One of the main functions of drilling fluids is lubrication and cooling of the drill bit, which can reduce torque and drag and increase lateral distances during horizontal or extended reach drilling. A high coefficient of friction (CoF) between the drill string and the wellbore raises the probability of pipe sticking, increases hook load during tripping, reduces the lifespan of equipment, limits the length of the production hole section and can cause other major drilling problems. Recently, a finite element method (FEM) was implemented to analyze interactions between the wellbore and the drill string (Hareland et al, 2012). The results suggested that a low CoF significantly improves efficiency and overall cost of horizontal or extended reach drilling.
A common method for measuring the CoF of drilling fluids in the laboratory uses an OFI lubricity tester (part #112-00, OFI Testing Equipment, USA), where 150 in-pounds of force is applied between a hardened steel block and a steel ring rotating at 60 rpm. Results of the laboratory tests on several commercial oil-based drilling fluid systems are given in Figure 1.
Figure 1 An impact of the 2nd generation nForcer™ nanoparticle additive on the coefficient of friction in commercial oil-based drilling fluids.
The data shows that nanoparticles, at a low concentration of 0.5 wt%, reduce the average CoF of commercial oil-based drilling fluids by up to 48%. Preliminary analysis suggests that nanoparticles are able to fill in surface roughness and asperities of the metal, giving rise to a smoother, better-lubricated surface. Furthermore, this deposition keeps out debris and moisture, thus improving corrosion resistance and lifespan of the equipment.
Laboratory experiments demonstrate effectiveness of the nForcer™ in improving the coefficient of friction in a variety of commercial oil-based drilling fluids. Forthcoming field trials will evaluate performance of nanoparticle-based drilling fluids in downhole conditions, at which point more results will follow. Stay tuned.
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