A small, portable top-drive system, which can be installed in as little as 4 hr with little or no derrick modification, can help land rigs drill difficult or extended reach wells, according to Tesco Drilling Technology in Calgary.
The portable top drive is typically installed during rig up before the well is spudded or while waiting for cement after the surface hole is drilled.
Some of the obstacles to installing top drives on land rigs have been the type of equipment available, the need for major derrick modifications, and the capital cost.
As an alternative to buying a top drive, drilling contractors and oil companies can lease Tesco's top drives for short-term or long-term projects.
Tesco rents five of its top drives to operators and contractors.
The rental rate is about $3,000/day, varying with contract duration and location.
A complete new unit costs about $1.1 million, depending on size, configuration (land skid unit or helicopter transportable), and accessories.
Tesco Drilling Technology's portable top drive systems use hydraulic power and an independent diesel engine as the prime mover. Thus, they can operate on either electrical or mechanical rigs.
The use of hydraulic power instead of electric motors makes the top drive small enough to fit into a wide range of derricks, even those on small land rigs.
The units are designed for rigs that must be dismantled and moved after each well. To reduce the amount of derrick modifications, the systems are designed to fit on any rig that can make a conventional kelly connection with a 42-ft kelly and a 31-ft single. The compact unit can operate in the tapered area above the monkey board.
A free-standing track system eliminates reactive torque in the derrick. Thus, no welding on the mast is required for installation, and the only modification is for slightly more room at the monkey board, according to Tesco.
The first portable skid package went into the field in 1992.
In its first 6 months of operation, this unit was installed on six rigs, drilled seven horizontal well, and operated for about 2,000 hr with only 12.5 hr total downtime.
UNIT NO. 5
Talisman Energy Inc. contracted the new unit No. 5 for 1 year for use in a deep-gas development project in the overthrusted foothills in the Sukunka region of Northeast British Columbia.
Many of the wells in this area are deviated and have sloughing shale sections. Reaming and backreaming are required on many wells.
In this area, Talisman air drills certain intervals to re duce drilling costs (Fig. 1). With a conventional rig making connections every 30 ft, much time is spent losing and then regaining pressure in the air system at each connection.
The top drive reduces total drilling time because drilling is performed with stands, and fewer connections are required. Additionally, reaming with stands is more effective than with singles.
Fig. 2 shows the single skid containing the top drive, hydraulic service loop, torque track, diesel engine, and hydraulic service system.
The diesel engine supplies 800 hp to the hydraulic system.
The hook load is rated to 350 tons, and the top drive can deliver up to 35,000 ft-lb of torque.
The extend mechanism allows the driller to move the top drive over the mousehole for making mousehole connections, handling bottom hole assemblies, and helping the derrickman at the monkey board (Fig. 3). The elevator links can tilt forward for tripping and backward for reaming to the floor or picking up joints.
UNIT NO. 6
Unit No. 6 was sold to Parker Drilling Co. for use in Southeast Asia. According to Tesco, the unit was designed for Parker Drilling as the world's first complete helicopter-transportable top drive system.
The 5-in. top chive is rated to 500 tons and can generate up to 40,000 ft-lb of torque. The unit is 11 ft long and weighs 10,000 lb. The power unit supplies 800 hp to the hydraulic system.
The entire unit, including the power pack, can be separated into 5,500-lb loads for helicopter transportation to remote drilling locations.
Following testing in December 1993, the unit was broken down into smaller loads and flown from Calgary to Singapore in a Boeing 747 aircraft.
The unit was put into service earlier this year.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
