NORWAY:

Advanced wells from traditional rigs

Nils Reimers, Maritime Hydraulics, AS and Dag Haverstad, Top Drives

Directional drilling technology has emerged from large offshore developments and can now become a keystone for new onshore and shallow water developments. It provides better drainage as well as access, but it also puts new demands on the drilling rig, because much of the well is drilled without rotating the drill pipe.

An advanced power swivel or top drive system is required to orient the drillstring from surface to allow a bent, pressure-powered motor on the bottom to kick the deviation up from vertical. High rotation speeds and high continuous torque capacity are later required to overcome friction and help the cuttings to surface as the well extends out horizontally.

Obviously, when the rig is not adapted to such requirements, efficiency drops radically. With more than 70% of the well being deviated, the economics become challenging.

Technology migration. Maritime Hydraulics AS (MH), a drilling technology supplier to the North Sea, started a study to produce a radical portable top drive in 1998. The goal was to make a "no compromise" unit and even enhance the latest solutions from extended reach and horizontal wells. This, of course, represented a significant challenge when combined with a tough unit-cost target. MH-Pyramid, Inc., the U.S. branch, provided insight into the operational and dimensional parameters, while Rockwell Inc. and MH engineering resources worked to come up with motor solutions.

Portable top drive allows directional drilling using smaller, onshore and shallow water rigs.

Some specific user requirements for maintenance and logistics were also given. New data proved that safe access was the best way to ensure proper maintenance. That in turn would improve reliability, and several new solutions for better and safer access were doubled with protection functions. A modular design philosophy was also applied to offer module exchange as an alternative to onsite repair.

After six months of field trials, the PTD 500 AC is now finally presented in detail. The machine is rated to 500 t and is powered by one or two 800-hp AC motors. Continuous trials have been conducted on a land rig operated by Crosco in Croatia. Crosco is now upgrading three rigs with similar machines.

Unique directional drilling features. The PTD 500 AC is supported by a remote variable frequency unit. A small, all-weather control panel controls the unit from the rig floor, including the digital tool-face orienting system. This infinite orientation system was developed with support from users with long experience in a challenging environment. The AC motor makes obsolete the airflex brakes required for other power sources and makes the full motor torque available at zero rotation. This makes it possible to orient even extreme fluid displacement motors over unlimited periods of time. Other control features are included for free rotation while tripping out of hole.

A 2 x 800-hp version of the product is designed to lift the rig to a level where the available rotary torque makes the rig the strongest around. This machine allows extreme reach, rotary steering and "big bite" drilling bits. One such machine is now in the field.

Efficiency and safety. The extensive functionality combined with compact design has been obtained through close cooperation with suppliers. All liners have designated quick-connectors and an integrated function control unit on the machine itself removes the need for multiple control lines. Even the two-motor version takes less room in the derrick than most units with half the power. Weight is reduced accordingly and the rig-up/down time is less than 12 hr.

In addition to the safe access features, the bi-directional link tilt system for drill pipe handling eliminates all manual interference with the machine. This is critical with the high rotary forces available. The torque-wrench is designed to make and brake 60,000 ft-lb.