Lubricants and accelerated test methods for expandable tubular application

Tubular expansion for well construction is a process accomplished by pulling (or pushing) a mandrel through a pipe downhole. This can be described as a tribological system that consists of the pipe and mandrel surface, a lubricant layer and a fluid. A successful expansion requires a lubricant that, not only ensures manageable expansion forces, but also provides a robust solution for downhole application. The desired lubricant should separate the mandrel from the pipe during a downhole plastic deformation and be thermally stable, chemically compatible with drilling fluids and withstand a long shelf life in harsh environments. This paper describes a process for optimal lubricant selection using accelerated testing with a dedicated setup that mimics demanding down hole conditions during expansion processes. Three commercially available lubricants, commonly used in tubular expansion or other similarly demanding applications, and a novel solid lubricant, developed specifically for tubular expansion applications, were tested. The test campaign focused on the influence of drilling fluids and temperature on the friction, wear and lubrication efficiency. The novel solid lubricant showed superior performance compared to conventional lubricants demonstrating lower friction factor with expansion forces between 13% and 49% lower than with conventional expandable tubular lubricants, outstanding resilience in coping with alien particles in the drilling fluid, ability to mitigate the onset of stick-slip phenomena and good corrosion protection for the expandable tubular. It was therefore selected and successfully used in field-trial applications.