Extending the reach in horizontal, deviated wells can recover more reserves
Following are a few of the world records set with wireline-based, downhole robotics:
- Hibernia depth record: Ran to 30,888 ft (9,415 m) in one run
- Longest distance driven in one run: 20,500 ft (6,248 m), in the Gulf of Mexico in a well with an 83° deviation
- Heaviest tool string conveyed (including a Formation Tester): 3,200 lbs (1,451 kg) in a well with a 102º deviation in Norway
- Highest temperature: 388° F (198° C) in Canada.
Coiled tubing alternative
To supplement the wireline tractor, a fluid driven version also is available. This coiled tubing (CT) tractor extends the reach of coiled tubing in highly deviated or tortuous wells where conventional intervention techniques cannot reach. For instance, when using the standard coiled tubing alternative, there are lateral reach limitations due to coil buckle, causing forward motion to stop while running in hole. Furthermore, common effects such as unexpected friction can limit coiled tubing reach.
The fluid-driven CT tractor extends coiled tubing’s lateral reach capability in both horizontal and deviated wells because of the pulling force it puts at the end of the coil. Typically, the CT tractor can extend the reach 1,000 ft (305 m) beyond any other method. It pulls the coiled tubing into the wellbore, overcoming the tendency of the coil to buckle and lock up. This allows the use of a smaller diameter coil with less wall thickness or composite coiled tubing, which reduces the reel weight while reducing problems associated with crane lifting limitations. One CT tractor can apply up to 3,500 lbs of pull force in a standard configuration. Different configurations can triple the pull force to 10,000 lbs when stacking three CT tractors.
Mechanical services
The remotely operated, downhole robotic technologies have expanded beyond the scope of conveying tools in extended reach wells. Since 2003, it has been possible to combine tractor conveyance systems with a variety of downhole robotic tools to perform a variety of mechanical services in horizontal and highly deviated wells, and even vertical wells. There are wireline, downhole robotic systems performing valve manipulations, plug setting/pulling, cleaning and milling operations (with integrated debris bailing chambers), sliding sleeve exercises, and even nipple removing.
HSE benefits
A coiled tubing or wireline tractor is about 20 ft (6 m) long and a few inches wide. Because of small equipment size, interventions can be done with such a high degree of precision that they do not affect the rest of the reservoir or risk damaging the well or the surrounding environment. This contrasts to the very large equipment weighing up to many tons required by traditional intervention methods.
As to logistics, there are ample benefits. The tractors can fly on a helicopter and do not depend on a drilling rig. The equipment requires a crew of two people to operate, especially important offshore where logistical limitations are high.
Because the equipment is remote controlled, it can be operated miles away from the actual point of intervention, which means ecological systems in the area are not affected by the interventions. This is crucial in sensitive areas such as the Alaskan tundra where rolling in heavy equipment could have consequences
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Volume 68 Issue 9
September 2008
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