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Smooth Slide

Computer controlled top drive system helps eliminate the guesswork in directional drilling
[Print Article: May 2009] Given the current drilling environment where every dollar spent is scrutinized and room for error is consistently shrinking, operators are constantly seeking to reduce costs, improve drilling efficiency and ensure the safety of all personnel. And state-of-the-art computer enhanced directional steering control systems which orient the tool face more effectively when slide drilling are proving their worth in the field.

Take for instance Canrig Drilling Technology Ltd.'s Rockit Directional Steering Control System, which is a patented software add-on to the company's AC top drive control systems.

A wholly-owned subsidiary of Nabors Industries Inc., Houston-based Canrig originally developed the technology in the mid-1990s and has continued to advance it since. However, the system really began to take flight earlier this decade when AC top drives usurped DC drives as the industry standard.

"You've got a bigger range of operating parameters on the AC drive because the newest versions can now go up to 60 RPM for oscillating speed and the newest versions can now put in anything up to 40 wraps one way and 40 wraps the other way, if that was needed," explains Colin Gillan, project manager for Canrig.

According to Gillan, Canrig's system offers a simple user interface providing powerful tools to the directional driller to increase their control over the steerable motors and turbodrills used in slide drilling and to improve weight transfer to the bit.

In slide drilling, solving the problems of toolface setting and control are fundamental to successful projects. The system solves both these problems in a manner the rig driller and directional driller can readily understand and use.

Highly deviated wellbores produce sidewall and low side frictional forces which render slide drilling less effective than rotary drilling. Canrig says its system provides a drill pipe oscillation program which reduces these frictional forces and improves the efficiency of slide drilling.

The net result of the improved control and weight on bit is an increased rate of penetration, and significant reduction in non-productive and costly flat time associated with traditional methods of toolface setting and control, such as the old chalking of pipe method and manually rotating the pipe using the manual console controls of a top drive.

"It helps you set the toolface before going on bottom to start a portion of slide drilling. We can cut down that flat time significantly by basically just letting the guy type into the touch screen keypad the amount of angular change he wants -if he wants 90 degrees to the right he just types it in and hits go and the top drive turns it 90 degrees to the right, or whatever variation of that he needs right or left," Gillan explains.

"Once he is on bottom he can continue to use the same controls to help him steer the toolface while he is sliding."

Gillan adds that Rockit also allows the driller to oscillate the drill string from the surface, which dramatically reduces friction. The oscillation or rocking can be programmed from a fraction to several revolutions, precisely executed under computer control. The amount of oscillation left and right is controlled by the operator to provide maximum drill string rocking without affecting tool face orientation.

"The purpose of that is to cut down side wall friction and to allow more weight, more effectively, to get to the bit and therefore improve contact," Gillan says.

Canrig's directional control steering system is comprised of a programmable logic controller, (PLC), a sensor package, a human machine interface (HMI) and a control package. Working together, Gillan says these components allow the rig driller or directional driller complete control of rotary pipe speed, direction of rotation and angular offsets, from a fraction of a revolution to multiple revolutions.

The directional drilling control system shares the PLC used by the main top drive control systems. According to Gillan, these real-time computers are capable of supervising control variables using millisecond loops and are capable of multiple alerts and intervention logic ladders.

A position feedback signal from an encoder mounted on the top drive informs the PLC of the exact position of the top drive quill, or main drive shaft. A torque sensor also measures the exact amount of torque necessary to rotate the drill pipe, given the current loading conditions generated downhole.

A ruggedized touch screen computer provides the user control of the system. A single screen shows the real time status of the top drive quill, allowing the driller to use an on screen rotation set point, substituting for the traditional chalk mark on the pipe, to track the rotational set point of the pipe.

The system has been shown to extend the operating envelope of mud motor drilling systems, enabling complex three-dimensional wells to be drilled which previously were only drillable with rotary steerable drilling systems.

This system is easy to install and involves little additional time or equipment and works in conjunction with any mud motor/measurement while drilling system in the world. The basic training of directional or drill crew rig personnel can typically be completed in one hour.

One long-time directional driller who has used the Canrig system extensively says it works as advertised. "I like the Rockit as it lets you drill with much less weight on bit. You can move or control the toolface without pulling off bottom. I use the Rockit any time I am sliding, except for time drilling," says Tony Fish, a senior directional driller with Schlumberger.

"It has cut down on how long it takes to get a slide done. When you have a motor stall and need to pick up, it will bring your toolface back to your starting point, removing the need for a chalk scribe line or guess work until the MWD resyncs. Counting wraps is done for you in a controlled manner."

Gillan says Canrig is continuing on with the next evolution of the Rockit technology. "We have some pretty good plans going forward to integrate more drilling parameter data on our Rockit screen," he says. "We also presented a paper at the March SPE/IADC Conference in Amsterdam and it was well received."

"What we're trying to do is get a single screen that the directional driller can use to steer his downhole motor and give him all the important parameters he needs on one screen to ... keep his motor on a specific toolface heading."

• Paul Wells


Colin Gillan, Canrig, Tel: (281) 774-5600, E-mail: [email protected]

  • AUTOPILOT A software add-on to Canrig's AC top drive control system is improving the efficiency of slide drilling.
  • BETTER STEERING Canrig's user interface provides powerful tools to the directional driller, enhancing control over steerable motors and turbodrills.
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