DrillLink/CyberLink saves offshore operators time and money with automated control

Driller selects ON/OFF at throttle control panel and monitors downlinking progress via indicator lights.

When initially developed and later popularized as DrillLink before its digital companion was introduced, this new technology was referred to as an automated rig controller. At the outset, engineers decided which equipment could be controlled first; the one offering the least risk and the most benefits. The mud pump was chosen because there was less anxiety from crews than with rotating or hoisting machines and the estimated 20% annual growth of directional and horizontal wells indicated that downlinking to rotary steerable tools would be extremely beneficial economically, especially in deepwater.

The premise was that by controlling drilling with automation, young and inexperienced drillers could be protected from potentially costly mistakes affecting rig equipment and resulting in expensive downtime. As more rigs have applied this technology, that concept has proven valid.

Engineering for improved rig operations

DrillLink is a simple, reliable, repeatable autopilot for drillers. A key feature is that rigs can be retrofitted with no capital investment. As indicated, the first applications involved generating command sequences for downlinking to rotary steerables, but now it is used for formation evaluation tools and related equipment that actually can be reconfigured downhole. It also is used to send commands to an electronic autodriller.

From a rig floor perspective, DrillLink is installed between the driller’s console and various drilling machines. The existing throttle signal from the SCR rheostat to the SCR is rerouted to the DrillLink controller by moving one wire per channel. Various backups are included to ensure reliability and as fail-safes to return to manual operations if necessary. DrillLink operates with most SCR and AC drives, with work under way to connect to various mechanical rigs.

With the digital controls on most newer rigs, the driller sits in a chair and controls the rig with a joy stick and touchscreen. The driller changes the pump speed by tapping on the screen to “increase” or “decrease” the signal. Or, the driller can call up the keypad and type in a specific number as a target speed. CyberLink is added outside of this control network and connected digitally in a manner that maintains full network capability and security. CyberLink works with Cyberbase controls and is scheduled for integration with Amphion systems in 2009.

Actual operation is designed to be as simple as possible, with emphasis on the driller having only one switch. “On” allows the service company to send a command, and at any time the driller can switch it “off” to get manual control.

This automated tool delivers several advantages:

• Virtually eliminates communications errors with downhole tools, and more frequent on-bottom downlinks saves time
• Sharper command pulses allow sequences to be transmitted closer to drilling flow rates to reduce wellbore stresses
• Since this tool promotes more frequent, smaller course corrections, the result is a straighter wellbore which translates into:

  - Less dogleg severity

  - Reduced drilling torque

  - Easier running of completion strings

• Service companies can build pulldown, easy-load command menus potentially reducing offshore personnel by cross-training technicians.

Peak level operations

Among the ways DrillLink and CyberLink optimize drilling, envelope protection will prove extremely valuable. Maximum limits can be set. For example, pumping too fast in weak zones could cause friction pressure in the annulus to fracture the formation. Also, excessive trip speeds can surge the wellbore. By limiting pump speed and tripping velocities, forces on the wellbore can be minimized.

Case study: Improving drilling, reliability

In field application, improved drilling efficiencies are the norm with DrillLink or CyberLink. The following case study illustrates this.

From a drillship in water depths of approximately 4,300 ft (1,311 m), two wells were drilled in the Gulf of Mexico. For wellbore steering of the first well, 113 downlinks were conducted within the downhole equipment’s operating limits, with all but three attempts successful. When the digital word length of these three downlinks was altered from 18 seconds to 60 seconds, these follow-up downlinks were successful, too.

Employing a similar casing program, a second (near-vertical) well was drilled, with only three automated downlinks attempted within the downhole tool’s operating limits. While one downlink was prevented due to mud pump failure, another failure likely occurred when the directional driller unplugged a network connection before logging off. To remedy these, client application software was modified. Overall, the automated downlinking success rate was 96% overall (111 of 115 attempts).

Efficiencies were as significant for rig crews as was the success rate. Although manual downlinking normally can be completed in about four minutes, the directional driller spends 12 minutes for set-up and execution. The new system, in contrast, works as follows:

• Driller receives call from directional driller for permission to send downlink sequence
• Driller, when ready, flips switch allowing directional driller to send downlink sequence
• Using service company’s software, directional driller initiates the sequence and monitors status with “abort anytime” capability
• With sequence running, driller resumes normal activities
• Upon downlink completion, driller turns off controller by reversing switch position, preventing sending of further commands.

For the two wells combined, the efficiency gain was approximately 24 hours, with time savings based on time required for the driller to make each attempt sending a command sequence. As a practical matter this means that the more the driller concentrates on manual control, the less productive.

About the author

Fred Florence, based in Austin, Texas, is product line manager with NOV M/D Totco (www.nov.com). NOV M/D Totco is a product group of National Oilwell Varco. For additional information, contact [email protected].

Editor’s note: The case study presented in this article was excerpted, with SPE permission, from a technical paper presented at the 2008 IADC/SPE Drilling Conference.

Rig safety not compromised

DrillLink and CyberLink can be used by novices without jeopardizing rig safety. The only moving part is a relay in DrillLink, and CyberLink is fully digital and does not affect reliability of the rig’s control network. Service company software is pre-programmed to avoid errors and speed downlinking. (Adding real-time modeling provides envelope protection to prevent operations outside of prescribed limits.)

Above all, the driller is always in control. Only with the driller’s permission can the service company access the drilling machine via DrillLink and CyberLink. The driller’s throttle is the datum and the controller’s software continually compares the driller’s throttle to instructions received from the service company’s laptop. Because no value greater than 100% is allowed, the system physically cannot exceed the driller’s throttle.

If necessary, the driller can take control in either of two ways. One is to turn off DrillLink, thereby closing the relay. The other is to adjust the throttle up or down more than a 10% threshold, which immediately aborts any sequences sent.