Mechanical friction is one of the most important aspects in highly inclined wellbores such as extended reach drilling (ERD) and through tubing extended reach drilling (TTERD). Friction caused by the contact between the drill string and the well casing or borehole is dependent to the drilling weight and fluid properties. Drilling fluids play an important role on mechanical friction and using oil based drilling fluids with higher lubricity can reduce torque and drag and minimize stick and slip concerns. Reducing mechanical friction will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells.
This paper presents results from experimental laboratory tests where mechanical friction has been investigated in non-circular wellbore geometry. The experiments have been conducted as part of a research project in the tribology lab in Technical University of Luleå. The project was sponsored by the Research Council of Norway and four oil companies.
Friction behavior has been investigated for two different drilling fluids; water based and oil based drilling fluids both with and without solid particles. A pin on disc setup was used for these experiments where a spherical steel pin was sliding on a rotational disc made of granite. Friction force has been measured in constant sliding speed and in presence of particles in wet condition. The test results show that mechanical friction is smaller with oil based than water based drilling fluids in the presence of solid particles. In addition, the friction coefficient depends to the particle types and is higher when solid particles were added to the lubricants.
Such experiments in a tribology laboratory are important to identify the effect of drilling fluid on mechanical friction from a basic point of view isolated from the other wellbore parameters. Test results and the experimental approach could therefore be of value for any one working with drilling and well construction.