Numerical simulation investigations of the applicability of THAI in situ combustion process in heavy oil reservoirs underlain by bottom water

The presence of a bottom water(BW)layer in heavy oil reservoirs can present substantial problems for efficient oil recovery for all recovery techniques.Hence,it is necessary to know how particular production processes are affected by different BW layer thicknesses,and how standard production procedures can be adapted to handle such reservoirs.Toe-to-heel air injection(THAI)is a thermally efficient process,generating in situ energy in the reservoir by burning a fraction of the oil-in-place as coke and has the potential to economically and environmentally friendly work in reservoirs with BW layer.However,to ascertain that,studies are needed first.These are conducted via numerical simulations using commercial reservoir thermal simulator,CMG STARS.This work has shown that the shape of the combustion zone in THAI remains forward-leaning even in the presence of a BW layer,indicating that the process is stable,and that there is no oxygen bypassing of the combustion front.However,the oil recovery rate is highly negatively affected by how large the thickness of the BWzone is,and the severity of such effect is determined to be proportional to the thickness of the BW layer.This study also shows that there is a period of low oil production rate which corresponds to mobilised oil displacement into the BW zone which in turn causes a surge in water production rate.The practical implication of this is that prolonged period of low oil production rates will expose companies and/or investors to higher risk due to the oil market volatility.In this study,it is also revealed that the height of the mobilised oil that is displaced into the BW zone equates to that of the displaced and replaced water thereby implying that when the BW layer thickness is 50%that of the oil layer(OL),less than 50%of the mobilised oil will be recovered when the entire reservoir is swept by the combustion front.Therefore,conclusively,applying the THAI process in its conventional form in reservoirs containing bottom water is not recommended,and as a result,a new strategy is needed to enhance process economics by improving the oil production and hence recovery rates.

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

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 z24 oAPI oil produced at 8000 kPa versus the 2050 cm3 of z17.5 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.There-fore,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.

Lag times in toe-to-heel air injection(THAI)operations explain underlying heavy oil production mechanisms

From a time value of revenue point of view,it is preferred that the time between reservoir stimulation and oil production response is small.Heavy oil combustion processes have a lag time between air injection and liquid production,but the common practice in production data analysis uses simultaneous injection and production data when seeking a relationship between them.In this research,the time scales of production for the Kerrobert toe-to-heel air injection(THAI)heavy oil project in Saskatchewan,Canada,is analyzed by using cross correlation analysis,i.e.time delay analysis between air injection and oil production.The results reveal two time scales with respect to production response with two distinctive recovery mechanisms:(1)a short time scale response(nearly instantaneous)where oil production peaks right after air injection(directly after opening production well)reflecting cold heavy oil production mechanisms,and(2)a longer time scale(of order of 100-300 days)response where peak production occurs associated with the collective phenomena of air injection,heat generating reactions,heat transfer,and finally,heated mobilized heavy oil drainage to the production well.This understanding of the two time scales and associated production mechanisms provides a basis for improving the performance of THAI.

Simulation of catalytic upgrading in CAPRI,an add-on process to novel in-situ combustion,THAI

Based on the analysis of recent projections by the International Energy Agency(IEA),to meet the growing and subsequently declining demands of oil from now to 2040,we need up to around 770 billion barrels of oil.Since the worldwide total proved reserves of easy-and-cheaper-to-produce conventional oils is roughly only 520.2 billion barrels,the remaining 249.8 billion barrels must be obtained from unconventional petroleum resources(i.e.heavy oils and bitumen).These resources are however very difficult and costly to upgrade and produce due to their inherently high asphaltene contents which are reflected in their very high viscosities and large densities.However,still they should prove attractive development prospects if,as much as practicably possible,their upgrading can be performed in conjunction with in situ or downhole catalytic upgrading processes.Such projects will contribute significantly towards smoother and greener transition to full decarbonisation.Advanced technologies,such as the toe-to-heel air injection coupled to its add-on in situ catalytic process(i.e.THAI-CAPRI processes),have the potential to develop these reserves,but require further developmental understanding to realise their full capability.In this work,a new detailed procedure for numerically simulating the THAI-CAPRI processes is presented.The numerical model is made-up of Athabasca-type bitumen and it has a horizontal producer(HP)well that is surrounded by an annular layer of alumina-supported cobalt-oxide-molybdenum-oxide(CoMo/γ-Al2O3)catalyst.The simulation is performed using the computer modelling group(CMG)reservoir simulator,STARS.This new work has shown that the choice of the frequency factor of the catalytic reactions allowed model validation based on the degree of catalytic upgrading in form of API gravity.Overall,the work herein identifies the important parameters,such as API gravity,peak temperature,oil production rate,cumulative oil production,produced oxygen concentration,temperature distribution profile,extent of coke deposition on the catalyst surface,etc.,governing the successful operation of the THAI-CAPRI processes.In particular,this study has shown that even in the vicinities of the mobile oil zone(MOZ)where the catalytic upgrading is expected to be taking place,the catalyst surfaces are covered with high concentration of coke.This finding is in parallel to the observations reported from experiment of CAPRI process alone.Therefore,it is concluded that when experimental studies of the THAI-CAPRI processes are to be conducted,a catalyst regeneration mechanism must be put in place in order to prolong the effectiveness and thus the life of the catalyst so that proper field operation design can be made.Additionally,the study has also shown that the temperature of the MOZ is less than 306°C and that implies that an external source of heating the annular catalyst layer must be provided in order to effect the catalytic upgrading in the THAI-CAPRI processes.Thus,a new study should look at the feasibility of targeted heating(in the case of microwave)or conductive or resistive heating(in the case of electrical heating)to raise the temperature of the annular catalyst layer to that required to achieve the catalytic upgrading.

A review of in situ upgrading technology for heavy crude oil

With the growing demand of oil worldwide,heavy oil has increasingly become vital in the world energy market.However,further development of heavy oil reservoirs are limited by regular enhanced oil recovery(EOR)methods.In situ upgrading technology provides potential for the development of heavy oil and bitumen reservoirs.This study reviews three categories of in situ upgrading methods:solvent-based,in situ combustion(ISC),and catalytic.Solvent-based methods,including cyclic solvent injection,vapor extraction,and hybrid processes,have recently received attention and have been progressed in both laboratory and field applications.However,high solvent costs in relation to the low price of heavy oil have continued to limit the field applications of these techniques.ISC,which may have the potential to develop particularly harsh reservoirs with extremely viscous crude oil,involves complex reaction mechanisms and consists of three main steps:oxidation,combustion,and gas flooding.Yet,complex operating conditions and a low success rate have restricted its application.Catalytic methods,which have demonstrated the potential to refine and upgrade crude oil in a more economic and environmentally friendly way,are often accompanied by conventional thermal EOR methods,such as steam flooding and ISC,and involve a series of hydroprocessing or hydrotreating reactions,such as hydrocracking,hydrodesulfurization,hydrodenitrogenation,hydrodeoxygenation,and hydrodemetallization.However,the high cost and complexity of the reaction mechanisms have limited their applications.