Abstract
An Operator in Colombia was experiencing torque issues in a water-based fluid system while drilling wells in the Middle Magdalena and Llanos basins. To address these torque issues, a novel solid lubricant was presented to the operator by the fluid service provider and product manufacturer. Through an extensive lab testing profile, utilizing traditional testing protocols in addition to introducing tribology, the lubricant was selected for field trials. Further testing of the field samples was completed, and data collected from the wellsite demonstrated torque reduction and increased rate of penetration (ROP) allowing the operator to complete the interval.
Tribology uses a different approach to explain stick-slip phenomena and variations of torque and drag. Tribometer results are plotted on a Stribeck curve to display the coefficient of friction as a non-linear function of the contact load. This shows the continuous variations in the different lubrication regimes. The coefficient of friction (COF), static, is due to the contact between bottom hole assembly (BHA) and wellbore is recurrent while drilling directional wellbores.
Tribometer results demonstrated the solid lubricant adhered to the disk asperities, reducing the difference between static and dynamic coefficients of friction. This reduction was confirmed during the field trial and additionally the ROP was increased after the addition of the lubricant. Use of a single value COF to build torque and drag modeling produces an oversimplified representation of a lubricant’s COF improvement. When instead using a tribometer to create a Stribeck curve a lab’s results produce applicable data, as it incorporates variations of rotation and load. More attention should be dedicated to the performance of lubricants in the boundary condition in directional wells as this represents the torque required to initiate rotation and overcome differential pressure while making connections. Use of the novel lubricant reduces static COF and breakover torque.
Tribology, the science of friction, lubrication and wear has been used in automotive, space, pharmaceutical and mechanical engineering industries among others for years for the design and evaluation of solid and liquid lubricants. Unfortunately, this is not a common practice in the oil and gas industry. Tribology allows better understanding of wellbore lubrication throughout the different regimes and under differing loads. Tribology is a new method to measure the complex phenomena of lubricity in the oilfield. It helps better understand items such as stick-slip and torque variations while drilling and how they can be explained through analyzing their behavior along the Stribeck curve.
