A Novel Tribometer Designed to Evaluate Geological Sliding Contacts Lubricated by Drilling Muds

Abstract Great interest in improving lubricity, or reducing friction, of drilling muds used for horizontal oil well drilling is motivated by increasing the horizontal reach that can be attained by a single drilling site. However, there are a limited number of commercially available devices that can be used to evaluate novel drilling mud solutions under sliding conditions that accurately replicate those encountered in the field, and those that are available are often prohibitively expensive. Here, the design of a low-cost lubricity meter, or tribometer, is documented. The purpose-built tribometer is capable of varying rotating speeds, applied normal loads, temperature, and counter surface materials. In particular, the counter surface of the tribometer can be either a steel surface, as is often used in the industrial lubricity meters available in corporate laboratories, or a geological core specimen taken from the drill site. The novel instrument was then used to evaluate four commercially available water-based drilling fluid lubricant additives, dissolved in distilled water, for both a steel-on-steel contact and a steel-on-rock contact. The steel-on-steel contact shows that the tribometer replicates the results of tests typically conducted in drilling fluid labs, thus verifying the performance of the newly developed tribometer. Additional results show that the friction and performance of the lubricant depend significantly on the materials used: steel-on-steel contacts show much lower friction than steel-on-sandstone contact. Finally, a weak dependence on the applied load is shown for a number of lubricant additives examined.