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

The multiple advantages that the RRL concept will bring to Coil Tubing Underbalanced Drilling versus both jointed pipe and the conventional coiled tubing market are illustrated below.

Ability To Remain Underbalance
Without Connections
The nature of coil tubing allows continuous bottom hole pressure conditions to be maintained without potentially going over balance during a connection. A connection using jointed pipe due to the change in the bottom hole pressure regime caused by cycling the pumps can lead to the well going overbalance thus negating any advantages of underbalance drilling.

This risk is mitigated with the RRL unit where steady state bottom hole conditions can be maintained and monitored providing effective bottom hole pressure management.

Increased Overall ROP
After a connection with jointed pipe a period of time is required to reach steady state bottom hole pressure conditions before drilling can commence. This obviously has a negative impact upon the actual time spent on bottom. This issue is multiplied when a Kelly drive rig is used as opposed to a Top Drive due to the increased number of connections (2/3 more).

The ability to trip at speed and safely with coil tubing is unmatched by jointed pipe and these benefits are harnessed by the RRL unit.

Coil tubing is limited by its ability to transfer weight to the bit in long horizontal sections. This is due to the effect of frictional lock up on the coil preventing steady transfer of weight to the bit. This is overcome by either using expensive lubricants or by running to bottom at high speed and then allowing the weight to decrease as he coil eventually locks up. This is repeated and has the effect of excessive motor wear by stalling, limited ROP and excessive coil fatigue by the constant picking up of the coil tubing while it is under full pump pressure.

Overcoming the frictional lock up allows a steady transfer of weight to the bit which overcomes the problems outlined above. In addition much of the lock up is generated by cuttings bed build up which drags on the coil in the horizontal section, this is counteracted with the RRL unit due to its ability to rotate both while drilling and while tripping out of the well.

The four advantages of the RRL unit outline above will lead to an increase in overall ROP, reduced well times and reduced costs.

Decreased Motor Wear
The reduced number of connections and variations in bottom hole pressure decreases the number of potential motor stalls which in turn has a positive effect upon motor life (increased MTBF) and maximises the amount of on bottom drilling time.

Increased Coiled Tubing Life
Coil tubing fatigue is a limiting factor to coil tubing drilling deployment due to both cost and logistics. Modelling of the RRL coil tubing drilling system has shown a potential increase in CT life of in excess of 300%.

The fatigue of coiled tubing is the result of the cumulative strain damage that occurs from coiling, uncoiling and straightening the tubing while running in or pulling out of a well. The easiest and most logical way of extending the fatigue life of the coiled tubing, would be to reduce the number of coiling, uncoiling and straightening operational segments applied to the coiled tubing while running in or pulling out of a well. A conventional coiled tubing unit normally applies six (6) fatigue operational segments to the coiled tubing during a round trip.

These are:
1. Off the reel and running into the well
2. Strait to bend running into the gooseneck,
3. Bend to strait leaving the gooseneck entering into the injector head and well and vice versa pulling out of the well.

By removing the gooseneck and placing the reel directly above the injector, 66.6% of the coiling, uncoiling and straightening operational segments are removed and thereby extending the fatigue life by 300%.

However during a “Real Time” operation of this type of coiled tubing unit, a unit which drilled close to 100 wells (Transocean Canada). Experience proved that the unit could in fact cycle the coiled tubing close to 400% over the limits on the standard fatigue simulations used by the industry.

Read about a research project done in conjunction with Professor Steve Tipton of the University of Tulsa in Oklahoma, that provides real time fatigue monitoring of coil whilst stationary and during rotation.

The additional cycle life came from not running the coiled tubing over the gooseneck thereby putting a higher strain on the coiled tubing then spooling on and off the reel.

The benefits of this in reduced development costs are obvious due to the reduction in the number of reels that would need to be purchased in a campaign. A secondary benefit would be an overall reduction in well time as less cuts of the coil would need to be made on a single well to move the fatigue point in the string of pipe.

This has implications for activities where the movement of the pipe is minimal during operations and repeated cycles are made on a single part of the coil (fishing, milling, sidetracking, slow hard rock drilling).

 

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