New ‘walking’ rigs use a box-on-box design to operate on multiwell pads in sensitive, space-restricted areas. (See video of rig)

rig, B-Series

B-Series rigs are each equipped with a Columbia Walking System (in photo). The system allows the rig to travel up to 100 ft (30.5 m) without moving the backyard and with full setback. A well-to-well move can be accomplished in as little as one hour, and it can return to a previously drilled well with an accuracy of plus or minus one-sixteenth of an inch. (Image courtesy of Nabors Drilling USA)

Drilling customers today are looking for the latest technology with compact but powerful equipment. They want faster moving features, enhanced safety elements, better power distribution, and greater control of torque and rate of penetration. These features allow operators to drill more efficiently and move more rapidly. Nabors Drilling USA (NDUSA) is meeting these drilling demands with a series of programmable AC electric (PACE) rigs.

The original PACE Academy rig debuted in 2005. Built by Nabors Canada, it is a 1,000-hp AC electric rig with programmable logic control. NDUSA unveiled its M-Series PACE rig two years later. These 1,000-hp rigs move in record time, averaging complete relocation in less than four days. In addition, these rigs have set numerous field drilling records in the growing shale plays. In 2007, the company successfully adapted multiwell offshore platform designs — Super Sundowner (SSD) — for land operations. The SSD compact arrangement minimizes the rig footprint in areas where location size is limited, such as the Rocky Mountains. The SSD rigs have realized significant increases in per-well productivity and are built to skid when drilling on a pad.

To address the importance of US shale gas, NDUSA recently reinvented its PACE model, which operates on multiwell pads in shale plays in the northern part of the US. The B-Series is a custom-designed box-on-box 1,500-hp rig specifically built for use in such plays, particularly North Dakota’s Bakken Shale. 


Numerous rig designs and variations of the PACE format were evaluated, including self-elevating hydraulically raised masts and substructures. When considering the extreme weather conditions and winterization required for working in the northern regions of the country, it was decided that a box-on-box type rig was the preferred option. Several improvements were made to the standard box-on-box design to make the rig move faster from pad to pad.  

Approximately two-thirds of the way through the construction of the inaugural rigs — B-01 and B-02 — the customer requested that NDUSA look at options to change the rig design to accommodate multiwell pads while carrying out simultaneous operations. The final well configuration selected by the customer required NDUSA to turn the substructure and mast 90 degrees, install a walking system, change the electrical grasshopper to a telescoping drag chain, and relocate the solids control equipment to optimize the design of the flowline.

Unique components of the B-Series
B-Series rigs are each equipped with a Columbia Walking System. Various NDUSA subsidiaries have been working with Columbia on the development of land rig moving systems since 1976.   Moving technology has evolved from the pioneering rigs in Alaska to pad drilling in the Rocky Mountains and now to a new walking fleet using PACE technology.  

Other features
B-Series rigs boast a variety of other features, including a Canrig TM80. This fully automated floor wrench is programmable logic controlled (PLC). Remote-control capability allows the unit to be activated from the driller’s console or from various rig floor locations. Pipe range is 23/8-in. to 8½-in. The maximum torque makeup is 60,000 ft/lb, and the maximum torque breakout is 80,000 ft/lb.  

The rig also is equipped with a Canrig PowerCAT automated catwalk. It is designed to individually index racked drill collars, drillpipe, and casing into a center carrier where they can be lifted to the drill floor. It can safely raise subs, casing, logging tools, or utility baskets. The PowerCAT eliminates the need for pickup and lay down services when running casing. With its remote-controlled capability, the unit can be operated from the drill floor or from ground level.

A Canrig 1250AC, 500-ton top drive system is standard equipment on B-Series rigs. It is powered by a single 1,150-hp AC motor with a continuous torque rating of more than 51,400 ft/lb at 118 rpm. B-Rigs are equipped with a driller’s cabin featuring an ergonomic chair and integrated joystick control utilizing PLC technology. Touch-screen controls provide state-of-the-art monitoring and control of rig equipment and drilling parameters.    

B-Rigs are powered by three Caterpillar 3512C engines rated at 1,476 hp, each driving one Kato 1365 KW generator for a total of 4,428 hp. A single house uses the Canrig Rig Control and Power System, 600-Volt AC power generation, variable frequency drive, and Smart MCCs. A 1,500-hp AC drawworks is available on the rig. It is powered by two 1,150-hp AC motors featuring regenerative AC braking and autodrill functionality.  

The mast is 147 ft (45 m) high and is manufactured to API-4F specifications. The maximum static hook load capacity is 800,000 lb on 12 lines. Two 1,600-hp mud pumps control the flow of drilling fluids. Each is powered by one 1,500-hp AC motor and equipped with hydraulic liner retention and pump rod systems. The two-tank mud system has a capacity of approximately 1,000 bbl and four 6-in. by 8-in. centrifugal pumps powered with 75-hp motors. Solids control is handled by two M-I Swaco Mongoose PT dual motion adjustable shakers. One Brandt vacuum degasser, desander, and desilter is standard equipment on the rig.    

The seven-station PLC-operated accumulator unit is equipped with one electric triplex and two air-operated pumps and is manufactured in accordance with API 16D. A remote panel is mounted on the drill floor. Additional equipment includes a dedicated man-rider winch, two hydraulic winches, camera system/intercom system, and a rotating mousehole.
The system allows the rig to travel from wellhead to wellhead on a pad in a fraction of the time required for conventional rigs. This unique system can move approximately 30 in. in 90 seconds.  The rig is capable of walking up to 100 ft (30.5 m) without moving the backyard and with full setback. A well-to-well move can be accomplished in as little as one hour. The B-Rig can then be returned to a previously drilled well with an accuracy of plus or minus one-sixteenth of an inch.

The moving process is relatively simple. Four jack cylinders lift the rig, while four travel cylinders push it along the stomper feet on rollers. The jack cylinders then lower the rig, and the travel cylinders retract for another pushing cycle. The Columbia Walking System allows the rig to move in a very safe and precisely controlled manner. The steering system employs manually adjusted steering arms with pin positions for each steering mode. Steering adjustments are made by hand while the load is off the rollers, reducing the exposure of employees to the hazards associated with traditional well-to-well moves. It has simple crab and spin modes to move longitudinally or transversely. This range of maneuverability allows the operator to quickly locate the rig over the well bore and then easily move between wells after completion.

Another key component of the B-Series is the 20-ton blowout preventer (BOP) handling system, designed to transport the BOP stack in a single piece and to safely and quickly upright and manipulate the BOP stack at well center. The BOP handler enhances personnel safety and saves time and cost by reducing the nipple-up and -down time. One-piece transportation of the BOP stack eliminates the need to break the stack down for moving. The BOP handler can raise the stack to vertical and precisely position it on the wellhead without manual intervention, providing a high degree of safety during handling. It also makes cutting casing and setting wellhead spools safer and more efficient.

The box-on-box substructure has a 25-ft (7.6-m) floor height and 21 ft (6.4 m) of clear height under the rotary beams. It is rated for 800,000-lb rotary load with a 500,000-lb setback load.

Two B-Rigs are now at work in the Bakken shale. NDUSA is building four more, three of which will be deployed before the end of the year. The walking system and the proven success of AC technology keep this new series of PACE rigs in high demand.