This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 157031, ’Application of Nanotechnology in Drilling Fluids,’ by Katherine Price Hoelscher, SPE, Guido De Stefano, SPE, Meghan Riley, SPE, and Steve Young, SPE, M-I SWACO, prepared for the 2012 SPE International Oilfield Nanotechnology Conference and Exhibition, Noordwijk, The Netherlands, 12-14 June. The paper has not been peer reviewed.
The potential to apply water-based drilling fluids confidently in unconventional shale formations has been studied using engineered nanoparticles to minimize shale permeability by physically plugging the nanometer-sized pores. Nanoparticle technology and testing protocols were developed using the Marcellus and the Mancos as shale candidates. Nanoparticles in this study are specifically designed to plug the nanometer-sized shale pores physically, thereby reducing pressure transmission in the shale.
Silica nanoparticles are commercially available and can be engineered to meet all specifications needed for the purpose. The particle size can vary between 5 and 100 nm. The right sizes of nanoparticles can be selected, and, in combination with a correct fluid-loss package, the particles can minimize the fluid/rock interaction. Surface treatment on the nanosilica particle has been discovered to have a major influence on the final performance.
An investigation into using nanoparticles as a drilling-fluid additive to enhance wellbore stability has been successful. The nanomaterial works by virtually shutting off water movement between the formation and wellbore. In shale formations with nanodarcy permeability, such as the Marcellus, the usual drilling-fluid method of relying on a filter cake to reduce fluid loss (or leakoff) cannot be used because a filter cake may not form because of the extremely low permeability of the shale. The solution for this problem is to engineer a nanoparticle that will be added to the drilling fluid to plug the pores of the shale and shut off water loss.
The hurdle to maintaining wellbore stability in shale formations is to control the water interaction with the rock. The water enters the shale through pores, which vary in size from approximately 3 to 100 nm, inducing fractures and, thereby, reducing the stability of the wellbore. By effectively plugging the exposed pores of the rock and not allowing water to enter, wellbore stability is retained. One conventional bridging theory is referred to as the one-third rule of filtration (Abrahm’s theory), where the material used to plug a pore is required to be approximately one-third to one-seventh of the size of median pore opening. There are other theories with varying size requirements for the plugging material; however, none is perfect. An ideal plugging material also will accommodate the variability in pores within the formation.