Coiled Tubing Technology for Extending the Reach in Sand-Screen-Completed and Openhole Wells
Authors: Elrashidi Karim , Livescu Silviu , Watkins Tom , Phan Truong 
Published: November 2016

Well intervention operations in extended-reach wells with sand, proppant, or other fill or in openhole wells are becoming important especially in the Middle East, where many exiting long openhole laterals need to be stimulated to maintain existing production. New laboratory and field results with a lubricant and a 2 ⅛-in. fluid hammer tool are shown to significantly increase the coiled tubing (CT) reach in laterals with sand. These results can be extended to openhole wells, as the coefficients of friction (CoF) between CT and metal casing completely covered with sand or an openhole are similar.

While theoretically increasing the CT diameter could extend the CT reach, in practice, this may not be always possible due to completion size limitations or logistical challenges with onshore road transport or offshore crane lifting/deck loading limitations. Hydraulic technologies such as fluid hammer tools and downhole tractors have extended the CT reach significantly in cased wells, but their successful application in long openhole laterals has not been reported in literature. In addition, metal-on-metal lubricants are used in cased wells with laterals longer than 10,000 ft, but their application in similarly long sand-screen-completed or long openhole laterals is much more limited due to the higher friction.

In this paper, laboratory and field results with a lubricant and a new 2 ⅛-in. fluid hammer tool are presented for sand-screen-completed wells. The lubricant was initially tested in laboratory for compatibility with representative formation rock samples. Given the fact that the lubricant itself contains a clay stabilizer component, it performs better than other commercial lubricants tested in low-, medium-, and high-permeability rock samples. The fluid pumped through the CT and 2 ⅛-in. fluid hammer tool creates pressure pulses with frequency of 8 Hz by opening and closing a valve inside the tool. These pressure pulses generate axial and radial forces that act simultaneously on counteracting the friction force between the CT and the formation: the axial force increases the bottom hole assembly (BHA) tensile load; and the radial force reduces the normal contact force, and thus the friction force. Combining the effects of the lubricant and the new 2 ⅛-in. fluid hammer tool in a pre-job CT modeling software results in CoFs reduced by 50-60%, from a default value of 0.36 without any friction reduction technology to 0.15-0.18 when both the lubricant and the tool are used. Laboratory testing with the lubricant alone showed that CoF between CT and a surface completely covered by sand decreases by 40-50%, from the default value of 0.36 to 0.18-0.22, for temperatures between 20 and 98°C. These CoFs were validated against field data from a sand-screen-completed well in the North Sea. Friction reduction of this magnitude is expected to significantly extend the CT reach in long openhole laterals.

In this paper, the lubricant and the new 2 ⅛-in. fluid hammer tool are briefly described and the data acquired during the laboratory testing and field operation is discussed. These results improve the current industry understanding of the CT friction in sand-filled cased wells and openhole wells and show great benefits in using the extended-reach CT technology consisting of the lubricant, the 2 ⅛-in. fluid hammer tool, and the CT modeling software for extending the CT reach in sand-filled cased and openhole laterals.