experience to date:

• The bit should be chosen as if it were to be run in a conventional motor assembly. • Toolface control is critical to the success of the VertiTrak System. EZ Steer™

Technology has proven to be the most effective method of controlling toolface. • Bit aggressiveness, blade count and the size of cutters should be optimized to most

effectively drill the formations that will be encountered. Avoid artificially selecting higher blade counts or smaller cutter sizes for the purpose of toolface control.

• Bit stability is another critical component to the success of the system. EZ Steer also significantly reduces whirl and stick-slip, which have been known to cause catastrophic damage and steering problems.

• Both high and low imbalance designs have been used successfully to reduce vibration. The high imbalance approach has been particularly effective for big bits (12.25" and above). Genesis secondary stability features like LMM™ and Chordal Drop Management are recommended to help limit the damage caused by system vibration.

• The gauge should be very robust. The VertiTrak System delivers 6600 lbs. of force per steering pad to push the wellbore back to vertical. This can cause heavy wear on the gauge pads. We recommend an unaggressive TSP gauge in most cases.

• There is plenty of side-cutting ability in the standard Genesis gauge to deliver the 1.5° DLS theoretical drop rate of the VertiTrak System. At a minimum, use the standard gauge length for a given bit diameter to aid in hole quality.

Visit the PDC Bit Selection for VertiTrak web page (http://172.25.1.77/prodlines/vertitrak) for more information.