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.