This presentation is about Application of Electrical Heating in Enhanced Oil Recovery(EOR)

1. Electrical Heating
Present By:
Saeid Javidi
Course Instructor:
Dr.B.Sedaee Sola
Autumn 2015
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2. Introduction
Electrical Heating for heavy-oil recovery is not a new idea but
the commercialization and wider application of this technique
require detailed analyses to determine optimal application
conditions.
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3. Introduction
• Electrical Heating is a thermal process which can be applied to a well
to increase its productivity. The productivity increase is substantial and
comes about because of the removal of thermal adaptable skin
effects(Visco-Skin for Example) and the reduction of oil viscosity in
the vicinity of the wellbore.
• DHEH allows production enhancement and thus improvement of
recovery factor, with significantly lower investment costs when
compared with those typically associated with the implementation of
thermal technologies such as steam injection
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4. Conventional steam injection candidates such as steam
injection and hot water injection are limited to relatively
shallow, thick, permeable, and homogenous sands that
are onshore.
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5. Figure 1 describes how the process works.
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6. The essential components of an electrical heating system are:
• power supply,
• power delivery system,
• Electrode assembly,
• ground return.
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7. This technology uses a three-phase system designed to provide
a defined wattage according to different application and type of
cables.
The heat section is set downhole and is connected to the
surface with a power cable.
It generates heat to near wellbore region, decreasing viscosity
and friction and consequently increasing oil mobility.
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8. Salient features of the process are:
• It is a continuous, not a cycle process. Electrical Heating
occurs simultaneously with production of fluids.
• Low frequency Power(not microwave frequency) is used.
• All the downhole equipment can be contained within a single
wellbore.
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9. The variable frequency(2 to 60 Hz), power supply(Isted,1992), is
capable of delivering up to 300 kW of power. The power delivery
system may consist of tubing , cables or a combination of both. The
electrode assembly consist of bare casing pipe with fiberglass electrical
isolation joints attached to the ends.
The length of electrode and location in the reservoir is a matter of
engineering design.
The current return or ground can be the casing string above the
fiberglass insulation.
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10. Current leaves the power supply and is conducted down the power
delivery system to the electrode assembly. The electrode is in electrical
contact with reservoir formation. From the electrode, the current is
forced to flow through the reservoir and return to the power supply up
the casing.
The electrical path in the reservoir is primarily electrolytic because the
conducting path is through the connate water in the reservoir. The
connate water is heated by electrical losses and the remaining fluids and
rock are heated by thermal conduction.
The heated radius, the distance at which the oil viscosity is much
reduced, can be three to seven meters(Vermeulen,1988)
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11. The amount of power to stimulate the well effectively is governed by
the production rate as cooler fluids flow from the reservoir towards the
well as the hot fluids are produced.
Too much power can result in excessive temperatures and can damage
the electrode assembly.
The use of reservoir simulation to define operating power for a
particular flow rate is therefore critically important.
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12. Visco-Skin
The visco-skin is a zone of high oil viscosity that develops in
the low pressure region near the wellbore. It occurs in most
naturally producing oil wells, but is especially prevalent in
saturated heavy oils of 10 to 24° API gravity(McGee, 1989).
Visco-Skin can best described by reference to figure 2.
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13. 13
Figure 2

14. Radially approaching the wellbore from the reservoir, the pressure
decreases rapidly to the producing pressure. As the pressure drops, more
and more gas evolves from the oil into the gaseous phase.
A result of gas evolving from the oil is a viscosity profile like that
shown in Figure 2. The oil viscosity reaches the maximum at the
wellbore and decreases rapidly to the original oil viscosity in the
Reservoir.
The region of high oil viscosity usually extends only 1 to 2 meters into
the reservoir.
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15. As a result, flow is impaired. The magnitude of the
productivity decrease(Visco-Skin) depends on the ratio of oil
viscosity at the wellbore to live oil viscosity,(viscosity
parameter Pμ).
In heavy oil reservoirs, Pμ is typically grater than 10 and
productivity decrease caused by Visco-Skin is typically two or
three times(McGee,1991).
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16. Field Case Comparison
The well was drilled into the sparky formation in the Frog Lake area and
completed for electrical heating in June 1988. The oil there is heavy and
oil can be produced under primary conditions. Figure 3(5) Shows the
production history of the well. Peak production was 7.1 𝑚3
𝑑𝑎𝑦 and
declined to 3.0 𝑚3
𝑑𝑎𝑦 before electrical heating. The well produced for
153 operating days and then was electrically stimulated immediately the
production rate increased to over 12 𝑚3
𝑑𝑎𝑦. The input power during
stimulation averaged 15kW.
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17. Figure 3
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18. 18

19. Field Case Comparison
The development and subsequent removal of the visco-skin in the near
wellbore region is one explanation to account for the oil production
during primary production and the rapid increase in production after a
short period of thermal stimulation.
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20. 20
Figure 4

21. The extent of the visco-skin during primary production had to be
calculated. The simulator was set to compositional mode and the oil
viscosity distribution after 153 days was calculated and is shown in
figure(4). As shown in the figure, the region of high oil viscosity is
within one meter of the wellbore. The viscosity parameter is to be about
ten, which is based on experimental work of Beal(Beal,1946).
At the onset of electrical heating more than a threefold increase in
production was observed in the field. This was achieved at initial power
rates of less than 5kW.
When the electrical heating option was turned on in the simulator, a
production response match was attained. The simulator verified the
removal of visco-skin as a mechanism of production stimulation.
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22. It is important to estimate the operating temperature of the
electrode during electrical heating since the downhole
equipment may fail at temperatures above 100°C.
Figure(5) shows that the calculated temperature distribution in
the reservoir around the electrode. These calculations are based
on oil flow of 10 𝑚3
𝑑𝑎𝑦 and input power of 30kW.
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23. 23
Figure 5

24. Since the flowrate changes during the life of the well, a curve showing
the input power necessary for an electrode temperature of 100°C for
various flowrates is required. This curve is shown in Figure 8, and is
referred to as the P-Q Curve (Power Flowrate). Operating the system
above the line will result in peak temperatures greater than 100°C.
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25. 25
Figure 6

26. A reservoir simulator , Tetrad, has been modified to incorporate the
electrical heating equations. The simulator includes treatment of the
electrical conductivity as a function of temperature, salinity and
saturation. The simulator was validated against analytical calculations
and field data. It has been used to design several electrode completions
and assist in developing operating strategies for field implementation of
the electrical heating process.
The simulator verified the existence of a visco-skin in the near wellbore
region of a heavy oil well and the subsequent response of the well to
electrical heating and removal of the visco-skin.
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27. Field Case Comparison
“Tetrad” is a commercial numerical reservoir simulator that can operate
in four main modes;
a) Black Oil
b) Multicomponent
c) Thermal
d) Geothermal
It is the simulator which was modified to incorporate electrical heating.
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28. The simulations showed that the DHEH cable will increase the
temperature of the surrounding fluid and that the heat transferred will
increased production as a function of reducing the viscosity and
allowing the fluid to flow better.
In addition to the improved flow conditions and as a result of the
reduced viscosity, bottomhole heating has been reported to produce
several benefits, such as less friction inside the production tubing above
the pump. This allows the pump to work more efficiently, with lower
backpressure.
Case studies have demonstrated that formation heating stimulates the
mobility of oil by the thermal expansion experienced by gaseous phase
of crude. The heated oil liberates dissolved gases in the solution. This
process forms a layer of gas that, when heated, will expand, pushing the
fluid upward. Likewise, water, when present in a limited amount in the
reservoir, will be converted to steam, which in turns expands and
increases bottomhole pressure, also acting as a pushing agent. 28

29. It is important to note that flow rates have a significant impact on the
temperature obtained. Oil that is static will absorb thermal energy, as
opposed to oil that is moving away from the heat source. As a result, the
higher the flowrate, the lower the amount of heat that is absorbed, and
thus there is a smaller impact on production.
The balance between heat input and oil produced is delicate.
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30. Conclusions
The calculations also indicate the electrical heating process can
substantially increase production from a well. Because of the small
heated radius, the process is more a wellbore stimulation process than a
reservoir heating scheme. However, since the visco-skin is tightly bound
to the wellbore, the process is effective in increasing productivity.
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31. References
1. K.VINSOME, B.C.W.McGEE, F.E.VERMEULEN, F.S.CHUTE, Electrical
Heating, PETSOC-94-04-04
2. Downhole Electrical Heating for Enhanced Heavy-Oil Recovery, SPE-
0314-0132-JPT
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32. Thanks For Your Attention
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