DRILLING TECHNOLOGY: Suite of tools, including drag reducer, developed for CT-drilled lateral wells

Increasing CT bit weight

Apr 1st, 2001
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The friction drag reduction tool significantly extends the reach of horizontal well sections drilled with coiled tubing.
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The friction drag reduction (FDR) tool brought to the market by Extech enables the length of extended-reach and horiz-ontal wells drilled with coiled tubing (CT) to be substantially extended. Extech has entered into a cooperation agreement with Smith Services, which uses the tool in its CT tool portfolio.

The FDR tool was developed and tested at Rogaland Research (RF) in Stavanger as part of a joint industry project supported by Saga Petroleum and Shell International Exploration and Production BV. "The tool breaks the friction in the CT by creating oscillations and reversing the movement of the coil," explains Extech President Sonny Sola. "The theory was known about for a long time, but the trick was to make it work in practice."

The tool, which incorporates a unique patented concept, uses fluid flow to generate axial oscillation in the CT and bottom-hole assembly (BHA), thus significantly reducing the friction forces. In acceptance tests carried out at RF's test facilities using 600 meters of 1.75-in. CT and a BHA weighing 600 kg, the friction force during run-in and pull-out from the 7-in. test well was reduced by up to 80%.

The tool is a double-acting hydraulic cylinder with mechanical valves that cause a minor reciprocating movement. A set of springs facilitates the operation of the valves. The mass of the BHA below the friction drag reducer in the drilling string directs most of the oscillating action back up the CT string. The tool is available in various sizes ranging from 2 1/16-in. to 4 3/4-in. outside diameter, with corresponding overall lengths of 24-in. and 74-in.

It is possible to control the movement of oscillations in a well section up to 10,000 ft long, says Sola. The tool makes it possible to achieve up to 6,000 ft in increased reach in certain horizontal wells. Alternatively, it can be used to increase the bit weight by up to 250% in CT drilling, or to increase the force available to transport other tools, such as packers or fishing tools, through long horizontal wellbores.

Simulation modeling

Extech - Extended Reach Technology AS - has also developed software that permits the whole CT operation to be simulated before it takes place. "This way, we can be 97% sure we can do a job before we start," says Sola. A shock absorber has also been developed to shield tools placed downstream of the FDR in the CT string from the vibrations.

Following completion of the prototype development, the company has spent the last 12 months further developing the tool for commercial application. It is proving a versatile piece of equipment, and in different configurations it is now also used in sand clean-out, logging, perforating, mechanical manipulation, and drilling operations.

Extech has now extended the use of the technology to further applications, though these have not yet been accepted for field operations. They include a CT hydraulic tractor known as the FDR Tractor, for which purpose the stroke length has been extended from 4-in. to 36-in. The FDR Tractor develops a high traction force of 10,000-18,000 lb, and making 30 strokes a minute, makes rapid progress down the wellbore. The tool is available in outer diameter sizes of 2 7/8-in to 4 -in.

Another new development, which was also backed by Shell, is an abrasive jet milling system. With some adjustment of the design and the use of a patented milling bit, the system can be used for through-tubing re-entry drilling of multilateral wells.

The bit, which acts by eroding the steel casing, has a fast penetration rate - 1.9 meters per hour, Sola says. Abrasive sand in gel form is delivered to the bit through a high-pressure inner string. The milling system can be installed in any CT unit in a matter of hours, Sola says.

Non-drilling functions

The FDR can also be used in non-drilling CT operations, for example, in clearing pipelines blocked with wax or hydrates. Here again it extends the distance over which such operations can be made.

Extech is now focusing on extending the technology beyond CT operations. A number of future uses have been identified. For example, during completion operations, the tool can be put inside the liner and used to pull it along the hole. Other applications include conventional drilling and ultra-short radius drilling.

Extech currently has some 60 FDRs rented out to Smith Services for use in its eastern hemisphere operations, and receives a share of profits as payment. The company is open to negotiating arrangements with other service companies in areas not covered by the agreement with Smith Services, Sola says.

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