Increasing Lubricity of Downhole Fluids for Coiled Tubing Operations

Abstract

Abstract The requirement for intervention operations in long lateral-reach wells continues to grow. In 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 about half such a lateral. While 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 CTs reasonable operational range 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 about a 15-20% reduction in the coefficient of friction (CoF) from a generic 0.24 to 0.19. Occasionally, smaller CoF values could be obtained 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 using 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 regain permeability and aging tests have also been performed. Arising from the trials is a new lubricant that reduced the linear CoF by approximately 40-60% (0.10 to 0.14) 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.