Hybrid coiled-tubing system offers stimulation option for extended-reach wells

A new hybrid coiled-tubing (CT) system is enabling the efficient use of CT in extended-reach wells. Fraser McNeil of Halliburton discussed the system and its application during the 2011 SPE/ICOTA Coiled Tubing and Well Intervention Conference and Exhibition last week in The Woodlands.

Deeper well completions with extended-reach horizontal laterals have presented unique problems when needing to perform live well intervention operations, Mr McNeil said. While larger CT sizes are preferred in order to achieve higher treatment rates and cleanup rates and in getting to the target depth when running in hole, “the ever-increasing depths of the wells present difficulties for large CT.”

A hybrid system that uses both CT and jointed pipe has been developed and applied in the Bakken Shale west of Westby, Mont. The goal of the system, according to Mr McNeil, is to combine the advantages of CT and jointed pipe in extended-reach wells and eliminate the disadvantages.

The primary disadvantage of a CT drilling system is its inability to reach target depth on long, extended-reach wells while applying sufficient weight and torque at the bit to drill. Current methods that enable to CT to drill at these depths are more expensive than conventional systems and may not deliver the desired results, according to Mr McNeil.

Also, when limited to the use of small outside-diameter (OD) CT, the fluid flow rate pumped may be limited by pressure and velocity, which limits the stimulation processes, especially in deep-reach wells, he said.

Jointed pipe offers some advantages for live well intervention operations in deep-reach wells as it provides large-OD pipe with higher pump rates and lower pump pressures, has a higher pull capacity, carries less risk of cutting and damaging pipe, and can achieve deeper horizontal penetration before lock-up.

“The hybrid system is designed to use both CT and jointed pipe in a single workstring,” Mr McNeil said. “This enhances the capabilities of jointed pipe by reducing the overall job time and improving safety and efficiency for deeper wells, multi-zone fracture treatments, cleanout service applications and completion tubing installation.”

The solution was applied in the Bakken, where optimum production is achieved by creating numerous multiple transverse fractures and each fracture must be contained within the lower, middle and upper formations. The hybrid system enabled low-rate, hydrajet-assisted fracturing to limit unwanted fracture growth, Mr McNeil said.

The CT and jointed pipe that made up the system were run successfully without chemical or mechanical aid to target depth, and the time to reach target depth was greatly reduced compared with the use of standard stick pipe. The time to move between zones was also decreased. Eighteen zones were completed in four days.

For more information, please see SPE 142769 “New Hybrid System Brings the Flexibility of Coiled Tubing to Long, Extended-Reach Wells,” by F. McNeil, S.D. Lindsay, R. Lyons and R.P. Gracey.