Pad drilling techniques coupled with advanced drilling rig designs along with hydraulic fracturing and horizontal drilling have been among the most important innovations driving U.S. production growth over the last decade.

Pad drilling was modeled after offshore drilling operations, where multiple wellbores are drilled from one platform. A few years ago land drilling companies began setting rigs on rails to slide or skid them to the next hole. This practice was used very successfully in natural gas formations in Colorado and on the manmade THUMS Islands in Long Beach, Calif. Then rig manufacturers employed hydraulic and mechanical technologies to develop the first “walking rigs,” which started appearing in the Barnett Shale as early as 2004.

Operators were asking for rigs with more efficient mobilization capabilities, automated pipehandling functions and modern alternating current (AC) variable frequency drive (VFD) controls to reduce their well cycle times, improve drilling efficiencies and improve safety.
Modern walking rigs met that demand.

In 2006, according to Drillinginfo statistics, multiwell pads employing walking rigs made up about 5% of wells drilled in nine U.S. unconventional plays (Bakken, Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, Niobrara, Permian and Woodford). By third-quarter 2013 the percentage had risen to 58%. Today the number of these new mobile rigs has surpassed the number of older conventional units. Also, older rigs are being retrofitted with the newer technologies at a fraction of the cost of a newbuild. The primary purpose is to decrease mobilization complications and increase efficiencies.

Continuing this focus, Integrated Drive Systems (IDS) has developed the new patent-pending ReelRig distributed power and control system that greatly enhances walking rig mobilization and operations.

The ReelRig system is a significant step change in the way drilling rigs are powered. It has effectively eliminated many maintenance, troubleshooting and safety issues the industry experiences with standard cables.

Recently, Orion Drilling added two walking rigs to its fleet that employ this new distributed power and control system. Orion has another newbuild planned for 2015 designed around the ReelRig concept and has plans to retrofit an older rig with the system.

Tangled mess of cables
Drilling rigs employ multiple systems that require electrical power to operate, run, lift, rotate, pump, illuminate, etc. Every control panel, every light, every motor or piece of rotating equipment requires a power connection. It all starts in what is called the “backyard” with the power control house, generators and electrical plug panel. Traditionally, this can be a spider web of 20 to 40 cables or more connected to the plug panel, most carrying 600 v for power circuits and others for communication, instrumentation and control.

On a walking rig, the network of cables must “travel” with the rig across the pad as the rig moves from one wellbore to the next, getting farther away from the power house with each move. There are hundreds of feet of multiple cables chasing in, around, over and under the rig structure, involving sometimes more than 200 or more plugs or cable connectors and a traditional “festoon” cable-handling system that unfolds like an accordion as the rig travels.

Problems with these systems are many. Multiple connection points can be broken or compromised, requiring wasted hours of troubleshooting and repair, not to mention safety concerns. Because of the cables, rig moves are cumbersome, often requiring extra personnel and equipment to move safely.

System streamlining
The new IDS distributed power and control system replaces a traditional centralized power network with a clean, streamlined power, control and cable-handling system designed specifically for moving rigs over drill pad sites more safely and efficiently. The distributed system positions VFDs and programmable logic controllers near the driven equipment.

It involves eliminating multiple power and control cables and connectors by adding a transformer to the backyard power house area, “stepping up” the power from 600 v to 4,160 v, sending that power through a single medium-voltage cable, “stepping down” the voltage at the rig via another transformer, then distributing the power closer to where it is needed on the rig.

A single control cable (eight fiber-optic and four emergency stop circuits) is backed up with a redundant wireless network, assuring uninterrupted operation and control without multiple connectors and “noise” problems associated with long runs of cable.

Instead of a plug panel that looks like a tangled mess of extension cords, there is a single-power cable connection point that includes ground-fault/check protection and a three-key safety lockout mechanism. Additionally, there is a skid-mounted power cable spool, or “reel,” that attaches to the walking rig substructure. The spool pays out or reels in the power cable as the rig moves farther away from or closer to the power house during rig moves. Additionally, there is a companion reel that handles the rig’s fiber communication
system’s cable in a similar fashion.

From the spool the power cable is connected to another transformer on the rig where the 4,160-v power is stepped back down to 600 v and then distributed to the local equipment room (LER) and driller’s cabin on the rig floor. The VFDs and motor control centers for the drawworks, top drives and other rig floor equipment are housed in the LER (on the rig floor) closer to the driven equipment.

The entire ReelRig system consists of the power control house with mud system VFDs, transformers, cable and cable-handling system/skid, LER VFDs, driller’s cabin with integrated driller’s controls, AC drawworks controls and AC topdrive controls.

According to Wayne Squires, president of Orion Drilling, “This new system has revolutionized the way we power our rigs. It’s safer, more efficient, reduces cable weight and footage and dramatically reduces power system maintenance and troubleshooting. Our rig moves are faster and require fewer people and no cranes. In short, this system has solved the electrical limitations to walking a rig.”