Oil Recovery Improvements Based on Pickering Emulsions Stabilized by Cellulose Nanoparticles and Their Underlying Mechanisms: A Review

Abstract

The use of nanocellulose (NC)-based Pickering emulsions represents an advancement in chemically enhanced oil recovery (cEOR) methods. The main challenge of cEOR is to develop stable and efficient fluids for applications under reservoir conditions. Pickering emulsions have emerged as a possible solution for stabilizing chemical injection fluids. These emulsions are stabilized by solid particles instead of surfactants and have been the focus of research over the past decade because of their high stability. Although these emulsions present promising solutions, most research has focused on nonbiodegradable inorganic particles, raising concerns about their environmental impact. In this context, nanocellulose (NC) has emerged as an innovative and sustainable alternative due to its biodegradability, abundance, and unique surface chemistry. This contribution presents an exploratory literature review on the use of Pickering emulsions, focusing on nanocellulose in the context of enhanced oil recovery (EOR) as an alternative for fluid stabilization under reservoir conditions. The main mechanisms of oil recovery, such as interfacial tension reduction, in situ crude oil emulsification, capillary disjunction, pressure, and fluid rheological behavior, are discussed. This Review highlights the great potential of nanocellulose-based Pickering emulsions to make EOR processes more sustainable and emphasizes the need for further studies to understand the mechanisms involved. A total of 176 scientific articles were analyzed and evaluated to provide insights and contribute to the advancement of cEOR, in addition to addressing the challenges encountered.

Figure 1

Graphical representation of a classic emulsion (based on a surfactant) and a Pickering emulsion. The nanoparticles are adsorbed at the oil–water interface and stabilize the droplets in place of the surfactant molecules. Created with BioRender.com.

Figure 2

Wettability of solid particles and contact angle leading to the formation of O/W or W/O emulsions.^, Created with BioRender.com.

Figure 3

a) and b) SEM images of polymerized styrene–water emulsions stabilized by bacterial cellulose nanocrystals, c) and d) Cryo-SEM images of a drop of water covered with ellipsoids, e) and f) Cryo-SEM images of drops of dodecane coated with microgels, g) array of cubic particles at the oil–water interface, h) peanuts mounted at the oil–water interface in interdigitating stacks, and (i) SEM images of microbowls but not at the O/W interface. Reprinted with permission from J. Controlled Release2019, 309, 302–332. 10.1016/J.JCONREL.2019.07.003. Copyright 2019, Elsevier.

Figure 4

Illustration of the bounded coalescence theory; the double arrows outline the approaching droplets. Created with BioRender.com.

Figure 5

Representation of the structure of cellulose in plant biomass. Lignocellulose contains large amounts of lignin and hemicellulose. Created with BioRender.com.

Figure 6

Molecular structure of cellulose and schematic representation of the production of CNCs and CNFs from wood pulp with their morphological and chemical structures. Created with BioRender.com.

Figure 7

Schematic representation of CNC extraction steps from cellulose fibers through acid-catalyzed hydrolysis. The amorphous regions are hydrolyzed in an acidic medium, whereas the crystalline regions remain with the structure intact, producing CNCs with high crystallinity and a rod-shaped morphology. Adapted with permission from Prog. Polym. Sci.2021, 119. 10.1016/j.progpolymsci.2021.101418. Copyright 2021, Elsevier. Created with BioRender.com.

Figure 8

Schematic illustration of typical microfluidization (A), high-pressure homogenization (B), microgrinding (C), and high-intensity ultrasound (D) processes used to produce NFCs. Adapted with permission from Prog. Polym. Sci.2021, 119. 10.1016/j.progpolymsci.2021.101418. Copyright 2021, Elsevier.

Figure 9

Schematic representation of the main surface modification techniques applied to cellulose NPs. The functional groups introduced are highlighted in orange. Adapted with permission from Sci. Total Environ.2021, 775, and 145871. 10.1016/J.SCITOTENV.2021.145871. Copyright 2021, Elsevier.

Figure 10

Schematic representation of the structuring of nanoparticles forming a wedge film, resulting in a structural disjoining pressure gradient. Adapted with permission from Int. Nano Lett.2019, 9 (3). 10.1007/s40089-019-0272-8. Copyright 2019, Spring Nature. Created with BioRender.com.

Figure 11

Scheme illustrating isolated droplets covered by colloidal particles at low volume fractions (a), medium volume fractions (b), and high volume fractions (c) of the dispersed phase. Created with BioRender.com.