In-Situ Upgrading of Heavy Oils by Low-Temperature Oxidation in the Presence of Caustic Additives

Abstract

The literature of the past thirty years shows that the low- temperature oxidation (LTO) of hydrocarbon liquids generally results in a more viscous end product. The In Situ Combustion Research Group at The University of Calgary has found, however, that upgrading can occur during LTO in the presence of caustic additives. Because it was believed that caustic inhibits oxidation reactions as evidenced by a reduction in or absence of coke formation, and allows the oil to upgrade by thermal cracking via a free radical mechanism, a systematic study was undertaken to investigate the effect of caustic on the LTO of heavy oil. To date, nearly 200 LTO tests have been performed on Athabasca bitumen. These experiments were carried out by varying caustic concentrations, temperatures, oxygen partial pressures, total cell pressures, and run times. All effluent gases were analyzed using gas chromatography, the pH of free water was measured, and hydrocarbon products underwent determination of coke and asphaltene contents, viscosity, and density. CHN and S analyses were carried out on the whole oil, and coke and asphaltene fractions. Several instances of upgrading were observed. Optimum conditions occurred at lower caustic concentrations, lower temperatures, lower oxygen partial pressures, and longer run times. The amount of oxygen reacted appears to be the most critical parameter affecting the system. The presence of caustic apparently did not inhibit the oxidation reactions from taking place, but, rather, modified the process by impeding the asphaltene fraction from converting to coke. Introduction The amount of information available on the LTO of crude oils is relatively limited. Several published studies investigate the chemical and physical changes accompanying LTO of many different grades of oil. Studies on the LTO of Athabasca bitumen described by Babu and Cormack show a decline in the aromatic content, an increase in asphaltenes content, and a stable saturates content. The same authors report a steady increase in coke production with the extent of oxidation. The overall trend is for a conversion from aromatics to resins, from resins to asphaltenes, and from asphaltenes to coke. This transformation to a heavier, more polar oil results in increased viscosities and densities. Millour et al. describe and relate the oxygen uptake to coke deposition, and Severin et al. provide a relationship between viscosity and the percent increase in oxygen concentration in the oxidizing gas. It has been accepted, therefore, that LTO causes undesirable changes in the chemical and physical properties of oil. It may, however, be beneficial to subject an oil to LTO. Unpublished experimental work performed by co-workers at The University of Calgary showed that a pre-oxidized oil underwent accelerated thermal cracking compared to an unoxidized sample of the same oil when subjected to the same reaction conditions. It was thought that pre-oxidation of the oil incorporated oxygen into the structure, thereby providing labile bonds which more readily generated free-radicals. Introduction of oxygen into the molecular structure of the oil can have two consequences; either a downgraded or an upgraded product. P. 529

Physical and Numerical Simulation of an Extra-Heavy Crude Oil Downhole Upgrading Process Using Hydrogen Donors Under Cyclic Steam Injection Conditions

“…4 and Table 2) only 9°API crude oil and, no tetralin conversions. For the former run, the oil percentage of recovery was slightly smaller (1-2%) than that found in the upgrading process, which is consistent with the results reported by Shu et al [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] and Kaskale and Farouq Ali 7 . However, a reduction from 0.8 to 3% in the percentage of tetralin conversion was observed in the Upgrading Process ( Table 2, run 3) in comparison with the bench scale experiments (run 1).…”

“…Several routes for underground crude oil upgrading have been reported. These concepts involve the following: Downhole steam distillation 1 , deasphalting [2][3][4][5] , underground visbreaking [6][7][8][9] , hydrogen [10][11][12][13][14][15][16][17] or hydrogen precursor injection [18][19][20][21][22] and in situ combustion [23][24][25] . With the exemption of the later route, the numerical simulation of downhole upgrading processes has been relatively less studied.…”

“…These authors found that the upgraded crude is mainly generated at the hotter area (T >220°C) of the reservoir with an overall increase of 13% in the recovery of oil, compared with the cold production simulation 7 . The concepts described by Shu et al [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] and Kaskale and Farouq Ali 7 were designed to increase the oil production by enhancing oil mobility due to visbreaking of heavy fractions (asphaltenes). Whereas, the main goal of this work is to increase the quality of the crude oil by reaction with a hydrogen donor in the presence of the mineral formation and natural gas.…”

Kinetics and mechanisms of the catalytic thermal cracking of asphaltenes adsorbed on supported nanoparticles

“…The latter (i.e., cold process) is used to improve the crude oil by dilution or destabilization, and deposition of the asphaltene components in the reservoir by injecting solvents that have a direct impact on viscosity reduction (Luo et al 2007b;Cavallaro et al 2005). The more frequently employed thermal techniques for heavy oil upgrading address breaking the heavier compounds of oil using combustion processes (Moore et al 1999;Cavallaro et al 2008), low-temperature oxidation (Xu et al 2000;Wichert et al 1995), aquathermolysis (Jiang et al 2005;Fan et al 2004;Maity et al 2010), and pyrolysis, also called thermal cracking or thermolysis (Speight 1970;Kumar et al 2011;Monin and Audibert 1988;Nassar et al 2013a). However, most of these techniques do not exceed 20 %-25 % oil recovery or 50 % for the steam-assisted gravity drainage (SAGD) process (Butler 1998;Nasr et al 2003;Hashemi et al 2013).…”

Study of the Ignition Characteristics of Light Fractions of Crude Oil and Their Surrogate Fuels under a Range of Low-to-Medium Temperatures

“…At the same time, a number of researchers have conducted multiple studies about promoting the reservoir heat release and realizing reservoir spontaneous combustion at low temperatures. − Wichert et al and He et al studied the effects of different metal particles and salts on the ISC process. Hamedi et al , and Rezaei et al found that nanoparticles could be used to promote thermal cracking at low temperatures and the stability of the combustion front propagation at high temperatures.…”