With Functionalization, Nanodiamonds May Increase Durability of PDC Cutters
Authors: Wilson Adam 
Published: February 2015

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 157039, ’The Trick Is the Surface - Functionalized Nanodiamond PDC Technology,’ by Soma Chakraborty, SPE, Gaurav Agrawal, SPE, Anthony DiGiovanni, SPE, and Dan Scott, SPE, Baker Hughes, prepared for the 2012 SPE International Oilfield Nanotechnology Conference and Exhibition, Noordwijk, The Netherlands, 12-14 June. The paper has not been peer reviewed.

With downhole conditions shifting toward more challenging conditions, nanoparticles have been explored for more demanding applications. As a result of their inherent extremely high surface energy, these very small particles tend to attract each other or exist as clusters. Thus, nanoparticles can exist as micrometer-sized clusters, exhibiting overall micrometer features instead of nanometer characteristics. To derive the true benefits of a nanoparticle, it is crucial to exfoliate and derivatize the surface so the system is truly “nano.” Derivatization, or “functionalization,” further stabilizes the nanoparticles in chemical matrices. In this context, nanodiamonds have been functionalized for polycrystalline diamond applications such as polycrystalline diamond compact (PDC) cutters for drill bits.

Introduction

Nanodiamond is an interesting candidate for increasing the durability of PDC cutters as well as their abrasion resistance. As one possible means of increasing overall PDC diamond density and lowering the amount of metallic binder, nanodiamonds could lower the localized microstructural stress as their coefficient of thermal expansion is matched to that of the micrometer diamond. Diamond-to-diamond bonding is likewise straight-forward, compared with a nondiamond nano-sized second phase.

Several varieties of nanodiamond are commercially available. One variety is obtained from milling synthetic micrometer diamond, which results in large size distributions. Another variety is the shock-wave nanodiamond, which is composed of sintered granules, with granule size dependent on the starting graphene. The most extensively used variety is the detonation nanodiamond, which has a very narrow size distribution, with average crystallite size of 5–7 nm. The surface functionality and reactivity are dependent on the generation method and purification techniques.

Similar to most nanoparticles, nanodiamond has very high surface energy because of its extremely small size. To minimize the surface energy, it aggregates into micrometer- or submicrometer-sized hard clusters. These aggregates are very difficult to break or control during bulk processing. A PDC synthesized from aggregated nanodiamond would have inhomogeneous diamond distribution, which would ultimately lead to inferior performance and poor reliability with respect to the baseline feed. To overcome the problem, nanodiamond particles are functionalized or surface derivatized to covalently attach organic moieties onto their surface. The surface functional groups get covalently bonded onto the nanodiamond surface on the basis of the synergy of the surface active sites and associated reactivity of the bonding fragment.