Coiled Tubing (CT) intervention operations in extended reach wells (more than 10,000 ft in the lateral length) have become quite common in North America. In general, a 2.0″ CT has enough weight to reach the target depth in a 5,000 ft lateral. Therefore, to reach a 10,000 ft lateral, the use of metal-to-metal friction reducer (MFR) or lubricants will be required to work in conjunction with downhole extended reach tools. However, in some interventions, only lubricants can be used, without the downhole extended reach tool.
Various lubricants are available in the CT industry. Based on field operations, a typical lubricant could reduce the coefficient of friction (CoF) by about 20%, while a high performance lubricant could reduce the CoF by up to 50%. In order to reach the bottom of a long lateral well, it is imperative that coiled tubing operators are using the most optimal lubricant in correct applications.
In this paper, a linear friction apparatus was introduced and used to evaluate the friction reduction performance of 7 lubricants at various concentrations. With a test fixture, both the static and dynamic CoFs were measured. In addition, the performance of the lubricants was also evaluated with the introduction of polyacrylamide (a fluid friction reducer, FR), the salinity, and sand in the fluid system.
The test results indicated that only a few lubricants could effectively deliver CT extended reach. In general, the static CoF of the lubricants was 10% to 30% higher than the dynamic friction. An increase in water salinity and the presence of sand in the wellbore had a negative effect on the performance of the lubricant.
A higher lubricant concentration resulted in a lower friction coefficient, especially for the high salinity and sand conditions. However, the use of a fluid friction reducer could be detrimental to the lubricant friction performance when the FR concentration is more than 1%.