Coiled tubing drilling has proven to be a valuable asset in petroleum recovery; however, the application of this technology has also posed its own unique challenges. One of the greatest challenges has been devising a way to orient downhole toolface without the ability to rotate the drillstring. The operation of the patented indexing tool described in this paper, only one of two currently available on the market, achieves toolface orientation by using available hydraulic forces already present during the drilling process: air, gas, or mud.
Actuation is achieved through a flow-operated orienter. The mud or other sources of hydraulic power drive a cam that rotates the toolface. The design of this tool also helps to ensure actuation accuracy by restricting drilling fluid flow until orientation is achieved. Flow will resume only when the toolface is in the correct position, thus reducing possible errors.
Successfully in use for five years on Alaska's North Slope, the indexing tool has a simple design and yet is durable enough to withstand downhole stresses and operate in virtually any environment. Technical and operational features, and the benefits of those features to drillers are discussed in detail in this paper. The indexing tool has also been used successfully as a coiled tubing fishing tool.
Its unique design and operation makes it a cost-effective technique in coiled tubing drilling and a unique achievement in downhole technology.
The industry has seen a steady growth in the area of using coiled tubing for drilling and reentering wells, with a corresponding increase in the challenges that exist for the design and development of equipment for use during these operations. Since use of coiled tubing precludes downhole rotation, one of the primary challenges has been how to influence the drillstring so as to direct it to a predetermined geographical subterranean target without being able to rotate downhole from the surface. That is, how to steer toward a target.
In general, two means of accomplishing coiled tubing orientation have been explored. The first method requires use of bent housing motors (fig 1) and pads which can be mechanically/hydraulically actuated from the surface to create deflection and thereby direct the path of the drilling.
The second method, and topic of this paper, is the use of an orienter indexing tool. The orienter is used to rotate the bottomhole assembly with a bent housing motor, (fig 2) using the direction of the bend as the "pointer" for the direction of the Well.
The orienter is used with a bent housing motor to rotate the bottomhole assembly in the direction of the bend. There are several means of achieving this rotation:
Electrically activated hydraulic pumps, which utilize the wire in place inside the coil for the wired guidance systems;
The use of hydraulic lines inside the coil to actuate hydraulic orienter pumps downhole to create rotation; Or,
The use of the mud flow hydraulics to achieve rotation based on piston effect and surface area for transferring hydraulic power to rotational torque.