Note: Descriptions are shown in the official language in which they were submitted.
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IN-SITU COMBUSTION FOR OIL RECOVERY
Background of the Invention
The invention relates to a method and system for
heating a hydrocarbon containing formation, such as a
coal layer or an oil shale deposit, surrounding a heat
injection well.
Application of heat to oil shale formations is
described in U.S. Patent Nos. 2,923,535 to Ljungstrom and
4,886,118 to Van Meurs et al. These prior art references
disclose that electrical heaters transmit heat into an
oil shale formation to pyrolyze kerogen within the oil
shale formation. The heat may also fracture the formation
to increase permeability of the formation. The increased
permeability may allow formation fluid to travel to a
production well where the fluid is removed from the oil
shale formation. In some processes disclosed by
Ljungstrom, for example, an oxygen containing gaseous
medium is introduced to a permeable stratum, preferably
while still hot from a preheating step, to initiate
combustion.
U.S. Patent No. 2,548,360 describes an electrical
heating element placed within a viscous oil within a
wellbore. The heater element heats and thins the oil to
allow the oil to be pumped from the wellbore. U.S. Patent
No. 4,716,960 describes electrically heating tubing of a
petroleum well by passing a relatively low voltage
current through the tubing to prevent formation of
solids. U.S. Patent No. 5,065,818 to Van Egmond describes
an electrical heating element that is cemented into a
well borehole without a casing surrounding the heating
element.
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U.S. Patent No. 6,023,554 to Vinegar et al. describes
an electrical heating element that is positioned within a
casing. The heating element generates radiant energy that
heats the casing. A granular solid fill material may be
placed between the casing and the formation. The casing
may conductively heat the fill material, which in turn
conductively heats the formation.
U.S. Patent No. 4,570,715 to Van Meurs et al., which
is incorporated by reference as if fully set forth
herein, describes an electrical heating element. The
heating element has an electrically conductive core, a
surrounding layer of insulating material, and a
surrounding metallic sheath. The conductive core may have
a relatively low resistance at high temperatures. The
insulating material may have electrical resistance,
compressive strength and heat conductivity properties
that are relatively high at high temperatures. The
insulating layer may inhibit arcing from the core to the
metallic sheath. The metallic sheath may have tensile
strength and creep resistance properties that are
relatively high at high temperatures.
U.S. Patent No. 5,060,287 to Van Egmond, which is
incorporated by reference as if fully set forth herein,
describes an electrical heating element having a copper-
nickel alloy core.
Combustion of a fuel may be used to heat a formation.
Combusting a fuel to heat a formation may be more
economical than using electricity to heat a formation.
Several different types of heaters may use fuel
combustion as a heat source that heats a formation. The
combustion may take place in the formation, in a well
and/or near the surface.
US patent Nos. 4,662,443; 4,662,439 and 4,648,450
disclose fireflooding methods to combust hydrocarbons
within an underground formation, wherein an oxidizer,
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such as air, is pumped into the formation. The oxidizer
may be ignited to advance a fire front towards a
production well. Oxidizer pumped into the formation may
flow through the formation along fracture lines in the
formation. Ignition of the oxidizer may not result in the
fire front flowing uniformly through the formation.
It is also known to use a flameless combustor to
combust a fuel that is injected into a heater well. U.S.
Patent Nos. 5,255,742 to Mikus, 5,404,952 to Vinegar et
al., 5,862,858 to Wellington et al., and 5,899,269 to
Wellington et al., which are incorporated by reference as
if fully set forth herein, describe flameless combustors.
Flameless combustion may be accomplished by preheating a
fuel and combustion air to a temperature above an auto-
ignition temperature of the mixture. The fuel and
combustion air may be mixed in a heating zone to combust.
In the heating zone of the flameless combustor, a
catalytic surface may be provided to lower the auto-
ignition temperature of the fuel and air mixture. In
these known flameless combustors fuel and oxidant are
injected into the heater well through separate supply
conduits or as a mixture through a single supply conduit,
whereas the exhaust gases are vented to surface via an
exhaust conduit which may co-axially surround the fuel
and/or oxidant supply conduit(s).
It is also known to supply heat to a formation from a
surface heater. The surface heater may produce combustion
gases that are circulated through wellbores to heat the
formation. Alternately, a surface burner may be used to
heat a heat transfer fluid that is passed through a
wellbore to heat the formation. Examples of fired
heaters, or surface burners that may be used to heat a
subterranean formation, are illustrated in U.S. Patent
Nos. 6,056,057 to Vinegar et al. and 6,079,499 to Mikus
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4 07. 03. 2003
et al., which are both incorporated by reference as if 014P)
fully set forth herein.
The system and method according to the preamble of
claims 1 and 8 are known from US patent No. 3,010,513. In
the known system the formation around a heater well is
fractured and the fractures are filled with combustable
solids and propping material. The known system creates a
irregular heating pattern in the surrounding formation as
the fractures are of irregular length and shape.
A disadvantage of the known surface and downhole
heaters wherein fuel, oxidant andJor exhaust gases are
circulated through a heater well is that the casing and
other conduits in the heater well need to be made of a
high temperature resistant steel grade and in particular
the casing is exposed to high compressive forces as a
result of the thermal expansion of the surrounding
formation. The casing in the heater well has therefore to
be made of an expensive high-temperature and corrosion
resistant stainless steel grade. Also the supply of fuel
or, if an electrical heater is installed, supply of
electrical power generally requires a complex
infrastructure and is therefore expensive.
A disadvantage of the known fireflooding methods is
that fractures are created in irregular patterns in the
hydrocarbon containing formation and that only hydro-
carbons'near'the fractures are oxidised, so that only the
formation is heated in a rather irregular and
uncontrollable manner.
It is an object of the present invention to alleviate
the disadvantages of the known fireflooding, injected
fuel combustion and electrical heating methods and to
provide an inexpensive downhole heating method and system
AMENDED SHEET
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which transmit a controlled amount of heat in a uniform
manner into the formation.
Summary of the Invention _
In accordance with an aspect of the present invention a system for
transmitting heat into a hydrocarbon containing formation
surrounding a heat injection well comprises:
an oxidizing fluid source;
an oxidant supply conduit disposed in the wellbore of
the heat injection well, wherein the conduit is
configured to provide an oxidizing fluid from the
oxidizing fluid source to a reaction zone in the
formation during use, and wherein the oxidizing fluid is
selected to oxidize at least a portion of the hydro-
carbons in the formation in the vicinity of the wellbore
zone during use such that_heat is generated at the
reaction zone; and
a combustion gases exhaust conduit disposed in the
wellbore of the h_eat injection well for transmitting
combustion gases through the wellbore of the heat
injection well away from the reaction zone and wherein
the oxidant supply conduit is configured to supply the
oxidising fluid through the reaction zone by gas phase
diffusion and/or convection.
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In accordance with another aspect of the present
invention, there is provided a system for transmitting heat
into a hydrocarbon containing formation surrounding a heat
injection well, the system comprising: an oxidizing fluid
source; an oxidant supply conduit disposed in the wellbore
of the heat injection well, wherein the conduit is
configured to provide an oxidizing fluid from the oxidizing
fluid source to a reaction zone in the formation during use,
and wherein the oxidizing fluid is selected to oxidize at
least a portion of the hydrocarbons in the formation in the
vicinity of the wellbore zone during use such that heat is
generated at the reaction zone; and a combustion gases
exhaust conduit disposed in the wellbore of the heat
injection well for transmitting combustion gases through the
wellbore of the heat injection well away from the reaction
zone, wherein the oxidant supply conduit is configured to
supply the oxidising fluid through the reaction zone by gas
phase diffusion or convection.
In accordance with another aspect of the present
invention, there is provided a method for transmitting heat
into a hydrocarbon containing formation surrounding a heat
injection well, the method comprising: injecting an oxidant
through an oxidant supply conduit disposed in the wellbore
of the heat injection well to a reaction zone in the
formation, inducing the oxidizing fluid to oxidize at least
a portion of the hydrocarbons in the formation in the
vicinity of the wellbore such that heat and combustion gases
are generated in the reaction zone; and removing at least
part of the combustion gases through an exhaust conduit
disposed in the wellbore of the heat injection well away
from the reaction zone wherein the oxidant supply conduit
supplies the oxidising fluid through the reaction zone by
gas phase diffusion or convection..
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Preferably, the system is configured to allow heat to
transfer substantially by conduction from the reaction
zone to a selected section of the formation during use.
It is also preferred that the oxidant supply and
combustion gases exhaust conduits are equipped with
pressure regulation devices which control the pressure in
the reaction zone such that at least a substantial part
of the combustion gases generated at the reaction zone
are vented to the earth surface through the combustion
gases exhaust conduit.
In some cases the pressure generating device can be
used to allow part of the combustion gases to exhaust to
the earth surface and part to penetrate the process zone.
This may allow for a higher pressure in the wellbore than
in the region away from the wellbore. This pressure
differential may cause the oxidizing fluid to reach the
reaction zone more rapidly and/or in larger quantities
thereby allowing increased heat generation from the
reaction zone.
Suitably, the oxidant injection conduit and the
combustion gases exhaust conduit extend co-axially to
.each other from a wellhead of the heater well into the
hydrocarbon bearing formation , and the oxidant injection
conduit protrudes from the lower end of the oxidant
injection conduit through at least a substantial part o.f
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the hydrocarbon bearing formation and the protruding
lower part of the oxidant injection conduit is equipped
with an array of oxidant injection ports via which in us
oxidant is injected at a subsonic or supersonic velocity
into an annular space between the oxidant injection
conduit and the reaction zone.
The oxidant injection conduit may be an air injection
conduit and be provided with an air injection pump and
the air injection conduit and combustion gases exhaust
conduits may be each provided with a pressure control
valve for controlling the pressure in the annular space
between the perforated lower part of the oxidant
injection conduit and the reaction zone such that said
pressure is substantially equal to a pore pressure in at
least part the surrounding hydrocarbon containing
formation and transfer of combustion gases into the
formation is inhibited. But in some cases partial
penetration of the combustion gases into the formation
may be allowed in order to accelerate the transfer of
oxidising fluid to the reaction zone and increase the
heat generation there.
To start up or support the in-situ combustion process
the heater well may be equipped with an electric heater
for transmitting heat into the reaction zone or with a
fuel injection conduit for injecting additional fuel into
the reaction zone.
Detailed description of the invention
The invention will be described in more detail and by
way of example with reference to the accompanying
drawings, in which:
FIG. 1 depicts an embodiment of a natural distributed
combustor heat source;
FIG. 2 depicts a portion of an overburden of a
formation with a heat source;
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FIGS. 3 and 4 depict embodiments of a natural
distributed combustor heater; and
FIGS. 5 and 6 depict embodiments of a system for
heating a formation.
In accordance with the invention a hydrocarbon
containing formation is heated by in-situ oxidation of
hydrocarbons in the formation surrounding a heat
injection well, which system is also referred to as a
natural distributed combustor (NDC) heating system . The
generated heat may be allowed to transfer by convection
to a section of the formation surrounding the heater well
to heat it, whereas transfer of combustion gases from the
reaction zone into the formation is inhibited or
partially inhibited.
A temperature sufficient to support oxidation may be,
for example, at least about 200 C or 250 C. The
temperature sufficient to support oxidation will tend to
vary, however, depending on, for example, a composition
of the hydrocarbons in the hydrocarbon containing
formation. Water may be removed from the formation prior
to heating. For example, the water may be pumped from the
formation by dewatering wells. The heated portion of the
formation may be near or substantially adjacent to an
opening in the hydrocarbon containing formation. The
opening in the formation may be a heater well formed in
the formation. The heater well may be formed as in any of
the embodiments described herein. The heated portion of
the hydrocarbon containing formation may extend radially
from the opening to a width of about 0.3 m to about
1.2 m. The width, however, may also be less than about
0.9 m. A width of the heated portion may vary. In certain
embodiments the variance will depend on, for example, a
width necessary to generate sufficient heat during
oxidation of carbon to maintain the oxidation reaction
without providing heat from an additional heat source.
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After the portion of the formation reaches a
temperature sufficient to support oxidation, an oxidizing
fluid may be provided into the opening to oxidize at
least a portion of the hydrocarbons at a reaction zone,
or a heat source zone, within the formation. Oxidation of
the hydrocarbons will generate heat at the reaction zone.
The generated heat will in most embodiments transfer from
the reaction zone to a pyrolysis zone in the formation.
In certain embodiments the generated heat will transfer
at a rate between about 650 watts and 1650 watts per
meter as measured along a depth of the reaction zone.
Upon oxidation of at least some of the hydrocarbons in
the formation, energy supplied to the heater for
initially heating may be reduced or may be turned off. As
such, energy input costs may be significantly reduced,
thereby providing a significantly more efficient system
for heating the formation.
In an embodiment, a conduit may be disposed in the
opening to provide the oxidizing fluid into the opening.
The conduit may have flow orifices, or other flow control
mechanisms (i.e., slits, venturi meters, valves, etc.) to
allow the oxidizing fluid to enter the opening. The term
"orifices" includes openings having a wide variety of
cross-sectional shapes including, but not limited to,
circles, ovals, squares, rectangles, triangles, slits, or
other regular or irregular shapes. The flow orifices may
be critical flow orifices through which fluids flow at a
high, e.g. supersonic, speed to provide a substantially
constant flow of oxidizing fluid into the opening,
regardless of the pressure in the opening.
In some embodiments, the number of flow orifices,
which may be formed in or coupled to the conduit, may be
limited by the diameter of the orifices and a desired
spacing between orifices for a length of the conduit. For
example, as the diameter of the orifices decreases, the
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number of flow orifices may increase, and vice versa. In
addition, as the desired spacing increases, the number of
flow orifices may decrease, and vice versa. The diameter
of the orifices may be determined by, for example, a
pressure in the conduit and/or a desired flow rate
through the orifices. For example, for a flow rate of
about 1.7 standard cubic meters per minute and a pressure
of about 7 bar absolute, an orifice diameter may be about
1.3 mm with a spacing between orifices of about 2 m.
Smaller diameter orifices will tend to plug more
easily than larger diameter orifices due to, for example,
contamination of fluid in the opening or solid deposition
within or proximate to the orifices. In some embodiments,
the number and diameter of the orifices can be chosen
such that a more even or nearly uniform heating profile
will be obtained along a depth of the formation within
the opening. For example, a depth of a heated formation
that is intended to have an approximately uniform heating
profile may be greater than about 300 m, or even greater
than about 600 m. Such a depth may vary, however,
depending on, for example, a type of formation to be
heated and/or a desired production rate.
In some embodiments, flow orifices may be disposed in
a helical pattern around the conduit within the opening.
The flow orifices may be spaced by about 0.3 m to about
3 m between orifices in the helical pattern. In some
embodiments, the spacing may be about 1 m to about 2 m
or, for example, about 1.5 m.
The flow of the oxidizing fluid into the opening may
be controlled such that a rate of oxidation at the
reaction zone is controlled. The oxidizing fluid may also
cool the conduit such that the conduit is not
substantially heated by oxidation.
FIG. 1 illustrates an embodiment of a natural
distributed combustor configured to heat a hydrocarbon
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containing formation. Conduit 512 may be placed into
opening 514 in formation 516. Conduit 512 may have inner
conduit 513. Oxidizing fluid source 508 may provide
oxidizing fluid 517 into inner conduit 513. Inner
conduit 513 may have critical flow orifices 515 along its
length. Critical flow orifices 515 may be disposed in a
helical pattern (or any other pattern) along a length of
inner conduit 513 in opening 514. For example, critical
flow orifices 515 may be arranged in a helical pattern
with a distance of about 1 m to about 2.5 m between
adjacent orifices. Critical flow orifices 515 may be
further configured as described herein. Inner conduit 513
may be sealed at the bottom. Oxidizing fluid 517 may be
provided into opening 514 through critical flow
orifices 515 of inner conduit 513.
Critical flow orifices 515 may be designed such that
substantially the same flow rate of oxidizing fluid 517
may be provided through each critical flow orifice.
Critical flow orifices 515 may also provide substantially
uniform flow of oxidizing fluid 517 along a length of
conduit 512. Such flow may provide substantially uniform
heating of formation 516 along the length of conduit 512.
Packing material 542 may enclose conduit 512 in
overburden 540 of the formation. Packing material 542 may
substantially inhibit flow of fluids from opening 514 to
surface 550. Packing material 542 may include any
material configurable to inhibit flow of fluids to
surface 550 such as cement, sand, and/or gravel.
Oxidation products 519 typically enter conduit 512
from opening 514. Oxidation products 519 may include
carbon dioxide, oxides of nitrogen, oxides of sulphur,
carbon monoxide, and/or other products resulting from a
reaction of oxygen with hydrocarbons and/or carbon.
Oxidation products 519 may be removed through conduit 512
to surface 550. Oxidation product 519 may flow along a
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face of reaction zone 524 in opening 514 until proximate
an upper end of opening 514 where oxidation product 519
may flow into conduit 512. Oxidation products 519 may
also be removed through one or more conduits disposed in
opening 514 and/or in formation 516. For example,
oxidation products 519 may be removed through a second
conduit disposed in opening 514. Removing oxidation
products 519 through a conduit may substantially inhibit
oxidation products 519 from flowing to a production well
disposed in formation 516. Critical flow orifices 515 may
also be configured to substantially inhibit oxidation
products 519 from entering inner conduit 513.
A flow rate of oxidation product 519 may be balanced
with a flow rate of oxidizing fluid 517 such that a
substantially constant pressure is maintained within
opening 514. For a 100 m length of heated section, a flow
rate of oxidizing fluid may be between about 0.5 standard
cubic meters per minute to about 5 standard cubic meters
per minute, or about 1.0 standard cubic meters per minute
to about 4.0 standard cubic meters per minute, or, for
example, about 1.7 standard cubic meters per minute. A
pressure in the opening may be, for example, about 8 bar
absolute. Oxidizing fluid 517 may oxidize at least a
portion of the hydrocarbons in heated portion 518 of
hydrocarbon containing formation 516 at reaction
zone 524. Heated portion 518 may have been initially
heated to a temperature sufficient to support oxidation
by an electric heater, as shown in FIG. 5, or by any
other suitable system or method described herein. In some
embodiments, an electric heater may be placed inside or
strapped to the outside of conduit 513.
In certain embodiments it is beneficial to control
the pressure within the opening 514 such that oxidation
product and/or oxidation fluids are inhibited from
flowing into the pyrolysis zone of the formation. In some
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instances pressure within opening 514 will be balanced
with pressure within the formation to do so. In other
embodiments some of the combustion products may be
allowed to flow into the formation in order that the
pressure differential so created will accelerate the flow
of oxidizing fluid towards the reaction zone an thus
increase the heat generation rate.
Although the heat from the oxidation is transferred
to the formation, oxidation product 519 (and excess
oxidation fluid such as air) may be substantially
inhibited from flowing through the formation and/or to a
production well within formation 516. Instead oxidation
product 519 (and excess oxidation fluid) is removed
(e.g., through a conduit such as conduit 512) as is
described herein. In this manner, heat is transferred to
the formation from the oxidation but exposure of the
pyrolysis zone with oxidation product 519 and/or
oxidation fluid may be substantially inhibited and/or
partially or totally prevented.
In certain embodiments, some pyrolysis product near
the reaction zone 524 may also be oxidized in reaction
zone 524 in addition to the carbon. Oxidation of the
pyrolysis product in reaction zone 524 may provide
additional heating of formation 516. When such oxidation
of pyrolysis product occurs, it is desirable that
oxidation product from such oxidation be removed (e.g.,
through a conduit such as conduit 512) near the reaction
zone as is described herein, thereby inhibiting
contamination of other pyrolysis product in the formation
with oxidation product.
Conduit 512 may be configured to remove oxidation
product 519 from opening 514 in formation 516. As such,
oxidizing fluid 517 in inner conduit 513 may be heated by
heat exchange in overburden section 540 from oxidation
product 519 in conduit 512. Oxidation product 519 may be
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cooled by transferring heat to oxidizing fluid 517. In
this manner, oxidation of hydrocarbons within
formation 516 may be more thermally efficient.
Oxidizing fluid 517 may transport through reaction
zone 524, or heat source zone, by gas phase diffusion
and/or convection. Diffusion of oxidizing fluid 517
through reaction zone 524 may be more efficient at the
relatively high temperatures of oxidation. Diffusion of
oxidizing fluid 517 may inhibit development of localized
overheating and fingering in the formation. Diffusion of
oxidizing fluid 517 through formation 516 is generally a
mass transfer process. In the absence of an external
force, a rate of diffusion for oxidizing fluid 517 may
depend upon concentration, pressure, and/or temperature
of oxidizing fluid 517 within formation 516. The rate of
diffusion may also depend upon the diffusion coefficient
of oxidizing fluid 517 through formation 516. The
diffusion coefficient may be determined by measurement or
calculation based on the kinetic theory of gases. In
general, random motion of oxidizing fluid 517 may
transfer oxidizing fluid 517 through formation 516 from a
region of high concentration to a region of low
concentration. Convection of oxidizing fluid from the
injection orifices to the reaction zone will be governed
by the pressure differential between the wellbore and the
reaction zone based on the laws of fluid flow through
porous media.
With time, reaction zone 524 may slowly extend
radially to greater diameters from opening 514 as
hydrocarbons are oxidized. Reaction zone 524 may, in many
embodiments, maintain a relatively constant width. For
example, reaction zone 524 may extend radially at a rate
of less than about 0.91 m per year for a hydrocarbon
containing formation. For example, for a coal containing
formation, reaction zone 524 may extend radially at a
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rate between about 0.5 m per year to about 1 m per year.
For an oil shale containing formation, reaction zone 524
may extend radially about 2 m in the first year and at a
lower rate in subsequent years due to an increase in
volume of reaction zone 524 as reaction zone 524 extends
radially. Such a lower rate may be about 1 m per year to
about 1.5 m per year. Reaction zone 524 may extend at
slower rates for hydrocarbon rich formations (e.g., coal)
and at faster rates for formations with more inorganic
material in it (e.g., oil shale) since more hydrocarbons
per volume are available for combustion in the
hydrocarbon rich formations.
A flow rate of oxidizing fluid 517 into opening 514
may be increased as a diameter of reaction zone 524
increases to maintain the rate of oxidation per unit
volume at a substantially steady state. Thus, a
temperature within reaction zone 524 may be maintained
substantially constant in some embodiments. The
temperature within reaction zone 524 may be between about
650 C to about 900 C or, for example, about 760 C.
The temperature within reaction zone 524 may vary
depending on, for example, a desired heating rate of
selected section 526. The temperature within reaction
zone 524 may be increased or decreased by increasing or
decreasing, respectively, a flow rate of oxidizing
fluid 517 into opening 514. A temperature of conduit 512,
inner conduit 513, and/or any metallurgical materials
within opening 514 usually may not, however, exceed the
temperature at which the metallurgical materials will
begin to deform or corrode rapidly.
An increase in the diameter of reaction zone 524 may
provide relatively rapid heating of hydrocarbon
containing formation 516. As the diameter of reaction
zone 524 increases, an amount of heat generated per time
in reaction zone 524 may also increase. Increasing an
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amount of heat generated per time in a reaction zone will
in many instances provide for an increased heating rate
of formation 516 over a period of time, even without
increasing the temperature in the reaction zone or the
temperature at conduit 513. Thus increased heating may be
achieved over time without installing additional heat
sources, and without increasing temperatures. In some
embodiments the heating rates may be increased while
allowing the temperatures to decrease (allowing
temperatures to decrease may often lengthen the life of
the equipment used).
By utilizing the carbon in the formation as a fuel,
the natural distributed combustor may save significantly
on energy costs. Thus, an economical process may be
provided for heating formations that may otherwise be
economically unsuitable for heating by other methods.
Also, fewer heaters may be placed over an extended area
of formation 516. This may provide for a reduced
equipment cost associated with heating formation 516.
The heat generated at reaction zone 524 may transfer
by thermal conduction to selected section 526 of
formation 516. In addition, generated heat may transfer
from a reaction zone to the selected section to a lesser
extent transfer by convection. Selected section 526,
sometimes referred to herein as the "pyrolysis zone," may
be substantially adjacent to reaction zone 524. Since
oxidation product (and excess oxidation fluid such as
air) is typically removed from the reaction zone, the
pyrolysis zone can receive heat from the reaction zone
without being exposed to oxidation product, or oxidants,
that are in the reaction zone. Oxidation product and/or
oxidation fluids may cause the formation of undesirable
formation products if they are present in the pyrolysis
zone. For example, in certain embodiments it is desirable
to conduct pyrolysis in a reducing environment. Thus it
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is often useful to allow heat to transfer from the
reaction zone to the pyrolysis zone while inhibiting or
preventing oxidation product and/or oxidation fluid from
reaching the pyrolysis zone.
Pyrolysis of hydrocarbons, or other heat-controlled
processes, may take place in heated selected section 526.
Selected section 526 may be at a temperature between
about 270 C to about 400 C for pyrolysis. The
temperature of selected section 526 may be increased by
heat transfer from reaction zone 524. A rate of
temperature increase may be selected as in any of the
embodiments described herein. A temperature in
formation 516, selected section 526, and/or reaction
zone 524 may be controlled such that production of oxides
of nitrogen may be substantially inhibited. Oxides of
nitrogen are often produced at temperatures above about
1200 C.
A temperature within opening 514 may be monitored
with a thermocouple disposed in opening 514. The
temperature within opening 514 may be monitored such that
a temperature may be maintained within a selected range.
The selected range may vary, depending on, for example, a
desired heating rate of formation 516. A temperature may
be maintained within a selected range by increasing or
decreasing a flow rate of oxidizing fluid 517. For
example, if a temperature within opening 514 falls below
a selected range of temperatures, the flow rate of
oxidizing fluid 517 may be increased to increase the
combustion and thereby increase the temperature within
opening 514. Alternatively, a thermocouple may be
disposed on conduit 512 and/or disposed on a face of
reaction zone 524, and a temperature may be monitored
accordingly.
In certain embodiments one or more natural
distributed combustors may be placed along strike and/or
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horizontally. Doing so tends to reduce pressure
differentials along the heated length of the well,
thereby tending to promote more uniform heating and
improved control.
In some embodiments, a presence of air or molecular
oxygen, 02, in oxidation product 519 may be monitored.
Alternatively, an amount of nitrogen, carbon monoxide,
carbon dioxide, oxides of nitrogen, oxides of sulphur,
etc. may be monitored in oxidation product 519.
Monitoring the composition and/or quantity of oxidation
product 519 may be useful for heat balances, for process
diagnostics, process control, etc.
FIG. 2 illustrates an embodiment of a section of
overburden with a natural distributed combustor as
described in FIG. 1. Overburden casing 541 may be
disposed in overburden 540 of formation 516. Overburden
casing 541 may be substantially surrounded by materials
(e.g., an insulating material such as cement) that may
substantially inhibit heating of overburden 540.
Overburden casing 541 may be made of a metal material
such as, but not limited to, carbon steel.
Overburden casing may be placed in reinforcing
material 544 in overburden 540. Reinforcing material 544
may be, for example, cement, sand, concrete, etc. Packing
material 542 may be disposed between overburden
casing 541 and opening 514 in the formation. Packing
material 542 may be any substantially non-porous material
(e.g., cement, concrete, grout, etc.). Packing
material 542 may inhibit flow of fluid outside of
conduit 512 and between opening 514 and surface 550.
Inner conduit 513 may provide a fluid into opening 514 in
formation 516. Conduit 512 may remove a combustion
product (or excess oxidation fluid) from opening 514 in
formation 516. Diameterof conduit 512 may be determined
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by an amount of the combustion product produced by
oxidation in the natural distributed combustor. For
example, a larger diameter may be required for a greater
amount of exhaust product produced by the natural
distributed combustor heater.
In an alternative embodiment, at least a portion of
the formation may be heated to a temperature such that at
least a portion of the hydrocarbon containing formation
may be converted to coke and/or char. Coke and/or char
may be formed at temperatures above about 400 C and at a
high heating rate (e.g., above about 10 C/day). In the
presence of an oxidizing fluid, the coke or char will
oxidize. Heat may be generated from the oxidation of coke
or char as in any of the embodiments described herein.
FIG. 3 illustrates an embodiment of a natural
distributed combustor heater. Insulated conductor 562 may
be coupled to conduit 532 and placed in opening 514 in
formation 516. Insulated conductor 562 may be disposed
internal to conduit 532 (thereby allowing retrieval of
the insulated conductor 562), or, alternately, coupled to
an external surface of conduit 532. Such insulating
material may include, for example, minerals, ceramics,
etc. Conduit 532 may have critical flow orifices 515
disposed along its length within opening 514. Critical
flow orifices 515 may be configured as described herein.
Electrical current may be applied to insulated
conductor 562 to generate radiant heat in opening 514.
Conduit 532 may be configured to serve as a return for
current. Insulated conductor 562 may be configured to
heat portion 518 of the formation to a temperature
sufficient to support oxidation of hydrocarbons.
Portion 518, reaction zone 524, and selected section 526
may have characteristics as described herein. Such a
temperature may include temperatures as described herein.
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Oxidizing fluid source 508 may provide oxidizing
fluid into conduit 532. Oxidizing fluid may be provided
into opening 514 through critical flow orifices 515 in
conduit 532. Oxidizing fluid may oxidize at least a
portion of the hydrocarbon containing formation in at
reaction zone 524. Reaction zone 524 may have
characteristics as described herein. Heat generated at
reaction zone 524 may transfer heat to selected
section 526, for example, by convection, radiation,
and/or conduction. Oxidation product may be removed
through a separate conduit placed in opening 514 or
through an opening 543 in overburden casing 541. The
separate conduit may be configured as described herein.
Packing material 542 and reinforcing material 544 may be
configured as described herein.
FIG. 4 illustrates an embodiment of a natural
distributed combustor heater with an added fuel conduit.
Fuel conduit 536 may be disposed into opening 514. It may
be disposed substantially adjacent to conduit 533 in
certain embodiments. Fuel conduit 536 may have critical
flow orifices 535 along its length within opening 514.
Conduit 533 may have critical flow orifices 515 along its
length within opening 514. Critical flow orifices 515 may
be configured as described herein. Critical flow
orifices 535 and critical flow orifices 515 may be placed
on fuel conduit 536 and conduit 533, respectively, such
that a fuel fluid provided through fuel conduit 536 and
an oxidizing fluid provided through conduit 533 may not
substantially heat fuel conduit 536 and/or conduit 533
upon reaction. For example, the fuel fluid and the
oxidizing fluid may react upon contact with each other,
thereby producing heat from the reaction. The heat from
this reaction may heat fuel conduit 536 and/or
conduit 533 to a temperature sufficient to substantially
begin melting metallurgical materials in fuel conduit 536
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and/or conduit 533 if the reaction takes place proximate
to fuel conduit 536 and/or conduit 533. Therefore, a
design for disposing critical flow orifices 535 on fuel
conduit 536 and critical flow orifices 515 on conduit 533
may be provided such that the fuel fluid and the
oxidizing fluid may not substantially react proximate to
the conduits. For example, conduits 536 and 533 may be
mechanically coupled such that orifices are oriented in
opposite directions, and such that the orifices face the
formation 516.
Reaction of the fuel fluid and the oxidizing fluid
may produce heat. The fuel fluid and the oxidizing fluid
may have characteristics herein. The fuel fluid may be,
for example, natural gas, ethane, hydrogen or synthesis
gas that is generated in the in situ process in another
part of the formation. The produced heat may be
configured to heat portion 518 to a temperature
sufficient to support oxidation of hydrocarbons. Upon
heating of portion 518 to a temperature sufficient to
support oxidation, a flow of fuel fluid into opening 514
may be turned down or may be turned off. Alternatively,
the supply of fuel may be continued throughout the
heating of the formation, thereby utilizing the stored
heat in the carbon to maintain the temperature in
opening 514 above the autoignition temperature of the
fuel.
The oxidizing fluid may oxidize at least a portion of
the hydrocarbons at reaction zone 524. Generated heat
will transfer heat to selected section 526, for example,
by radiation, convection, and/or conduction. An oxidation
product may be removed through a separate conduit placed
in opening 514 or through an opening 543 in overburden
casing 541. Packing material 542 and reinforcing
material 544 may be configured as herein.
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FIG. 5 illustrates an embodiment of a system
configured to heat a hydrocarbon containing formation.
Electric heater 510 may be disposed within opening 514 in
hydrocarbon containing formation 516. Opening 514 may be
formed through overburden 540 into formation 516.
Opening 514 may be at least about 5 cm in diameter.
Opening 514 may, as an example, have a diameter of about
13 cm. Electric heater 510 may heat at least portion 518
of hydrocarbon containing formation 516 to a temperature
sufficient to support oxidation (e.g., about 260 C).
Portion 518 may have a width of about 1 m. An oxidizing
fluid (e.g., liquid or gas) may be provided into the
opening through conduit 512 or any other appropriate
fluid transfer mechanism. Conduit 512 may have critical
flow orifices 515 disposed along a length of the conduit.
Critical flow orifices 515 may be configured as described
herein.
For example, conduit 512 may be a pipe or tube
configured to provide the oxidizing fluid into
opening 514 from oxidizing fluid source 508. For example,
conduit 512 may be a stainless steel tube. The oxidizing
fluid may include air or any other oxygen containing
fluid (e.g., hydrogen peroxide, oxides of nitrogen,
ozone). Mixtures of oxidizing fluids may be used. An
oxidizing fluid mixture may include, for example, a fluid
including fifty percent oxygen and fifty percent
nitrogen. The oxidizing fluid may also, in some
embodiments, include compounds that release oxygen when
heated as described herein such as hydrogen peroxide. The
oxidizing fluid may oxidize at least a portion of the
hydrocarbons in the formation.
In some embodiments, a heat exchanger disposed
external to the formation may be configured to heat the
oxidizing fluid. The heated oxidizing fluid may be
provided into the opening from (directly or indirectly)
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the heat exchanger. For example, the heated oxidizing
fluid may be provided from the heat exchanger into the
opening through a conduit disposed in the opening and
coupled to the heat exchanger. In some embodiments the
conduit may be a stainless steel tube. The heated
oxidizing fluid may be configured to heat, or at least
contribute to the heating of, at least a portion of the
formation to a temperature sufficient to support
oxidation of hydrocarbons. After the heated portion
reaches such a temperature, heating of the oxidizing
fluid in the heat exchanger may be-reduced or may be
turned off.
FIG. 6 illustrates another embodiment of a system
configured to heat a hydrocarbon containing formation.
Heat exchanger 520 may be disposed external to
opening 514 in hydrocarbon containing formation 516.
Opening 514 may be formed through overburden 540 into
formation 516. Heat exchanger 520 may provide heat from
another surface process, or it may include a heater
(e.g., an electric or combustion heater). Oxidizing fluid
source 508 may provide an oxidizing fluid to heat
exchanger 520. Heat exchanger 520 may heat an oxidizing
fluid (e.g., above 200 C or a temperature sufficient to
support oxidation of hydrocarbons). The heated oxidizing
fluid may be provided into opening 514 through
conduit 521. Conduit 521 may have critical flow
orifices 515 disposed along a length of the conduit.
Critical flow orifices 515 may be configured as described
herein. The heated oxidizing fluid may heat, or at least
contribute to the heating of, at least portion 518 of the
formation to a temperature sufficient to support
oxidation of hydrocarbons. The oxidizing fluid may
oxidize at least a portion of the hydrocarbons in the
formation.
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In another embodiment, a fuel fluid may be oxidized
in a heater located external to a hydrocarbon containing
formation. The fuel fluid may be oxidized with an
oxidizing fluid in the heater. As an example, the heater
may be a flame-ignited heater. A fuel fluid may include
any fluid configured to react with oxygen. An example of
a fuel fluid may be methane, ethane, propane, or any
other hydrocarbon or hydrogen and synthesis gas. The
oxidized fuel fluid may be provided into the opening from
the heater through a conduit and return to the surface
through another conduit in the overburden. The conduits
may be coupled within the overburden. In some
embodiments, the conduits may be concentrically placed.
The oxidized fuel fluid may be configured to heat, or at
least contribute to the heating of, at least a portion of
the formation to a temperature sufficient to support
oxidation of hydrocarbons. Upon reaching such a
temperature, the oxidized fuel fluid may be replaced with
an oxidizing fluid. The oxidizing fluid may oxidize at
least a portion of the hydrocarbons at a reaction zone
within the formation.
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