Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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EFFECTIVE SOLVENT EXTRACTION SYSTEM INCORPORATING
ELECTROMAGNETIC HEATING
STATEMENT REGARDING FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0001] [Not Applicable]
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] [Not Applicable]
BACKGROUND OF THE INVENTION
[0003]Oil sand deposits are found predominantly in the Middle East, Venezuela,
and
Western Canada. The term "oil sands" refers to large subterranean land forms
composed of reservoir rock, water and heavy oil and/or bitumen. The Canadian
bitumen deposits, being the largest in the world, are estimated to contain
between 1.6
and 2.5 trillion barrels of oil. However, bitumen is a heavy, black oil
which, due to its
high viscosity, cannot readily be pumped from the ground like other crude
oils.
Therefore, alternate processing techniques must be used to extract the bitumen
deposits from the oil sands, which remain a subject of active development in
the field of
practice. The basic principle of known extraction processes is to lower the
viscosity of
the bitumen, typically by the transfer of heat, to thereby promote flow of the
bitumen
material and recovery of same.
[0004] A variety of known extraction processes are commercially used to
recover
bitumen from oil deposits. Steam-Assisted Gravity Drainage, commonly referred
to as
SAGD, is one known method. A SAGD process is described, for example, in
Canadian
patent number 1,304,287. Figure 1 is a representation of the subsurface
arrangement
of a typical prior art SAGD system 50. A boiler (not shown) on the surface
supplies
steam to steam injection piping 14 through connection 12. Steam is injected
into
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subsurface formation 16 at intervals along the length of steam injection
piping 14. The
steam serves to heat subsurface formation 16, which reduces the viscosity of
any
hydrocarbons present in subsurface formation 16. Producer piping 18 is
configured to
accept the hydrocarbons where the hydrocarbons can be pumped to the surface
through connection 20 for collection and processing.
[0005] The range of temperatures, and corresponding viscosities, required to
achieve
an economic flow rate is dependent on the hydraulic permeability of the
reservoir in
question. SAGD, as with most recovery strategies, is focused on increasing
bitumen
temperature within a limited region around a steam injection well. Once
injected, the
steam condenses within the bitumen deposit and its latent heat is transferred
to the
deposit by convection. The reduced-viscosity oil is then allowed to flow by
gravity
drainage to an underlying point of the reservoir, to be collected by a
horizontal
production well. The heavy oil/bitumen is then brought to the surface for
further
processing. Various pumping equipment and/or systems may be used in
association
with the production well.
[0006]Although effective, stand alone SAGD processes have several associated
inefficiencies. First, the process is very energy intensive, requiring a great
amount of
energy for heating the volumes of water needed to generate the steam used for
the heat
transfer process. In addition, the amount of steam required is usually
dictated by the
need to maintain a certain pressure in the reservoir; this usually translates
into a higher
temperature than is optimally needed to mobilize the bitumen and, therefore,
the
expenditure of unnecessary energy. Further, as indicated above, upon releasing
its
heat to the formation, the injected steam condenses into water, which mixes
with the
mobilized bitumen and often leads to additional inefficiencies. For example,
the water is
generally recycled through boilers and, therefore, this requires costly de-
oiling and
softening processes/equipment. In addition, the original or initial separation
of the
bitumen and water requires further processing and costs associated with such
procedures. Also, as common with other known active heating methods,
significant
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energy input to the deposit is often transferred to neighboring geological
structures and
lost by way of conduction. Thus, the process becomes considerably energy
intensive in
order to achieve sufficient heating of the target formation.
[0007]SAGD operating temperature must be at the saturation temperature
corresponding to the pore pressure in the reservoir, or the minimum
temperature
required for economic bitumen drainage rate, whichever is higher. Typical
operating
temperature is above 200 C. For the SAGD process, saturated steam at
approximately
95 percent quality is injected, and saturated liquid water drains out the
producer. As a
result, neglecting piping and other losses, the ratio of heat delivered to the
reservoir to
heat required to produce the steam is
Qres xhfg
Qsteam hf ¨ ha 1- xhfg
Where
Qres is the heat delivered to the reservoir
Qsteam is the heat required to produce the steam
X is steam quality, typically 0.95 at the injection point
hf is the enthalpy of saturated liquid at the process temperature and pressure
hfg is the latent heat of vaporization
ha is the enthalpy of the water feed to the steam generator
[0008]The enthalpies vary with the saturation temperature and pressure. For
10%
piping losses and a steam generator efficiency of 0.85, then the effective
heat
conversion efficiency (heat to reservoir divided by heat to steam generator)
is 0.85, with
heat recovery in both boiler blowdown and produced fluids. Field experience
energy
consumption for SAGD varies widely. SAGD performance is often measured in
terms of
SOR (steam oil ratio). As a point of reference for comparison with other
processes,
numerical predictions for energy consumption at the reservoir for SAGD under
favorable
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conditions (uniform, isotropic hydraulic permeability, typical Athabasca
bitumen, 30 m
pay zone thickness) varies from 0.9 to 1.25 GJ/bbl heat at the reservoir per
bbl bitumen
produced. These correspond to SOR at the reservoir of 5 and 3, respectively
[0009] Dilution is another technique that has been used for the extraction of
bitumen
from oil sand or heavy oil deposits. The solvent based methods, such as VAPEX
(vapor
extraction), involve a dilution process wherein solvents, such as light
alkanes or other
relatively light hydrocarbons, are injected into a deposit to dilute the heavy
oil or
bitumen. This technique reduces the viscosity of the heavy hydrocarbon
component,
= thereby facilitating recovery of the bitumen-solvent mixture that is
mobilized throughout
the reservoir. The injected solvent is produced along with bitumen material
and some
= solvent can be recovered by further processing. Although solvent based
methods avoid
the costs associated with SAGD methods, the production rate of solvent based
methods
over the range of common in-situ temperatures and pressures has been found to
be
less than steam based processes. The solvent dilution methods also require
processing facilities for the extraction of the injected solvent. Finally,
these methods
tend to accumulate material quantities of liquid solvent within the depleted
part of the
reservoir. Such solvents can only partially be recovered at the end of the
process
thereby representing an economically significant cost for the solvent
inventory.
[0010] In order to understand the benefits of solvent processes, it is
instructive to
examine the basic phenomenology of gravity drainage, first developed and
quantified
for SAGD processes. A simplified representation of SAGD drainage is shown in
Figure
2.
[0011] In his landmark paper, Butler (1981) showed that SAGD drainage can be
approximated by:
Q = 20.519Kgabit
rnvs
Where
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Q is the bitumen drainage volume per unit length of well per unit time
(1) is porosity
So is oil saturation (noted by Butler as actually being change in oil
saturation in the zone
K is effective permeability for oil flow (a fraction of the total
permeability)
g is gravitational acceleration
a is the thermal diffusivity of the pay zone
AH is the gravitational head (distance from the top of the pay zone to the
producer)=
m is a dimensionless constant which is dependent upon the conditions
used and upon the nature of the heavy oil (bitumen for SAGD applications), and
us is the kinematic viscosity of the heavy oil (bitumen as in SAGD
applications).
In current practice, flow predictions for given conditions are estimated using
reservoir
simulator codes that perform numerical analysis of the conditions. However,
the driving
parameters are as expressed explicitly in the Butler model above which clearly
shows
that drainage rate is inversely proportional to the square root of the
kinematic viscosity.
Butler also demonstrated via an energy balance that the rate of advance of the
condensation line is governed by the thermal diffusivity of the material as
shown in the
equation. This represents an additional limitation on the maximum drainage
rate of a
SAGD process for a given viscosity. The addition of RF heating mitigates the
thermal
diffusivity rate limitation and thereby reduces the time required for
reservoir drainage.
Bitumen and heavy oil properties vary over a wide range, but all exhibit an
extremely
strong variation in viscosity with temperature as exemplified in Figure 3.
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[0012]One issue faced in known solvent extraction methods relates to a
physical
limitation. Bitumen deposits within the Alberta Athabasca region are too cold
for the
solvent to be commercially effective. At common reservoir temperatures, which
are
generally in the range of 10 - 15 C, the solvent dilution process is too slow
to be
economically viable. For a solvent extraction process to be effective, the
bitumen
deposit should preferably be at a threshold temperature of 40 - 70 C.
[0013] One solution to address the above problem has been to use steam as a
heating
means to render the solvent process more efficient. In this regard, a
combination of
SAGD and VAPEX methods has been proposed in order to combine the benefits of
both
while mitigating the respective drawbacks. Known as a solvent aided, or
solvent
assisted process, or SAP, this method involves the injection of both steam and
a low
molecular weight hydrocarbon into the formation. Gupta et al. (J. Can. Pet.
Tech.,
2007, 46(9), pp. 57-61) teach a SAP method, which comprises a SAGD process
wherein a solvent is simultaneously injected into the formation with the
steam. As
indicated in this reference, a SAP process has been found to improve the
economics of
SAGD methods.
[0014] However, the above combination of steam and solvent processes has also
been
found to have disadvantages. As with typical SAGD processes, much of the heat
contained in the steam is also lost to the rock and other material bounding
the reservoir
and is not retained by the bitumen itself. Thus, the energy efficiency of such
method is
low.
[0015]Another solution comprises the use of heated solvent being applied to
the
reservoir, such as with the N-SOLVTM process. The principle of this process
being that
the use of heated solvent may raise the temperature of the reservoir to the
desired level
for an effective dilution process. However, the vapor formed by heating the
solvent has
a low heat of vaporization, and therefore requires large volumes of solvent to
be
condensed during condensation to effectively raise the temperature of the
bitumen.
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[00116] Recently, as an alternative to the steam and solvent methods discussed
above,
another method of producing hydrocarbons from bitumen deposits involves the
use of
electromagnetic (EM) heating. In this method, one or more antennae are first
inserted
into the bitumen reservoir. A power transmitter is used to power the antennae,
which
induces an RE field through the reservoir. The absorbed RE energy heats the
water
and oil/bitumen within the reservoir, thereby resulting in flow of the
hydrocarbon
material. A production well is then used to withdraw the mobilized
hydrocarbons, similar
to the previously discussed methods. One example of an EM process is taught in
US
patent no. 7,441,597, which teaches the use of EM heating to produce heavy oil
from a
reservoir. In such a process, an antenna is provided in a first horizontal
well, and is
powered to heat the surrounding heavy oil with RE energy. A second horizontal
well is
positioned below the first and is used as a production well into which the
mobilized
heavy oil flows. However, the EM heating method has been found to be very cost
intensive, particularly due to the inefficiencies in transferring the
generated power to the
formation.
[0017]Electromagnetic heating uses one or more of three energy forms: electric
currents, electric fields, and magnetic fields at radio frequencies. Depending
on
operating parameters, the heating mechanism may be resistive by Joule effect
or
dielectric by molecular moment. Resistive heating by Joule effect is often
described as
electric heating, where electric current flows through a resistive material.
The electrical
work provides the heat which may be reconciled according to the well known
relationships of P = 12 R and Q =12 R t. Dielectric heating occurs where polar
molecules,
such as water, change orientation when immersed in an electric field and
dielectric
heating occurs according to P = w Cr" CO E2 and Q = w Er" E0 E2 t, Where P is
the power
density dissipated in the media, 0) is the angular frequency, Er" is the
complex
component of the material permittivity, co is the permittivity constant of
free space, E is
the electric field strength, Q is the volumetric heat, and t is time. Magnetic
fields also
heat electrically conductive materials through the formation of eddy currents,
which in
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turn heat resistively. Thus magnetic fields can provide resistive heating
without
conductive electrode contact.
[0018] Electromagnetic heating can use electrically conductive antennas to
function as
heating applicators. The antenna is a passive device that converts applied
electrical
current into oscillating electromagnetic fields, and electrical currents in
the target
material, without having to heat the structure to a specific threshold level.
Preferred
antenna shapes can be Euclidian geometries, such as lines and circles.
Additional
background information on dipole antennas can be found at S.K. Schelkunoff and
H.T.
Friis, Antennas: Theory and Practice, pp 229 - 244, 351 ¨ 353 (Wiley New York
1952).
The radiation pattern of an antenna can be calculated by taking the Fourier
transform
of the antenna's electric current flow.
Modern techniques for antenna field
characterization may employ digital computers and provide for precise RF heat
mapping.
[0019]Antennas, including antennas for electromagnetic heat application, can
provide
multiple field zones which are determined by the radius from the antenna r and
the
electrical wavelength A (lambda). Although there are several names for the
zones they
can be referred to as a near field zone, a middle field zone, and a far field
zone. The
near field zone can be within a radius r < A/2-rr (r less than lambda over 2
pi) from the
antenna, and it contains both magnetic and electric fields. The near field
zone
energies are useful for heating hydrocarbon deposits, and the antenna does not
need
to be in electrically conductive contact with the formation to form the near
field heating
energies. The middle field zone is of theoretical importance only. The far
field zone
occurs beyond r > A / ir (r greater than lambda over pi), is useful for
heating
hydrocarbon formations, and is especially useful for heating formations when
the
antenna is contained in a reservoir cavity. In the far field zone, radiation
of radio
waves occurs and the reservoir cavity walls may be at any distance from the
antenna
if sufficient energy is applied relative the heating area. Thus, reliable
heating of
underground formations is possible with radio frequency electromagnetic energy
with
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antennas insulated from and spaced from the formation. The electrical
wavelength
may be calculated as A =27c/13, where 13 = Im(y), where lm(y) indicates the
imaginary
component of y, and y =(jco (a+jo)s))1/2.
Where:
A Is the wavelength;
13 is the wavenumber;
y is the phase propagation constant;
w is the angular frequency;
p. is the magnetic permeability;
a is the material conductivity; and
E is the material permittivity.
[0020] Susceptors are materials that heat in the presence of RF energies. Salt
water is
a particularly good susceptor for electromagnetic heating; it can respond to
all three
RF energies: electric currents, electric fields, and magnetic fields. Oil
sands and
heavy oil formations commonly contain connate liquid water and salt in
sufficient
quantities to serve as an electromagnetic heating susceptor. "Connate" refers
to
liquids that were trapped in the pores of sedimentary rocks as they were
deposited.
For instance, in the Athabasca region of Canada and at 1 kHz frequency, rich
oil sand
(15 weight percent % bitumen) may have about 0.5 - 5% water by weight, an
electrical
conductivity of about 0.01 s/m, and a relative dielectric permittivity of
about 120. As
bitumen becomes mobile at or below the boiling point of water at reservoir
conditions,
liquid water may be a used as an electromagnetic heating susceptor during
bitumen
extraction, permitting well stimulation by the application of RF energy. In
general,
electromagnetic heating has superior penetration and heating rate compared to
conductive heating in hydrocarbon formations. Electromagnetic heating may also
have
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properties of thermal regulation because steam is not an electromagnetic
heating
susceptor. In other words, once the water is heated sufficiently to vaporize,
it is no
longer electrically conductive and is not further heated to any substantial
degree by
continued application of electrical energy.
[0021] Heating subsurface heavy oil bearing formations by prior RF systems has
been
inefficient due to traditional methods of matching the impedances of the power
source
(transmitter) and the heterogeneous material being heated, uneven heating
resulting in
unacceptable thermal gradients in heated material, inefficient spacing of
electrodes/antennae, excessive electricity usage due to high process
temperature, poor
electrical coupling to the heated material, limited penetration of material to
be heated by
energy emitted by prior antennae and frequency of emissions due to antenna
forms and
frequencies used. Antennas used for prior RF heating of heavy oil in
subsurface
formations have typically been dipole antennas. U.S. Patent nos. 4,140,179 and
4,508,168 disclose dipole antennas positioned within subsurface heavy oil
deposits to
heat those deposits.
[0022] When RF heating is substituted for steam in an otherwise similar
extraction
process, the heat applied to the reservoir must be less than the SAGD
reservoir heat,
and the overall RF energy conversion process must be very efficient to achieve
energy
parity. This is driven by the energy loss associated with electric power
generation (for a
fossil fuel plant). For example, assume that an RF process requires 53% of the
heat
applied to the reservoir for the same flow rate as a SAGD process. Assume that
system
also converts 70% of the input electrical power to RF heat in the reservoir,
and that the
electric power is provided at 35% efficiency. That system would require 2.2 GJ
of heat
input to the power station to deliver the same amount of oil as the SAGD
system
delivering 1 GJ to the reservoir.
[0023] As discussed above, several methods are currently known for producing
oil from
bitumen reservoirs. The common element for all such known methods comprises
the
reduction in the viscosity of bitumen in the reservoir. Some methods, such as
SAGD or
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N-SOLVTM, involve the injection of heated media (water and= solvent,
respectively) as
the heat source. The use of EM heating avoids the use of such heat delivering
media.
However, known electromagnetic heating methods are typically adapted to
completely
remove the requirement for any water or solvent from being used (see, for
example, in
US 7,441,597). And as discussed above, each of these known methods involve
several
disadvantages, including a high cost.
[0024]The recovery of bitumen from reservoirs such as oil sands continues to
be of
interest particularly in view of the world's increasing energy demand. As
such, the need
to improve extraction efficiency of hydrocarbon containing reservoirs
continues to gain
importance. Despite the various prior art attempts discussed above, there
exists a need
for an efficient and cost-effective method for in situ recovery of bitumen
and/or heavy oil
from underground reservoirs.
[0025]The present system, described herein, stands unique in providing a
method
wherein EM heating is used initially as a pre-conditioning phase, not to
result in
production of oil but to increase the temperature of the bitumen, at least
within a defined
region, to a level where solvent vapor can be used as the final production
medium. The
solvent achieves this goal by diluting the pre-conditioned, i.e. pre-heated,
bitumen and
results in mobility thereof into a production well.
[0026]The following references are provided are related to the present subject
matter.
The entire contents of all references listed in the present specification,
including the
following documents.
[0027] Butler, R.M. "Theoretical Studies on the Gravity Drainage of Heavy Oil
During .In-
Situ Steam Heating", Can J. Chem Eng, Vol 59, 1981.
[0028] References Relating To Solvent Injection
[0029]Butler, R. and Mokrys, I., "A New Process (VAPEX) for Recovering Heavy
Oils
Using Hot Water and Hydrocarbon Vapour", Journal of Canadian Petroleum
Technology, 30(1), 97-106, 1991.
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[0030]Butler, R. and Mokrys, I., "Recovery of Heavy Oils Using Vapourized
Hydrocarbon Solvents: Further Development of the VAPEX Process", Journal of
Canadian Petroleum Technology, 32(6), 56-62, 1993.
[0031]Butler, R. and Mokrys, I., "Closed Loop Extraction Method for the
Recovery of
Heavy Oils and Bitumens Underlain by Aquifers: the VAPEX Process", Journal of
Canadian Petroleum Technology, 37(4), 41-50, 1998.
[0032]Das, S.K. and Butler, R.M., "Extraction of Heavy Oil and Bitumen Using
Solvents
at Reservoir Pressure" CIM 95-118, presented at the CIM 1995 Annual Technical
Conference in Calgary, June 1995.
[0033]Das, S.K. and Butler, R.M., "Diffusion Coefficients of Propane and
Butane in
Peace River Bitumen" Canadian Journal of Chemical Engineering, 74, 988-989,
December 1996.
[0034]Das, S.K. and Butler, R.M., "Mechanism of the Vapour Extraction Process
for
Heavy Oil and Bitumen", Journal of Petroleum Science and Engineering, 21, 43-
59,
1998.
[0035]Dunn, S.G., Nenniger, E. and Rajan, R., "A Study of Bitumen Recovery by
Gravity Drainage Using Low Temperature Soluble Gas Injection", Canadian
Journal of
Chemical Engineering, 67, 978-991, December 1989.
[0036]Frauenfeld, T., Lillico, D., Jossy, C., Vilcsak, G., Rabeeh, S. and
Singh, S.,
"Evaluation of Partially Miscible Processes for Alberta Heavy Oil Reservoirs",
Journal of
Canadian Petroleum Technology, 37(4), 17-24, 1998.
[0037]Mokrys, I., and Butler, R., "In Situ Upgrading of Heavy Oils and Bitumen
by
Propane Deasphalting: The VAPEX Process", SPE 25452, presented at the SPE
Production Operations Symposium held in Oklahoma City OK USA, March 21-23
1993.
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[0038] Nenniger, J.E. and Dunn, S.G., "How Fast is Solvent Based Gravity
Drainage?",
CIPC 2008-139, presented at the Canadian International Petroleum Conference,
held in
Calgary, Alberta Canada, 17-19 June 2008.
[0039] Nenniger, J.E. and Gunnewick, L., "Dew Point vs. Bubble Point: A
Misunderstood
Constraint on Gravity Drainage Processes", CIPC 2009-065, presented at the
Canadian
International Petroleum Conference, held in Calgary, Alberta Canada, 16-18
June 2009.
[0040] References Relating To Electromagnetic Heating
[0041] Bridges, J.E., Sresty, G.C., Spencer, H.L. and Wattenbarger, R.A.,
"Electromagnetic Stimulation of Heavy Oil Wells", 1221-1232, Third
International
Conference =on Heavy Oil Crude and Tar Sands, UNITAR/UNDP, Long Beach
California, USA 22-31 July 1985.
[0042] Carrizales, MA., Lake, LW. and Johns, R.T., "Production Improvement of
Heavy
Oil Recovery by Using Electromagnetic Heating", SPE115723, presented at the
2008
SPE Annual Technical Conference and Exhibition held in Denver, Colorado, USA,
21-
24 September 2008.
[0043] Carrizales, M. and Lake, L.W., "Two-Dimensional COMSOL Simulation of
Heavy-
Oil Recovery by Electromagnetic Heating", Proceedings of the COMSOL Conference
Boston, 2009.
[0044]Chakma, A. and Jha, K.N., "Heavy-Oil Recovery from Thin Pay Zones by
Electromagnetic Heating", SPE24817, presented at the 67th Annual Technical
Conference and Exhibition of the Society of Petroleum Engineers held in
Washington,
DC, October 4-7, 1992.
[0045]Chhetri, A.B. and Islam, M.R., "A Critical Review of Electromagnetic
Heating for
Enhanced Oil Recovery", Petroleum Science and Technology, 26(14), 1619-1631,
2008.
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[0046]Chute, F.S., Vermeulen, F.E., Cervenan, M.R. and McVea, F.J.,
"Electrical
Properties of Athabasca Oil Sands", Canadian Journal of Earth Science, 16,
2009-2021,
1979.
[0047] Davidson, R.J., "Electromagnetic Stimulation of Lloydminster Heavy Oil
Reservoirs", Journal of Canadian Petroleum Technology, 34(4), 15-24, 1995.
[0048] Hu, Y., Jha, K.N. and Chakma, A., "Heavy-Oil Recovery from Thin Pay
Zones.by
Electromagnetic Heating", Energy Sources, 21(1-2), 63-73, 1999.
[0049]Kasevich, R.S., Price, S.L., Faust, DI. and Fontaine, M.F., "Pilot
Testing of a
Radio Frequency Heating System for Enhanced Oil Recovery from Diatomaceous
Earth", SPE28619, presented at the SPE 69th Annual Technical Conference and
Exhibition held in New Orleans LA, USA, 25-28 September 1994.
[0050]Koolman, M., Huber, N., Diehl, D. and Wacker, B., "Electromagnetic
Heating
Method to Improve Steam Assisted Gravity Drainage", 5PE117481, presented at
the
2008 SPE International Thermal Operations and Heavy Oil Symposium held in
Calgary,
Alberta, Canada, 20-23 October 2008.
[0051]Kovaleva, L.A., Nasyrov, N.M. and Khaidar, A.M., "Mathematical Modelling
of
High-Frequency Electromagnetic Heating of the Bottom-Hole Area of Horizontal
Oil
Wells, Journal of Engineering Physics and Thermophysics, 77(6), 1184-1191,
2004.
[0052]McGee, B.C.W. and Donaldson, R.D., "Heat Transfer Fundamentals for
Electro-
thermal Heating of Oil Reservoirs", CIPC 2009-024, presented at the Canadian
International Petroleum Conference, held in Calgary, Alberta, Canada 16-18
June,
2009.
[0053]Ovalles, C., Fonseca, A., Lara, A., Alvarado, V., Urrecheaga, K.,
Ranson, A. and
Mendoza, H., "Opportunities of Downhole Dielectric Heating in Venezuela: Three
Case
Studies Involving Medium, Heavy and Extra-Heavy Crude Oil Reservoirs"
SPE78980,
presented at the 2002 SPE International Thermal Operations and Heavy Oil
Symposium
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and International Horizontal Well Technology Conference held in Calgary,
Alberta,
Canada, 4-7 November 2002.
(0054] Rice, S.A., Kok, A.L. and Neate, C.J., "A Test of the Electric Heating
Process as
a Means of Stimulating the Productivity of an Oil Well in the Schoonebeek
Field", CIM
92-04 presented at the CIM 1992 Annual Technical Conference in Calgary, June 7-
10,
1992.
[0055] Sahni, A. and Kumar, M. "Electromagnetic Heating Methods for Heavy Oil
Reservoirs", SPE62550, presented at the 2000 SPE/AAPG Western Regional Meeting
held in Long Beach, California, 19-23 June 2000.
[0056]Sayakhov, F.L., Kovaleva, L.A. and Nasyrov, N.M., "Special Features of
Heat
and Mass Exchange in the Face Zone of Boreholes upon Injection of a Solvent
with a
Simultaneous Electromagnetic Effect", Journal of Engineering Physics =and
Thermophysics, 71(1), 161-165, 1998.
[0057]Spencer, Hi., Bennett, K.A. and Bridges, J.E. "Application of the
IITRI/Uentech
Electromagnetic Stimulation Process to Canadian Heavy Oil Reservoirs" Paper
42,
Fourth International Conference on Heavy Oil Crude and Tar Sands, UNITAR/UNDP,
Edmonton, Alberta, Canada, 7-12 August 1988.
[0058]Sresty, G.C., Dev, H., Snow, R.H. and Bridges, J.E., "Recovery of
Bitumen from
Tar Sand Deposits with the Radio Frequency Process", SPE Reservoir
Engineering, 85-
94, January 1986.
[0059]Vermulen, F. and McGee, B.C.W., "In Situ Electromagnetic Heating for
Hydrocarbon Recovery and Environmental Remediation", Journal of Canadian
Petroleum Technology, Distinguished Author Series, 39(8), 25-29, 2000.
SUMMARY OF THE INVENTION
[0060]The present system includes a method of producing hydrocarbons from a
subterranean reservoir containing the hydrocarbons comprises pre-heating at
least a
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portion of a subterranean reservoir by exposure to electromagnetic radiation
from a
electromagnetic radiation source, injecting through at least one injection
well extending
into the subterranean reservoir a solvent into the reservoir to dilute the
hydrocarbons
contained in the pre-conditioned portion, and producing through at least one
production
well extending into the subterranean reservoir a mixture of hydrocarbons and
solvent.
[0061]The method may include pre-heating at least a portion of the
subterranean
reservoir to about 400 to 70 C. The pre-heated portion of the subterranean
reservoir
may extend from the electromagnetic radiation source to the production well.
The
electromagnetic radiation source may comprise at least one radio frequency
antenna.
The radio frequency antenna(s) may be comprised of production well piping,
including
injection well piping and/or production well piping.
(0062] The present system also includes an apparatus for producing
hydrocarbons from
a subterranean reservoir containing the hydrocarbons comprises at least one
radio
frequency antenna configured to transmit radio frequency energy into a
subterranean
reservoir, the subterranean reservoir containing hydrocarbons, a power source
to
provide power to the at least one radio frequency antenna, at least one
injection well
configured to inject a solvent from a solvent supply source into the
subterranean
reservoir to lower the viscosity of the hydrocarbons, and at least one
production well
configured to produce a mixture comprising hydrocarbons and solvent from the
subterranean reservoir.
[0063]The radio frequency antenna(s) may be adapted to generated radio
frequency
energy at a frequency of about 1kHz to 1GHz. The injection well(s) and
production
well(s) may be generally horizontal. The injection well(s) may be positioned
above the
production well(s). The injection well(s) and production well(s) may be in the
same
vertical plane, whereby the injection well(s) are vertically above the
production well(s).
Further, the radio frequency antenna(s) may include at least one radio
frequency
antenna comprised of injection well piping and at least one radio frequency
antenna
comprised of production well piping. The radio frequency antenna(s) may be in
close
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proximity to the least one injection well. The hydrocarbons may comprise heavy
oil
and/or bitumen.
[0064]
[0065]The method may include operating the radio, frequency antenna(s) to
control
temperature in a region of the subterranean reservoir around the production
well to
manage asphaltene precipitation. The electromagnetic radiation may have a
frequency
of about 1kHz to 1GHz. The radio frequency antenna(s) may be in close
proximity to
the least one injection well.
[0066] The method may include vaporizing residual solvent in the subterranean
reservoir by continued exposure of the subterranean reservoir to
electromagnetic
radiation after hydrocarbon production, and recovering the vaporized residual
solvent.
The method may also include recovering residual solvent from the subterranean
reservoir after hydrocarbon production by performing a cyclic operation of
radio
frequency heating and depressurization of the subterranean reservoir.
[0067] Other aspects of the invention will be apparent from this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0068] FIG. 1 depicts a perspective view of a typical prior art SAGD system.
[0069] FIG. 2a is a schematic depicting a SAGD system in operation.
[0070] Figure 2b depicts the moving oil interface as hydrocarbon is recovered
using the
SAGD system.
[0071] Figure 3 illustrates bitumen viscosity as a function of temperature.
[0072] Figure 4 depicts an ESEIEH process with the injector operating as an
antenna.
[0073] Figure 5 illustrates initial RF preheating of the reservoir with radio
frequency
energy to create a mobile zone between the injector and producer.
[0074] Figure 6 illustrates the ESEIEH process with a formed solvent chamber.
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[0075]Figure 7 depicts the solvent¨bitumen interface with a mixed region.
[0076]Figure 8 illustrates the solvent diffusion coefficient as a function of
temperature.
(0077] Figure 9 illustrates the a hexane-hydrocarbon mixture viscosity as a
function of
hexane mole fraction at several temperatures.
[0078] Figure 10 illustrates temperature profiles at the solvent-hydrocarbon
interface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS=
[0079]The subject matter of this disclosure will now be described more fully,
and one or
more embodiments of the invention are shown. This invention may, however, be
embodied in many different forms and should not be construed as limited to the
'embodiments set forth herein. Rather, these embodiments are examples of the
invention, which has the full scope indicated by the language of the claims.
[0080] For clarity of understanding, the following terms used in the present
description
will have the definitions as stated below.
[0081]As used herein, the terms "reservoir", "formation", "deposit", are
synonymous and
refer to generally subterranean reservoirs containing hydrocarbons. As
discussed
further below, such hydrocarbons may comprise bitumen and bitumen like
materials.
[0082]"Oil sands", as used herein, refers to deposits containing heavy
hydrocarbon
components such as bitumen or "heavy oil", wherein such hydrocarbons are
intermixed
with sand. Although the invention is described herein as being applicable to
oil sands, it
will be understood by persons skilled in the art that the invention may also
be applicable
to other types of reservoirs containing bitumen or heavy oil, or other
hydrocarbon
materials in reservoirs with lower permeability. However, for convenience, the
terms "oil
sands" and "bitumen" are used for the purposes of the following description
and will be
understood to refer generally to any of the above mentioned hydrocarbon
reservoirs and
materials. The choice of such terms serves to facilitate the description of
the invention
and is not intended to limit the invention in any way.
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[0083]The term "solvent" refers to one or more hydrocarbon solvents used in
hydrocarbon recovery methods as known in the art. In a preferred embodiment,
the
solvents of the invention are hydrocarbons comprising chain lengths of C2 to
C5. The
solvent may comprise a mixture of one or more hydrocarbon components. As used
herein, the terms "light solvent" or "light hydrocarbon" will be understood as
comprising
one or more alkane components preferably having a length of C2 to C5, and more
preferably C3 (i.e. propane). The light solvent may comprise a mixture of
hydrocarbons,
each preferably having a length less than C4 and wherein the mixture has an
average
chain length of approximately C3. In a further preferred aspect, at least 1/2
v/v of the
light solvent mixture is comprised of propane (C3). As known in the art, the
choice of
solvents depends on the reservoir or anticipated operating pressure
[0084] The term "natural gas liquids" or "NGL" will be understood as
comprising alkane
hydrocarbons generally having lengths of C2 to C6, and which are normally
condensation products in the course of natural gas processing.
[0085]According to an aspect of the present system, there is provided a method
of
recovering, or producing heavy oils and bitumen, which comprises a unique,
coupled
combination of electromagnetic (EM) heating and solvent extraction. More
specifically,
the present system involves a method wherein heavy oil and/or bitumen in a
reservoir is
heated to a level wherein a solvent extraction process becomes efficient. As
discussed
above, such native reservoirs are typically at a temperature of 100 - 15 C
and a
temperature of between 40 - 70 C is required to cause the desired
hydrocarbon
components to flow at commercial levels with a coupled solvent process.
[0086] In general, the present system provides in one aspect, a new in-situ
bitumen and
heavy oil extraction process that combines EM heating to precondition a heavy
oil
and/or bitumen reservoir to a desired temperature, preferably between 40 and
70 C.
The process may be referred to as Enhanced Solvent Extraction Incorporating
Electromagnetic Heating, or "ESEIEH" (pronounced "easy").
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[0087]According to an aspect of the present system, the aforementioned heating
may
be achieved through the application of electromagnetic heating via antennae
that may
be part of the drilling or completion apparatus. When the reservoir reaches
the desired
temperature within a desired region, an appropriate solvent is then injected
into the
reservoir. The solvent partially mixes with the oil and further reduces its
viscosity and
partially displaces the hot-diluted oil. The choice of solvent and well
configuration may
be similar to existing solvent injection processes. The process also shares
similarities
with existing electromagnetic heating processes. However, the combination of
the two
approaches as provided in the present invention is novel and unique, as will
be
apparent to persons skilled in the art upon reviewing the present description.
[0088]According to one aspect, the present system provides a new method and
apparatus for the recovery of hydrocarbons from buried hydrocarbon deposits
under
elevated pressure and low temperature. It has potential application to any
heavy oil or
bitumen formation that is too deep to mine (i.e. deeper than 100m). As known
in the art,
heavy oil is defined as oil with API gravity below 20 and bitumen is described
as oil with
API gravity below 12. Oil viscosity at reservoir temperatures varies from 100
mPas to
100,000,000 mPas.
[0089]1n general, a process according to the present system combines the
stimulation
of the target reservoir with EM heating and its conditioning to minimal
temperatures
such that the combination of temperature enhanced oil mobility and solvent
mixing
becomes optimal in achieving commercial extraction rates while minimizing
energy
requirements in base pre-heating of the oil. At that point a pre-selected
solvent is
injected. The solvent partially mixes with the oil, making it even less
viscous and
partially displaces the heated and diluted oil towards a production well. A
preferred but
not necessary condition of the process is the application of the
electromagnetic heating
through an antenna that is positioned in a horizontal well that also is used
for the
injection of solvent. Oil is produced through another horizontal well that is
placed in a
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distance below the injector/heater well, as known in the art from processes
such as
VAPEX or the well configuration as otherwise applied in SAGD.
[0090] In one aspect, the present system eliminates the need for water as an
injection
fluid and, therefore, the need for generating steam. As such, the present
system avoids
the significant energy requirements with processes such as SAGD, as well as
the
commensurate reduction in greenhouse gas emissions. It also reduces the burden
on
surface facilities to process or separate the oil as it has significantly
reduced water
content.=
[0091]The present system may comprise several steps. For example, first, a
well
configuration is provided, which combines wells that will be used as injectors
and
producers, respectively. The injector wells serve to inject solvent into the
reservoir,
while the producer wells serve to produce the mobilized heavy oil or bitumen
(collectively referred to hereinafter as "bitumen" for convenience, unless
otherwise
indicated). In a preferred embodiment, the well configuration of the SAGD
process is
considered, wherein a pair of parallel horizontal wells is drilled, with one
well being
provided at a deeper depth than the other. The upper well is used as the
injector and
the lower well as the producer. Such well arrangement is shown in Figure 4,
which
illustrates a bitumen containing reservoir 10, as well as an injector well 12
and a
production well 14, situated below the injector well. In another, preferred
aspect of the
invention, the injector well is also used as, or contains within, the antenna
for the EM
heating. A power transmitter is provided, generally at the surface (i.e. above
ground),
which may be powered by any power source. The antenna induces a radiofrequency
(RF) field and electromagnetically (EM) heats the in-situ water and heavy
oil/bitumen via
transmission of electrical energy to the reservoir fluids, which results in a
greater
molecular motion, or heating. In another, preferred embodiment of the present
system,
both the injector and producer are used as, or contain within, the antennae
for the EM
heating.
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[0092]The power transmitter is preferably adapted to power the antenna in a
pre-
specified, flexible, variable and controllable manner. Such an arrangement
allows for
dynamic impedance management, frequency of operation and high efficiency
coupling
of the power source as the physical properties of the formation change as
formation
properties vary with the removal of produced fluids. The information required
for the
optimum performance of the antenna comprise the permittivity and impedance
changes
in the formation as temperature, fluid composition and fluid state in the
formation
change.
[0093]As illustrated in Figure 5, the RE-induced heating (or EM heating)
initially heats
connate water and oil near the antenna. Water and the heated bitumen drain to
the
producer creating a flow pathway. The flow pathway thus created is then used
as the
primary conduit to inject a solvent from the antenna/injector well 12. As
water is a
primary susceptor for electromagnetic heating, the depleted region 11 absorbs
less heat
from the antenna and this allows more efficient penetration of the
electromagnetic
heating into the reservoir. The RE heating is applied so as to maintain the
reservoir 10
(Figure 4) temperature at a level that is sufficient to allow efficient
application of a
solvent extraction process. In a preferred embodiment of the present system,
the
reservoir is maintained at a temperature of 40-70 C. More preferably, such
temperature is maintained at least in the vicinity of the injected solvent,
which dissolves
the partially heated bitumen. The solvent/bitumen mixture then drains towards
the
production 14 well at rates that are comparable, or accretive, to SAGD. Figure
6
illustrates the area of pre-heated bitumen 16, the depletion chamber 18 where
recovered oil is extracted. One advantage of the proposed process is the fact
that
directional RE heating creates zones where the solvent can advance and strip
oil in a
manner that is expected to be better controlled than conventional VAPEX or its
derivatives.
[0094] Figure 7 shows the physical principle of the solvent extraction
process. In
principle, a solvent vapor comes into contact with bitumen and through
diffusion it
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creates a mobile, dilute bitumen stream which in turn drains towards a
production well
via gravity. However, with the present system (using the ESEIEH process),
directional
RF-induced EM heating provides the initial energy to quickly and efficiently
heat the
bitumen, reducing viscosity by several orders of magnitude while
simultaneously
increasing the solvent diffusion within the bitumen, while the solvent mixing
provides
additional oil viscosity reduction to generate threshold and higher commercial
rates.
Ethane, propane, butane, pentane, or any mixture of the above, or even
aromatic
solvents can be used. As Figure 3 indicates by example, heating of bitumen in
the
vicinity of 80 C can induce four orders of magnitude in viscosity reduction
with only
one-third of the energy requirement for conventional SAGD type steam
injection. This,
coupled with an expected four orders of magnitude increase in diffusion
coefficient
when increasing the reservoir temperature from 10 C to approximately 80 C
(see
Figure 8), leads to less solvent requirements for oil / bitumen mobilization
(see Figure
9).
[0095]A steam extraction process typically requires about 8kg of oil sand,
heated to a
temperature of 100-260 C to mobilize 1kg of bitumen. Steam production
requires
combustion of fuel that could reach up to 30 A of the heating value of the
bitumen (for
an SOR approaching 5), and produces associated greenhouse gas (e.g. CO2)
emissions. Introduction of solvents that can produce oil at acceptable rates
can
potentially reduce energy efficiency and greenhouse gas emissions. In solvent
extraction processes, concentration gradients provide the driving force to
push solvent
into bitumen and mobilize it. Nenniger and Dunn (2008) demonstrate that most
of that
solvent driving force is consumed within a few microns of the raw bitumen
interface in
what is referred to as a "concentration shock". This shock arises from the
strong
dependency of diffusion coefficients on concentration. In the solvent rich
phase of the
shock, diffusion is very fast, while on the side of the native bitumen shock,
diffusion is
very slow. This is due to the bitumen viscosity and the fact that the
diffusion coefficient
is inversely related to the viscosity.
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[0096] Electromagnetic (EM) heating methods are superior to other energy
sources for
heating a hydrocarbon reservoir in conjunction with a solvent recovery
process.
Electromagnetic heating can penetrate energy beyond the solvent chamber-
hydrocarbon interface and establish a higher temperature at the interface
between
solvent and native hydrocarbon compared to a process that relies on heat
conduction to
transport thermal energy across the dilution zone into the native hydrocarbon.
It is
worth noting that steam processes rely on heat conduction to deliver heat into
the native
hydrocarbon beyond the its condensation zone.
[0097] Figure 10 shows a schematic of the solvent chamber-hydrocarbon
interface
during a heated solvent recovery process. ; In the solvent chamber the solvent
concentration Cs is at a maximum and decreases throughout the mixed region.
The
interface between the solvent chamber and a mixed region of solvent and native
hydrocarbons is depicted by line A. The solvent concentration is at a minimum
at the
interface between the mixed region and the native hydrocarbon depicted by line
B, and
is essentially zero a short distance into the hydrocarbon. The curved dotted
line
between interface A and T4 represents an example temperature profile that
results from
heat conduction (or heat diffusion) into the hydrocarbon. T3 represents the
solvent
chamber temperature, and T4 is the temperature at interface B that results
from heat
conduction between interface A and B. The curved dotted line between interface
A and
T5 represents an example temperature profile that results from electromagnetic
heating
that penetrates through interface B. T5 represents the temperature at
interface B as a
result of electromagnetic heating. For the same chamber temperature T3 it is
possible
to achieve a higher interface B temperature with electromagnetic heating than
with any
method that relies on heat conduction through the mixed region (T5>T4). This
is a
direct result of the energy penetration and volumetric heating provided by
electromagnetic heating.
[0098]The temperature at interface B is of critical importance in a solvent
hydrocarbon
recovery process because the interface temperature determines the rate at
which the
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hydrocarbon will drain down the interface and be recovered.
Higher temperature
decreases the viscosity of the native hydrocarbon and subsequently increases
the
diffusion rate of the solvent into the hydrocarbon. Das and Butler (1996)
suggested that
the solvent diffusion coefficient D is related to the hydrocarbon viscosity t
by the
relation:
(0099]D a*.a-b where a, b > 0 equation 1
[00100]
Because hydrocarbon viscosity is a strong inverse function of
temperature, equation 1 indicates that the solvent diffusion coefficient
increases
dramatically as temperature increases. Furthermore, at a given temperature, a
higher
solvent concentration Cs in the hydrocarbon produces a lower mixture
viscosity.
Therefore, increasing the interface temperature has a two-fold effect; it
lowers the
viscosity of the hydrocarbon which improves the diffusion rate of the solvent
into the
hydrocarbon, and the resultant increased diffusion produces a critical solvent
concentration Cs more quickly within the hydrocarbon resulting in higher
hydrocarbon
recovery rates compared to other heating methods.
[00101]
Nenniger and Dunn (2008) showed that for a large number of literature
data, the recovered oil mass flux, for solvent based recovery of bitumen, is a
function of
the bitumen mobility. This correlation can be extended to show that mass flux
is
proportional to the square root of a characteristic time tc=10p/p, where k is
the formation
permeability, (1) is the formation porosity, p is the oil density and p is the
oil viscosity.
This simple dependency is directly analogous to a diffusion dependency on time
for the
shock front. Adapting this correlation one can calculate temperature dependent
volumetric production rates of shock fronts surrounding horizontal production
wells.
Since the characteristic time contains terms (density, viscosity) that are
temperature
dependent, the field rates become equations of the type F(m3/day).=--aTCC)8
where a
and 'p, have to be determined for different reservoirs independently. As an
example, for
a well of 500m and a formation of 20m in thickness with a permeability of 5D
and a
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bitumen with density at 15 C of 1.015 gicm3 and viscosity at 25 C of 1.3
million cP,
the coefficients a and 13 are of the order of 0.0028 and 2.7924 respectively.
As a result,
predictions of field flow rates with temperature for this specific system are
of the order of
the numbers presented in Table 1.
[00102] Table 1: Expected rates from a solvent based bitumen recovery
process
Temperature, C Field rate, m3/d
0.25
1.7
5.4
12.0
22.3
37.2
57.2
83.1
115.4
154.8
201.9
257.3
321.5
395.2
478.8
572.9
678.0
=
= 90 794.6
923.2
100 1064.3
Thus with a successful heating of the oil solvent interface, a substantial
production rate
can be achieved at temperatures substantially below operating steam
temperatures.
Where the process of the present system differs from condensing solvent
processes
such as the proposed NSOLVTM is that the condensing solvent latent heat is not
used
to introduce the required reservoir fluid heating. As discussed above, the
present
invention achieves heating using EM (RF-induced) heating. Thus, issues
regarding the
selection of the solvent associated are not of concern with process of the
present
invention. For example, the NSOLVTM process is quite vulnerable to poisoning
from
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non-condensable gases. Sensitivity work by Nenniger et al. (2009) showed that
non-
condensable gases have a huge impact on the ability of a condensing vapor to
deliver
heat to the solvent ¨ oil interface. As an inherent advantage, the EM RF
heating
approach of this invention bypasses this problem.
[00103] The present system reduces the energy requirements to recover the
hydrocarbons. As Table 1 indicates, oil rates similar to SAGD can be produced
at
temperatures as low as 40 C, whereas SAGD typically operates above 200 C.
Energy
consumption is related to the process temperature, and therefore ESEIEH, in
this
example, uses on the order of 13 percent [(40 C -10 C)/(240 C -10 C), where
the initial
reservoir temperature is 10 C] of the underground energy required by SAGD.
This is an
oversimplified comparison of the two process but it illustrates the basic
thermodynamic
principle behind the claimed energy savings.
[00104] Residual solvent in the reservoir may constitute a significant
volume of
material in comparison with the total bitumen removed. Many candidate solvents
represent significant commercial value, and reclamation of the residual
solvent in that
case is a significant factor in total cost of the recovered bitumen. An
advantage of the
present approach is that the remaining solvent may be recovered by further RF
heating
to vaporize remaining solvent and recovering the vaporized solvent through the
injection, production, or other well, or by reducing the pressure of
subsurface geological
formation, or by performing a cyclic operation of RF heating and
depressurization. The
residual solvent may also be reclaimed by cycling a low economic value gas
(such as
CO2 or N2) through the reservoir
[00105] Some components of an apparatus according to one aspect of the
present
system will now be described. As discussed above, the process involves RF-
induced
heating of the bitumen within a reservoir. Typical tube transducers currently
available in
the market can operate at frequencies in the range of kHz to GHz. It is
envisioned that
a commonly available 5MW output power transmitter is more than sufficient for
this
process. The transmitters are known to be durable with decades of operating
life.
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[00106]
Optimum transmission occurs when transmitter impedance matches the
complex conjugate of the load impedance, consisting of the combined antenna
and
formation impedance. The load impedance range is estimated from measured
complex
dielectric permittivity of representative samples incorporated in a detail
numerical model
that estimates the absorbed RF power dissipation as a function of time and
position in
the formation. The model estimates temperature distribution, and the
distribution of
gases, water, and bitumen as a function of position and time, with changing
power
dissipation associated with distributed change in dielectric permittivity.
Dielectric
permittivity of oil sands is strongly affected by water content and
temperature (Chute
1979). The drive point impedance is the ratio of the electric field intensity
E divided by
the current I at the antenna input. This is a complex quantity, that is
typically
represented by a Smith chart.
[00107]
It is important to note that this impedance is a function of the antenna
design and resultant electric field distribution throughout the reservoir, and
changes with
time due to the compositional and temperature changes in the reservoir.
Optimum
power transfer occurs when the impedance of the power output is the complex
conjugate of the drive point impedance. Usually, RF transmitters are designed
for a
specified output impedance, typically 50 ohms or 75 ohms, although custom
impedance
values are possible. A matching circuit takes the power output from the
transmitter
power supply, and delivers it to the drive point with the desired impedance.
The
matching circuit may be incorporated in the transmitter subsystem, or may be a
separate entity. When the impedance match is imperfect, power is reflected
back to the
transmitter, and is measured via VSWR (variable standing wave ratio)
monitoring.
Imperfect impedance matching results in loss of coupling quantified by the
Power
Transfer Theorem taught in innumerable engineering texts.
[00108]
Moreover, excessive energy reflected into the transmitter can destroy
critical internal components. If VSWR exceeds acceptable limits for the
transmitter, the
transmitter is decoupled from the load to prevent damage. The antenna design
and
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operating frequency is designed to provide effective heating and heat
penetration for the
material permittivity, while also providing a drive point impedance that is
compatible with
matching to a transmitter, including the aforementioned range. In operation,
drive point
impedance change is deduced from reflections analysis and known permittivity
behavior. The matching circuit is dynamically changed, to maintain high
efficiency
coupling. There are many embodiments of this process. Given that RF heating of
in
situ oil sands has been investigated by numerous inventors and none have
recognized
and quantified this process, development of this system approach is beyond
ordinary
skills in the art.
[00109] Electromagnetic stimulation is documented in the literature. In
1981 the
IIT Research Institute conducted two small-scale tests in the oil-sand
deposits of
Asphalt Ridge, Utah (Sresty et al. 1986). Multiple vertical wells were drilled
into a 5-m
thick oil sand from just above its outcrop location. Radio-frequency power (at
2.3 MHz
increasing to 13.5 MHz) was used to heat the formation to about 160 C and
bitumen
was produced by gravity drainage into a sump that had been tunneled below the
formation. Another test was conducted four years later to stimulate a well in
a 150 API
oil reservoir in Oklahoma with reportedly encouraging results (Bridges et al.,
1985).
Electric heat stimulation of a well producing from the VVildmere Field on the
Lloydminster formation in Canada was also reported (Spencer et al., 1988) to
cause the
well's production rate to increase from 1m3/d to 2.5m3/d.
[00110] Thus, the present system provides in one aspect, a method for
recovering
hydrocarbons (i.e. heavy oil and/or bitumen) from a reservoir, or hydrocarbon
deposit,
comprising the steps of: drilling at least one injection well and at least one
production
well; providing RF antennas in the injection wells; generating EM radiation
through the
RF antennae to heat the formation containing the hydrocarbons (preferably, the
heating
initially extends between the injection wells and the production wells so as
to create a
"communication pathway" there-between); and injecting a solvent through the
injection
wells to produce solvent enriched hydrocarbons at the production wells.
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[00111]
The injection and production wells may be horizontal, with the injection
wells being above the production wells, generally parallel, or generally, in
the same
vertical plane. The injection wells may be provided as a series of vertical
wells, with the
production wells provided horizontally and in proximity to the injection
wells.
[00112]
The EM radiation may be used to heat the formation to a temperature of
about 40 C to 70 C. The RF energy is preferably applied at a frequency of
about 1
kHz to 1 GHz. The RF antennae may be provided on the injection wells, or
provided
separate from the injection wells. The RF antennae may also be provided on the
injection and producer wells. The duration of heating from each antenna can be
controlled to achieve optimum heating rates throughout the process of solvent
extraction of hydrocarbons.
[00113]
The RF power provided may be used to control the temperature at the
producer to ensure proper subcool operation (i.e. the producer remains
immersed in the
hydrocarbon not in the gas). The RF power may also be used to control the
solvent/oil
ratio in the region of the producer such that asphaltene precipitation that
may clog
reservoir pores is properly managed. Higher temperature results in a lower
solvent/oil
ratio and lower probability of asphaltene precipitation, lower temperature
results in the
converse. The solvent of the present system may be polar. Preferably, the
solvent is
propane. The injection solvent may be continuously circulated through the
hydrocarbon
deposit to establish and enlarge solvent vapour chambers to facilitate
mobilization and
leaching of the heavy oil and/or bitumen.
[00114]
In Figure 4, electromagnetic heating antenna and injector 12 and
producer 14 may optionally take advantage of the typical horizontal well
configuration
applied in SAGD, as both processes rely on gravity drainage following the
mobilization
of reservoir oil. For example, well piping may be used to form an antenna and
then
serve as a combined electromagnetic heating antenna and injector 12. Such a
configuration is fully compatible with capabilities of extant drilling and
completion
technology, and also extant producer pipe designs that admit bitumen while
excluding
CA 02816297 2014-10-31
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31
sand. This is significant in terms of time to field and corollary inventions
required to
exploit the process in the field. An example of such a configuration is
disclosed in U.S.
patent 7,441,597.
[00115] The benefits of combined solvent and RF heating may be enhanced for
some applications., present or future, with antenna approaches that include
but are not
limited to those enumerated in Table 2. Preferred antenna shapes can be
Euclidian
geometries, such as lines and circles. These are fully incorporated in the RF
processes
described in this submission. The antenna may comprise a system of linear
electric
conductors situated in the hydrocarbon and conveying electric currents. The
antenna
macrostructure is preferentially linear in shape as the wells are
substantially linear in
shape. The time harmonic electric currents transduce one or more of waves,
electric
fields, magnetic fields, and electric currents into the hydrocarbon which are
dissipated
there to provide heat. The antennas provide electric circuits may be made open
or
closed circuit at DC such as dipoles and elongated loops which provide trades
in
impedance, heating pattern, and installation methods. The energies are
transduced
according to the Lorentz relation, and other relations, into the surroundings.
Transmission lines (not shown) are used between the surface and the
hydrocarbon
formation to minimize unwanted heating in the overburden.
[00116] Table 2. Example antenna types that may be used for RF heating
Antenna Configuration DC Continuity
Dipole No
Monopole No
Loop Yes
Half Loop Yes
