Note: Descriptions are shown in the official language in which they were submitted.
CA 02591337 2007-05-31
DOWNHOLE STEAM GENERATION SYSTEM AND METHOD
FIELD OF THE INVENTION
[0001] The present invention relates generally to a device, system and method
for generating
steam downhole. More particularly, the present invention relates to an
electrical steam generation
system that enables efficient production of downhole steam without the heat
and pressure losses
realized by surface steam generation equipment.
BACKGROUND OF THE INVENTION
[0002] In heavy oil recovery, the use of steam to assist in oil recovery is
well known. For
example, it is common to drill parallel horizontal wells into formations at
different levels containing
heavy oil or bitumen. Such wells have been used in both Steam Assisted Gravity
Drainage (SAGD)
and Vapor-Extraction (VAPEX) production methods. In the SAGD system, steam is
applied to an
upper (or injection) well to contact heavy hydrocarbons inherent within the
pores of the formation to
decrease the viscosity of the hydrocarbons. In the VAPEX system, heated
solvents are applied. The
steam or solvent increases temperature and pressure within the formation to
reduce hydrocarbon
viscosity which results in hydrocarbons collecting in a lower production (or
recovery) well.
[0003] The current methods of injecting steam downhole are energy and capital
intensive.
Steam plants on the surface produce steam in boilers usually utilizing natural
gas or other fossil fuels
as a combustible fuel. The capital costs associated with designing, building
and operating a surface
steam plant are significant requiring years of production from the formation
to make the infrastructure
investment worthwhile. As a result, heavy oil recovery using surface steam
production is generally
only utilized for large scale projects with the result that smaller scale
projects that could benefit from
steam injection to aid hydrocarbon recovery are not utilized.
[0004] In addition, delivering high pressure steam to the formation is
inefficient as the steam
must be transported under pressure through lengthy surface and well pipes to
the formation. As the
horizontal and vertical distances in a typical wellbore can be many thousands
of feet, significant losses
in steam pressure and temperature result thereby reducing the efficiency of
the process.
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100051 As a result, there has been a need for steam production facilities with
lower
infrastructure costs that can deliver steam more efficiently to downhole
formations.
SUMMARY OF THE INVENTION
[0006] In accordance with the invention, there is provided a method of
creating in situ steam
in a well for hydrocarbon recovery comprising the steps of: positioning a
downhole electrical steam
generating system in the well adjacent a hydrocarbon bearing formation;
continuously forming
downhole steam within the well from in situ water; and, maintaining a high
intra-well pressure to
promote hydrocarbon recovery. In a preferred embodiment, the electrical steam
generating system is
conveyed to the hydrocarbon bearing formation by coiled tubing.
[0007] In further embodiments, high intra-well pressure is maintained by
adding water to the
injection well from the surface or is maintained by a sealed wellhead. In
other embodiments, steam is
generated in an injection well and hydrocarbons are recovered from a recovery
well or steam is
generated in the well and hydrocarbons are simultaneously recovered from the
well. Still further, the
system may include at least two generation systems are operatively connected
together to enable steam
generation at separate locations within the well.
[0008] In accordance with another embodiment, a downhole steam generation
system for
hydrocarbon recovery is provided comprising: a housing having openings
operatively containing an
electrical immersion heater, a connector system for connecting the electrical
immersion heater to an
electrical cable, and, a surface power unit for delivering electrical power to
the electrical heater
through the electrical cable.
[0009] The electrical immersion heater preferably includes a thermocouple
operatively
connected to the surface power unit for controlling the surface temperature of
the immersion heater.
100101 Other aspects and features of the present invention will become
apparent to those
ordinarily skilled in the art upon review of the following description of
specific embodiments of the
invention in conjunction with the accompanying figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Embodiments of the present invention will now be described with
reference to the
attached Figures, wherein:
Figure 1 is a schematic diagram showing a typical deployment of a steam
generation system in
accordance with one embodiment of the invention;
Figure 2 is an isometric view of a steam generation system in accordance with
one embodiment of the
invention;
Figure 3 is a side view of a steam generation system in accordance with one
embodiment of the
invention;
Figure 3A is a cross-sectional view of a steam generation system in accordance
with one embodiment
of the invention;
Figure 3B is a cross-sectional view of a connector system of a steam
generation system in accordance
with one embodiment of the invention;
Figure 3C is a cross-sectional view of a downhole end of a steam generation
system in accordance
with one embodiment of the invention;
Figure 4 is a schematic diagram of the deployment of a steam generation system
in accordance with a
further embodiment of the invention;
Figure 4A is schematic cross-sectional view of a connector system at a
downhole end of a steam
generation system in accordance with one embodiment of the invention; and
Figure 4B is schematic cross-sectional view of a connector system at an uphole
end of a steam
generation system in accordance with one embodiment of the invention.
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DETAILED DESCRIPTION
[0012] Generally, the present invention provides a device, system and method
for electrically
producing steam downhole.
[0013) With reference to the Figures, a downhole steam generation system and
methods of
deployment are described. The system includes a downhole heating device 10,
conductors 12 and a
surface control unit 14. As shown in Figures 2, 3, 3A, 3B, 3C and 3D, the
downhole heating device 10
generally includes a housing l0a with openings l Ob encasing an immersion
heating element (IHE) 10c
and a conductor connection system I Od.
Downhole Heating Device 10
Housing IOa
[0014] The housing 10 of the downhole heating device is a hollow cylindrical
element with
openings I Ob designed to allow the passage of fluids into the housing and to
contact the IHE where the
production of steam occurs. The openings lOb are generally of a fixed
dimension having sizes and
positions designed a) to allow sufficient fluids to enter the housing, b) to
provide structural integrity to
the housing and c) to protect the immersion IHE downhole. In a preferred
embodiment, the housing is
constructed of 100% stainless steel and is preferably the same material as the
outer surfaces of the IHE
so as reduce the risk of deterioration by dissimilar metal and/or galvanic
corrosion. Appropriate grades
of stainless steel can be used to comply with industry standards enabling use
of the system in both
sweet and sour gas wells. The housing is adapted for attachment to coiled
tubing by any suitable
means known to those skilled in the art including specialized connectors and
locking systems. In a
preferred embodiment, the housing includes a bullnose end 10e that facilitates
pushing the downhole
heating device to a desired location (discussed below).
Immersion Heating Element IOc
[0015] The IHE I Oc is an electric resistance heating element designed to
operate between
ambient temperatures and a maximum temperature, the maximum temperature being
approximately
1400 F. Generally, it is preferred that the maximum temperature can be
achieved within a few seconds
of applying power to the IHE through power supplied through the conductor 12
and surface control
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unit 14. The THE is thermatically controlled by an integral thermocouple (not
shown) that
communicates with the surface control unit 14. Preferably, under normal
operating conditions, in order
to maximize the operating life of the IHE and to prevent hydrocarbon cracking,
the IHE is operated at
temperatures in the range of 400-500 F.
[0016] The IHE is preferably powered by a 480 volt alternating current, single
phase power
source delivering 12,000 Watts or approximately 300 Watts per square inch of
IHE surface area. In a
typical embodiment, the IHE will be approximately 20-40 inches in length and
have an outside
diameter of approximately 0.6 inches.
[0017] In various embodiments of the downhole heating element, additional
functionality
may be incorporated within the IHE such as fluid detection sensors and/or
pressure sensors. Over
temperature protection may also be provided.
[0018] The resistance heating element is encased within an IHE housing to
protect the
resistance heating element. The construction is also sealed to prevent contact
of fluids with the
resistance heating element.
100191 The IHE is mounted within the housing by any suitable means. As shown
in Figure
3A and Figure 3B, the IHE is secured to a mounting wall lOf by a bushing l Og.
Connectors lOd
[0020] As shown in Figures 3A and 3B, the system includes connectors that
ensure a robust
electrical connection between the IHE and conductors for the operating
temperatures and downhole
conditions. In addition, the connectors must also provide sufficient
mechanical strength in tension,
compression and torsion for the operating conditions. As shown, the connectors
include a pin
connector lOd over which a corresponding female connector (not shown) may be
placed. To ensure
longevity in operation, the IHE and connectors may also be welded into place.
Conductors 12
[0021] Power is delivered to the IHE through conductors 12. The conductors are
designed to
deliver power over at least 2500 feet to the IHE while enabling the surface
controller to maintain an
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IHE surface temperature 1 F. The conductors must provide sufficient
mechanical strength to support
the weight of the conductors over these distances and have appropriate
coverings to provide the
appropriate abrasion resistance.
Surface Control Unit and Power Supply 14
[0022] As described above, the surface control unit 14 controls the delivery
of power to the
IHE through the conductors. Power may be delivered through mains or on-site
generated power. In a
generator application, the generator is preferably truck 8 or trailer mounted
allowing ready delivery of
the surface control unit 14 to the well-site. Known diesel generators may be
used and should be
capable of delivering single and three phase power to within 1% of the desired
voltage. A suitable
truck- or trailer-mounted genset for a 45kVA/36kW generator delivering roughly
12,000 Watts to the
IHE will consume roughly 6 liters of diesel fuel per hour.
[0023] The surface control unit 14 allows the control and delivery of power to
the IHE. The
SCU will preferably include appropriate displays and switches to enable an
operator both to set and
monitor power levels.
Operation
[0024] In operation, the downhole heating device is configured to a coiled
tubing 12a system
with the conductor 12 carried within the coiled tubing in order to protect the
conductor and to allow
the downhole heating device to be pushed to a desired location within a
wellbore 20. The surface
control unit 14 may be mounted on a truck or trailer for delivery to the well
site. After delivery to the
well site, the appropriate connections between the coiled tubing, conductor,
downhole heating device
and surface control unit are made.
[0025] Once attached to the coiled tubing, the downhole heating device is
conveyed to the
desired location. In various formations, the formation may provide sufficient
in situ water to generate
the desired temperatures and pressures of steam within the formation for
hydrocarbon recovery.
Alternatively, additional water may be added to the annular space 20a between
the wellbore 20 and
coiled tubing 12a. Downhole pressure may be maintained either by hydrostatic
pressure above the
heating device 10 or by appropriate wellhead systems as is known in the art.
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[0026] The methodology is similarly effective in solvent flood methods where
hydrocarbon
solvents are added to the well.
[0027] Heating losses and hence the cost of downhole heating is reduced
significantly over
past techniques which lead to significant improvements in sweep efficiency.
[0028] In addition to heavy oil recovery, the system may also be used in the
stimulation of
conventional vertical wells through alternating steam and production steps,
often referred to as "huff
and puff'. In this methodology, the downhole heating device is conveyed to the
stimulation zone and
the formation is stimulated. The downhole heating device may be removed from
the well and standard
production of the well may follow. In a still further embodiment, specialized
well heads may be
utilized allowing both pumping equipment and the downhole heating device to be
positioned in the
same well thereby obviating the need to remove the downhole heating device
before production.
Series Operation
[0029] In further embodiments of the invention, it may be desired to provide
stimulation in
horizontally or vertically separated zones of the same well bore 20. As shown
in Figure 4, separate
downhole heating devices 10' and 10" are shown separated by a section of
coiled tubing within a well
bore 20. Downhole heating device 10' may be a downhole heating device as
described above whereas
10" is a distinct assembly. In particular, embodiment 10" is distinct from
embodiment 10' to allow
conductors to pass across or through the housing, through coiled tubing
section 11 to downhole
heating device 10". As shown, the uphole ends of 10' and 10" are similar
whereas the downhole end
of 10' is provided with a bull nose 10e. The downhole end of 10" may include a
connector system
similar to that described above. The housing of 10" is distinct in allowing
conductors to pass along or
through the housing to the connectors. As shown in Figures 4A and 4B, coiled
tubing 11 may be
attached to housing 10a. In Figure 4A, the conductors 12 are attached to a
connector lOd as described
above. Within connector lOd, the conductors are split and are passed through
appropriate openings
I Oh and along channels 10i. Channels l0i may be covered by coverings l Oj. At
the opposite end of the
housing, conductors pass through further openings to a downhole connector 13
which allow a further
conductor 12' and tubing section 11' to connect to 10" thus permitting 10' to
be connected in series
with 10".
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[0030] The above-described embodiments of the present invention are intended
to be
examples only. Alterations, modifications and variations may be effected to
the particular
embodiments by those of skill in the art without departing from the scope of
the invention, which is
defined solely by the claims appended hereto.
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