Engineers continue to develop and implement new technologies to improve drilling in emerging land plays and in ever-increasing water depths.

AC power

Nabors’ PACE M-Series rigs have AC-powered components. Photo courtesy of Nabors Drilling USA LP.

More rigs are moving to AC electric power. This particular innovation began offshore and is now being commoditized on land rigs.

AC-powered motors have highly responsive and accurate speed and torque control. AC drives use induction motors, which are efficient, relatively quiet, and relatively low-maintenance.

In 1994, Shell and Statoil were the first to install an AC drilling drive, on the Troll A platform, designed by ABB AS. Now, 15 years later, AC drilling systems are being incorporated into a new fleet of drillships to ply Brazilian waters.

DMPT drillship

Petrobras’ need for 14 new drillships has spawned innovative collaboration.

Brazil’s Projemar and Netherlands-based Huisman are promoting a new drillship design capable of drilling with a subsea blowout preventer (BOP) in water to 10,000 ft (3,050 m) deep, or with a surface BOP system in water to 15,000 ft (4,570 m) deep. The new drillship, to be built in Brazil, will be able to drill to a total depth (TD) of 40,000 ft (12,190 m).

The vessel will incorporate a dual multipurpose tower (DMPT) with a vertical box structure instead of the traditional lattice-work derrick. The box is designed to provide both structural support and storage, thus saving deck space.

Petrobras already has 11 drillships under construction at Samsung and Daewoo yards in South Korea with delivery dates from June 2010 to June 2012. Additional future rigs are expected to be built in Brazil.

New land rigs

Bandera Drilling Co.’s new AC-powered triple rigs are customized and designed for horizontal drilling and can reach 15,000 ft TD. This design features variable-frequency drive, derrick with 500,000-lb hook load capacity, Canrig 275-ton 500-hp AC top drive, Iron Derrickman, iron roughneck, and 1,200-hp drawworks from RigTech with Eaton airbrakes and hydraulic disc brakes. Gray Oil Tools designed the iron roughneck specifically for this rig. It is a remotely operated system that replaces manual tongs and pipe spinner.

The prototype of the ST-12000 design, Rig 9, was completed in early 2009 and has been drilling both horizontal and vertical wells in Texas.

Coiled tubing drilling

Xtreme Coil Drilling Corp.’s innovative coil-over-top-drive (COTD) dual-purpose land rigs drill with larger coil to reach hydrocarbons in deeper horizons. Xtreme has three rigs in the US Rocky Mountains and 10 rigs in Mexico (four of those added this year). The company recently customized a rig, XTC 200DTR-PLUS, for Middle East drilling. This rig has an AC-powered, 200,000-lb Xtreme Coil injector head, to which the company added new functionality to allow hydraulic manipulation and connection to a live well pressure lubricator. The mast was modified to handle lubricator assemblies of up to 120 ft (37 m) for pressure deployment of downhole tools. Xtreme also designed a new substructure for the rig that will elevate it above typical wellheads in the Middle East and North Africa.

Sometimes combining technologies can lead to new breakthroughs. XTO Energy recently drilled wells in the Permian basin with an Xtreme COTD rig and customized 77?8-in. polycrystalline diamond compact bits from Ulterra Drilling Technologies. In the second hole, XTO set a field record (Prentice NE Unit), drilling the production section (about 4,300 ft or 1,311 m) in only 53.25 hours, breaking the rotary drilling record of 67.5 hours.

An Xtreme COTD rig achieved similar breakthroughs drilling in the Wattenberg field of the Denver-Julesberg basin. The rig clocked “spud-to-spud” times of just over 50 hours in 8,000 ft (2,440 m) directional wells. The operator said technological advances were fundamental to achieving time and depth improvements.

Improving rig moves

Due to a newly developed, comprehensive rig move plan, PACE M-Series rigs have achieved record times for rig moves (less than a day) and high-performance skids (less than 2.5 hours in Colorado and North Texas).

Nabors Drilling USA LP launched the new programmable AC electric rigs in 2007, and there are now 50 working in North America. These compact rigs feature 1,000-hp AC drawworks with regenerative AC braking, AC-powered mud pumps, Canrig 6027 AC integrated top drives, and climate-controlled driller’s cabins. The rigs are designed to drill efficiently and move rapidly.

Slide drilling

Drilling directional wells relies on using either rotary steerable systems (RSS) or slide drilling. In many cases, RSS may either not be available, or the operator may decide the cost cannot be justified. Directional drilling is then accomplished with a downhole mud motor and a bent sub. Slide drilling is often inefficient and risky because of the torque and drag and chance of excessive tortuosity.

Canrig Drilling Technology Ltd. has developed a new directional steering control system — Rockit — that facilitates oscillation control, tool face orientation, and bearing offset control when slide drilling. The Rockit control screen also provide measurement-while-drilling toolface data integrated with steering information, a toolface advisory sector showing the driller where to maintain the toolface, and a driller’s scorecard that generates a quality metric on toolface control.

The Rockit system has been used in the Barnett, Haynesville, and Woodford shale wells and also in western Wyoming’s Pinedale field.

RSS tool

Complex drilling will increasingly rely on rotary steerable systems and fine-tuning bit behavior to drill intricate well geometries. Smith International has developed a 4-D modeling tool to predict drilling system performance and behavior — Integrated Dynamic Engineering Analysis System (IDEAS). Hart recognized this development with a Meritorious Award for Engineering Innovation earlier this year.

Risers, or not?

Offshore wells are commonly drilled with 21-in.-diameter, low-pressure drilling risers, but increased water depths have approached the practical (engineering and cost) limits for such large risers. Wells drilled in ultra-deep water need longer drilling risers, and high-pressure slim risers have been under discussion for years as a cost-effective solution.

Riserless drilling with a closed-loop circulation system is also being considered. Reelwell AS is promoting riserless drilling with its Reelwell Drilling Method (RDM) as a competent tool for managed pressure drilling. According to Reelwell, RDM is particularly useful when drilling in environments with narrow pressure margins such as deep water, high-pressure/high-temperature (HP/HT), and depleted reservoirs.

Deep drilling requires HP/HT equipment capable of withstanding high pressures and high temperatures, particularly problematic for electronics and seals. Handling long well bores, whether vertical or horizontal, requires derricks and top drives with immense hook load capacities and sufficient racking space for tubulars. Riserless drilling eliminates the need to stack and rack large drilling risers.

Deepwater risers

Houston-based MCS International Ltd. has carried out advanced subsea engineering research and development that has led joint industry projects (JIP) to collaboratively develop solutions. The company spent four years working on a JIP on flexible risers in the Gulf of Mexico and began looking at API code revisions in 2001.

API’s Recommended Practice for Design, Selection, Operation, and Maintenance of Marine Drilling Riser Systems (16Q) was issued in 1993 and governs the use of driller risers. This year, MCS revised API RP16Q for the second edition, updated to include newly developed procedures for deepwater drilling riser design, including weak-point analysis, drift-off analysis, soil-structure modeling, and coupled analysis. MCS also produced an associated Technical Report (API 16TR1) containing methodologies and worked examples.

This and other flexible riser work was the subject of press conferences and a number of technical sessions at the Offshore Technology Conference (OTC) in May of this year.

As with many advances in technology, those in the riser domain are happening steadily, not dramatically. As Dr. Pieter Wybro, deputy chief executive and chief technology officer of INTECSEA, said at OTC, progress is neither linear nor rapid, “We make changes by nudging the limits, not by leaps and bounds.”