DRILLING

New rig design improves drilling efficiency

Reduces drilling time for shallow wells up to 50%

Ron Isinger, Precision Drilling Corporation, Alberta

lant drilling rig technology moved forward in the early 1990s when Precision Drilling Corp., in conjunction with PanCanadian Petroleum Ltd., designed and implemented a new slant drilling rig. This new design represented an important milestone in heavy oil drilling. Its longer-than-standard drill pipe – 45 ft (13 m) vs. 30 ft (9m) – offered significant benefits of flexibility and operational capabilities, which led to the term, "Super Single."*

Background

In the 1980s a new alternative appeared in horizontal drilling. The well would start vertical, then be deviated to horizontal with downhole mud motors, measurement-while-drilling (MWD) and bent-sub technology. The process increased production, but the mud motors, and sophisticated directional drilling techniques and equipment were expensive.

The 1990s saw the revival of slant technology, which was used most successfully in heavy-oil drilling at shallow depths. This differed from directional drilling in several ways:

• It followed a shorter, more direct route. Wells could be spudded at an angle – usually 30° to 45° – and then aimed straight at the target, Fig. 1.
• It was less expensive, faster and more productive than directional horizontal drilling.
• Slant drilling allowed shallow heavy-oil deposits to be developed from one or several pad locations, which vary in number of wells. Pad drilling also emerged as a way to minimize environmental impact because it allows multiple-well access to larger areas and targets beneath sensitive areas, such as lakes and towns.

Fig. 1. The new rig design has drilled more than 5,000 wells, achieving drilling rates of 607 ft/hr (185 m/hr).

The technique started by drilling from a slant angle at the surface (45° max. in 1.5° increments), and zeroed in on shallow-depth targets with a 150-ft (50-m) radius. The technique did not require downhole motors or MWD technology. Improvements to the technology, combined with customer cooperation reduced time and well costs up to 50% on heavy-oil pad projects.

The Evolution Of Super Single Rigs

Customer feedback and operational experience provided insight into a far-reaching set of issues including pad location and size, safety, drilling efficiencies, design innovations and other enhancements to leverage the benefits of the rig design. By 1993, the rig had a depth rating of 6,600 ft (2,200 m). With each generation, additional quantitative and anecdotal data enabled further improvement of the performance, capabilities and operational efficiencies. Today, with the fifth and sixth generations now deployed, the rig makes up 8.1% of the company’s 246-rig fleet.

The success of the rig can be attributed to technology that controls critical functions, makes the work environment safer for rig crews and improves equipment control. Combined with pad drilling, the slant concept offers fast and simple movement from site to site and the ability to perform more than just a single type of well drilling.

Remote-Control Features

Fully mechanized, using state-of-the-art technologies to minimize manual labor, the rig’s remote-control features reduce the crew’s exposure to harsh weather. These features include:

• Hydraulic tubular handling arm
• Hydraulic power wrenches for make-up and break-out of tubulars
• Hydraulic power wrench carrier
• Hydraulic top drive
• Hydraulic BOP handler and hydraulic pulldown
• Pneumatic tubular slips
• Hydraulic pipe tables for gravity indexing of tubulars and casings to and from the catwalk
• Hydraulic tubular kickers and indexer systems that index tubulars from the catwalk individually into the tubular handling boom, or kick tubulars out of the handling boom and onto storage racks or tables.

In addition to efficiency gains, this high level of equipment control has the specific benefit of drastically reducing connection times. The hydraulic pipe tables lift joints of drill pipe to the catwalk, where the hydraulic pipe arm is located. The indexers then roll the joints onto the catwalk and into the pipe arm, which lifts the joints individually to the derrick. A top drive screws directly into each joint, eliminating the need for an awkward and heavy kelly. The entire connection process takes less than a minute, a fraction of the usual three to five minutes required by conventional single and double rigs, Fig. 2.

Fig. 2. Its top drive and hydraulic pipe- handling arm improve drilling efficiency and crew safety.

Maintenance costs are the same as those for single, telescopic double and jackknife double rigs. The reliability of the system is reflected in mechanical downtime of less than half a percent.

Personnel requirements on the rig remain the same. Someone still needs to operate the controls, run the equipment, perform basic maintenance, disassemble the rig and rig up at the next drill site. The chief difference is that the equipment does most of the work, eliminating the labor-intensive and dangerous component of tubular handling. This not only makes the entire process more efficient, but also improves safety considerably.

Safety

Most injuries to drilling crews occur while they are handling tubulars, with most of those injuries occurring on the rig floor and catwalk. The rig’s control processes help to alleviate this problem. The remote-controlled hydraulic tubular handling boom enables the derrickmen to safely remove and add tubulars and accessories to the drillstring mechanically rather than manually. The boom also provides for the handling of casing. Drilling crews no longer must move tubulars from racks to the catwalk or position them on the rig floor. Beyond that, hydraulic safety lockouts for mast position pinning and crown maintenance reduce the need for personnel to climb the mast, Fig. 3.

Fig. 3. The hydraulic tubular handling system lays down each joint during every trip out.

Drilling Efficiency and Versatility

The rig, which has reached drilling rates as high as 607 ft/hr (185 m/hr), can drill vertical, deviated wells, and underbalanced wells to 9,000 ft (3,000 m). The sixth-generation rig design uses programmable logic controls to monitor the position of traveling blocks and employ a fail-safe disc brake to control the block speed as it approaches the crown. The system also slows the block as it nears the rig floor. This level of PLC control enhances process efficiency and helps prevent potential damage to the rig floor and the crown. A tri-parameter auto-drilling system enables the controls to make adjustments on its own if drilling should deviate from safe operating parameters, thus reducing the potential for human error.

The rig can be moved quickly. For example, a typical double rig racks drill pipe and collars in the derrick in 62-ft stands. Before it can be moved to another well, the stands must be run back in the hole and broken into single joints before laying the pipe down. However, the slant rig’s tubular handling system lays down each joint during every trip out. The tubulars can be moved at any time without breaking down stands.

The rig design is also simple and compact, requiring only eight loads for well-to-well movements on a pad (including boilers and tubulars). In some cases, movements on a pad can be completed within two hours. The rig can also be moved one to two miles in four hours and is easily disassembled for highway transportation.

Since 1990, 19 rigs have drilled more than 5,000 wells, and the global market is expected to grow as the rigs’ benefits become known. They are now used in Canada, Mexico, Venezuela and Kazakhstan.

Feedback From The Field

Over the past five years, Lane Dunham, drilling manager with EOG Resources Canada, Inc., has used the rig for well depths of 1,500 ft to 7,500 ft (500 m to 2,300 m), because of greater flexibility and savings in rig time and operating costs due to the rig design’s efficiencies and ruggedness. He experienced penetration rates of 500 ft/hr (150 m/hr), almost doubling the drilling efficiencies.

Dunham also observed quicker connection times, reporting, "The drill pipe is 45 ft (13 m) long – that’s 50% more than conventional single rigs, which use the standard 30-ft (9-m) drill pipe. This means you don’t have to stop drilling as often to add joints to the drillstring. Connection times typically take one minute with the rig, and that can add up to time saved on the program." Dunham adds that because there are fewer connections, there is less wear and tear on the mud motor and drillbit components, and therefore, most wells can be drilled with one bit.

Perhaps one of the biggest time savers, reports Dunham, is the rig’s design of the remote-controlled tubular handling equipment and the top drive. Rather than manually racking the drill pipe on the rig floor before logging, a hydraulic arm operated remotely by the rig crew lays the drill pipe on the pipe racks.

"Once we are done logging, we can run the casing immediately because the pipe has already been laid down," he explained.

For Dunham, the savings have been up to 12 hr for a typical 6,500-ft (2,000-m) well. These time-savings can be a significant advantage for oil companies with multiple well sites such as Petro-Canada’s 50-well drilling program in northern Alberta. The intensive and demanding program, led by Drilling Superintendent Dough Fletcher, employs SAG-D (steam-assisted gravity drainage) recovery method for extracting oil. In this technique, one horizontal well is drilled on top of another horizontal well. Steam is pumped down the top well to heat up the tar sand so the oil flows from the top well to bottom well.

Since employing the rig in January of 2001, Petro-Canada has been able to reduce mechanical downtime to nearly zero, achieving an overall budget time savings of nearly 30%, and has eliminated lost time accidents completely.

In addition to the same 50% reduction in connection time as Dunham, Fletcher has also found it easier to orient downhole motors and back-ream with the rig.

Petro-Canada has been able to move the rig and spud the next well in less than two hours from the time it’s released from the previous well. With four pads and 50 wells, the rig’s mobility was a significant factor in improving the efficiency of Petro-Canada’s drilling program.

Part of the rig’s efficiency also has to do with the top-drive design, as Fletcher explains, "The rig is much faster because you’re operating at a higher range of rpms and you can have much quicker connection times."

He adds that the top-drive capabilities also reduce the risk of experiencing stuck pipe. Petro-Canada has drilled more than 105,000 ft (32,000 m) in the last eight months and experienced zero stuck pipe incidents. That’s drilling mainly in tar sand, sand and gravel, but also clay, shale and silt.

One of Petro-Canada’s most notable accomplishments has been its safety performance. The program has had zero lost-time accidents among its crew since employing the rig. With 50 to 60 people a day on the rig, drilling at a steady pace, an accident-free record is remarkable. Fletcher says he owes this in large part to the remote-controlled tubular handling features of the rig.

This is true regardless of geographic location. In Venezuela, Pearl Turner, operations manager with PetroZuata, drills in the Zuata field – a heavy-oil sand / shale formation. His drilling program included 240 multi-lateral horizontal wells, which used the rig (PD735). Turner says that with the rig’s air slips and iron roughneck and pipe handling arm, trips can be made without a crewmember other than the driver and derrickman. The driller and derrickman controlling the hydraulics can trip in and out of the hole.

PetroZuata also experienced faster rig moves compared to conventional drilling rigs. Normally, conventional rigs take at least 30 hours to move from pad to pad. The rig (PD 735) used by PetroZuata took only 15 hours to move to another pad. Due to its size and compact design, the rig can be prepared to move in two hours and rigged up in the same amount of time.

Continuous back-reaming was also listed as an advantage of the rig because each joint is handled by making up the top drive into the pipe. He adds that the rig can pick up casing joints as regular joints and run casing without needing a power tong. The necessary torque for the casing can be applied by the rig’s top drive system.

In PetroZuata’s case, PD 735 Super Single rig broke a world record in drilling time, achieving 5,193 ft in one day. The rig routinely drills 8,000-ft measured-depth horizontal wells at a true vertical depth of 2,100 ft without any issues.

Overall, the rig had no significant limitations with the exception of its drawworks and pulling capacity. The small size may pose problems for some of the larger projects.

Although Petro-Canada is using the rig only on horizontal SAG-D wells at a 45° slant for this particular program, the rig also works well on vertical wells. According to Fletcher, the company’s SAG-D program in northern Alberta is expected to be completed four months ahead of budgeted schedule.

The author
	Ron Isinger is the engineering manager for Precision Drilling Corporation Contract Drilling Group, and is based in Alberta, Canada. He has been involved in rig design and construction in the oilfield for 22 years.