Paraffin gelation kinetics.

Paraffin deposition is a ubiquitous phenomenon in the petroleum production and processing industry. Incipient paraffin wax-oil gel deposits can form on the interior surface of a petroleum transport pipeline if the temperature of the pipe wall drops below the wax appearance temperature of the fluid and a negative radial temperature gradient exists at the pipe wall. Model paraffin fluids were formulated to study the gelation and deposition process; differential scanning calorimetry measurements indicate that homogenous nucleation represents the primary kinetic limitation associated with the crystallization process. Gelation occurs when growing n-paraffin crystals interlock to form volume-spanning crystal networks which occlude the remaining liquid oil among the crystals. At near-quiescent conditions, low-temperature rheological gels can form with a solid fraction as low as 0.5% by weight. Cross-polarized images of wax-oil gel morphologies indicate crystal lengths of approximately 10--20 mum. A microstructural gelation model was developed based on percolation theory, and predicts reduced incipient gel solid fractions at higher crystal aspect ratios. Sharp crystal edges and ordered crystal faces associated with monodisperse paraffin fluids are found to hinder the paraffin crystal-crystal interactions which result in gelation. The porous microstructure of a wax-oil gel facilitates molecular diffusion of heavy paraffin components from the bulk fluid into the occluded liquid regions of the deposit. Paraffin components with a number of carbon atoms greater than a critical carbon number diffuse into a deposit with time, and vice versa, causing an increase in the solid fraction of a deposit with time in a process known as aging. Laboratory deposition experiments performed using a cold finger indicate that the distribution of paraffin components in a petroleum fluid has a large influence on deposition behavior. Fluids with larger wax contents exhibit lower experimental values of the critical carbon number because of reduced thermodynamic solubility conditions. Component deposition behavior is also dependent upon molecular architecture; linear paraffins are favored to crystallize over branched and cyclic components. When deposition occurs under conditions of bulk precipitation, an upper critical carbon number establishes an upper bound to the range of paraffin components which contribute to the aging process.Ph.D.Applied SciencesChemical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125185/2/3186725.pd

High-Temperature Core Flood Investigation of Nanocellulose as a Green Additive for Enhanced Oil Recovery

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