Summary
The requirement for intervention operations in long-reach lateral wells continues to grow. In the US, it is not uncommon to be asked to run coiled tubing (CT) in 10,000-ft laterals. In general terms, a 2-in. CT typically has enough weight reserves to perform work to approximately half such a lateral. Even though increasing the CT diameter remains a theoretical option to improve reach, practically, it creates logistical challenges with both road transport and offshore crane-lifting/deck-loading limitations. Although fluid-hammer tools and downhole tractors have extended the reasonable operational range of CT significantly, they also increase circulating pressures and operational complexity. To reach a 10,000-ft lateral, the use of metal-on-metal lubricants will be required to work in conjunction with the other systems.
Obviously, the use of lubricants is not new. Typical real-life results of current systems are approximately a 15 to 20% reduction in the coefficient of friction (CoF) from a generic 0.24 to 0.19. Occasionally, one could obtain smaller CoF values in the field. However, these actual results compare poorly to laboratory testing with a high-pressure rotational friction test.
An extensive set of laboratory measurements was carried out with a linear-friction measuring device to understand and quantify the mechanical, chemical, and thermal metal-on-metal wet frictional effects. Particular attention was paid to the synergy between lubricants and the other commonly circulated brines and fluid friction reducers. Other tests, such as regained-permeability and aging tests were also performed.
Arising from the trials is a new lubricant that reduced the linear CoF by approximately 40 to 60% (0.10 to 0.12) under downhole conditions. Friction reduction of this magnitude is expected to make it feasible to run CT in 10,000-ft laterals without the use of fluid-hammer tools or tractors.
The paper details the new testing method, technical background of frictional drag, existing lubricant case histories, the new laboratory data, details of compatibility tests, and two new-lubricant case histories.