Abstract
Recent studies have discovered a substantial viscosity increase of aqueous cellulose nanocrystal (CNC) dispersions upon heat aging at temperatures above 90 °C. This distinct change in material properties at very low concentrations in water has been proposed as an active mechanism for enhanced oil recovery (EOR), as highly viscous fluid may improve macroscopic sweep efficiencies and mitigate viscous fingering. A high-temperature (120 °C) core flood experiment was carried out with 1 wt. % CNC in low salinity brine on a 60 cm-long sandstone core outcrop initially saturated with crude oil. A flow rate corresponding to 24 h per pore volume was applied to ensure sufficient viscosification time within the porous media. The total oil recovery was 62.2%, including 1.2% oil being produced during CNC flooding. Creation of local log-jams inside the porous media appears to be the dominant mechanism for additional oil recovery during nano flooding. The permeability was reduced by 89.5% during the core flood, and a thin layer of nanocellulose film was observed at the inlet of the core plug. CNC fluid and core flood effluent was analyzed using atomic force microscopy (AFM), particle size analysis, and shear rheology. The effluent was largely unchanged after passing through the core over a time period of 24 h. After the core outcrop was rinsed, a micro computed tomography (micro-CT) was used to examine heterogeneity of the core. The core was found to be homogeneous.
Highlights
The average oil recovery factor (RF) on the Norwegian Continental Shelf (NCS) is 47% and on a global basis the average recovery factor remains less than 40% [1]
Similar materials called cellulose nanocrystals (CNCs) were studied as early as 1949 [27] and described as rod-like cellulose micelles by Rånby and Ribi [28], and the current study focuses on CNC material
The results collectively demonstrate that a certain aging period is required under high temperature conditions to obtain a dramatic increase in shear viscosity for CNCs in low salinity water [18]
Summary
The average oil recovery factor (RF) on the Norwegian Continental Shelf (NCS) is 47% and on a global basis the average recovery factor remains less than 40% [1]. It is essential to target the residual oil remaining in petroleum reservoirs and achieve higher recovery factors from existing fields. One of the technologies is called enhanced oil recovery (EOR) and includes any technique where fluids/material that are not normally present in a reservoir is injected into it. The three primary categories of EOR include: thermal, chemical and miscible or solvent injection [3]. The method applies heat to reduce oil viscosity, facilitating mobilization of oil towards the production well. The main idea is to add chemicals to the water flooding stage to either increase the mobility ratio (polymer), reduce the interfacial tension (surfactant), or create micro-emulsions (alkali). Chemical flooding with polymer additives is considered the most promising EOR method [6] for implementation on the Norwegian continental shelf
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