Abstract
The incorporation of catalysts to enhance downhole upgrading in the Toe-to-Heel Air Injection (THAI) process is limited by deactivation due to coking arising from the cracking of heavy oil. This study aims to reduce the catalyst deactivation problems that can occur with upgrading of heavy oils. Ultradispersed catalyst particles could potentially replace pelleted catalysts which may be difficult to regenerate once deactivated during the THAI operation. The dispersed particles could potentially be applied once through, down-hole for in situ upgrading of heavy oil. The catalyst studied was finely crushed pelleted Ni–Mo/Al2O3 catalyst (2.4μm). The product distribution of liquid, coke and gas may be influenced by the presence of a suitable hydrogen source which promotes hydroconversion reactions rather than simple cracking. In order to improve liquid yield whilst suppressing coke formation, the effect of cyclohexane as hydrogen-donor solvent was studied in a stirred batch reactor (100mL) at temperature 425°C, initial pressure 17.5bar, agitation 500rpm, and a short reaction time of 10min. The use of cyclohexane was evaluated against that of hydrogen gas. The reaction under hydrogen atmosphere significantly reduced coke yield by 41.3% compared with a nitrogen environment under the same conditions. Also, the coke decreased by 6.2–45.4% as the cyclohexane:oil ratio increased from 0.01 to 0.08 (g·g−1) relative to 4.67wt.% of coke observed without added cyclohexane in ultradispersed catalytic upgrading under nitrogen environment. As the cyclohexane:oil ratio increases, the produced oil API gravity and middle distillate fractions (200–343°C) increase whilst the viscosity decreases. An estimated 0.073 CH:oil ratio was found to suppress coke formation in a similar manner to upgrading under hydrogen atmosphere at the same conditions.
Highlights
The vast reserves of unconventional oil deposits such as heavy oil, bitumen/oilsands, and oil shale could potentially supplement to the declining light oil reserves
The data showing the extent of upgrading of the heavy oil and the effect of cyclohexane (CH) as hydrogen-donor solvent in comparison to the use of hydrogen is evaluated in terms of API gravity increase, viscosity reduction, asphaltene reduction and yield of distillate
The role of cyclohexane as a hydrogen-donor solvent in increasing the yield of upgraded oil whilst decreasing the coke yield, using ultradispersed Ni–Mo/Al2O3 catalyst, during Toeto-Heel Air Injection (THAI) process for recovery and upgrading of heavy oil was investigated at 425 °C, under hydrogen and nitrogen atmospheres
Summary
The vast reserves of unconventional oil deposits such as heavy oil, bitumen/oilsands, and oil shale could potentially supplement to the declining light oil reserves. In the light of this, enhanced oil recovery processes such as steam and/or in situ combustion techniques are used to heat up the heavy oil reservoir in order mobilise the oil for production. Emplacement of catalyst packing around the horizontal production well (Catalytic upgrading Process In situ, CAPRI) has been developed to augment the THAI process to achieve further upgrading of the produced oil [2,3]. The reactions involving heavy oil taking place on the catalyst are known to produce solid coke deposits.
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