Water-based drilling fluids are an economical and environmentally appealing option for wellbore construction. Both conventional and high-performance varieties of water-based systems typically use biopolymers to provide viscosity, suspend solids, and control fluid loss in the wellbore. Some examples include both naturally occurring biomaterials produced by plants or bacteria (e.g., starch, guar, xanthan) as well as their chemically modified analogues. However, new materials that could help improve efficiency, rate of penetration (ROP), or high-pressure/high-temperature (HP/HT) performance are necessary to expand the use of economical water-based systems in increasingly demanding conditions. Recently identified nanostructured biomaterials, such as nanocellulose, have been observed to have outstanding mechanical, structuring, and thermal properties and are known to be potent viscosifiers at low concentrations. This paper discusses a study that investigates the performance of water-based fluids by either replacing or augmenting their common oilfield biopolymers with cellulose nanofibrils (CNFs). In this study, CNFs produced from technical-grade kraft pulp were mixed in aqueous dispersions with commercial biopolymer viscosifiers, such as xanthan and guar gum. Measurements were made of rheology, dispersion stability, CNF/biopolymer interaction, and filtration behavior as they relate to desirable fluid properties. Unexpected synergies were discovered when the CNFs were blended with secondary biopolymers. Increases or decreases observed in system viscosity were dependent upon the type of biopolymer mixed with nanocellulose but independent of the mass balance of the ingredients. In some mixtures, lower biopolymer concentrations increased viscosity within mixed systems while other mixtures decreased viscosity with increased concentrations. The implications of these unusual findings suggest that performance efficiency can be tailored simply by mixing CNFs with biopolymers that are already used extensively in water-based fluids, allowing an operation to use less material. This discovery can enable a new method to maintain drilling fluid properties during drilling operations with the added benefit of increased temperature stability. By modifying the surface of CNFs with secondary biopolymers, a wide range of fluid behaviors were achieved through changes in surface chemistry, surface morphology, and gel-network formation. Such nanocellulose fluid systems could serve as a renewable, nontoxic, and potentially cheaper alternative to synthetic polymers in high-performance, water-based fluids with the added benefit of controlling and helping to improve fluid properties using a mixture with common oilfield biopolymers.

Water-based drilling fluids provide an economical and environmentally attractive option for wellbore construction. Despite the development of high performance water-based fluids, consistent demonstration of drilling performance comparable to oil-based fluids has proven to be elusive. Both traditional and high-performance water-based systems typically use biopolymers to provide filtration control, viscosity, and suspension properties. These biopolymers include naturally occurring materials, such as celluloses, starches, hydrocolloids, and bacterially engineered polymers, such as xanthan gum. Although several options exist, new materials are always desired to improve efficiency or enhance high pressure, high temperature (HPHT) performance. Recently identified nano-structured biomaterials, such as nanocelluloses, have been used in the development of advanced materials systems because of their outstanding mechanical, structuring, and thermal properties; they are also potent viscosifiers at relatively low concentrations (~0.5 wt %). This paper explores the rheological, thermal, and fluid loss properties of as-produced and covalently modified cellulose nanofibers in saline water-based fluids. Results are compared to a commercial xanthan gum viscosifier as used in saline water-based drilling fluids. Cellulose nanofibrils were produced from kraft pulp wood fibers by using known methods based on mechanical shearing. Using a standard concentration in water, measurements were made of complex rheology, filtration (API LPLT test), and equivalent and total surface charge. The nanocellulose materials were then modified by means of simple chemical reactions to tailor the surface properties, and then compared to the original material. The same battery of tests was run in control experiments performed with a commercial xanthan gum-based viscosifier. By modifying the surface of nanocellulose with new covalently bound functional groups, a wide range of fluid behaviors was achieved through the control of the resulting changes in surface chemistry. Unlike nanomaterials based on graphitic carbon, such as nanotubes and graphene, cellulose features a natural polymer backbone chemistry having three available hydroxyl sites on each cellulose repeat unit. The secondary alcohol group at position 6 on the β-D-glucopyranose ring is especially well-suited for site-selective reactions, such as oxidation. The new surfaces created with each new functional group provide different modes of interaction with salt ions, water molecules, and other biopolymers in the fluid to change fluid properties. This work introduces a new renewable, non-toxic, and potentially less expensive alternative to synthetic polymers for viscosity and filtration control in high-performance water-based drilling and completion fluids. Furthermore, nanocellulose materials can be modified through simple chemical reactions to provide improved performance or to tailor their effects and interactions with other components.