Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B36/00—Heating, cooling or insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
  • E21B36/02—Heating, cooling or insulating arrangements for boreholes or wells, e.g. for use in permafrost zones using burners

Definitions

• This invention relates to a flameless combustion apparatus and method.
• U.S. Patent Nos. 4,640,352 and 4,886,118 disclose conductive heating of subterranean formations of low permeability that contain oil to recover oil therefrom.
• Low permeability formations include diatomites, lipid coals, and oil shales. Formations of low permeability are not amiable to secondary oil recovery methods such as steam, carbon dioxide, or fire flooding. Flooding materials tend to penetrate formations that have low permeabilities preferentially through fractures. The injected materials bypass most of the formation hydro ⁇ carbons. In contrast, conductive heating does not require fluid transport into the formation. Oil within the formation is therefore not bypassed as in a flooding process.
• U.S. Patent No. 5,255,742 discloses a flameless combustor useful for heating subterranean formations that utilizes preheated fuel gas and/or combustion air wherein the fuel gas is combined with the combustion air in increments that are sufficiently small that flames are avoided. Creation of NO x is almost eliminated, and cost of the heaters can be significantly reduced because of less expensive materials of construction. Preheating the fuel gas in accordance with the method disclosed in this prior art reference may result in coke formation unless CO2, H2, or steam is added to the fuel gas. Further, start-up of the known heater is a time consuming process because it must operate at temperatures above the uncatalized autoignition temperature of the fuel gas mixture.
• Catalytic combustors are also known.
• U.S. Patent No. 3,928,961 discloses a catalytically-sup- ported thermal combustion apparatus wherein formation of N0 X is eliminated by combustion at temperatures above auto-ignition temperatures of the fuel, but less than those temperatures at which result in substantial formation of oxides of nitrogen.
• a flameless combustor for combustion of a fuel and oxidant mixture
• the combustor comprising: a combustion chamber in communication with an inlet and with a combustion product outlet; a mixed fuel and oxidant supply in communication with the inlet; and a catalyst surface within the combustion chamber wherein the catalyst surface is effective to cause oxidization of an amount of fuel wherein the oxidization of the amount of fuel does not result in a temperature above an uncatalyzed autoignition temperature of the fuel and oxidant mixture .
• the flameless combustor of the present invention results in minimal production of nitrous oxides because temperatures that would result from adiabatic combustion of the fuel-oxidant mixture are avoided. Other measures to remove or prevent the formation of nitrous oxides are therefore not required. Relatively even heat distribu- tion over a large area and long lengths are possible, and relatively inexpensive materials of construction for the combustor of the present invention can be used because of lower combustion temperatures.
• Acceptable catalyst materials include noble metals, semi-precious metals, and transition metal oxides.
• oxidation catalysts are useful in the present invention. Mixtures of such metals or metal oxides could also be usef l .
• the flameless combustor of the present invention is particularly useful as a heat injector for heating subterranean formations for recovery of hydrocarbons.
• the catalytic surfaces also improve operability and start-up operations of such heat injectors.
• the present invention eliminates a need to transport fuels and oxidants in separate conduits to the combustion zone in such heat injectors. This results in significant cost savings .
• a method of heating a subterranean formation by flameless combustion comprises: installing a combustion tubular which defines a downhole combustion chamber in a wellbore within the formation to be heated; feeding fuel and oxidant to the chamber via an inlet; inducing the fuel and oxidant mixture to flow along a catalyst surface within the combustion chamber wherein the catalyst surface is effective to cause oxidization of an amount of fuel at such a rate that the average temperature in the combustion chamber remains below the uncatalyzed autoignition temperature of the fuel and oxidant mixture; and allowing combustion products to flow to the surface via a combustion product outlet conduit within the wellbore.
• the combustion chamber is defined by a lower portion of a well casing and a plug near the bottom of the well casing and the catalyst surface is provided by a catalyst coating on the inner and/or outer surface of a tubular which is co-axially suspended within the well casing such that an axial spacing is maintained between a lower end of the suspended tubular and the plug.
• the suspended tubular is used as a mixed fuel and air inlet conduit and the annular space between the suspended tubular and the well casing is used as a combustion product outlet conduit or vice versa.
• FIG. 1 shows a combustor according to the present invention
• FIG. 2 is a plot of methane consumption vs. temperature in a test apparatus demonstrating the present invention.
• flameless combustion is accomplished by preheating combustion air and fuel gas sufficiently that when the two streams are combined the temperature of the mixture exceeds the autoignition temperature of the mixture, but to a temperature less than that which would result in the oxidation upon mixing being limited by the rate of mixing. Without a catalyst surface present, preheating of the streams to a temperature between about 815 °C and about 1260 °C and then mixing the fuel gas into the combustion air in relatively small increments will result in flameless combustion.
• a catalyzed autoignition temperature In turbulent flow, fluid in a boundary layer that contacts the catalytic surface will be oxidized almost quantitatively, but almost no oxidation will occur outside of the boundary layer if the bulk temperatures remain below the non-catalyzed autoignition temperatures of the mixture.
• reaction in the temperature range between the catalyzed autoignition temperature and the noncatalyzed autoignition temperature is mass-transfer limited, at a rate that is relatively independent of temperature. This is suggested in references such as U.S. Patent No. 4,065,917.
• This mass transfer limited reaction mechanism is utilized in the present invention to control distribution of heat generation within the combustion chamber of the flameless combustor. Heat generation and heat removal can be balanced so that the average stream temperature of the mixed oxidant, fuel, and combustion products remains between the catalyzed autoignition temperature and the noncatalyzed autoignition temper ⁇ ature.
• the heater of the present invention can be controlled by such variables as fuel-oxidant ratio, fuel-oxidant flowrate.
• the heat load may be subject to controls.
• An important feature of the flameless combustor of the present invention is that heat is removed along the axis of the combustion chamber so that a temperature is maintained that is significantly below the adiabatic combustion temperature. This almost eliminates formation of NO x s, and also significantly reduces metallurgical requirements resulting in a relatively inexpensive combustor.
• FIG. 1 a combustor within a heat injection well capable of carrying out the present invention is shown.
• a formation to be heated, 1 is below an overburden, 2.
• a wellbore, 3 extends through the overburden and to a position that is preferably near the bottom of the formation to be heated.
• a vertical well is shown, but the wellbore could be deviated or horizontal.
• Horizontal heat injector wells may be provided in formations that fracture horizontally to recover hydrocarbons by a parallel drive process. Shallow oil shale formations are examples of formations where horizontal heaters may be useful. Horizontal heaters may also be effectively used when thin layers are to be heated to limit heat loss to overburden and base rock.
• the wellbore is cased with a casing, 4.
• the lower portion of the wellbore may be cemented with a cement, 7, having characteristics suitable for withstanding elevated temperatures and transferring heat.
• a cement which is a good thermal insulator, 8, is preferred for the upper portion of the wellbore to prevent heat loss from the system.
• a combustion mixture conduit, 10 extends from the wellhead (not shown) to the lower portion of the wellbore.
• High temperature cements suitable for cementing casing and conduits within the high temperature portions of the wellbore are available. Examples are disclosed in U.S. Patent Nos. 3,507,332 and 3,180,748. Alumina contents above about 50 percent by weight based on cements slurry solids are preferred.
• a cement plug 23 is shown at the bottom of the casing, the cement plug being forced down the casing during the cementing operation to force cement out the bottom of the casing.
• Catalyst surfaces 20 are provided within the combustion chamber 14 to provide a limited region wherein the oxidation reaction temperature is lowered. Distribution of these catalyst surfaces 20 as a coating which covers at least part of the inner and/or outer surface of a lower portion of the conduit 10 provide for distribution of heat release within the combustion chamber.
• the catalyst surfaces are sized to accomplish a nearly even temperature distribution along the casing. A nearly even temperature profile within the casing results in more uniform heat distribution within the formation to be heated. A nearly uniform heat distribution within the formation will result in more efficient utilization of heat in a conductive heating hydrocarbon recovery process.
• heat be removed from the combustion chamber along the length of the combustion chamber.
• heat is transferred to the formation around the wellbore.
• the heater of the present invention could also be used in other applications, such as steam generation and chemical industry process heaters and reactors .
• the mixed fuel and air react within the wellbore volume adjacent to the catalyst surfaces 14 forming combustion products.
• the combustion products travel up the wellbore and out an exhaust vent (not shown) at the wellhead through the combustion product conduit 10. From the exhaust vent, the combustion products may be routed to atmosphere through an exhaust stack (not shown) .
• the combustion gases may be treated to remove pollutants, although nitrous oxides would not be present and would not therefore need to be removed. Additional energy recovery from the combustion products by an expander turbine or heat exchanger may also be desirable.
• Preheating of the fuel gases to obtain flameless combustion without a catalyst would result in significant generation of carbon unless a carbon formation suppressant is included in the fuel gas stream.
• the need to provide such a carbon formation suppressant is therefore avoided by operating the heater at a temperature that is less than the carbon formation temperature.
• Cold start-up of a well heater of the present invention may utilize combustion with a flame. Initial ignition may be accomplished by injecting pyrophoric material, an electrical igniter, a spark igniter, temporally lowering an igniter into the wellbore, or an electrical resistance heater.
• the burner is preferably rapidly brought to a temperature at which a flameless combustion is sustained to minimize the time period at which a flame exists within the wellbore. The rate of heating up the burner will typically be limited by the thermal gradients the burner can tolerate.
• the combustion mixture conduit can be utilized as a resistance heater to bring the combustor up to an operating temperature.
• an electrical lead 15 can be connected with a clamp 16 or other connection to the combustion mixture conduit 10 near the wellhead below an electrically insulating coupling to supply electrical energy.
• Electrical ground can be provided near the bottom of the borehole with one or more electrically conducting centralizers 17 around the combustion mixture conduit 10.
• Centralizers on the combustion mixture conduit above the electrically grounding centralizers are electrically insulating centralizers. Sufficient heat is preferably applied to result in the combustion mixture being, at the location of the initial catalyst surface, at a temperature that is above the catalyzed autoignition temperature but below the noncatalyzed auto ignition temperature.
• Thickness of the combustion mixture conduit can be varied to result is release of heat at preselected segments of the length of the fuel conduit. For example, in a well heat injector application, it may be desirable to electrically heat the lowermost portion of the wellbore in order to ignite the mixed gas stream at the highest concentration of fuel, and to burn the fuel before exhaust gasses are passed back up through the wellbore.
• Thin section 21 is shown in the combustion mixture conduit to provide a surface of elevated temperature for start-up of the combustor. Oxidation reaction temperature of the fuel gas-oxidant mixture is lowered by provision of a noble metal surface, or another effective catalyst surface.
• Catalytic surface is preferably provided on the either the inside, outside, or both inside and outside surface of the combustion products conduit 10.
• a surface, or a tubular or other noble metal containing surface could be separately placed within the combustion chamber.
• Other noble metal coated surfaces could be provided, for example, in the combustion product annulus outside of the combustion gas conduit. This additional catalyst surface could ensure that complete combustion occurred within the wellbore, where generation of heat is desired.
• Start-up of the flameless combustor of the present invention can be further enhanced by provision of supplemental oxidants during the start-up phase, or by use of a fuel that has a lower autoignition temperature such as hydrogen.
• Preferred supplemental oxidants include supplemental oxygen and nitrous oxide.
• Hydrogen could be provided along with a natural gas stream, and could be provided as shift gas, with carbon monoxide present and carbon dioxide present .
• Start-up oxidants and/or fuels are preferably only used until the combustor has been heated to a temperature sufficient to enable operation with methane (natural gas) as fuel and air as the oxidant (i.e., the combustor has heated to a temperature above the catalyzed autoignition temperature of methane in air) .
• US patent 5,255,742 disclosed using an electrical resistance nicro e heater to generate heat for start-up of the flameless combustor. Such an electrical heater may be used in the practice of the present invention.
• Noble metals such as palladium or platinum, or semi-precious metal, base metal or transition metal can be coated, preferably by electroplating, onto a surface within the combustion chamber to enhance oxidation of the fuel at lower temperatures.
• the metal could then be oxidized as necessary to provide a catalytically effective surface.
• Such catalytic surface has been found to be extremely effective in promoting oxidation of methane in air at temperatures as low as 260 °C. This reaction rapidly occurs on the catalytic surface and in the adjacent boundary layer.
• An advantage of having a significant catalytic surface within the combustion chamber is that the temperature range within which the flameless combustor can operate can be significantly increased.
• a thermal reactor was used to establish temperatures at which oxidation reactions would occur with various combinations of fuels, oxidants and catalyst surfaces.
• the reactor was a 2.54 cm stainless steel pipe wrapped with an electrical resistance heating coil, and covered with insulation.
• a thermocouple for temperature control was placed underneath the insulation adjacent to the outer surface of the pipe. Thermocouples were also provided inside the pipe at the inlet, at the middle, and at the outlet. Test ribbons of noble metals or stainless steel strips with noble metal coatings were hung in the pipe to test catalytic activity. Air preheated to a - 13 - temperature somewhat below the desired temperature of the test was injected into the electrically heated test section of the pipe.
• a 3.048 m long test combustor was used to test the results of the 2.54 cm reactor in a distributed combustor application.
• a 2.54 cm outer diameter fuel gas line was provided within a 5.08 cm internal diameter combustion line.
• the fuel injection line provided a conduit for fuel to a fuel injection port located near an inlet end of the combustion line.
• the 5.08 cm internal diameter combustion line was placed within an insulated pipe, and thermocouples were placed along the fuel supply line.
• Two different combustion lines were utilized.
• One combustion line was fabricated from a strip of "HAYNES 120" alloy. The strip was electro brush plated on one side with palladium to an average thickness of 0.000254 cm.
• the strip was then break formed, swedged and welded into a 3.048 m long pipe with the palladium coating on the inside surface.
• the other combustion line was a standard 7.62 cm pipe of "HAYNES 120" alloy.
• a "MAXON” burner was used to supply combustion gases to the 3.048 m long combustion pipe, and varying amounts of air and/or other additives are mixed with the exhaust from the "MAXON” burner in a mixing section between the burner and the combustion line.
• three electric heaters, each with its own controller, were placed outside and along the length of the combustion line.

Landscapes

• Geology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mining & Mineral Resources (AREA)
• Geochemistry & Mineralogy (AREA)
• Fluid Mechanics (AREA)
• Environmental & Geological Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Gas Burners (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Fluidized-Bed Combustion And Resonant Combustion (AREA)
• Cylinder Crankcases Of Internal Combustion Engines (AREA)
• Wick-Type Burners And Burners With Porous Materials (AREA)
• Gasification And Melting Of Waste (AREA)
• Incineration Of Waste (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=21737072

Family Applications (1)

Country Status (19)

Families Citing this family (6)

Family Cites Families (6)

• 1996
  • 1996-12-17 AT AT96944608T patent/ATE183810T1/de not_active IP Right Cessation
  • 1996-12-17 WO PCT/EP1996/005754 patent/WO1997024510A1/en not_active Ceased
  • 1996-12-17 CN CN96199385A patent/CN1079884C/zh not_active Expired - Lifetime
  • 1996-12-17 EA EA199800601A patent/EA000250B1/ru not_active IP Right Cessation
  • 1996-12-17 AU AU13034/97A patent/AU713893B2/en not_active Ceased
  • 1996-12-17 IL IL12480596A patent/IL124805A/xx not_active IP Right Cessation
  • 1996-12-17 CA CA002240646A patent/CA2240646C/en not_active Expired - Lifetime
  • 1996-12-17 KR KR10-1998-0704982A patent/KR100440993B1/ko not_active Expired - Lifetime
  • 1996-12-17 DK DK96944608T patent/DK0870101T3/da active
  • 1996-12-17 DE DE69603979T patent/DE69603979T2/de not_active Expired - Lifetime
  • 1996-12-17 JP JP52401197A patent/JP3825807B2/ja not_active Expired - Lifetime
  • 1996-12-17 ES ES96944608T patent/ES2138842T3/es not_active Expired - Lifetime
  • 1996-12-17 EP EP96944608A patent/EP0870101B1/de not_active Expired - Lifetime
  • 1996-12-17 TR TR1998/01221T patent/TR199801221T2/xx unknown
  • 1996-12-17 BR BR9612695A patent/BR9612695A/pt not_active IP Right Cessation
  • 1996-12-25 MA MA24442A patent/MA24041A1/fr unknown
  • 1996-12-26 EG EG119196A patent/EG20999A/xx active
  • 1996-12-26 JO JO19961947A patent/JO1947B1/en active
• 1999
  • 1999-10-27 GR GR990402749T patent/GR3031660T3/el unknown

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events