Petroleum Research (Jun 2022)
Effect of operating pressure on the performance of THAI-CAPRI in situ combustion and in situ catalytic process for simultaneous thermal and catalytic upgrading of heavy oils and bitumen
Abstract
According to the analysis of the 2020 estimates of the International Energy Agency (2020), the world will require up to 770 billion barrels of oil from now to 2040. However, based on the British Petroleum (BP) statistical review of world energy 2020, the world-wide total reserve of the conventional light oil is only 520.2 billion barrels as at the end of 2019. That implies that the remaining 249.8 billion barrels of oil urgently needed to ensure a smooth transition to a decarbonised global energy and economic systems is provided must come from unconventional oils (i.e. heavy oils and bitumen) reserves. But heavy oils and bitumen are very difficult to produce and the current commercial production technologies have poor efficiency and release large quantities of greenhouse gases. Therefore, these resources should ideally be upgraded and produced using technologies that have greener credentials. This is where the energy-efficient, environmentally friendly, and self-sustaining THAI-CAPRI coupled in situ combustion and in situ catalytic upgrading process comes in. However, the novel THAI-CAPRI process is trialled only once at field and it has not gained wide recognition due to poor understanding of the optimal design parameters and procedures. Hence, this work reports the first ever results of investigations of the effect of operating pressure on the performance of the THAI-CAPRI process. Two experimental scale numerical models of the process based on Athabasca tar sand properties were run at pressures of 8000 kPa and 500 kPa respectively using CMG STARS. This study has shown that the higher the operating pressure, the larger the API gravity and the higher the cumulative volume of high-quality oil is produced (i.e. a 2300 cm3 of ≈24 oAPI oil produced at 8000 kPa versus the 2050 cm3 of ≈17.5 oAPI oil produced at 500 kPa). The study has further shown that despite presence of annular catalyst layer, the THAI-CAPRI process operates stably. However, it is found that a more stable and safer operation of the process can only be achieved at optimal pressure that should lie between 500 kPa and 8000 kPa, especially since at the lower pressure, should the process time be extended, it will not take long before oxygen breakthrough takes place. The simulations have shown in details that at higher pressures, the catalyst bed is easily and rapidly coked and thus the catalyst life will be very short especially during actual field reservoir operations. Since the oil drainage flux into the HP well at field-scale is different from that at laboratory-scale, and at field-scale, the combustion front does not propagate inside the HP well, it will be practically very challenging to regenerate or replace the coke-deactivated annular catalyst layer in actual reservoir operations. Therefore, it is concluded that during field operation designs, an optimum pressure must be selected such that a balance is obtained between the combustion front stability and the degree of catalytic upgrading, and between the catalyst life and its effectiveness.
