A field study, laboratory test and cost estimation of solid and liquid lubricants in directional wells to reduce friction coefficient and improve ROP

Abstract

Drilling fluid is being used to facilitate drilling operation from the surface to a target formation. Due to the complexity of well geometry in directional drilling operations and high torque and drag forces, minimizing the coefficient of friction (CoF) is important. Excessive torque and axial drag cause mechanical erosion on the drill string, which ultimately leads to fatigue, wash out and twist off. Field data for 9 wells in one of the Iranian oilfields showed that slide drilling was practically impossible beyond 4000 m due to the unexpected high torque and drag during directional drilling despite the presence of liquid lubricants in drilling fluid at concentrations up to 5 vol% as per drilling program. Based on the results, the primary source of torque and drag in the wells with proper hole conditioning is sliding friction. Using different types of lubricant in drilling fluid system is the most practical methods to reduce the drag force (sliding friction) caused by the contact between drillstring and well casing or borehole. This paper investigates the effect of solid and liquid lubricants on the CoF in laboratory and field applications. Based on the successful implementation, a specific instruction was designed for the use of glass bead as a solid lubricant in drilling fluid to reduce the CoF. Cost estimation indicates that compared to the liquid lubricants, solid lubricants can reduce drilling fluid costs significantly. Moreover, based on Experimental results, no more than 5–6 percent of liquid lubricants can be used to reduce friction coefficient. This limitation, along with the issue of lubrication regimes, leads us to use solid lubricants. Laboratory and field test results showed that addition of glass bead as a solid lubricant can improve the performance of water-based drilling fluids as evidenced by improvement in ROP up to 240% (average ROP: 160%).