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Enhanced oil recovery methods have remarkable influences in heavy oil recovery. The high viscosity in heavy oil and tar sand reservoirs is a major obstacle in the extraction process. While thermal recovery methods are often considered, there are unconventional reservoirs where conventional techniques for long - term production can damage the formation. In these cases, traditional thermal recovery methods are not recommended - rather electrical EOR (EEOR) methods are utilized.
Electrical heating is an EOR process that works on the principle of transferring heat into the reservoir via electrical means. It involves injection of electrical energy to the reservoir, heating the area and causing an increase in oil temperature. Heating up the reservoir reduces the oil viscosity, thus, making it easier to flow. While electrical heating is a relatively new technique, advances in the past couple of years have allowed for testing by theoretical, laboratories, and field trial research in areas including, Russia, the United States of America, Canada and other countries.<ref name=":6">Mukhametshina, A., and Martynova, E. (2013). Electromagnetic Heating of Heavy Oil and Bitumen: A Review of Experimental Studies and Field Applications. ''J. Pet. Engineering'' '''2013,''' 476519:1-7. <nowiki>http://dx.doi.org/10.1155/2013/476519</nowiki></ref> Focus on electrical enhanced oil recovery (EEOR) processes is of great importance, because of the abundance of heavy oil, tar sand and bitumen reserves in Canada, Venezuela, countries of the former USSR, the United States of America and China. <ref>Salager, J.L., Briceño, M.I., and Bracho, C.L. (2001). Heavy Hydrocarbons Emulsions. In Encyclopedic Handbook of Emulsion Technology, 455-495, ed. J. Sjöblom. New York City: Dekker</ref><ref>Smalley, C. (2000). Heavy Oil and Viscous Oil. In Modern Petroleum Technology, Vol. 1 Upstream, Ch. 11, 409-435, sixth edition, ed. R.A. Dawe. New York City: Wiley & Sons Inc.</ref><ref>Layrisse, I. (1999). Heavy Oil Production in Venezuela: Historical Recap and Scenarios for Next Century. Presented at the SPE International Symposium on Oilfield Chemistry, Houston, Texas, 16-19 February 1999. SPE-53464-MS. <nowiki>http://dx.doi.org/10.2118/53464-MS</nowiki></ref>
 
Electrical heating is an EEOR process that works on the principle of transferring heat into the reservoir via electrical means. These methods supply electrical energy to the reservoir, heating the area and causing an increase in oil temperature. Heating up the reservoir reduces the oil viscosity thus, making it easier for materials to flow. While electrical heating is a relatively new technique, advances in the past couple of years has allowed for testing by theoretic, laboratories, and field trial research in areas including, Russia, the United States of America, Canada and other countries.<ref name=":0">Mukhametshina, A., and Martynova, E. 2013. Electromagnetic Heating of Heavy Oil and Bitumen: A Review of Experimental Studies and Field Applications. ''J. Pet. Engineering'' '''2013,''' 476519:1-7. http://dx.doi.org/10.1155/2013/476519</ref> Focus on EEOR processes is of great importance because of the abundance of heavy oil, tar sand and bitumen reserves in Canada, Venezuela, countries of the former USSR, the United States of America and China.<ref>Salager, J.L., Briceño, M.I., and Bracho, C.L. 2001. Heavy Hydrocarbons Emulsions. In Encyclopedic Handbook of Emulsion Technology, 455-495, ed. J. Sjöblom. New York City: Dekker</ref><ref>Smalley, C. 2000. Heavy Oil and Viscous Oil. In Modern Petroleum Technology, Vol. 1 Upstream, Ch. 11, 409-435, sixth edition, ed. R.A. Dawe. New York City: Wiley & Sons Inc.</ref><ref>Layrisse, I. 1999. Heavy Oil Production in Venezuela: Historical Recap and Scenarios for Next Century. Presented at the SPE International Symposium on Oilfield Chemistry, Houston, Texas, 16-19 February 1999. SPE-53464-MS. <nowiki>http://dx.doi.org/10.2118/53464-MS</nowiki></ref>
==Basic processes==
==Basic processes==
The EEOR technique works on the basis of using electrical means (e.g. sound waves, radiofrequency (RF) waves, inductive heating and DC heating). The primary function of this processes is to increase the mobility of oil for it to flow easily towards the production well. The electrical energy that is supplied either raises the temperature of the reservoir or creates vibrations in the hydrocarbon molecules. <ref name=":4">Mohsin Rehman, M., and Meribout, M. 2012. Conventional versus electrical enhanced oil recovery: a review. ''J Petrol Explor Prod Technol'' '''2:'''157-167</ref>
The EEOR technique works on the basis of using electrical means (e.g. radiofrequency (RF) waves, inductive heating and DC heating). The primary function of this process is to increase the mobility of oil for it to flow easily towards the production well. The electrical energy that is supplied either raises the temperature of the reservoir or creates vibrations in the hydrocarbon molecules. <ref name=":4">Mohsin Rehman, M., and Meribout, M. 2012. Conventional versus electrical enhanced oil recovery: a review. ''J Petrol Explor Prod Technol'' '''2:'''157-167</ref>
 
Heating the reservoir is either done by a steam chamber or direct heating into the near-wellbore.It can also be achieved by gravity damage using SAGD heating method to heat the formation. The amount of power required for each well and formation is dictated by the production rate and operational requirements. More energy is needed to compensate for the increased flow rate. Since the electrical heating system operates when oil is being produced, there is no need to inject any fluid into the reservoir. As a result, no formation damage occurs. However, electrical heating is used to heat the steam chamber, brine compromises an electrical heating path, and electrical energy is lost because of heat. Steam is generated when the water saturation decreases, or the amount of the water is heated by electric current.


The frequency of the electric current determines the mode of electrical heating.The alternating electric field causes polar molecules to align and relax. The molecular movement could cause a lot of heat.
Heating the reservoir is either done by a steam chamber or direct heating into the near wellbore. The amount of power required for each well and formation is dictated by the production rate and operational requirements. The frequency of the electric current determines the mode of electrical heating. The alternating electric field causes polar molecules to align and relax. The molecular movement generates heat. Electrical heating design's key goal is to reduce electrical losses while localizing heating.


The four critical components of electric heating applications are:
The four critical components of electric heating applications are:
Line 14: Line 10:
#Power supply system.
#Power supply system.
#Electrode assembly.
#Electrode assembly.
#Ground return system.
#Ground return system.  


Electrical heating design's key goal is to reduce electrical losses while localizing heating. The current return for a single well unit is the casing string above the fiberglass, with an isolated electricity joint between the casing and the electrode. The current passes from the power conditioning unit to the electrode assembly, then through the oil formation and back to the power conditioning unit configuration. As a result, heating reduces the viscosity of the oil.           
==Major mechanisms==
==Major mechanisms==
Electric heating can be divided into three categories depending on the frequency of the electrical current being used. These include:
Electric heating can be divided into three categories depending on the frequency of the electrical current being used. These include:


#Low frequency electric heating (also referred to as resistive).
#Low-frequency electric heating (also referred to as resistive).
#High frequency electric heating (commonly called microwave heating).
#High-frequency electric heating (commonly called microwave heating).
#Inductive heating (IH).
#Inductive heating (IH).


===Low frequency electric heating===
===Low frequency electric heating===
[[File:Low - Frequency Heating.png|thumb|374x374px|'''Fig. 1''' - Schematic of low frequency electric heating mechanism.<ref name=":42">Mohsin Rehman, M., and Meribout, M. 2012. Conventional versus electrical enhanced oil recovery: a review. ''J Petrol Explor Prod Technol'' '''2:'''157-167</ref>|link=https://petrowiki.spe.org/File:Low_-_Frequency_Heating.png|alt=]]Low frequency electric heating is often referred to as Ohmic/Joule heating. Electric current is passed through the formation and due to power dissipation <ref name=":42" /> heat is produced resulting in an increased reservoir temperature. This method is employed by using two wells drilled into the formation. One well represents the anode and the other the cathode. The electrodes are cased and effectively insulated in the adjacent formations. A potential difference is provided between the two electrodes, and a current is allowed to pass through the formation. The alternating current frequency ranges from 0.1 to 60 cycles/sec. <ref>Kern, L., 1974. ''Method of Producing Bitumen from a Subterranean Tar Sand Formation''. U.S. Patent 3,848,671.</ref> The interstitial salty water present in the formation conducts electricity well increasing hydrocarbon vibration ultimately increasing the local reservoir temperature. The heat produced near the electrodes can easily vaporize the salinated water, increasing the resistance of the conducting path and impeding heat transfer. Calculating an accurate yet optimal electrical conductivity for the formation is therefore vital in these operations.
[[File:Low - Frequency Heating.png|thumb|374x374px|'''Fig. 1''' - Schematic of low frequency electric heating mechanism.<ref name=":4" />|link=https://petrowiki.spe.org/File:Low_-_Frequency_Heating.png|alt=]]Low-frequency electric heating is often referred to as Ohmic/Joule heating. Electric current is passed through the formation and due to power dissipation <ref name=":4" /> heat is produced resulting in an increased reservoir temperature. This method is employed by using two wells drilled into the formation. One well represents the anode and the other the cathode. The electrodes are cased and effectively insulated in the adjacent strata. A potential difference is provided between the two electrodes and a current is allowed to pass through the formation. The current frequency ranges from 0.1 to 60 cycles/sec. <ref>Kern, L., (1974). ''Method of Producing Bitumen from a Subterranean Tar Sand Formation''. U.S. Patent 3,848,671.</ref> The interstitial salty water present in the formation conducts electricity, ultimately increasing the local reservoir temperature. The heat produced near the electrodes can easily vaporize the salinated water, increasing the resistance of the conducting path and impeding heat transfer. Calculating an accurate yet optimal electrical conductivity for the formation is therefore vital in these operations.


The electrical conductivity in the formation can be calculated by the Archie and Humble's relation <ref name=":42" />:
The electrical conductivity in the formation can be calculated by the Archie and Humble's relation <ref name=":4" />:


<math>R=\frac{0.62R_w}{\phi^{2.15}S_w^2}
<math>R=\frac{0.62R_w}{\phi^{2.15}S_w^2}
</math>            , ....................(1)
</math>            , ....................(1)


where φ is porosity of the reservoir, Sw is the water saturation and Rw is the resistivity of brine given in ohm-m. The term Rw illustrates the dependance of water resistivity on temperature and is defined as:
where φ is the porosity of the reservoir, Sw is the water saturation and Rw is the resistivity of brine given in ohm-m. The term Rw illustrates the dependence of water resistivity on temperature and is defined as:


<math>R_w = \frac{R_{wt}\bigl(T_r-251.65\bigr)}{T-251.65}</math>    , ....................(2)
<math>R_w = \frac{R_{wt}\bigl(T_r-251.65\bigr)}{T-251.65}</math>    , ....................(2)


where T is the initial temperature of reservoir in Kelvin while Tr is the reservoir temperature after passage of electric current through it.  [[File:High Frequency EEOR.png|'''Fig. 2 -''' Schematic of high frequency electric heating mechanism. <ref>Chhetri AB, Islam MR (2008) A critical review of electromag- netic heating for enhanced oil recovery. Pet Sci Technol 26(14):1619–1631</ref>|alt=|link=https://petrowiki.spe.org/File:High_Frequency_EEOR.png|thumb|341x341px]]
where T is the initial temperature of the reservoir in Kelvin while Tr is the reservoir temperature after the passage of electric current through it.  [[File:High Frequency EEOR.png|'''Fig. 2 -''' Schematic of high frequency electric heating mechanism. <ref>Chhetri AB, Islam MR (2008) A critical review of electromag- netic heating for enhanced oil recovery. Pet Sci Technol 26(14):1619–1631</ref>|alt=|link=https://petrowiki.spe.org/File:High_Frequency_EEOR.png|thumb|341x341px]]
===High frequency electric heating===
===High-frequency electric heating===
High frequency electric heating operates within frequency ranges of 300 to 300,000 MHz. Such high frequencies with short wavelengths are classified as microwaves. This is why high frequency electric heating is commonly referred to as microwave heating.
High-frequency electric heating operates within frequency ranges of 300 to 300,000 MHz. Such high frequencies with short wavelengths are classified as microwaves. This is why high-frequency electric heating is commonly referred to as microwave heating.
 
In microwave heating, microwaves interact with the water molecules present in the formation. These molecules are set into circulatory and oscillatory motion <ref>Okassa FD, Godi A, De Simoni M, Manotti M, Maddinelli G., (2010). A nonconventional EOR technology using RF/MW heating coupled with a new patented well/reservoir interface. In: SPE annual tech- nical conference and exhibition. Society of Petroleum Engineers</ref> generating frictional heat which then may be transferred to its neighbors (mainly the matrix and the oil) ultimately elevating the temperature of the reservoir. The extent of temperature elevation is determined by the amount of microwave energy absorbed by the fluids. <ref name=":0">Li, D. 2019. Comparative Evaluation of Electrical Heating Methods for Oil Sand Reservoirs (Unpublished doctoral thesis). University of Calgary, Calgary, AB. <nowiki>http://hdl.handle.net/1880/110916</nowiki></ref> As shown in Fig.2., an oil reservoir is heated up under radiation of microwaves emitted from an antenna located in the wellbore and the oil is being produced to the surface through a production well.[[File:Inductive Heating.png|thumb|343x343px|'''Fig. 3 -''' Schematic of Inductive electric heating mechanism. <ref name=":7">Ali, S. M., and B.. Bayestehparvin. (2018). "Electrical Heating — Doing the Same Thing Over and Over Again …." Paper presented at the SPE Canada Heavy Oil Technical Conference, Calgary, Alberta, Canada, doi: <nowiki>https://doi.org/10.2118/189724-MS</nowiki></ref>|alt=]]
 
===Inductive heating===
Inductive heating and hydrocarbons have been known since at least 1929.<ref>Henry, I.W., (1929). ''Process and Apparatus for the production, from Hydrocarbon Material, of Gasses or Liquids of'' ''Changed Molecular Weight''. U.S. Patent 321,910.</ref> It was not until the early 1980's, that the Fisher brothers engineered a way to implement this process for in-situ recovery on a larger scale. <ref>Fisher, S.T., (1981). Induction Heating of Oil Shale In Situ: Eddy Currents vs Displacement Currents. ''In Situ;(United States)'', '''5'''(3), pp. 221–237.</ref>
 
The frequency for inductive heating ranges from low to medium (10 kHz or more). Inductive heating generates heat near the wellbore typically in vertical wells. A large diameter coil is intertwined among the well (either vertically or horizontally) and heats the oil sands. <ref name=":7" /> The alternating electric and magnetic fields present around the coil cause eddy currents. These eddy currents flow through the metallic materials present in the formation producing heat and raising the temperature. <ref name=":4" />
 
The increase in temperature can be calculated as follows <ref name=":4" />:
 


In microwave heating, microwaves interact with the water molecules present in the formation. These molecules are set into circulatory and oscillatory motion<ref>Okassa FD, Godi A, De Simoni M, Manotti M, Maddinelli G (2010) A nonconventional EOR technology using RF/MW heating coupled with a new patented well/reservoir interface. In: SPE annual tech- nical conference and exhibition. Society of Petroleum Engineers</ref> generating frictional heat which then may be transferred to its neighbours (mainly the matrix and the oil) ultimately elevating the temperature of the reservoir. The extent of temperature elevation is determined by the amount of microwave energy absorbed by the oil. <ref name=":5">Li, D. (2019). Comparative Evaluation of Electrical Heating Methods for Oil Sand Reservoirs (Unpublished doctoral thesis). University of Calgary, Calgary, AB. <nowiki>http://hdl.handle.net/1880/110916</nowiki></ref>
<math>\rho C_p{dT \over dt} + \rho_f C_{pf} \overrightarrow{V_f} \overrightarrow{\bigtriangledown}\Tau = \overrightarrow{\bigtriangledown}\bigl(\lambda_c\overrightarrow{\bigtriangledown}\Tau\bigr)+P</math>    , ....................(3)


Shown in Fig.2., an oil reservoir is heated up under radiation of microwaves emitted from an antenna located in the wellbore and the oil is being produced to the surface through a production well.
where <math>C_p</math> and <math>\lambda_c</math> represent the density, specific heat capacity and thermal conductivity of the medium, respectively. <math>\rho_f C_{pf}</math> and <math>\overrightarrow{v_f}</math> are the density, specific heat capacity and superficial velocity of the fluid phase. The term P is the electromagnetic power that is dissipated per unit of volume and is a function of the electric field, <math>\overrightarrow{E}</math> and the effective conductivity of the medium, <math>\sigma</math>, and is given by:
[[File:Inductive Heating.png|thumb|343x343px|'''Fig. 3 -''' Schematic of Inductive electric heating mechanism. <ref name=":7" />|alt=]]


===Inductive heating===
<math>P = \frac{\sigma+\omega\varepsilon\tan\delta}{2}\times\left\vert \overrightarrow{E} \right\vert^2</math>     , ....................(4)
Inductive heating and hydrocarbons have been known since at least 1929.<ref>Henry, I.W., 1929. ''Process and Apparatus for the production, from Hydrocarbon Material, of Gasses or Liquids of'' ''Changed Molecular Weight''. U.S. Patent 321,910.</ref> It was not until the early 1980's, that the Fisher brothers engineered a way to implement this process for in-situ recovery on a larger scale.<ref>Fisher, S.T., 1981. Induction Heating of Oil Shale In Situ: Eddy Currents vs Displacement Currents. ''In Situ;(United States)'', '''5'''(3), pp. 221–237.</ref>


The frequency for inductive heating ranges from low to medium (10 kHz or more). Inductive heating generates heat near the wellbore typically in vertical wells. A large diameter coil is intertwined among the well (either vertically or horizontally) and heats the oil sands. <ref name=":7">'''Electrical Heating — Doing the Same Thing Over and Over Again ...'''</ref> The alternating electric and magnetic fields present around the coil causes eddy currents. These eddy currents flow through the metallic materials present in the formation producing heat and raising the temperature. <ref name=":43">Mohsin Rehman, M., and Meribout, M. 2012. Conventional versus electrical enhanced oil recovery: a review. ''J Petrol Explor Prod Technol'' '''2:'''157-167</ref>
===Additional electrical heating methods===
Other recently explored methods of electrical heating include:


The increase in temperature can be calculated as follows:
#Electromagnetic heating.
#Electrocarbonization.
#Electro-osmosis.
#Laser heating.
#Ultrasonic wave heating.
#Hybrid processes.


<math>\rho C_p{dT \over dt}+\rho_fC_{pf}\overrightarrow{V_f}\overrightarrow{\nabla\T} = \overrightarrow{\nabla}\cdot\bigl(\lambda_c\overrightarrow{\nabla\T}\bigr)+P</math>
Farouq Ali et al. (2018)<ref name=":7" /> have gone into detail about the above-explored methods. While these methods have yielded viable experimental results, due to the cost and logistics they are not widely used in the industry. As an example, ultrasonic wave heating has increased the recovery rate in a Western Siberian field in Russia to 10.2tons/day, an increase of 91% in hydrocarbon production. <ref>Abramov VO, Abramova AV, Bayazitov VM, Marnosov AV, Kuleshov SP, Gerasin AS (2016) Selective ultrasonic treatment of perforation zones in horizontal oil wells for water cut reduction. Appl Acoust 103:214–220</ref>


'''INSERT EQUATION HERE 3 <ref name=":43" />'''
A summary and description of the electrical heating methods can be found in Table 1. below. <ref name=":0" />
[[File:Electrical Heating Tech.png|center|thumb|747x747px|Table 1 - Summary of electrical heating methods.<ref name=":0" />]]


where....
==Electrical heating selection==
Each reservoir is unique, so understandably, different electrical techniques can be applied based on the characterization of the oil reservoir. Water saturation, salinity, mineralogy and frequency are all key factors in the successful implementation of electrical heating. <ref>Eskandari S, Jalalalhosseini S, Mortezazadeh E (2015) Microwave heating as an enhanced oil recovery method—potentials and effective parameters. Energy Sources Part A Recovery Util Environ Effects 37(7):742–749</ref>


<math>P = \frac{\sigma+\omega\varepsilon\tan\delta}{2}\times\left\vert \overrightarrow{E} \right\vert^2</math>
==Comparison between EEOR techniques and SAGD==
==Comparison between EEOR techniques and SAGD==
All thermal recovery methods for heavy oil, tar sands and bitumen reservoirs work on the principle of thermal energy being transferred to the oil, reducing the viscosity and allowing for flow towards the production well. The most popular thermal recovery method is Steam Assisted Gravity Drainage (SAGD), followed by CSS and steam floods. While often used in unconventional reservoirs, these methods have not been yet investigated in thinner, less permeable, heterogeneous reservoirs, or connected by water. <ref name=":52">Li, D. (2019). Comparative Evaluation of Electrical Heating Methods for Oil Sand Reservoirs (Unpublished doctoral thesis). University of Calgary, Calgary, AB. <nowiki>http://hdl.handle.net/1880/110916</nowiki></ref> For this reason, electrothermal methods have attracted more attention for the difficult reservoirs where conventional thermal methods are not expected to work. <ref name=":6">Wang, J., Bryan, J. L., & Kantzas, A. (2008, January). ''Comparative Investigation of thermal processes for marginal bitumen resources.'' In International Petroleum Technology Conference. International Petroleum Technology Conference.</ref>
All thermal recovery methods for heavy oil, tar sands and bitumen reservoirs work on the principle of thermal energy being transferred to the oil, reducing the viscosity and allowing for flow towards the production well. The most popular thermal recovery method is Steam Assisted Gravity Drainage ([[Steam assisted gravity drainage|SAGD]]), followed by CSS and steam floods. While often used in unconventional reservoirs, these methods have not been yet investigated in thinner, less permeable, heterogeneous reservoirs, or containing bottom water zones. <ref name=":0" /> For this reason, electrothermal methods have attracted more attention for the difficult reservoirs where conventional thermal methods are not expected to work. <ref name=":5">Wang, J., Bryan, J. L., & Kantzas, A., (2008). ''Comparative Investigation of thermal processes for marginal bitumen resources.'' In International Petroleum Technology Conference. International Petroleum Technology Conference.</ref>


Li (2019) published a comparison between the EEOR and SAGD in part of his dissertation. Reservoirs with different petrophysical properties of the Athabasca McMurray oil sands in Alberta, Canada were modeled using the Computer Modeling Group (CMG) STARS on bitumen reservoirs.
Li (2019) published a comparison between the EEOR and SAGD in part of his dissertation. Reservoirs with different petrophysical properties of the Athabasca McMurray oil sands in Alberta, Canada were modeled using the Computer Modeling Group (CMG) STARS on bitumen reservoirs.


#For a pay zone of 5m thickness, simulation results showed the electrical resistance heating to recover more bitumen than SAGD.<ref name=":52" />
#For a pay zone of 5m thickness, simulation results showed the electrical resistance heating to recover more bitumen than SAGD. <ref name=":0" />
#For a pay zone with a thick bottom water layer of 15m, SAGD methods were not useful. Electrical heating produced 14% bitumen after 14 years of production whereas SAGD methods only recovered 1%. <ref name=":52" />
#For a pay zone with a thick bottom water layer of 15m, SAGD methods were not useful. Electrical heating produced 14% bitumen after 14 years of production whereas SAGD methods only recovered 1%. <ref name=":0" />
#SAGD performance dramatically decreases in low permeability reservoirs. Luckily, low permeability has a small effect on the electrical resistance heating process.<ref name=":52" /> In the simulation of a 300mD reservoir, electric heating is reported to recover 12% of bitumen, while only 2% of bitumen is produced by SAGD.<ref name=":6" />
#SAGD performance dramatically decreases in low permeability reservoirs. Luckily, low permeability has a small effect on the electrical resistance heating process. <ref name=":0" /> In the simulation of a 300mD reservoir, electric heating is reported to recover 12% of bitumen, while only 2% of bitumen is produced by SAGD. <ref name=":5" />
 
An advantage that EEOR methods - specifically Microwave-Assisted Gravity Drainage (MWAGD) - have over SAGD is the speed at which heat transfer occurs. MWAGD is a rapid process and less time-consuming than conventional thermal methods. Additionally, MWAGD does not cause any consequential damage to the formation. <ref>Jha, K. N., & Chakma, A. (1999). ''Heavy-oil recovery from thin pay zones by electromagnetic heating.'' Energy Sources, 21(1-2), 63-73. Heavy Oil Conference and Exhibition. Society of Petroleum Engineers</ref> Moreover, reservoir heterogeneity does not significantly affect the overall energy efficiency in electrical heating processes. <ref>Rangel-German, E. R., Schembre, J., Sandberg, C., & Kovscek, A. R. (2004). ''Electrical-heating- assisted recovery for heavy oil''. Journal of Petroleum Science and Engineering, 45(3-4), 213-231.</ref>


An advantage that EEOR methods - specifically Microwave-Assisted Gravity Drainage (MWAGD) - have over SAGD is the speed at which heat transfer occurs. MWAGD is a rapid process, and less time consuming than the conventional thermal methods. Additionally, MWAGD does not cause any consequential damage to the formation.<ref>Jha, K. N., & Chakma, A. (1999). ''Heavy-oil recovery from thin pay zones by electromagnetic heating.'' Energy Sources, 21(1-2), 63-73. Heavy Oil Conference and Exhibition. Society of Petroleum Engineers</ref> Moreover, reservoir heterogeneity does not significantly affect the overall energy efficiency in electrical heating processes. <ref>Rangel-German, E. R., Schembre, J., Sandberg, C., & Kovscek, A. R. (2004). ''Electrical-heating- assisted recovery for heavy oil''. Journal of Petroleum Science and Engineering, 45(3-4), 213-231.</ref>
Despite the popular use of steam-based thermal recovery methods, unavoidable challenges arise. Injecting steam at temperature ranges of 200 to 250<sup>o</sup>C leads to overheating and heat loss. There are some instances where a top/bottom water or top/bottom gas cap is present in the reservoir. In these cases, steam injection processes are negatively affected since the steam chamber is in touch with these regions. <ref>Wacker, B., Karmeileopardus, D., Trautmann, B., Helget, A., & Torlak, M. (2011). ''Electromagnetic Heating for In-situ Production of heavy oil and bitumen Reservoirs.'' In Canadian Unconventional Resources Conference. Society of Petroleum Engineers.</ref> Fortunately, these challenges can be mitigated via EEOR methods.


Despite the popular use of steam based thermal recovery methods, unavoidable challenges arise. Injecting steam at temperature ranges of 200 to 250<math>^\circ</math>C''',''' leads to overheating and heat loss. There are some instances where a top/bottom water or top/bottom gas cap is present in the reservoir. In these cases, steam injection processes negatively affect enhanced oil production since the steam chamber is in touch with these regions. <ref>Wacker, B., Karmeileopardus, D., Trautmann, B., Helget, A., & Torlak, M. (2011, January). ''Electromagnetic Heating for In-situ Production of heavy oil and bitumen Reservoirs.'' In Canadian Unconventional Resources Conference. Society of Petroleum Engineers.</ref> Fortunately, these challenges can be mitigated via EEOR methods.
==Advantages and disadvantages of EEOR==
==Comparison of different EEOR techniques==
===Advantages of EEOR techniques===
===Advantages of EEOR techniques===
Electrical heating works on the basis of targeting part of the reservoir instead of heating the bulk reservoir. <ref name=":02">Mukhametshina, A., and Martynova, E. 2013. Electromagnetic Heating of Heavy Oil and Bitumen: A Review of Experimental Studies and Field Applications. ''J. Pet. Engineering'' '''2013,''' 476519:1-7. http://dx.doi.org/10.1155/2013/476519</ref> The advantage to this, is that the specific heated area can be heated up more effectively and with lower heat losses.
Electrical heating has numerous advantages over conventional thermal methods. Electrical heating works on the basis of targeting part of the reservoir instead of heating the bulk reservoir. <ref name=":6" /> The advantage to this is that the specific area can be heated up more effectively and with lower heat losses. Additionally, this proves that these techniques are more efficient and cost-effective when compared to the standard EOR methods. Another major advantage of EEOR methods is their applicability in heterogeneous reservoir environments. <ref>Carrizales M, Lake LW,. (2009). Two-dimensional COMSOL simulation of heavy-oil recovery by electromagnetic heating. In: COMSOL conference held in Boston, Massachusetts, USA</ref> Geology or characterization is not affected by employing electrical techniques allowing for EEOR to be suitably utilized in different reservoirs having different formation depths, formation porosity and permeability, temperature, pressure and thickness. <ref name=":8">Oliveira H, Barillas JL. 92009). Energetic optimization to heavy oil recovery by electromagnetic resistive heating (ERH). In: SPE Latin American and Caribbean Petroleum Engineering Conference, Colombia</ref>


These methods are less resources and energy intensive - and economically more expedient compared to other thermal recovery methods.
Additional advantages include <ref name=":0" />:


Electrical heating has numerous advantages over conventional thermal methods. For one, electrical heating methods are more efficient in heterogeneous reservoir environments.<ref>Carrizales M, Lake LW (2009) Two-dimensional COMSOL simulation of heavy-oil recovery by electromagnetic heating. In: COMSOL conference held in Boston, Massachusetts, USA</ref> This is why it is a popular  They are also advantageous in the following ways:
#'''Oil production rate improvements''' - Due to a reduction in water flowing in an oil reservoir because of elimination of water injection.
====Oil production rate improvements====
#'''Improved volumetric sweep efficiency ''-''''' Effective heating occurring in low permeability zones.
#'''Applicability in deep reservoirs ''-''''' Overcoming the limitation caused by high reservoir pressures in steam injection processes.
#'''Reduced energy requirements -''' Significantly lower operating temperatures equate to reduced energy requirements.
#'''Reduced sensitivity -''' No fluid injection eliminates sensitivity in reservoirs containing clays.
#'''Cost reduction -''' Elimination of equipment associated with fluid injection and reduction in energy lowers OPEX costs.
#'''Versatility -''' Some EEOR methods rely on the presence of the water phase to establish ionic conduction paths of heating. Others have the ability to have the heating adjusted to accommodate any water saturation, especially for low water content. <ref>Sresty, G.C., Dev, H., Snow, R.H. and Bridges, J.E., (1986). Recovery of Bitumen from Tar Sand Deposits with the Radio Frequency Process. ''SPE Reservoir Engineering'', '''1'''(01), pp. 85–94.</ref>
#'''Efficiency ''-''''' Significantly faster operations than SAGD and other EOR methods. EEOR operates during hydrocarbon production thus avoiding a differential in reservoir and wellbore pressure, consequently avoiding formation damage.


improvement of oil rates due , improvement of oil rates due to a reduction in water flowing in an oil reservoir because of elimination of water injection
#
#
===='''Cost Reduction'''====
The elimination of equipment and operating costs associated with fluid injection;
===='''Reduced Sensitivity'''====
===='''Reduced Energy Requirements'''====
===='''Improved Volumetric Sweep Efficiency'''====
Water saturation, salinity and frequency are all key factors in the successful implementation of electrical heating. <ref>Eskandari S, Jalalalhosseini S, Mortezazadeh E (2015) Microwave heating as an enhanced oil recovery method—potentials and effective parameters. Energy Sources Part A Recovery Util Environ Effects 37(7):742–749</ref>
===Disadvantages of EEOR techniques===
===Disadvantages of EEOR techniques===
ENTER SOMETHING HERE
One of the most common operation problems with EEOR is the possibility of high-water saturation zones in the wellbore. Most heating occurs in those zones. <ref name=":7" /> EEOR additionally raises the temperature of rocks and other inorganic materials present in the reservoir. While this can be seen as advantageous when looking at the Athabasca oil sands in Alberta, Canada, it is disadvantageous when one considers shales. <ref name=":7" /> It has also been reported that extensive use in crude oil reservoirs has resulted in formation damages due to the deposition of paraffin near the wellbore <ref>Mohsin M, Meribout M., (2015). An extended model for ultrasonic-based enhanced oil recovery with experimental validation. Ultrason Sonochem 23:413–423</ref>, reducing the formation permeability and ultimately decreasing oil production.


TABLE 1.1 FROM THE PAPER CAN BE APPLIED HERER
==Comparison of different EEOR techniques==
 
In addition, Inductive heating also raises the temperature of rocks and other inorganic materials present in the reservoir. The heat transfer from electromagnetic energy source to the porous rock media can be given by the energy equation
{| class="wikitable"
{| class="wikitable"
|+Table XX: Comparisons between EEOR Techniques <ref>Conventional and electrical EOR review: the development trend of ultrasonic application in EOR - Shafiai and Gohari 2020</ref>
|+Table 2 - Comparisons between EEOR Techniques <ref>Shafiai, S.H., Gohari,. (2020). A. Conventional and electrical EOR review: the development trend of ultrasonic application in EOR. ''J Petrol Explor Prod Technol'' 10, 2923–2945. <nowiki>https://doi.org/10.1007/s13202-020-00929-x</nowiki></ref>
!Electrical Enhanced Oil Recovery Method (EEOR)
!Electrical Enhanced Oil Recovery Method (EEOR)
!Benefits
!Benefits
!Limitations
!Limitations
|-
|-
|Inductive
|Low Frequency
|
|
*More safer, advanced, and high quality of the heating procedure, high efficiency and faster heating (Lucía et al. 2018)
*Suitable for reservoirs with high permeability or fractures. <ref name=":4" />
*Applicable on various types of reservoirs with different characteristics (Oliveira et al. 2009)
*Favourable for reservoirs whose thermal methods are not suitable (Rehman and Meribout 2012)
|
|
*Providing only limited heat around the wellbore (Hasanvan and Golparvar 2014)
*Non-uniform temperature pattern.<ref>Saeedfar A, Lawton D, Osadetz K., (2016). Directional RF heating for heavy oil recovery using antenna array beam-forming. In: SPE Canada heavy oil technical conference. Society of Petroleum Engineers</ref> To maintain continuity the temperature must be below the boiling point of water.
*Electrodes must be utilized which introduces the possibility of corrosion in high salt concentration reservoirs.<ref name=":4" />
|-
|-
|Low Frequency
|High Frequency
|
|
*Can be considered as an alternative for steam injection method and suitable for reservoirs with high permeability or fractures (Rehman and Meribout 2012)
*Propagation ability is independent of transporting material. <ref>Carrizales MA, Lake L, Johns RT. (2008). Production improvement of heavy-oil recovery by using electromagnetic heating. In: SPE annual technical conference and exhibition. Society of Petroleum Engineers</ref>
 
*Suitable for heavy oil reservoirs. <ref name=":9">Hasibuan, M.Y.; Regina, S.; Wahyu, R.; Situmorang, D.; Azmi, F.; Syahputra, R.; Batubara, L.P.Y.; Prabowo, F.; Setiawan, A.; Afin, M.F.; Afdhol, M.K.; Erfando, T. (2020). Electrical Heating for Heavy Oil: Past, Current, and Future Prospect. ''Preprints'' 2020, 2020010115 (doi: 10.20944/preprints202001.0115.v1).</ref>
*
*Favourable for offshore oil fields in terms of equipment compactness. <ref>Bientinesi M, Petarca L, Cerutti A, Bandinelli M, De Simoni M, Manotti M, Maddinelli G., (2013). A radiofrequency/microwave heating method for thermal heavy oil recovery based on a novel tight-shell conceptual design. J Pet Sci Eng 107:18–30</ref>
|
|
*Non-uniform temperature pattern (Saeedfar et al. 2016)
*Effective energy is only able to penetrate into the very near-wellbore region. <ref name=":10">Hasanvand MZ, Golparvar A., (2014).  A critical review of improved oil recovery by electromagnetic heating. Pet Sci Technol 32(6):631–637</ref>
*Production must be shut down during the recovery method. <ref name=":9" />
*Not suitable for water flooded reservoirs. <ref name=":4" />
*The source may get damaged because of the extensive heat produced. <ref name=":4" />
|-
|-
|MW & RF heating
|Inductive
|
|
*Propagation ability independent from transporting material (Carrizales et al. 2008)
*High quality of the heating procedure, high efficiency and faster heating. <ref>Lucía Ó, Domínguez A, Sarnago H, Burdío JM., (2018). Induction heating. Control Power Electron Convert Syst Chapter 21(2):265–287</ref>
*Covering heat distribution over a large volume of reservoir (Bientinesi et al. 2013; Saeedfar et al. 2016)
*Applicable on various types of reservoirs with different characteristics. <ref name=":8" />
*The geology of formation is not much effective on this method. Highly efficient method in the energy generation-radiation process. Favorable for off-shore oil fields in terms of equipment compactness (Bientinesi et al. 2013)
*Favourable for reservoirs whose thermal methods are not suitable. <ref name=":4" />
*Useful in reservoirs with low in situ water saturation. <ref name=":4" />  
|
|
*Effective energy only able to penetrate into the very near wellbore region (Hasanvand and golaparvar 2014)
*Providing only limited heat around the wellbore. <ref name=":10" />
*Limited penetration depth of microwaves in conductive mediums (watersaturated fluid) (Troch et al. 1996)
|-
|-
|Ultrasonic
|Ultrasonic
|
|
*Cost-saving and environmental-friendly method (Wang et al. 2020)
*Applicable recovery method during oil production operation. <ref>Sun R, Liang C, Liu J, Lin L, Xiong Q, Wu S., (2011). Effect of ultra- sonic treatment on damage relieving of porous media. In: 2011 international conference on electrical and control engineering (ICECE). IEEE</ref>
*Application while oil production operation is running (Sun et al. 2011)
*Suitable for high water-saturated and depleted reservoirs. <ref name=":4" />
*Precise positioning of wellbore stimulation (Mohsin and Meribout 2015) and stimulation for any interval of interest (Meribout 2018)
*Heavy oil lying behind the water is still applicable to be produced. <ref name=":9" />
*Suitable for high water-saturated and depleted reservoirs (Rehman and Meribout 2012)
|
|
*Low capacity and efficiency of ultrasonic cavitation (Wan et al. 2019)
*Low capacity and efficiency of ultrasonic cavitation. <ref>Wan C, Wang R, Zhou W, Li L.,(2019) Experimental study on viscosity reduction of heavy oil by hydrogen donors using a cavitating jet. RSC Adv 9(5):2509–2515</ref>
|}An advantage to low frequency electric heating is that it can be suitably utilized in different reservoirs having different formation depths, formation porosity and permeability, temperature, pressure and thickness.<ref>Oliveira H, Barillas JL et al (2009) Energetic optimization to heavy oil recovery by electromagnetic resistive heating (ERH). In: SPE Latin American and Caribbean Petroleum Engineering Conference, Colombia</ref>
*Not suitable with a slurry mixture of sand and water. <ref name=":9" />
 
*Not recommended for unconsolidated formations with compressive strength of less than 150psi. <ref name=":9" />
disadvantages to low frequency electric heating - include from paper from the same figure
|}
 
Advantage to microwave heating
 
There is also a limitation of this process that the penetration depth of RF/MW wave is relatively small and depends mainly on the frequency of operation and composition of a reservoir. Different from the electrical resistance heating methods that rely on the presence of the water phase to establish ionic conduction paths of heating, the RF heating can be adjusted to accommodate any water saturation, especially for low water content (Sresty et al., 1986). It has been suggested to heat a reservoir by applying microwaves at 2.45 GHz, because this frequency can produce the resonance effect of water (Kovaleva et al., 2010b). However, such strict control of source frequency may not be necessary in field applications.
==Applications==
==Applications==
Due to the favorable results of electric heating, technologies for electrical heating have grown quickly. Countries like Russia, USA, Canada and China have begun utilizing these methods for oil production in their unconventional reservoirs, since the mid - 1960's. Electrical field trials continue to be underway in these areas as technologies continue to advance and improve.
Due to the favorable results of electric heating, technologies for electrical heating have grown quickly. Countries like Russia USA, Canada and China have begun utilizing these methods for oil production in their unconventional reservoirs, since the mid - 1960's. Electrical field trials continue to be underway in these areas as technologies continue to advance and improve.
===United States of America===
===United States of America===
In 1981, Bridges et al. <ref name=":2">] J. E. Bridges, J. J. Krstansky, A. Taflove, and G. C. Sresty, “The IITRI in situ RF fuel recovery process,” ''Journal of Microwave Power'', vol. 18, no. 1, pp. 3–14, 1983.</ref> conducted field tests on tar sands in Asphalt Ridge, Utah, USA. Even though this was a pilot test, the results from electrical heating were favorable in the tar sands field. Temperatures exceeded 473K and 30-35% recovery was achieved in just 20 days. <ref name=":2" /> These results were encouraging and exceeded the expectations of researchers, continuation of heating would result in a greater continuation of hydrocarbon production. Also noted, the power loss was minimal in all of the experiments, which proved the efficiency of the heating. <ref name=":2" />
In 1981, Bridges et al. <ref name=":1">Bridges, J.E., Krstansky, J.J., Taflove, A., and Sresty, G.C., (1983) “The IITRI in situ RF fuel recovery process,” ''Journal of Microwave Power'', vol. 18, no. 1, pp. 3–14</ref> conducted field tests on tar sands in Asphalt Ridge, Utah, USA. Even though this was a pilot test, the results from electrical heating were favorable in the tar sands field. Temperatures exceeded 473K and 30-35% recovery was achieved in just 20 days.<ref name=":1" /> These results were encouraging and exceeded the expectations of researchers; continuation of heating would result in a greater continuation of hydrocarbon production. Also noted, the power loss was minimal in all of the experiments, which proved the efficiency of the heating. <ref name=":1" />
 
Kasevich et al. (1994) <ref name=":2">Kasevich, R.S., Price, S.L., Faust, D.L., and Fontaine, M.F., (1994) “Pilot testing of a radio frequency heating system for enhanced oil recovery from diatomaceous earth,” in ''Proceedings of the SPE Annual Technical Conference & Exhibition'', pp. 105–113, New Orleans, La, USA</ref> conducted a series of qualitative field tests in Bakersfield, California, United States of America in early 1992 to better understand EEOR methods underground. While oil production rates were not reported, Kasevich et al. successfully proved that the radio frequency producer used could efficiently focus its radiation pattern into the desired region by measuring return loss and electromagnetic radiation. <ref name=":2" />


Kasevich et al.<ref name=":3">R.S.Kasevich,S.L.Price,D.L.Faust,andM.F.Fontaine,“Pilot testing of a radio frequency heating system for enhanced oil recovery from diatomaceous earth,” in ''Proceedings of the SPE Annual Technical Conference & Exhibition'', pp. 105–113, New Orleans, La, USA, September 1994.</ref> conducted a series of qualitative field tests in Bakersfield, California, United States of America in early 1992 to better understand EEOR methods underground. While oil production rates were not reported, Kasevich et al. successfully proved that the radio frequency producer used could efficiently focus its radiation pattern into the desired region by measuring return loss and electromagnetic radiation. <ref name=":3" />
===Canada===
===Canada===
Commercial electric heating was first introduced in the Wildmere Field in Alberta, Canada in 1986. Wildmere Field is characterized as a heavy oil field with an oil viscosity of 20 Pa.s. It was reported that primary production methods yield 0.95 tonnes/day of oil production. EEOR methods were quickly introduced in the field (eight months after initial production began) and production increased to 3.18 tonnes/day. <ref name=":1">H. L. Spencer, “Electromagnetic Oil Recovery, Ltd,” Calgary, Canada, 1987.</ref> Also, another well in the same field tripled its oil production rate after the introduction of EM heating.
Commercial electric heating was first introduced in the Wildmere Field in Alberta, Canada in 1986. Wildmere Field is characterized as a heavy oil field with an oil viscosity of 20 Pa.s. It was reported that primary production methods yield 0.95 tonnes/day of oil production. EEOR methods were quickly introduced in the field (eight months after initial production began) and production increased to 3.18 tonnes/day. <ref name=":3">L. Spencer, (1987), “Electromagnetic Oil Recovery, Ltd,” Calgary, Canada</ref> Also, another well in the same field tripled its oil production rate after the introduction of EM heating.


Two pilot tests were conducted in 1988-1989 in the Lloydminster Heavy Oil Area, Saskatchewan, Canada. While long-term heating could not be achieved (due to equipment failure and unique reservoir conditions), the technical results looked promising. Water cut drop in the field decreased by 5%, while production rate doubled. <ref name=":1" /> This is directly related to the electric heating effects and improvement of oil mobility.
Two pilot tests were conducted in 1988-1989 in the Lloydminster Heavy Oil Area, Saskatchewan, Canada. While long-term heating could not be achieved (due to equipment failure and unique reservoir conditions), the technical results looked promising. Water cut in the field decreased by 5%, while production rate doubled. <ref name=":3" /> This is directly related to the electric heating effects and improvement of oil mobility.


==References==
==References==
<references />
<references />
==See also==
*[https://onepetro.org/IPTCONF/proceedings-abstract/20IPTC/1-20IPTC/D012S101R001/154703 Production Optimization Through Intelligent Multilateral Wells in Heavy Oil Fields via Electrical Heating]
*[[Enhanced oil recovery (EOR)]]
*[[Electromagnetic heating of oil]]
*[[Electromagnetic heating process]]<br />

Latest revision as of 22:48, 9 April 2021

Electrical heating is an EOR process that works on the principle of transferring heat into the reservoir via electrical means. It involves injection of electrical energy to the reservoir, heating the area and causing an increase in oil temperature. Heating up the reservoir reduces the oil viscosity, thus, making it easier to flow. While electrical heating is a relatively new technique, advances in the past couple of years have allowed for testing by theoretical, laboratories, and field trial research in areas including, Russia, the United States of America, Canada and other countries.[1] Focus on electrical enhanced oil recovery (EEOR) processes is of great importance, because of the abundance of heavy oil, tar sand and bitumen reserves in Canada, Venezuela, countries of the former USSR, the United States of America and China. [2][3][4]

Basic processes

The EEOR technique works on the basis of using electrical means (e.g. radiofrequency (RF) waves, inductive heating and DC heating). The primary function of this process is to increase the mobility of oil for it to flow easily towards the production well. The electrical energy that is supplied either raises the temperature of the reservoir or creates vibrations in the hydrocarbon molecules. [5]

Heating the reservoir is either done by a steam chamber or direct heating into the near wellbore. The amount of power required for each well and formation is dictated by the production rate and operational requirements. The frequency of the electric current determines the mode of electrical heating. The alternating electric field causes polar molecules to align and relax. The molecular movement generates heat. Electrical heating design's key goal is to reduce electrical losses while localizing heating.

The four critical components of electric heating applications are:

  1. Power conditioning unit.
  2. Power supply system.
  3. Electrode assembly.
  4. Ground return system.  

Major mechanisms

Electric heating can be divided into three categories depending on the frequency of the electrical current being used. These include:

  1. Low-frequency electric heating (also referred to as resistive).
  2. High-frequency electric heating (commonly called microwave heating).
  3. Inductive heating (IH).

Low frequency electric heating

Fig. 1 - Schematic of low frequency electric heating mechanism.[5]

Low-frequency electric heating is often referred to as Ohmic/Joule heating. Electric current is passed through the formation and due to power dissipation [5] heat is produced resulting in an increased reservoir temperature. This method is employed by using two wells drilled into the formation. One well represents the anode and the other the cathode. The electrodes are cased and effectively insulated in the adjacent strata. A potential difference is provided between the two electrodes and a current is allowed to pass through the formation. The current frequency ranges from 0.1 to 60 cycles/sec. [6] The interstitial salty water present in the formation conducts electricity, ultimately increasing the local reservoir temperature. The heat produced near the electrodes can easily vaporize the salinated water, increasing the resistance of the conducting path and impeding heat transfer. Calculating an accurate yet optimal electrical conductivity for the formation is therefore vital in these operations.

The electrical conductivity in the formation can be calculated by the Archie and Humble's relation [5]:

, ....................(1)

where φ is the porosity of the reservoir, Sw is the water saturation and Rw is the resistivity of brine given in ohm-m. The term Rw illustrates the dependence of water resistivity on temperature and is defined as:

, ....................(2)

where T is the initial temperature of the reservoir in Kelvin while Tr is the reservoir temperature after the passage of electric current through it.  

Fig. 2 - Schematic of high frequency electric heating mechanism. [7]

High-frequency electric heating

High-frequency electric heating operates within frequency ranges of 300 to 300,000 MHz. Such high frequencies with short wavelengths are classified as microwaves. This is why high-frequency electric heating is commonly referred to as microwave heating.

In microwave heating, microwaves interact with the water molecules present in the formation. These molecules are set into circulatory and oscillatory motion [8] generating frictional heat which then may be transferred to its neighbors (mainly the matrix and the oil) ultimately elevating the temperature of the reservoir. The extent of temperature elevation is determined by the amount of microwave energy absorbed by the fluids. [9] As shown in Fig.2., an oil reservoir is heated up under radiation of microwaves emitted from an antenna located in the wellbore and the oil is being produced to the surface through a production well.

Fig. 3 - Schematic of Inductive electric heating mechanism. [10]

Inductive heating

Inductive heating and hydrocarbons have been known since at least 1929.[11] It was not until the early 1980's, that the Fisher brothers engineered a way to implement this process for in-situ recovery on a larger scale. [12]

The frequency for inductive heating ranges from low to medium (10 kHz or more). Inductive heating generates heat near the wellbore typically in vertical wells. A large diameter coil is intertwined among the well (either vertically or horizontally) and heats the oil sands. [10] The alternating electric and magnetic fields present around the coil cause eddy currents. These eddy currents flow through the metallic materials present in the formation producing heat and raising the temperature. [5]

The increase in temperature can be calculated as follows [5]:


, ....................(3)

where and represent the density, specific heat capacity and thermal conductivity of the medium, respectively. and are the density, specific heat capacity and superficial velocity of the fluid phase. The term P is the electromagnetic power that is dissipated per unit of volume and is a function of the electric field, and the effective conductivity of the medium, , and is given by:

, ....................(4)

Additional electrical heating methods

Other recently explored methods of electrical heating include:

  1. Electromagnetic heating.
  2. Electrocarbonization.
  3. Electro-osmosis.
  4. Laser heating.
  5. Ultrasonic wave heating.
  6. Hybrid processes.

Farouq Ali et al. (2018)[10] have gone into detail about the above-explored methods. While these methods have yielded viable experimental results, due to the cost and logistics they are not widely used in the industry. As an example, ultrasonic wave heating has increased the recovery rate in a Western Siberian field in Russia to 10.2tons/day, an increase of 91% in hydrocarbon production. [13]

A summary and description of the electrical heating methods can be found in Table 1. below. [9]

Table 1 - Summary of electrical heating methods.[9]

Electrical heating selection

Each reservoir is unique, so understandably, different electrical techniques can be applied based on the characterization of the oil reservoir. Water saturation, salinity, mineralogy and frequency are all key factors in the successful implementation of electrical heating. [14]

Comparison between EEOR techniques and SAGD

All thermal recovery methods for heavy oil, tar sands and bitumen reservoirs work on the principle of thermal energy being transferred to the oil, reducing the viscosity and allowing for flow towards the production well. The most popular thermal recovery method is Steam Assisted Gravity Drainage (SAGD), followed by CSS and steam floods. While often used in unconventional reservoirs, these methods have not been yet investigated in thinner, less permeable, heterogeneous reservoirs, or containing bottom water zones. [9] For this reason, electrothermal methods have attracted more attention for the difficult reservoirs where conventional thermal methods are not expected to work. [15]

Li (2019) published a comparison between the EEOR and SAGD in part of his dissertation. Reservoirs with different petrophysical properties of the Athabasca McMurray oil sands in Alberta, Canada were modeled using the Computer Modeling Group (CMG) STARS on bitumen reservoirs.

  1. For a pay zone of 5m thickness, simulation results showed the electrical resistance heating to recover more bitumen than SAGD. [9]
  2. For a pay zone with a thick bottom water layer of 15m, SAGD methods were not useful. Electrical heating produced 14% bitumen after 14 years of production whereas SAGD methods only recovered 1%. [9]
  3. SAGD performance dramatically decreases in low permeability reservoirs. Luckily, low permeability has a small effect on the electrical resistance heating process. [9] In the simulation of a 300mD reservoir, electric heating is reported to recover 12% of bitumen, while only 2% of bitumen is produced by SAGD. [15]

An advantage that EEOR methods - specifically Microwave-Assisted Gravity Drainage (MWAGD) - have over SAGD is the speed at which heat transfer occurs. MWAGD is a rapid process and less time-consuming than conventional thermal methods. Additionally, MWAGD does not cause any consequential damage to the formation. [16] Moreover, reservoir heterogeneity does not significantly affect the overall energy efficiency in electrical heating processes. [17]

Despite the popular use of steam-based thermal recovery methods, unavoidable challenges arise. Injecting steam at temperature ranges of 200 to 250oC leads to overheating and heat loss. There are some instances where a top/bottom water or top/bottom gas cap is present in the reservoir. In these cases, steam injection processes are negatively affected since the steam chamber is in touch with these regions. [18] Fortunately, these challenges can be mitigated via EEOR methods.

Advantages and disadvantages of EEOR

Advantages of EEOR techniques

Electrical heating has numerous advantages over conventional thermal methods. Electrical heating works on the basis of targeting part of the reservoir instead of heating the bulk reservoir. [1] The advantage to this is that the specific area can be heated up more effectively and with lower heat losses. Additionally, this proves that these techniques are more efficient and cost-effective when compared to the standard EOR methods. Another major advantage of EEOR methods is their applicability in heterogeneous reservoir environments. [19] Geology or characterization is not affected by employing electrical techniques allowing for EEOR to be suitably utilized in different reservoirs having different formation depths, formation porosity and permeability, temperature, pressure and thickness. [20]

Additional advantages include [9]:

  1. Oil production rate improvements - Due to a reduction in water flowing in an oil reservoir because of elimination of water injection.
  2. Improved volumetric sweep efficiency - Effective heating occurring in low permeability zones.
  3. Applicability in deep reservoirs - Overcoming the limitation caused by high reservoir pressures in steam injection processes.
  4. Reduced energy requirements - Significantly lower operating temperatures equate to reduced energy requirements.
  5. Reduced sensitivity - No fluid injection eliminates sensitivity in reservoirs containing clays.
  6. Cost reduction - Elimination of equipment associated with fluid injection and reduction in energy lowers OPEX costs.
  7. Versatility - Some EEOR methods rely on the presence of the water phase to establish ionic conduction paths of heating. Others have the ability to have the heating adjusted to accommodate any water saturation, especially for low water content. [21]
  8. Efficiency - Significantly faster operations than SAGD and other EOR methods. EEOR operates during hydrocarbon production thus avoiding a differential in reservoir and wellbore pressure, consequently avoiding formation damage.

Disadvantages of EEOR techniques

One of the most common operation problems with EEOR is the possibility of high-water saturation zones in the wellbore. Most heating occurs in those zones. [10] EEOR additionally raises the temperature of rocks and other inorganic materials present in the reservoir. While this can be seen as advantageous when looking at the Athabasca oil sands in Alberta, Canada, it is disadvantageous when one considers shales. [10] It has also been reported that extensive use in crude oil reservoirs has resulted in formation damages due to the deposition of paraffin near the wellbore [22], reducing the formation permeability and ultimately decreasing oil production.

Comparison of different EEOR techniques

Table 2 - Comparisons between EEOR Techniques [23]
Electrical Enhanced Oil Recovery Method (EEOR) Benefits Limitations
Low Frequency
  • Suitable for reservoirs with high permeability or fractures. [5]
  • Non-uniform temperature pattern.[24] To maintain continuity the temperature must be below the boiling point of water.
  • Electrodes must be utilized which introduces the possibility of corrosion in high salt concentration reservoirs.[5]
High Frequency
  • Propagation ability is independent of transporting material. [25]
  • Suitable for heavy oil reservoirs. [26]
  • Favourable for offshore oil fields in terms of equipment compactness. [27]
  • Effective energy is only able to penetrate into the very near-wellbore region. [28]
  • Production must be shut down during the recovery method. [26]
  • Not suitable for water flooded reservoirs. [5]
  • The source may get damaged because of the extensive heat produced. [5]
Inductive
  • High quality of the heating procedure, high efficiency and faster heating. [29]
  • Applicable on various types of reservoirs with different characteristics. [20]
  • Favourable for reservoirs whose thermal methods are not suitable. [5]
  • Useful in reservoirs with low in situ water saturation. [5]  
  • Providing only limited heat around the wellbore. [28]
Ultrasonic
  • Applicable recovery method during oil production operation. [30]
  • Suitable for high water-saturated and depleted reservoirs. [5]
  • Heavy oil lying behind the water is still applicable to be produced. [26]
  • Low capacity and efficiency of ultrasonic cavitation. [31]
  • Not suitable with a slurry mixture of sand and water. [26]
  • Not recommended for unconsolidated formations with compressive strength of less than 150psi. [26]

Applications

Due to the favorable results of electric heating, technologies for electrical heating have grown quickly. Countries like Russia USA, Canada and China have begun utilizing these methods for oil production in their unconventional reservoirs, since the mid - 1960's. Electrical field trials continue to be underway in these areas as technologies continue to advance and improve.

United States of America

In 1981, Bridges et al. [32] conducted field tests on tar sands in Asphalt Ridge, Utah, USA. Even though this was a pilot test, the results from electrical heating were favorable in the tar sands field. Temperatures exceeded 473K and 30-35% recovery was achieved in just 20 days.[32] These results were encouraging and exceeded the expectations of researchers; continuation of heating would result in a greater continuation of hydrocarbon production. Also noted, the power loss was minimal in all of the experiments, which proved the efficiency of the heating. [32]

Kasevich et al. (1994) [33] conducted a series of qualitative field tests in Bakersfield, California, United States of America in early 1992 to better understand EEOR methods underground. While oil production rates were not reported, Kasevich et al. successfully proved that the radio frequency producer used could efficiently focus its radiation pattern into the desired region by measuring return loss and electromagnetic radiation. [33]

Canada

Commercial electric heating was first introduced in the Wildmere Field in Alberta, Canada in 1986. Wildmere Field is characterized as a heavy oil field with an oil viscosity of 20 Pa.s. It was reported that primary production methods yield 0.95 tonnes/day of oil production. EEOR methods were quickly introduced in the field (eight months after initial production began) and production increased to 3.18 tonnes/day. [34] Also, another well in the same field tripled its oil production rate after the introduction of EM heating.

Two pilot tests were conducted in 1988-1989 in the Lloydminster Heavy Oil Area, Saskatchewan, Canada. While long-term heating could not be achieved (due to equipment failure and unique reservoir conditions), the technical results looked promising. Water cut in the field decreased by 5%, while production rate doubled. [34] This is directly related to the electric heating effects and improvement of oil mobility.

References

  1. 1.0 1.1 Mukhametshina, A., and Martynova, E. (2013). Electromagnetic Heating of Heavy Oil and Bitumen: A Review of Experimental Studies and Field Applications. J. Pet. Engineering 2013, 476519:1-7. http://dx.doi.org/10.1155/2013/476519
  2. Salager, J.L., Briceño, M.I., and Bracho, C.L. (2001). Heavy Hydrocarbons Emulsions. In Encyclopedic Handbook of Emulsion Technology, 455-495, ed. J. Sjöblom. New York City: Dekker
  3. Smalley, C. (2000). Heavy Oil and Viscous Oil. In Modern Petroleum Technology, Vol. 1 Upstream, Ch. 11, 409-435, sixth edition, ed. R.A. Dawe. New York City: Wiley & Sons Inc.
  4. Layrisse, I. (1999). Heavy Oil Production in Venezuela: Historical Recap and Scenarios for Next Century. Presented at the SPE International Symposium on Oilfield Chemistry, Houston, Texas, 16-19 February 1999. SPE-53464-MS. http://dx.doi.org/10.2118/53464-MS
  5. 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 Mohsin Rehman, M., and Meribout, M. 2012. Conventional versus electrical enhanced oil recovery: a review. J Petrol Explor Prod Technol 2:157-167
  6. Kern, L., (1974). Method of Producing Bitumen from a Subterranean Tar Sand Formation. U.S. Patent 3,848,671.
  7. Chhetri AB, Islam MR (2008) A critical review of electromag- netic heating for enhanced oil recovery. Pet Sci Technol 26(14):1619–1631
  8. Okassa FD, Godi A, De Simoni M, Manotti M, Maddinelli G., (2010). A nonconventional EOR technology using RF/MW heating coupled with a new patented well/reservoir interface. In: SPE annual tech- nical conference and exhibition. Society of Petroleum Engineers
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See also