Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE lNV~N-llON:
method and apparatus for subterranean thermal conditioning
NAME OF lNV~N-lOR:
Robert Edward Isted
FIELD OF THE lNV~N-lION
The present invention relates to a method and apparatus
for subterranean thermal conditioning.
BACKGROUND OF THE lNV~NllON
It has long been recognized in the petroleum industry that
addition of heat to the productive interval in oil wells can
be very beneficial to stimulating and maintaining the
production rates of high viscosity heavy oil and waxy oil.
Steam injection is used extensively, but has certain
inherent characteristics that makes it disadvantageous to use
under certain circumstances. For example, some oil bearing
reservoirs also contain clay minerals which swell in contact
with fresh water. This swelling damages the permeability of
the reservoir rock and, therefore, its fluid productivity. In
many oil producing regions, fresh water supplies for generating
steam are limited. The condensed water from the injected steam
that is produced with the reservoir fluids must be separated
and extensively treated to reuse it for steam generation or to
dispose of it to near-surface aquifers. In oil reservoirs that
are more than a few meters thick, injected steam enters the
reservoir at its most permeable point, thus heating the region
near that point, but leaving large sections of exposed
productive reservoir unheated.
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An electrical heating system for well conditioning does
not need water injection thereby eliminating clay swelling
permeability problems, water supply, treating, and disposal as
considerations and the addition of heat may be beneficial in
reducing existing clay swelling. On the other hand the system
may use water, convert water to steam or use other fluid, if
advantageous to increase production, to destroy contaminants,
to promote fracturing or otherwise condition the well. The
invention may be of any required length and be configured to
have variable or constant heat release along the length thereby
enabling heating of the entire productive zone, and beyond,
at variable total as well as variable incremental heat rates
consistent with requirements.
Several configurations of electrical apparatus have been
proposed and tested in the field to thermally stimulate oil
producing reservoirs. One of the first methods implemented was
the suspension of electrical resistance heating elements on
an electrical power cable across from the interval to be
heated. Electrical current is delivered through the cables to
the resistance elements causing the resistance elements to
increase in temperature in proportion to their electrical
resistance and the square of the electrical current passing
through them. Heat is transferred to the produced fluid by
convection from the surface of the resistance elements, thereby
raising the temperature of the fluid in the well annulus. This
increase in temperature causes some heat to be transferred by
conduction through the wall of the well's production casing,
or liner, to the near wellbore region of the reservoir. The
temperature rise in the near wellbore region causes a reduction
in the viscosity of the oil flowing in that region, with a
consequent reduction in pressure drop there and an increase in
productivity due to the reduction in flow resistance. In order
to transfer a significant amount of the heat from the
resistance element surface to the near wellbore reservoir
region, a very high surface temperature must be generated.
High surface temperatures cause thermal coking of petroleum
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product and degradation of insulating and other material with
consequent failure of the device. As a result, this type of
electrical heater is no longer commonly used in the petroleum
industry.
Another type of electrical heating device that has been
extensively tested in the field involved the isolation of one
or more electrodes in the well production casing, or liner
string, which are used to conduct electrical current via the
connate water or conductive material in the reservoir. With
this type of device, the electrical resistivity of the
reservoir itself is utilized as a heating element. Again the
heat generated within a specific location is proportional to
the resistance and the square of the current passing through
that region. Several configurations of equipment have been
proposed and tested to effect near wellbore heating in this
way. One uses production casing in the well with a coating of
electrical insulation added to its surface except for the
region where the current is to pass to the reservoir.
Electrical current is passed to the reservoir by connecting one
pole of an AC electrical power source to the production casing
and the other pole to a ground electrode. These systems proved
to be impractical because of difficulties in maintaining a
perfectly impermeable electrically insulating membrane on a
long string of production casing that must withstand rough
handling in the field and extremes of temperature during
installation. In addition, the insulation degrades quickly due
to overheating causing the system to become inefficient and
ineffective after an impractically short period of operation.
This method also required completion of the subject well in a
specific manner such that installation in an existing well is
impractical in most instances.
Other system configurations based on the concept of
passing electrical current into the reservoir via electrodes
use two or more sections of electrically non-conducting
materials inserted in the casing string to isolate the
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electrode(s). With these configurations, AC electrical power
is conducted to the electrodes by a power cable or by the
well's production tubing that has been suitably insulated for
the purpose. While the published results of field tests of
these electrode systems have shown considerable promise for
effectively stimulating oil production, the systems have been
prone to premature failure and have several major inherent
disadvantageous characteristics which have limited their
acceptance by the petroleum industry. One inherent problem
with electrode systems is that they require either a new well
with a completion designed especially for the system or a very
extensive and often impractical re-working of an existing well.
Another problem is that oil reservoirs are not homogeneous and
are often formed of layers of sediment having differing
physical characteristics. Layers of sediment with differing
physical characteristics, respond differently to thermal
conditioning. With present systems this inevitably leads to
uneven heating, as they lack the ability to differentiate
between layers. The least productive layers, which typically
have low resistance, conduct most of the current such that the
required voltage for a reasonable release of heat in such
layers, is inadequate to effectively heat the production layers
which are typically composed of high resistance material. A
further limiting characteristic of the method is the highly
non-linear voltage gradient existing at the interface between
the electrode and isolation section. Most of the energy is
released near the ends of the electrodes resulting in high
temperatures in a local area with little increase in
temperature over the bulk of the electrode. In order to
release enough heat to stimulate productivity the electrode to
isolator connection can reach uncontrollably high temperature
levels causing failure of the electrode and/or adjacent
insulating and completion materials. Electrode systems require
the use of single phase alternating current with the return
current external to the supply cable. Alternating current is
used rather than direct current in order to maintain
electrolytic corrosion in the well to an acceptable level.
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Electrode systems that utilize either a power cable or an
insulated tubing string to deliver power to the electrodes can
be operated at AC frequencies below normal power frequencies.
This is done to minimize overheating that can occur in the
power delivery system due to the induced currents that are
generated in the ferromagnetic tubulars of the well and
accessories. Despite operating at quite low frequencies,
damaging overheating can result due to the high current
required to deliver significant power with the low resistance
common with this configuration. Electrode systems are
fundamentally limited in the combined length of the electrodes
being used, and, therefore, the thickness of exposed reservoir
face that can be heated. The reason for this is that the
efficiency of the electrode system is determined by the ratio
of the electrical impedance of the electrode divided by the
electrical impedance of the entire system. The impedance of
the electrode is inversely proportional to its length and a
function of the electrical resistivity of the reservoir
formation in contact with the electrode. The resistivity of
oil bearing formations varies greatly depending primarily on
its porosity and its saturation with oil, water and gas. Also,
the resistivity of the formation declines as its temperature
increases, therefore, the impedance of the electrode and the
efficiency of the system declines as the formation temperature
increases. One particularly intractable problem with electrode
systems is that electrical tracking seems to occur inevitably
across the surface of insulators exposed to the produced fluids
from the wells. These fluids are often composed of two liquid
phases, oil and salt water. At and below the electrical
potential differences used in these systems the movement of a
stream of conductive salt water across the isolating section
causes sparking which initiates a carbon track as the stream
of conductive liquid breaks or makes contact with the metallic
elements on either end of the insulator. With each spark
additional conductive material is deposited that effectively
extends the track thereby reducing the length of the isolating
section until a flash over renders the system inoperative. A
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similar phenomenon may take place within the reservoir, thus
adversely affecting the reservoir characteristics and causing
unstable electrical operating conditions. If operations
continue, production casing or isolator failure can occur,
requiring abandonment or expensive recompletion of the well.
Operation under these circumstances is characterized by sudden
current surges which cause the failure of delivery fuses and
or electrical cables. As a result of all these factors the
system has a short operating life and limited application.
Horizontal wells, that is petroleum wells in which the
production completion zone lies in a horizontal or near
horizontal plane, generally use steam to increase productivity,
with the same general limitations affecting vertical or near
vertical wells. United States Patent 5,539,853 which issued
to Jamaluddin in 1996 discloses a system in which heating
elements are deployed within a tubing section within the
production zone with hot gasses passing over the elements and
then discharging to the reservoir. Since the gases must be
supplied from the surface and penetrate into the formation, a
counterflow condition exists which is similar to that of steam
injection. Since the ambient gravitational and reservoir
pressure gradients are disrupted by the counter current flow
of the steam or gas, the full effect of heat addition is
compromised.
SUMMARY OF THE lNv~NllON
What is required is a method and associated apparatus for
subterranean thermal conditioning that will be less prone to
the drawbacks present in the teachings of the prior art.
According to one aspect of the present invention there is
provided a method for subterranean thermal conditioning. The
first step involves providing a tubular magnetic induction
apparatus. The second step involves positioning the magnetic
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induction apparatus into a subterranean environment. The third
step involves supplying voltage waves to the magnetic induction
apparatus thereby inducing a magnetic field in and adjacent to
the magnetic induction apparatus to thermally condition the
subterranean environment.
The method described above enables controlled thermal
conditioning. Due to the nature of the technology, problems
that led to equipment failure or undesirable outcomes with
alternative technologies are reduced or eliminated.
Although beneficial results may be obtained through the
use of the method, as described above, even more beneficial
results may be obtained when a further step is included of
generating electro-mechanical vibration by means of a steep
rise and fall in electrical voltage supplied to the magnetic
induction apparatus, such that magnetic attraction between the
magnetic induction apparatus and the ferromagnetic well casing
causes relative movement with each change in electrical
voltage. This imparts vibration of variable amplitude and
frequency which assists in production by agitating particles
so as to fluidize unconsolidated material to rearrange them to
establish a more permeable flow path. It also agitates
particles within the annular space so as to minimize settlement
and plugging and to reduce shear forces. It helps to fluidize
surrounding material when a tool becomes "sanded in", thus
allowing it to be more readily extracted.
According to another aspect of the present invention there
is provided an apparatus for subterranean thermal conditioning
which includes a tubular housing. A magnetically permeable
core is disposed in the housing. Electrical conductors are
wound in close proximity to the core. Means is provided for
electrically isolating the electrical conductors.
The electrical conductors for the apparatus, as described
above, receives electrical power from a Power Conditioning Unit
(PCU) located at the surface for the purpose of supplying
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electrical energy consisting of voltage waves with variable
voltage and frequency so controlled to generate the desired
response in the apparatus. The PCU may be equipped with
computer, microprocessors and application specific logic and
controls to optimize operating characteristics in response to
information obtained from instruments deployed downhole with
the apparatus.
Although beneficial results may be obtained through the
use of the apparatus, as described above, a production zone
which is to be thermally stimulated can be of a considerable
length. Even more beneficial results may, therefore, be
obtained when means are provided for electrically connecting
a plurality of housings, each having a magnetically permeable
core with electrical conductors wound in close proximity to the
core, to form a magnetic induction assembly. Such a magnetic
induction assembly can be made to substantially span a
production zone.
Although beneficial results may be obtained through the
use of the apparatus, as described above, hydrostatic pressure
in deep wells can exert considerable force upon the housing.
In some cases, this force is capable of crushing the housing
and damaging the components inside the housing. Even more
beneficial results may, therefore, be obtained when the means
for electrically isolating the electrical conductors includes
an insulating liquid. The insulating liquid inside the housing
helps to counteract hydrostatic pressure acting upon the
exterior of the housing. An alternative, and preferred, means
for electrically isolating the electrical conductors is a
substantially incompressible insulating gel.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more
apparent from the following description in which reference is
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made to the appended drawings, wherein:
FIGURE 1 is a side elevation view, in section, of a
magnetic induction assembly positioned in a vertical well in
accordance with the teachings of the present invention,
including adapter sub, primary electrical connection, and a
plurality of magnetic induction apparatus joined by means of
conductive couplings.
FIGURE 2 is a side elevation view, in section, of a
magnetic induction assembly positioned in a horizontal well in
accordance with the teachings of the present invention,
including adapter sub, primary electrical connection, and a
plurality of magnetic induction apparatus joined by means of
conductive couplings.
FIGURE 3 is a side elevation view, in section, of one of
the magnetic induction apparatus from the magnetic induction
assembly illustrated in FIGURE 1.
FIGURE 4 is a top plan view, in section, taken along
section lines 4-4 of the magnetic induction apparatus
illustrated in FIGURE 3.
FIGURE 5 is a side elevation view, in section, of the
primary electrical connection from the magnetic induction
assembly illustrated in FIGURES 1 and 2.
FIGURE 6 is an end elevation view, in section, taken along
section lines 6-6 of the primary electrical connection
illustrated in FIGURE 5.
FIGURE 7 iS a side elevation view, in section, of a male
portion of the conductive coupling from the magnetic induction
assembly illustrated in FIGURES 1 and 2.
FIGURE 8 is an end elevation view of the male portion of
the conductive coupling illustrated in FIGURE 7.
FIGURE 9 is a detailed side elevation view, in section,
of a portion of the male portion of the conductive coupling
illustrated in FIGURE 7.
FIGURE 10 is a side elevation view, in section, of a
female portion of the conductive coupling from the magnetic
induction assembly illustrated in FIGURES 1 and 2.
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FIGURE 11 is a side elevation view, in section, of the
male portion illustrated in FIGURE 7 coupled with the female
portion illustrated in FIGURE 10.
FIGURE 12 is a side elevation view, in section, of the
adapter sub from the magnetic induction assembly illustrated
in FIGURES 1 and 2.
FIGURE 13 is an end elevation view, in section, taken
along section lines 13-13 of the adapter sub illustrated in
FIGURE 12.
FIGURE 14 is a schematic diagram of a power control unit
to be used with the magnetic induction assembly illustrated in
FIGURES 1 and 2.
FIGURE 15 is an end elevation view, in section, of a first
alternative internal configuration for the magnetic induction
apparatus illustrated in FIGURE 3.
FIGURE 16 is an end elevation view, in section, of a
second alternative internal configuration for the magnetic
induction apparatus illustrated in FIGURE 3.
FIGURE 17 is an end elevation view, in section, of a third
alternative internal configuration for the magnetic induction
apparatus illustrated in FIGURE 3.
FIGURE 18 is a side elevation view, in section, of
instrument and sensor components deployed as part of the
magnetic induction assembly illustrated in FIGURES 1 and 2.
FIGURE 19 is an end elevation view, in section, of a
production tubing heater illustrated in FIGURES 1 and 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred method for thermal conditioning of an oil
well will now be described with reference to FIGURES 1 and 2.
The first step involves providing one or more magnetic
induction apparatus 20. The second step involves positioning
magnetic induction apparatus 20 into a subterranean
environment. An oil well 22 is illustrated that has a
ferromagnetic well casing 24. It is preferred that more than
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one magnetic induction apparatus 20 be used and that they be
joined together as part of a magnetic induction assembly,
generally indicated by reference numeral 26. The third step
involves inducing a magnetic field in and adjacent to
ferromagnetic well casing 24 by means of magnetic induction
apparatus 20 thereby producing heat to thermally condition oil
well 22. As an adjunct or additional step to this method
electro-mechanical vibrations may be generated by means of a
steep rise and fall in electrical voltage supplied to magnetic
10 induction apparatus 20. Magnetic attraction between magnetic
induction apparatus 20 and ferromagnetic well casing 24 causes
relative movement with each rise in electrical voltage. This
imparts vibration that can be varied in amplitude and frequency
by means of a power control unit, which will hereinafter be
15 described in relation to the components that is preferred be
included in magnetic induction assembly 26.
The preferred embodiment of magnetic induction assembly
26 will now be described with reference to FIGURES 1 through
20 19. Referring to FIGURE 1, magnetic induction assembly 26
includes an adapter sub 28, a electrical feed through assembly
30, and a plurality of magnetic induction apparatus 20 joined
by means of conductive couplings 32.
Referring to FIGURES 3 and 4, each magnetic induction
apparatus 20 has a tubular housing 34. Housing 34 may be
magnetic or non-magnetic depending upon whether it is desirable
to build up heat in the housing itself. Referring to FIGURES
1 and 2, it is preferred that housing 34 have external
30 centralizer members 36. Referring to FIGURES 3 and 4, a
magnetically permeable core 38 iS disposed in housing 34.
Electrical conductors 40 are wound in close proximity to core
38. Insulated dividers 42 are used as means for electrically
isolating the electrical conductors. It is preferred that
35 housing 34 be filled with an insulating liquid, which may be
transformed to a substantially incompressible gel 37 So as to
form a permanent electrical insulation and provide a filling
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that will increase the resistance of housing 34 to withstand
high external pressures. The cross sectional area of magnetic
core 38, the number of turns of conductors 40, and the current
originating from the power control unit may be selected to
release the desired amount of heat when stimulated with a
fluctuating magnetic field at a frequency such that no
substantial net mechanical movement is created by the
electromagnetic waves. Supplementally electro-mechanical
motion may be generated when stimulated with a steep rise and
fall electrical voltage wave such that the magnetic induction
apparatus 20 can respond to magnetic attraction to
ferromagnetic well casing 24, thereby causing a motion of
magnetic induction apparatus 20 or well casing 24 or both.
This motion can be controlled in amplitude by application of
a variable voltage and in frequency by the rate of change and
reversal of the magnetic field caused by the voltage wave
generated at the surface by a Power control unit (PCU). To
facilitate connection with the PCU there are power conducting
wires 41 and signal conducting wires 43. For reduced heat
release, a lower frequency, fewer turns of conductor, lower
current, or less cross sectional area or a combination will
lower the heat release per unit of length. Sections of
inductor constructed in this fashion allow the same current to
pass from one magnetic inductor apparatus 20 to another and,
since the heat release is proportional to current, overheating
in low productivity portions of the production zone can be
avoided with series wiring such that full heat release may be
achieved in other locations with the same current flow.
However, complex wiring configurations are not excluded. The
relative strength of mechanical motion may be varied in a
similar fashion to suit the particular needs. FIGURES 15, 16,
and 17, which will hereinafter be further described, illustrate
alternative internal configurations for electrical conductors
40 and core 38. Where close fitting of inductor poles to the
casing or liner is practical, additional magnetic poles may be
added to the configuration with single or multiple phase wiring
through each to suit the requirements. A number of inductors
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(ie. core 38 with electrical conductors 40) may be contained
in housing 34 with overall length to suit the requirements and
or shipping restraints. It is preferred, however, that a
multiplicity of housings 34 connect several magnetic induction
apparatus 20 together to form a magnetic induction assembly 26.
Several magnetic induction apparatus 20 are connected together
with flanged and bolted joints or with threaded ends similar
in configuration and form to those used in the petroleum
industry for completion of oil and gas wells. Referring to
FIGURES 1 and 2, at each connection for magnetic induction
apparatus 20 there is positioned a conductive coupling 32.
Conductive coupling 32 may consist of various mechanical
connectors and flexible lead wires that complete a conductive
connection. A preferred conductive coupling 32 iS illustrated
in FIGURE 11. Referring to FIGURE 11, conductive coupling 32
consists of a male portion 44 and a female portion 46 which are
coupled together in mating relation. Male portion 44,
separately illustrated in FIGURES 7 through 9 has coupling
threads 48. Female portion 46, separately illustrated in
FIGURE 10 has coupling threads 50. Referring to FIGURE 10,
female portion 46 includes a multiplicity of connector fingers
52. Referring to FIGURE 7, male portion 44 includes a
multiplicity of telescopically mating sleeves 54 that engage
connector fingers 52. Both fingers 52, as illustrated in
FIGURE 10, and sleeves 54, as illustrated in FIGURE 7 are
interleaved with insulation 56 to maintain relative positioning
and to isolate one from the other with respect to electrical
potential. The fingers 52 and sleeves 54 are so proportioned
that they do not project beyond a position wherein they may be
damaged during the joint make-up operation and further they do
not connect one to the other until adequate engagement of
coupling threads 48 and 50 ensures that both parts are properly
aligned to complete the connection. Referring to FIGURES 7 and
10, insulating blocks 60 surround fingers 52 of female portion
46 and sleeves 54 of male portion 44. A series of spring
loaded pins 58 are located within and project outwardly from
insulating block 60. Pins 58 are arranged to point toward each
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14
other in a radially staggered pattern. Referring to FIGURES
8 and 9, pins 58 engage plates 62 that have circular tracks 64.
The radial location of pins 58 iS such that each pin 58 follows
one of circular tracks 64 during make-up of the joint such that
a control signal may pass from one magnetic induction apparatus
to the next. Plates 62 are so arranged to contact the
appropriate pins 58 of each module at any and all rotational
positions. The plates 62 are readily removable to facilitate
replacement, if required at each assembly to ensure good
contact for the signals.
Where there are two production zones spacer sections (not
shown) may be placed between two of magnetic induction
assemblies 26. Spacer sections have no inductors, but are
equipped with electrical end connectors, as shown and described
with reference to FIGURES 7 through 11. This enables power and
control signals to pass zones with no oil production capability
which are located between two production zones each of which
has a magnetic induction assembly 26. Electrical transducer
signals pass from magnetic induction apparatus 20 to magnetic
induction apparatus 20 through said pins 58 and plates 62.
Referring to FIGURES 12, adapter sub 28 allows Electrical
Submersible Pump (ESP) cable 66 to be fed into top 68 of
magnetic induction assembly 26. Adapter sub 28 consists of a
length of tubing 70 which has an enlarged section 74 near the
midpoint such that the ESP cable may pass through tubing 70 and
transition to outer face 72 of tubing 70 by passing through a
passageway 76 in enlarged section 74, as illustrated in FIGURE
13. Adapter sub 28 has a threaded coupling 78 to which the
wellbore tubulars (not shown) may be attached thereby
suspending magnetic induction assembly 26 at the required
location and allowing retrieval of magnetic induction assembly
26 by withdrawing the wellbore tubulars.
Referring to FIGURE 5, ESP cable 66 iS coupled to an upper
most end 68 of magnetic induction assembly 26 by means of
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electrical feed through assembly 30. Electrical feed through
assembly 30, as illustrated, is manufactured by BIW Connector
Systems Inc. There are alternative electrical feed through
assemblies sold by Reda Pump Inc. and by Quick Connectors Inc.
which may be used. These assemblies are specifically designed
for connecting cable to cable, cable through a wellhead, and
cable to equipment and the like. The connection may also be
made through a fabricated pack-off comprised of a multiplicity
of insulated conductors with gasket packing compressed in a
gland around said conductors so as to seal formation fluids
from entering the inductor container. Electrical feed through
assembly 30 as illustrated in FIGURE 5, has the advantage that
normal oil field thread make-up procedures may be employed thus
facilitating installation and retrieval. Use of a standard
power feed through allows standard oil field cable splicing
practice to be followed when connecting to the ESP cable from
magnetic induction assembly 26 to surface. Referring to FIGURE
6, feed through assembly has centralizers members 36.
Referring to FIGURE 1 and 2, magnetic induction assembly
26 works in conjunction with a Power Conditioning Unit (PCU)
80 located at surface. PCU 80 utilizes single and multiphase
electrical energy either as supplied from electrical systems
or portable generators to provide modified output waves for
magnetic induction assembly 26. The output wave selected is
dependent upon the intended application. Square wave forms
have been found to be most beneficial in producing heat. A
pulsing wave has been found to be most beneficial in producing
vibrations. Maximum inductive heating is realized from waves
having rapid current changes (at a given frequency) such that
the generation of square or sharp crested waves are desirable
for heating purposes. The Heart of the PCU 80 is computer
processor 81. It is preferred that PCU 80 also includes solid
state wave generating devices such as Silicon Controlled
Rectifier (SCR) or Insulated Gate Bipolar Transistor (IGBT) 21
controlled from an interactive computer based control system
in order to match system and load requirements. One form of
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PCU may be configured with a multi tap transformer, SCR or IGBT
and current limit sensing on off controls so arranged to turn
60 Hz electrical power on and off in response to fluid flow or
lack thereof from the oil well production flow line. This
system, while it is inexpensive, has the disadvantage in that
it must be set at a power level such that at minimum flow there
is no danger of overheating or otherwise damaging the system
or well; and is not capable of generating the more effective
heating waves or the vibratory motion. The preferred system
consists of an incoming breaker, overloads, contactors,
followed by a multitap power transformer, an IGBT or SCR bridge
network and micro processor based control system to charge
capacitors to a suitable voltage given the variable load
demands. The output wave should then be generated by a micro
controller. The microcontroller can be programmed or provided
with application specific integrated circuits, in conjunction
with interactive control of IGBT and SCR, to control the output
electrical wave so as to enhance the heating action and the
vibratory motion as required to maximize conditioning.
Operating controls for each phase include anti shoot through
controls such that false triggering and over current conditions
are avoided and output wave parameters are generated to create
the insitu heating or other operations as required.
Incorporated within the operating and control system is a data
storage function to record both operating mode and response so
that optimization of the operating mode may be made either
under automatic or manual control. Referring to FIGURE 14, PCU
includes a supply breaker 82, overloads 84, multiple
contactors 86 (or alternatively a multiplicity of Thyristors
or Insulated Gate Bipolar Transistors), a multitap power
transformer 88, a three phase IGBT or comparable semiconductor
bridge 90, a multiplicity of power capacitors 92, IGBT 21
output semiconductor anti shoot through current sensors 94,
together with current and voltage sensors 96. PCU 80 delivers
single and multiphase variable frequency electrical output
waves for the purpose of heating, individual unidirectional
output wave, to one or more of magnetic induction apparatus 20,
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with long period and under current control such that mechanical
motion can be induced and the high current in rush of a DC
supply can be avoided. PCU 80 is equipped to receive the
downhole instrument signals interpret the signals and control
operation in accordance with program and set points. PCU is
connected to the well head with ESP cable 66, which may also
carry the information signals. Referring to FIGURE 18,
located within each magnetic induction apparatus 20 is an
instrument device 98 for the purpose of; receiving AC
electrical energy from the inductor supply, so as to charge a
battery 100, and which, on signal from PCU 80, commences to
sense, in a sequential manner, the electrical values of a
multiplicity of transducers 102 located at selected positions
along magnetic induction apparatus 20 such that temperatures
and pressures and such other signals as may be connected at
those locations may be sensed and as part of the same sequence.
One or more pressure transducers may be sensed to indicate
pressure at selected locations and said instrument outputs a
sequential series of signals which travel on the power supply
wire(s) to the PCU wherein the signal is received and
interpreted. Said information may then be used to provide
operational control and adjust the output and wave shape to
affect the desired output in accordance with control programs
contained within the PCU computer and micro controllers.
FIGURES 15 through 17 illustrate alternative internal
configuration for core 38 and electrical conductors 40
illustrated in FIGURE 4. FIGURE 15 illustrates a configuration
that was developed using a series of transverse plates 104
which allow magnetic induction apparatus 20 to flex. The
flexing is desirable in order to build angle to get around a
corner when the oil well has a horizontal or deviated portion.
FIGURES 16 illustrates a configuration developed with a series
of thin laminations 106 that are preferably twisted into a
helical configuration. The helical configuration causes
physical displacement of the string during operation, such that
the annular space within the wellbore is stirred. This
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18
minimizes the tendency for sand and particulate matter to
settle to the bottom of the hole, resulting in increased
availability for production. FIGURE 17 illustrates a
configuration that was developed to accommodate a flow tube
108. This allows passing liquids through concentric flow tube
108 for the purpose of flushing or cleansing the wellbore.
When oil is raised to surface, paraffin wax and the like
tend to precipitate out and adhere to the walls of the
production tubing. This can be addressed through the teaching
of the present invention. Referring to FIGURE 19, there is
illustrated a production tubing heater, generally identified
by reference numeral 109. This configuration has an outer
tubing 110 and an inner production tubing 112. Outer tubing
comes in two semi-circular sections 114 and 116 which fit
around production tubing 112 and are held in place by clamps
118. Core 38 and electrical conductors 40 are disposed between
outer tubing 110 and inner production tubing 112. When power
passes through core 38, heat is generated which heats
production tubing 112.
There are a variety of reasons why subterranean thermal
conditioning may be employed:
In an oil well:
a) Heating of the casing, reservoir rock, and reservoir fluids
in the near wellbore vicinity may be employed in order to
reduce the viscosity of the fluids flowing in the region such
that near wellbore pressure drop is reduced and fluid
production is stimulated;
b) Heating of the casing reservoir rock, and reservoir fluids
in the near wellbore may be employed to dissolve precipitated
solids like paraffin wax, asphaltines and resins which impede
the well's productivity, and to prevent the precipitation of
these solids from recurring;
c) Heating of the casing, reservoir rock, and reservoir fluids
in the near well bore may be employed to mitigate the effect
CA 02208197 1997-06-18
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of rock permeability reduction caused by an invasion of well
drilling fluids into the rock or by similar processes which
forms a "skin" or "skin damage" forming an impediment to oil
production;
d)It may also be employed for the in situ heating of solvents
or diluents injected intermittently or continuously for the
purpose of removing precipitated solids such as paraffin wax
from the well's perforations, production tubing and pump;
e) Heating of sections of the production tubing may be employed
in order to dissolve precipitated solids such as paraffin wax
or gas hydrates and prevent the recurrence of such
precipitation which impedes production; and
f) Heating of produced fluids in the well in order to reduce
their viscosity and thereby enhance the efficiency and
operability of the Well's pumping system.
In a gas well:
a) Heating of the casing and reservoir in the near wellbore
region may be employed to remove or mitigate the production
limiting effect of heavy oil or asphaltines which are carried
by the gas moving through the reservoir and deposited in the
near wellbore;
b) In wells that produce gas with high concentrations of
hydrogen sulfide, heating of the casing, reservoir rock and
reservoir fluids in the near wellbore region may be employed
to dissolve precipitated elemental sulphur and to prevent such
precipitation from occurring; and
c) In wells that produce gas with high concentrations of
hydrogen sulfide, heating of sections of the production tubing
may be employed to dissolve precipitated elemental sulphur and
preventing its recurrence.
There are also beneficial effects to be obtained from the
thermal conditioning of injection wells. Thermal conditioning
can be used to heat, in situ, the fluid being injected into the
well near its desired entry point into the target formation.
This improves the injectability of the fluid or enhances its
CA 02208197 1997-06-18
properties once it is in the formation. For example, thermal
conditioning would improve the solvent properties of water in
solution mining of potash. It would also improve the
effectiveness of an injected fluid used to sweep residual oil
from a pressure depleted reservoir.
It will be apparent to one skilled in the art that
modifications may be made to the illustrated embodiment without
departing from the spirit and scope of the invention as
hereinafter defined in the Claims.
