RRL Advantages Remain Underbalance w/o Connections Increase In Overall ROP Decreased Motor Wear Increased Coiled Tubing Life Increased Annular Velocity Increased Production Improved Hole Cleaning Uses Low Cost BHA Drill A Tanget Section Sidetracking Environmental Benefits

Increased Annular Velocity
The RRL coil size is 3.25 inch which will allow it to comfortably support a 4 ¾” BHA which in turn will allow it to drill a six inch hole.

Six inch hole sizes have been drilled with 2 7/8” coil in Eastern Alberta but problems have been encountered with this hole size due to low annular velocities between the 2 7/8” coil and 7” casing which has led to cuttings build up and hole condition issues.

The RRL coil size combined with rotation will mitigate against this.

Increased Production
Coil tubing drilling is firmly established as the best method to safely drill underbalance due to the absence of connections and direct human interaction with the tripping process. This has though in the past been constrained by hole size and hole cleaning ability. The ability to drill a six inch hole in a reservoir allows potentially increased production from a single well head, this in turn will lead to a lower density of wells through a field and therefore lower development costs.

Currently the ability to drill up to a 4 1/8” hole (RWD bit with a 3 1/8” BHA) with 2 7/8” coil limits the potential gas flow due to the increased pressure drop associated with the small wellbore size. If the wellbore size can be increased then the pressure drop associated with the flowing gas is less with a reduced probability of going overbalance in the well bore.

This is particularly pronounced in the horizontal well bore where the heel – toe effect can lead to the well being underbalance at the bit but overbalance at the heel of the well due to the frictional effect of the flowing gas from along the length of the well bore. This effect then negates any potential production increases associated with underbalance drilling and reduced reservoir impairment.

Improved Hole Cleaning
The major limitation of coiled tubing drilling is hole cleaning, this has always been considered a limiting factor in its deployment. To overcome this traditionally an intensive wiper trip philosophy has been adopted. This comprises a short wiper trip every thirty feet followed by a wiper trip to the shoe every three hundred feet or less depending on hole conditions. This had three negative impacts upon the drilling operation.

• Extended motor usage, as you are constantly flowing through the motor while wiper tripping rather than drilling.

• Increased coil fatigue due to the increased number of cycles picking up the coil for the wiper trips.

• Decreased overall rate of penetration due to less time spent on bottom drilling

The rotation of the coil overcomes many of the hole cleaning issues associated with coil tubing drilling. Even low RPM (5) has been noted to show improved hole cleaning in ultra short radius drilling therefore the planned RPM of twenty should bring marked advantages in removing the drilled materials from the wellbore.

The idea of slowly rotating coiled tubing to improve hole cleaning, increase reach, increase directional control and most importantly reducing torque and drag, came from the experience gathered from the ultra short radius drilling campaigns in Canada. Experienced proved that rotating 2-7/8” and 3-1/2” drill pipe between 1 to 5 RPM during drilling, dramatically improved hole cleaning, reach, and torque and drag values compared to slide drilling. (Paper no. 97-144 from CADE/CAODC Drilling Conference).

This led to the idea of developing a concept for the rotation of the coiled tubing surface equipment, thereby allowing the reel and injector to be slowly rotated during the drilling and wiper trip phases. Most of today’s coiled tubing drilling experts agrees, that adding the ability to rotate the coiled tubing during wiper tripping will increase hole-cleaning capability due to the increased swirling action created by rotating the coiled tubing and the BHA (bent sub).

Wiper trips would still be a part of the well cleaning philosophy but would not be required on as frequent a basis as the cuttings would be kept moving whilst the pipe is rotated. The coil tubing would be tripped out of the well whilst circulating to aid in well cleaning.

When compared to the RRL unit a traditional jointed pipe rig would have to back ream and pump out every connection while tripping to achieve the same effect. This is both time consuming and would make staying underbalance potentially very difficult which would again have a negative impact on any production benefits. MORE»

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