U.S. patent application number 10/604574 was filed with the patent office on 2005-02-03 for porous media gas burner.
Invention is credited to Mehta, S. A., Moore, Gordon, Sanmiguel, Javier, Ursenbach, Matthew.
Application Number | 20050026094 10/604574 |
Document ID | / |
Family ID | 34378575 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050026094 |
Kind Code |
A1 |
Sanmiguel, Javier ; et
al. |
February 3, 2005 |
POROUS MEDIA GAS BURNER
Abstract
A porous media gas burner is adapted to operate in a pressurized
environment. The burner may have three zones: a mixing zone, an
ignition zone and a reaction zone. The burner may be used as a
downhole burner in a formation heat treatment method for oil and
gas wells.
Inventors: |
Sanmiguel, Javier; (Calgary,
CA) ; Mehta, S. A.; (Calgary, CA) ; Moore,
Gordon; (Calgary, CA) ; Ursenbach, Matthew;
(Calgary, CA) |
Correspondence
Address: |
EDWARD YOO C/O BENNETT JONES
1000 ATCO CENTRE
10035 - 105 STREET
EDMONTON, ALBERTA
AB
T5J3T2
CA
|
Family ID: |
34378575 |
Appl. No.: |
10/604574 |
Filed: |
July 31, 2003 |
Current U.S.
Class: |
431/1 |
Current CPC
Class: |
E21B 36/02 20130101;
F23C 99/006 20130101 |
Class at
Publication: |
431/001 |
International
Class: |
F23C 011/04 |
Claims
1. A downhole formation heating system for a wellbore including a
well casing, the system comprising: (a) a gas burner comprising a
cylindrical housing defining an intake opening and a flue opening,
the housing comprising means for receiving a supply of fuel and
air; a mixing zone where the fuel and air are mixed; an ignition
zone comprising an igniter and a reaction zone, each zone
comprising a packed bed of porous media; (b) an igniter for
igniting the fuel and air within the gas burner; (c) fuel and air
supply tubing for delivering fuel and air to the burner; and (d)
means for delivering pressurized air or an inert gas in an annular
space between the well casing and the fuel and air supply
tubing.
2. The system of claim 1 wherein the porous media comprises ceramic
beads.
3. The system of claim 2 wherein the ceramic beads comprises
alumina beads.
4. The system of claim 1 wherein the mixing zone and reaction zone
comprise a pore size less than a minimum quenching distance under
standard conditions of a fuel gas and the ignition zone comprises a
pore size greater than the minimum quenching distance under
standard conditions of the fuel gas.
5. A method of heat treating a formation comprising the steps of:
(a) inserting a gas burner comprising a cylindrical housing
defining an intake opening and a flue opening, the housing
comprising means for receiving a supply of fuel and air; a mixing
zone where the fuel and air are mixed; an ignition zone comprising
an igniter and a reaction zone, each zone comprising a packed bed
of porous media, into a wellbore; (b) injecting a fuel gas and air
into the gas burner to create a combustible mixture and igniting
the mixture to create a combustion front; and (c) causing the
combustion front to travel out the gas burner and into the
formation.
6. The method of claim 5 wherein one zone of the gas burner has a
pore size smaller than a minimum quenching distance for an
operating condition of pressure and fuel.
7. A gas burner comprising a tubular housing adapted to operate in
a pressurized environment, the housing defining an intake opening
and a flue opening and comprising means for receiving a supply of
fuel and air; a mixing zone where the fuel and air are mixed
comprising a packed bed of porous media; an ignition zone
comprising a packed bed of porous media, and a reaction zone
comprising a packed bed of porous media; wherein the pore size of
the mixing zone and the reaction zone is smaller than a minimum
quenching distance of a fuel gas under standard conditions while
the pore size of the ignition zone is larger than the minimum
quenching distance.
8. The burner of claim 5 wherein the flue opening combines with a
pressure regulator for controlling the pressure within the gas
burner above atmospheric pressure.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to a porous media gas burner
and methods for its use. In particular, the invention relates to a
downhole gas burner used in formation heat treatment methods.
[0002] Combustion of gases in porous media is a process where a
combustible gaseous mixture is injected into a porous matrix and is
combusted within the porous matrix. Flames in porous media have
higher burning velocities and leaner flammability limits than open
flames. These effects are well known and are the consequence of
excess enthalpy combustion. Essentially, heat that is generated in
the combustion zone is transferred by radiation and conduction
through the solid phase of the porous media to unburned gases. As a
result, it is possible to achieve temperatures higher than the
adiabatic flame temperature, and the increase in burning velocities
can be significantly higher than the open flame laminar burning
velocity for the same mixture in an open space.
[0003] Formation heat treatment is a process that is intended to
improve hydrodynamic conditions around the wellbore. If formation
temperatures reach an adequate level, blocking water may be
vapourized, clay structure may be dehydrated, clay minerals may be
partially destroyed, and microfractures may be induced in the
formation near the wellbore. As a result, permeability around the
wellbore may be significantly improved.
[0004] It is known to use a downhole electrical heater in a
formation heating method. The electrical heater is placed as close
as possible to the target zone, and an inert gas such as nitrogen
is co-injected through the annulus. The temperature of the injected
gas may rise to as high as 800.degree. C. before entering the
formation. However, this method involves large energy requirements
which makes it cost-prohibitive, particularly with rising
electrical energy costs.
[0005] Combustion stimulation is a known technique to promote fluid
production in a formation. A combustion front is initiated in a
wellbore by means of a surface heater or burner and the front is
propagated into the formation to a distance of up to about 6
meters. The formation in this zone is reduced to clean burnt sand,
which is very fluid permeable. However, the well casing is
subjected to high temperatures, which is undesirable, and there is
an elevated risk of explosions or well burnouts using this
technique. It is necessary to maintain wellbore temperatures below
600.degree. C. in order to prevent damage to the liner, which
limits the temperature which may be reached in the formation.
[0006] Therefore, there is a need in the art for a gas burner which
may be used downhole in a formation heating process.
SUMMARY OF INVENTION
[0007] In one aspect, the invention may comprise a gas burner
comprising a tubular housing adapted to operate in a pressurized
environment, the housing defining an intake opening and a flue
opening and comprising means for receiving a supply of fuel and
air; a mixing zone where the fuel and air are mixed comprising a
packed bed of porous media; an ignition zone comprising a packed
bed of porous media, and a reaction zone comprising a packed bed of
porous media; wherein the pore size of the mixing zone and the
reaction zone is smaller than a minimum quenching distance of a
fuel gas under standard conditions while the pore size of the
ignition zone is larger than the minimum quenching distance.
[0008] In another aspect, the invention may comprise a downhole
formation heating system for a wellbore including a well casing,
the system comprising:
[0009] (a) a gas burner comprising a cylindrical housing defining
an intake opening and a flue opening, the housing comprising means
for receiving a supply of fuel and air; a mixing zone where the
fuel and air are mixed; an ignition zone comprising an igniter and
a reaction zone, each zone comprising a packed bed of porous
media;
[0010] (b) an igniter for igniting the fuel and air within the gas
burner;
[0011] (c) fuel and air supply tubing for delivering fuel and air
to the burner; and
[0012] (d) means for delivering pressurized air or an inert gas in
an annular space between the well casing and the fuel and air
supply tubing.
[0013] In another aspect, the invention may comprise a method of
heat treating a formation comprising the steps of:
[0014] (a) inserting a gas burner comprising a cylindrical housing
defining an intake opening and a flue opening, the housing
comprising means for receiving a supply of fuel and air; a mixing
zone where the fuel and air are mixed; an ignition zone comprising
an igniter and a reaction zone, each zone comprising a packed bed
of porous media, into a wellbore;
[0015] (b) injecting a fuel gas and air into the gas burner to
create a combustible mixture and igniting the mixture to create a
combustion front; and
[0016] (c) causing the combustion front to travel out the gas
burner and into the formation.
BRIEF DESCRIPTION OF DRAWINGS
[0017] The invention will now be described by way of an exemplary
embodiment with reference to the accompanying simplified,
diagrammatic, not-to-scale drawings.
[0018] FIG. 1 is a schematic representation of one embodiment of
the present invention.
[0019] FIG. 2 is a schematic representation of one embodiment of a
formation heat treatment system.
DETAILED DESCRIPTION
[0020] The present invention provides for a gas burner and methods
of using a gas burner. When describing the present invention, all
terms not defined herein have their common art-recognized
meanings.
[0021] In one embodiment, the invention comprises a gas burner as
shown schematically in FIG. 1. The burner generally includes a body
(10) which comprises a mixing zone (12), an ignition zone (14) and
a reaction zone (16) where combustion will take place. The body may
have any shape. In one embodiment, the body may be cylindrical or
conical or have both cylindrical and conical sections. The body is
preferably lined with a heat-refractory material such as a ceramic
liner.
[0022] As shown in FIG. 1, the mixing zone (12) and ignition zone
(14) comprise cylindrical portions of the tubular body (10) while
the reaction zone (16) comprises a truncated conical portion, with
an expanding diameter as the reactants flow away from the mixing
zone of the inlet end. In one embodiment, the outlet end diameter
of the reaction zone may be about twice that of the inlet end. The
reaction zone may have a length about 4 to 5 times the diameter of
the inlet end. The mixing and ignition zones may have a length
approximately equal to their diameter.
[0023] All three zones (12, 14, 16) may be packed with a porous
media bed within the burner. The packed bed may comprise heat
resistant ceramic spheres such as alumina beads or any other
suitable particulate material to create a porous media bed for
example, but not limited to, zirconia-alumina composites, silicon
carbide, or mullite (alumina-silicon dioxide). As shown in FIG. 1,
air or oxygen is provided to the burner in the mixing zone (12),
along with the combustible gas. The gases mix in the mixing zone
(12) and are ignited in the ignition zone (14) by means of an
igniter (not shown), which may be a small open flame burner or a
spark device. Once ignited, the flame front will be allowed to
advance into the reaction zone (16).
[0024] In one embodiment, the mixing zone (12) may be packed with
small size particles so that the pore size in the mixing zone is
smaller than the minimum quenching distance (MQD). The second
section would the ignition zone (14) and may be packed with larger
size particles so that the pore size is larger than the minimum
quenching distance. The size and nature of the reaction zone (16)
particles (pore size) would depend on energy and operational
requirements, type of fuel gas and operating conditions and could
be of either uniform size or a combination of sizes.
[0025] As used herein, the phrase "minimum quenching distance" or
"MQD" shall mean the minimum diameter or opening dimension through
which a flame may travel under standard conditions. It may be
observed that a flame in a mixture within a flammable range will be
extinguished if forced to propagate through a constriction. The
walls of the constriction exert a repressive influence on the
flame. A flame is quenched in a constriction because of two
mechanisms which otherwise permit flame propagation: the diffusion
of species, and the diffusion of heat. The walls of the
constriction may extract heat and the smaller the restriction, the
greater the surface to volume ratio will be. Similarly, the smaller
the constriction, the greater the number of collisions of the
active radical species with the wall, and the greater the number of
these species which are destroyed. Accordingly, one skilled in the
art will understand that increased temperature decreases the
quenching distance and that quenching distance decreases as
pressure increases.
[0026] MQD is a physical property of each fuel and may be
determined in the laboratory or by using the criteria of Peclet
number equal to 65. The Peclet number is a dimensionless parameter
that is based on the specific heat, laminar burning velocity,
density, thermal conductivity and thermal diffusivity of the gas
mixture, however the heating of the porous media bed will affect
the minimum quenching distance.
[0027] It is generally accepted that main driving factor in the
combustion of gases in a porous media is heat recirculation through
the porous media to preheat unburned reactants. This preheating of
the reactants may permit combustion even if the pore size is
smaller than the MQD of the porous media under standard
conditions.
[0028] In one embodiment, the burner (10) is adapted to operate in
a pressurized environment. The body of the burner (10) is designed
to withstand the desired pressure. This provides the opportunity to
integrate the burner in the middle of a process stream, so that
exhaust gases may be recovered at pressure for further treatment,
separation or other downstream processes. It may allow use in
subterranean hydrocarbon formations as will be subsequently
described. The porosity of the packed bed may be controlled for
specific applications. In one embodiment, the packed bed in the
mixing zone and the reaction zone has a pore size smaller than the
minimum quenching distance, while the ignition zone pore size may
be larger than the minimum quenching distance. The pore size,
combustible mixture flux, concentration of fuel gas in oxidant
(air), type of fuel and shape of the burner may be varied to permit
and optimize the process in a pressurized environment. A person
skilled in the art may determine these matters with minimal and
routine experimentation.The main effect of operating pressure in
the gas burner is a reduction in the combustion front velocity.
Maximum temperatures attainable when operating at elevated
pressures are generally lower than those temperatures observed for
the same gas mixtures and fluxes at atmospheric pressure. While the
effect of pore size is almost negligible at atmospheric operating
pressure, as the operating pressure is increased, the velocity of
the combustion front increases as the pore size decreases. At
elevated operating pressures, burning velocities appear to increase
as the inlet gas velocity increases. Additionally, burning
velocities appear to increase as the fuel gas concentration is
decreased.
[0029] The relatively smaller pore size of the mixing and the
reaction zone promotes mixing of the reactants and pre-heating of
the reactants due to heat transfer from the solid phase to the gas
phase. The relatively larger pore size of the ignition zone allows
easier ignition of the reactants and propagation of the flame into
the reaction zone.
[0030] The gas burner (10) may be used as a downhole gas burner to
be used in a formation heating method. Generally, the formation
heating method may comprise two stages. In a first stage, the
burner is placed in the wellbore at the level of the formation by
means of coiled tubing or the like. The tubing also provides the
means by which a combustible mixture is provided to the burner. The
combustible mixture may be a lean mixture of natural gas and air
which is below the flammability limits of natural gas at
atmospheric pressure. The mixture may sustain a combustion front
within the burner which expels hot flue gases into the formation.
If desired, the combustion front may be controlled to travel
outward from the burner into the formation. The combustion front is
controlled by increasing or decreasing the fuel gas flux, changing
the concentration of fuel gas in the mixture fuel-air (oxidant) and
by using different particle size or a combination of particle sizes
in the reaction zone. These variable elements may be varied either
singly or in combination.
[0031] Depending on the composition of the formation hydrocarbons,
the amount of oxygen in the flue gas and the flue gas temperature,
some oxidation/combustion reactions may start to take place in the
formation at the same time as gas combustion is occurring in the
burner. Once the combustion front leaves the burner, it is
preferred to increase the concentration of the fuel, so that the
temperature of the reaction front increases. This may be done
safely because the temperature in the burner and the wellbore will
not be high enough to facilitate or sustain combustion. In other
words, the burner becomes a flame arrester once the combustion
front travels outward into the formation.
[0032] The burner described herein may be used as a downhole burner
in alternative methods. As described above, the burner may be used
in well stimulation method where blocking water is vapourized,
clays may be partially destroyed, asphaltenic deposits may be
burned and microfractures in the formation may be propogated. In
another example, the downhole gas burner may be used in a downhole
steam generation method for cyclic or continuous steam injection in
deep heavy oil wells. In another example, the downhole gas burner
may be used in a high pressure air injection technique, where
combustion is initiated in the formation and air is then
continuously injected into the producing layer. The combustion of
inplace oil may provide thermal and gas drive to the oil
reservoir.
[0033] In one embodiment, with reference to FIG. 2, a downhole
burner (10) is positioned near the producing formation (20) by
means of continuous or coiled tubing (22) and anchored to the well
casing by means of an anchor (24). Air is injected through the
tubing (22) and a combustible gas such as natural gas is injected
through a separate tubing (26) to the burner. Air or an inert gas
such a nitrogen may be injected in the annulus between the well
casing and the tubing (22). The burner has a mixing zone (120), an
ignition zone (122) and a reaction zone (124), each packed with a
suitable porous media. As described above, in a preferred
embodiment, the particle size or minimum quenching distances in
each zone may be varied. The combustion front (126) will be
established in the reaction zone (124) and move outward into the
formation. At the same time, hot flue gases (128) are pushed
outward into the formation.
[0034] In each case, the ignition and combustion downhole and/or in
the formation may be initiated using a lean combustible mixture,
which may include waste gases. The lean mixture reduces the risk of
explosive mixtures accumulating in the system.
[0035] As will be apparent to those skilled in the art, various
modifications, adaptations and variations of the foregoing specific
disclosure can be made without departing from the scope of the
invention claimed herein. The various features and elements of the
described invention may be combined in a manner different from the
combinations described or claimed herein, without departing from
the scope of the invention.
EXAMPLES
[0036] The following examples describe specific embodiments which
are exemplary of the present invention. They are not intended to
limit the claimed invention.
Example 1
[0037] Porous Media
[0038] In one embodiment, the porous media comprises relatively
uniform alumina spheres (90% alumina and 10% silica) having the
following physical and hydrodynamic properties:
[0039] (a) specific heat capacity at 20.degree. C., J/kgK 920
[0040] (b) thermal conductivity at 20.degree. C., W/mK 16.7
[0041] (c) Density, kg/m.sup.3 3, 600
[0042] (d) diameter, m 5.6 E-3 to 2.9 E-3
[0043] (e) Porosity, fraction 0.383
[0044] (f) Pore size, m 2.31 E-3 to 1.18 E-3
[0045] (g) Permeability (Carman-Kozeny equation) m.sup.2 2.544 E-8
to 6.625 E-9
* * * * *