|Publication number||US3013609 A|
|Publication date||Dec 19, 1961|
|Filing date||Jun 11, 1958|
|Priority date||Jun 11, 1958|
|Publication number||US 3013609 A, US 3013609A, US-A-3013609, US3013609 A, US3013609A|
|Inventors||Ten Brink Karl C|
|Original Assignee||Texaco Inc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (42), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
K. C. TEN BRINK METHOD FOR PRODUCING HYDROCARBONS IN AN IN Dec. 19, 1961 SITU COMBUSTION OPERATION Filed June 1l, 1958 3 013,609 METHGD FOR PRODCNG HYDRGCARBGNS 1N AN IN SITU CGMBUSTIQN PERATION Karl C. Ten Brink, Houston, Tex., assigner to Texaco Inc., a corporation of Delaware Filed June 11, 1953, Ser. No. 741,341 3 Claims. (Cl. 16o-69) This invention relates to the production of hydrocarbons from hydrocarbon-containing formations. vMore particularly, this invention relates to a method of carrying out an in situ combustion operation for the production and recovery of hydrocarbons from a hydrocarboncontaining formation, such as a petroleum producing formation, tar sands, oil shales and the like. In accordance with one specific embodiment this invention is directed to a well completion assembly particularly useful in the production of hydrocarbons from underground formations by a method involving in situ combustion.
Various techniques have been proposed for the recovery of hydrocarbons from underground formations and for the treatment of hydrocarbon-containing formations. For example, for the recovery of petroleum from petroleum producing formations secondary reco-very operations which involve water flooding or thermal recovery methods such as in situ combustion, employing at least one injection well and at least one production well, have been proposed. As indicated hereinabove, the practice of this invention is particularly directed to thermal recovery methods such as methods involving in situ combustion for the production of petroleum and the like from underground formations.
Explanatory of an in situ com-bustion operation and indicative as to how an in situ co-mbustion operation may be carried out, a high temperature zone is established in an underground hydrocarbon or petroleum-containing formation in the vicinity of a wellbore penetratinggthe same. Suitable means for establishing or creating a high temperature zone within the wellbore penetrating a hydrocarbon-containing formation may comprise an electric heating device or a gas fired bottom hole igniter or heater. A suitable device for initiating in situ combustion and for establishing a high temperature zoneA within a wellbore is described in U.S. 2,722,278. Upon introducing a combustion-supporting gas, such as air, into the thus-heated wellbore adjacent the petroleum-containing `formation a resulting high temperature combustion zone is generated therein by the reaction between the oxygen and the combustible petroleum hydrocarbons or residues within the formation, such as combustible residues resulting from the distillation and/or thermal cracking of the petroleum hydrocarbons originally in place or introduced thereinto. This high temperature combustion zone (temperature in the range 700-2000 F., more or less) will commence to move into the formation outwardly from the wellbore upon continued introduction of air into the wellbore. Leaving this high temperature zone is a relatively high temperature gas stream which, as it moves outwardly into the formation, loses heat to the formaftion. By this method the high temperature combustion zone or flame front is moved for a considerable distance, for example a distance in the range 3-25', more or less, outwardly from the wellbore into the formation without further direct application of heat to the zone of the formation adjacent the wellbore. Continued direct application of heat to this zone, however, may sometimes be desir. able. The distance which the high temperature combustion zone moves radially outwardly, and as a result the volume of the petroleum-containing formation swept by 3,013,609 Patented Dec. 19, 1 961 rate of heat generation (combustion of combustible residues) and the rate of heat loss to the surrounding formation.
It has been postulated that the following mechanisms are important in the movement of the high temperature combustion zone outwardly from a wellbore into the petroleum producing formation during an in situ combustion operation therein. Although the exact mechanism of an in situ combustion is not definitely and completely known, the following sequence of events are postulated and are presented herein for the purpose of enabling one skilled in the art to better understand this invention.
As the high temperature combustion zone approaches any given volume of the hydrocarbon or petroleum-containing formation the temperature of this volume of formation rises. This results, first, in a reduction in the viscosity of the formation fluids therein (oil, water) due to temperature increase. These fluids may then be moved more readily under the influence of the hot combustion gas stream continuously emanating from the high temperature combustion zone. As the temperature continues to rise, distillations of the formation fluids begin. The products of these distillations condense in cooler regions of the formation removed from the high temperature combustion zone in the direction of liow of the hot combustion gases therein. The distillations continue as the temperature rises within the given portion of the formation until the heavier components remaining from the hydrocarbons or petroleum originally in place within the formation or introduced thereinto prior to initiating in situ combustion therein begin to crack and yield hydro-A combustion-supporting gas increases due to depletion of combustible residues in the preceding regions of the formation, a point will be reached at which the coke or other `combustible residues will begin to react with the oxygen with the resulting release of heat to the formation and the combustion gas stream emanating therefrom. This heat is carried away by the on-moving combustion gas stream and also to some extent by thermal conduction to adjoining regions of the formation. When the coke or combustible residue has been burned away there remains a volume of liquid-freeformation.
Another method of carrying out an in situ-combustion operation involving operations as ldisclosed hereinabove, I'
i.e., initiation of a high temperature zone within a wellbore and then causing an in situ combustion zone to move outwardly therefrom into the formation toward a production well, is known. In this method after the high temperature combustion zone has moved a suflicient distance outwardly from the wellbore, such as a distance in the range 5-50, air or other combustion-supporting l gas is injected into another `well removed from the well wherein in situ combustion was initiated. When these operations are carried out the in situ combustion zone or flame front moves countercurrently with respect to the flow ofthe combustion-supporting gas (air) within thev formation 'undergoing treatment, i.e., the in situ combustion zoneinoves toward the other well into which the combustion-'supporting gas is injected while the combusf tion-supporting gas as well as thel resulting hotrcombus- .tion gases and displacedhydrocarbons, partiallynoxygenl ated hydrocarbons, etc., mojvefrorn this other well ytoward the wel1 wherein in situ, combustion was initiated.v `Theg mechanisms-and technique for carrying out an in situ f. I combustion operation in accordance with thismethod j are completely disclosedv in U.S. 2,793,696; The dis- As the temperature con-` closures of this patent are herein incorporated and made part of this disclosure.
In an in situ combustion operation many difficulties arise in the production well, i.e., the well wherein the formation fluids displaced in the in situ combustion operation are recovered and produced. These wells in an in situ combustion operation are subjected to rather high temperature, above about 800 F. Under the high ternperature conditions experienced in an in situ combustion operation these wells are subject to failure due to tubing, liner or casing collapse brought on by the high temperatures in the wells. Additionally well fires sometimes occur therein. These Well fires arise due to the intermingling within the well of the produced hydrocarbons or partially oxygenated hydrocarbons with an oxidizing or oxygen-containing gas such as air. Further, in some instances the high temperatures experienced in an in situ combustion operation sometimes cause collapse of the wellbore itself, if the wellbore is unsupported, duc to the well fires or explosions within the wellbore.
Accordingly, it is an object of this invention to provide an improved in situ combustion operation for the production of hydrocarbons or partially oxygenated hydrocarbons from hydrocarbon-containing formations such as petroleum formations, tar sands, oil shales and the like.
Another object of this invention is to provide a method for carrying out an in situ combustion operation wherein the production well, i.e., the well wherein the resulting displaced formation uids are produced, is protected against the high temperatures experienced in an in situ combustion operation.
Yet another object of this invention is to provide a method for the elimination of well fires in a production well involved -in an in situ combustion operation.
Yet another object of this invention is to provide a method for the protection of the well and/or equipment of a production well involved in an in situ combustion operation.
Still another object of this invention is to provide a method `for the creation of a substantially non-oxidizing environment in the wellbore of a production well involved in an in situ combustion operation.
How these and other objects of this invention are accomplished will become apparent in the light of the accompanying disclosure and drawing which schematically illustrates one embodiment of the practice of this nvention particularly directed to a method of operating a product-ion well involved in an in situ combustion operation. In at least one embodiment of the practice of this invention at least one of the foregoing objects will be achieved.
In an in situ combustion operation wherein a well bore penetrates a hydrocarbon-containing formation which is undergoing in situ combustion and wherein formation fluids are displaced during the in situ combustion operation and are produced via the well bore, improved operation is obtained by cooling the wellbore adjacent the formation undergoing in situ combustion. The resulting produced formation fluids, gaseous hydrocarbons, liquid hydrocarbons, partially oxygenated hydrocarbons and combustion gases are cooled as they enter the well bore. Within the well bore the thus-produced liquids are collected at a location or sump therein relatively remote from that portion of the wellbore adjacent the formation undergoing in situ combustion and are recovered therefrom at the surface. Desirably suitable pumping means are located within the wellbore wherein the thus-produced liquids are collected as means for moving these liquids to the surface.
In the practice of this invention, particularly with respect to one embodiment thereofas illustrated in the accornpanying drawing, a wellbore 11 is shown penetrating a hydrocarbon-containing formation 12. As illustrated in the drawing the wellbore 11 extends through the hydrocarbon-containing formation 12 into an underlying formation 14, which may be the lower portion of formation 12., wherein the wellbore is bottomed. The wellbore 11, particularly that portion penetrating hydrocarbon-containing formation 12, is shown lined with cement 15. Also, as illustrated the wellbore is provided with a casing 16 extending through the hydrocarboncontaining formation 12 into the underlying formation 14. The casing, cement and formation are perforated at 1S to provide for the entry of the formation fluids displaced during the in situ combustion operation from the hydrocarbon-containing formation 12 into the interior of casing 16.
Within casing 16 is positioned a heat exchanger or cooler 19, such as a two-pass heat exchanger, which is provided with a conduit 20 for the supply of liquid coolant such as Water or formation brine and the like. The heat exchanger or cooler 19 is positioned within wellbore 11 adjacent the hydrocarbon-containing formation which is undergoing in situ combustion and located therein so as to cool or maintain the wellbore temperature at a relatively low level during the in situ combustion operation. Extending through well bore 11, and preferably through heat exchanger 19, as shown, is production tubing 21. Production tubing 21 is shown concentrically positioned within wellbore 11 and with reespect to heat exchanger 19. As illustrated production tubing 21 extends below heat exchanger 19 into the lower end of wellbore 11. This lower end of wellbore 11 serves as a sump for the collection of the formation liquids, such as liquid hydrocarbons, partially oxygenated hydrocarbons, water, ete., displaced into wellbore 11 during the in situ combustion operation.
Associated with production tubing 21 is a well pump 22 adapted to withdraw formation liquids which collect in the lower end of wellbore 11 and to pump the same via production tubing 21 for recovery at the surface through conduit 24. As illustrated, pump 22 is actuated by means of sucker rod 25 operatively connected at the upper end thereof to a suitable lifting or pumping means, not illustrated. As illustrated in the drawing, heat exchanger 19 is provided with spray nozzles 26 for spraying into the wellbore 11 the liquid coolant which is supplied via conduit 20 into heat exchanger 19 which is employed to cool the wellbore and the resulting produc-ed formation fluids by indirect heat exchange.
In the practice of this invention as illustrated in the accompanying drawing formation fiuids, including liquid hydrocarbons, partially oxygenated hydrocarbons as well as gaseous hydrocarbons and gaseous products of comhustion such as carbon dioxide, carbon monoxide, steam in varying amounts, are produced or displaced from the hydrocarbon-containing formation 12 during the in situ combustion operation as these formation fluids enter wellbore 11 via perforations 18. As the relatively hot formation `fluids enter wellbore 11 they are cooled by indirect heat exchange with the liquid coolant flowing within heat exchanger 19 positioned within wellbore 11 immediately adjacent the formation 12 undergoing in situ combustion. Due to the close proximity of the heat exchanger 19 to the wellbore 11 and casing 16 and production tubing 21 these elements are effectively protected against'unduly high temperatures during the in situv combustion operation, particularly as the high temperature combustion zone approaches wellbore 11. Accordingly, equipment failure such as casing collapse and tubing collapse and wellbore disruption is inhibited or avoided. As the formation fluids enter the wellbore 11 via perforations 18 they are cooled by cooler 19. Certain of the components will condense and collect in the lower end of wellbore 11 together with the produced formation liquids. The produced gases and vaporous formation fiuids lwithin wellbore 11 are withdrawn from wellbore 11 at the surface through suitable means such as conduit 28. The formation liquids which accumulate in the bottom of wellbore 11 are pumped therefrom by means of well pump 22 which is operated through sucker rod 25 and recovered at thc surface via conduit 24.
`In accordance with a specific feature of this invention in addition to the cooling of the wcllbore and associated well equipment adjacent the formation undergoing in situ combustion by indirect heat exchange with cooler 19, the wellbore and associated equipment therein are effectively cooled by direct contact with the liquid coolant introduced into heat exchanger 19 via line 2t). In accordance with this embodiment instead of returning the coolant, such as water, from cooler 19 back to the surface (by means not shown) the liquid coolant is forced through spray nozzles 26 associated with cooler 19 with the result that a liquid spray of coolant is forced into the wellbore 11 in the vicinity of the formation undergoing in situ combustion. This spray of liquid coolant by direct contact serves very effectively to cool the Wellbore and associated equipment therein. Additionally vaporization of the coolant provides a shielding, non-oxidizing atmosphere within the wellbore with the result that wellbore fires and explosions are avoided.
Any suitable coolant, liquid or non-combustible gas, may be effectively employed in the practice of this invention. Suitable coolants, in addition to water, include aqueous brines such as formation brines. Aqueous brines and the like are less desirable, however, since brines tend to deposit salt Within the Wellbore. Iin some instances the resulting produced formation uids such as liquid hydrocarbons and the like might be employed as the liquid coolant. ln those instances where formation vfluids are employed as coolants it Iwould be more desirable to return the formation fluids to the surface rather than spraying them within the wellbore.
As illustrated in the drawing, the pump Z2 is shown positioned in the lower end of wellbore 11, below formation 12. By thus positioning the pump 22 at a location in the Wellbore relatively remote from that portion of formation 12 undergoing in situ combustion the well pump is less likely to be exposed to unduly high temperatures during the in situ combustion operation. lf desired, however, well pump 22 may be positioned within or in close heat exchange relationship with cooler .19 so that cooler 19 effectively protects the well pump from high temperatures.
Although in the practice of this invention, as illustrated in the drawing, the wellbore 11 is shown lined with cement and provided with a casing, and perforated, an uncased or open wellbore might also be ernployed. 'In such a situation the produced formation uids enter directly the wellbore from the formation.
As will be apparent to those skilled in the art many modifications and improvements which do not depart from the spirit or scope of this invention will present themselves -to those skilled in the art in the light of this disclosure.
1. A method of producing hydrocarbons from a subsurface hydrocarbon-containing formation including the steps: (l) initiating in situ combustion Within said formation to heat the formation uids therein, (2) displacing the resulting heated formation fluids, including liquid hydrocarbons, during the in situ combustion operation from the zone of in situ combustion toward the well bore of a production well penetrating said formation, (3) cooling by indirect heat exchange with a relatively cool liquid the resulting relatively hot `formation fluids as they enter said well bore at a location adjacent said formation undergoing in situ combustion and by direct heat exchange by spraying coolant into contact with said well bore adjacent said formation to the extent nee'- essary to avoid equipment failure and Wellbore disrup` tion due to high temperature conditions experienced as a result of said in situ combustion, (4) collecting the resulting cooled formation fluids within said wellbore at a location therein remote from said formation, and (5) transferring the resulting cooled formation fluids from the last mentioned location via said wellbore to the surface.
2. A method of producing hydrocarbons from a subsurface hydrocarbon-containing formation which comprises subjecting said formation to an in situ combustion operation to displace said hydrocarbons from said formation toward a production well penetrating said formation, cooling the thus-displaced hydrocarbons leaving said formation as the displaced hydrocarbons enter the well bore of said production well adjacent said formation to coo-l the thus-displaced hydrocarbons therein to the extent necessary to prevent casing and tubing collapse and Wellbore disruption due to fire, explosion and other high temperature conditions as a result of said in situ combustion, collecting the thus-displaced hydrocarbons within said wellbore at a location therein relatively remote from said formation, and producing the resulting cooled hydrocarbons from said location, said cooling of the displaced hydrocarbons being accomplished by passing an aqueous liquid in indirect heat exchange with said displaced hydrocarbons and by spraying said aqueous liquid within said well bore adjacent said formation undergoing in situ combustion for direct heat exchange.
3. A method of producing formation hydrocarbons from a subsurface hydrocarbon-containing formation which comprises subjecting said for-mation to an in situ combustion operation to displace formation hydrocarbons within said formation toward a production well penetrating said formation, the Wellbore of-said well adjacent said producing formation being subjected to a relatively high temperature due to the aforesaid in situ combustion operation, cooling said wellbore adjacent said formation to maintain said wellbore relatively cool with respect to the in situ combustion operation being carried out Within said formation by indirect heat exchange with a liquid coolant flowing through said well and by direct heat exchange by spraying liquid coolant into contact with said well lbore adjacent said formation, and to the extent necessary to inhibit wellbore equipment failure and disruption due to high temperature conditions experienced in said wellbore as a result of said in situ combustion operation within said formation, collecting the displaced cooled hydrocarbons as they enter the wellbore from the formation undergoing in situ combustion, the resulting cooled hydrocarbons beingcollectedwithin said Wellbore at a location therein relatively remote from said formation, and producing the thus-collected hydrocarbons from said location of said wellborev References Cited in the le of this patent UNITED STATES PATENTS 1,263,618 Squires Apr. 23, 1918 2,349,536 Bancroft May 23, 1944 2,444,756 Steffen July 6, 1948 2,584,606 Merriam et al. Feb. 5, 1952 2,734,579 IElkins Feb. 14, 1956 (Page B-4l relied
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US1263618 *||Jan 26, 1918||Apr 23, 1918||Walter Squires||Recovery of oil from oil-sands.|
|US2349536 *||Nov 7, 1941||May 23, 1944||Bancroft Charles C||Apparatus for preventing clogging of oil wells|
|US2444756 *||Jan 4, 1946||Jul 6, 1948||Nat Secondary Recovery Corp||Apparatus for progressively heating oil sands surrounding oil wells|
|US2584606 *||Jul 2, 1948||Feb 5, 1952||Frederick Squires||Thermal drive method for recovery of oil|
|US2734579 *||Jun 28, 1952||Feb 14, 1956||Production from bituminous sands|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US3160208 *||Oct 6, 1961||Dec 8, 1964||Shell Oil Co||Production well assembly for in situ combustion|
|US3171482 *||Jul 31, 1961||Mar 2, 1965||California Research Corp||Method of increasing the production of petroleum from subterranean formations|
|US3180411 *||May 18, 1962||Apr 27, 1965||Phillips Petroleum Co||Protection of well casing for in situ combustion|
|US3202219 *||Feb 9, 1962||Aug 24, 1965||Phillips Petroleum Co||Apparatus for protection of in situ combustion wells|
|US3208516 *||May 13, 1963||Sep 28, 1965||Shell Oil Co||Control method in underground combustion drives|
|US3221813 *||Aug 12, 1963||Dec 7, 1965||Shell Oil Co||Recovery of viscous petroleum materials|
|US3227215 *||Nov 20, 1963||Jan 4, 1966||Phillips Petroleum Co||Apparatus for preventing well fires|
|US3298434 *||May 27, 1964||Jan 17, 1967||Graham Thomas T||Gasification of coal|
|US3349847 *||Jul 28, 1964||Oct 31, 1967||Gulf Research Development Co||Process for recovering oil by in situ combustion|
|US3357490 *||Sep 30, 1965||Dec 12, 1967||Mobil Oil Corp||Apparatus for automatically introducing coolant into and shutting down wells|
|US3406755 *||May 31, 1967||Oct 22, 1968||Mobil Oil Corp||Forward in situ combustion method for reocvering hydrocarbons with production well cooling|
|US3580336 *||Jan 6, 1969||May 25, 1971||Phillips Petroleum Co||Production of oil from a pumping well and a flowing well|
|US3592264 *||May 29, 1969||Jul 13, 1971||Mobil Oil Corp||Method and system for imposing pressure on a wellbore packer|
|US3662832 *||Apr 30, 1970||May 16, 1972||Atlantic Richfield Co||Insulating a wellbore in permafrost|
|US3915498 *||Sep 11, 1974||Oct 28, 1975||Occidental Petroleum Corp||Oil shale retort flue gas cooling and cleaning|
|US3952802 *||Dec 11, 1974||Apr 27, 1976||In Situ Technology, Inc.||Method and apparatus for in situ gasification of coal and the commercial products derived therefrom|
|US4093025 *||Nov 23, 1976||Jun 6, 1978||In Situ Technology, Inc.||Methods of fluidized production of coal in situ|
|US4215551 *||Oct 12, 1978||Aug 5, 1980||Johnes John W||Environmentally assisted heating and cooling system|
|US7631691||Dec 15, 2009||Exxonmobil Upstream Research Company||Methods of treating a subterranean formation to convert organic matter into producible hydrocarbons|
|US7669657||Mar 2, 2010||Exxonmobil Upstream Research Company||Enhanced shale oil production by in situ heating using hydraulically fractured producing wells|
|US8082995||Dec 27, 2011||Exxonmobil Upstream Research Company||Optimization of untreated oil shale geometry to control subsidence|
|US8087460||Jan 3, 2012||Exxonmobil Upstream Research Company||Granular electrical connections for in situ formation heating|
|US8104537||Jan 31, 2012||Exxonmobil Upstream Research Company||Method of developing subsurface freeze zone|
|US8122955||Apr 18, 2008||Feb 28, 2012||Exxonmobil Upstream Research Company||Downhole burners for in situ conversion of organic-rich rock formations|
|US8146664||May 21, 2008||Apr 3, 2012||Exxonmobil Upstream Research Company||Utilization of low BTU gas generated during in situ heating of organic-rich rock|
|US8151877||Apr 18, 2008||Apr 10, 2012||Exxonmobil Upstream Research Company||Downhole burner wells for in situ conversion of organic-rich rock formations|
|US8151884||Oct 10, 2007||Apr 10, 2012||Exxonmobil Upstream Research Company||Combined development of oil shale by in situ heating with a deeper hydrocarbon resource|
|US8230929||Jul 31, 2012||Exxonmobil Upstream Research Company||Methods of producing hydrocarbons for substantially constant composition gas generation|
|US8540020||Apr 21, 2010||Sep 24, 2013||Exxonmobil Upstream Research Company||Converting organic matter from a subterranean formation into producible hydrocarbons by controlling production operations based on availability of one or more production resources|
|US8596355||Dec 10, 2010||Dec 3, 2013||Exxonmobil Upstream Research Company||Optimized well spacing for in situ shale oil development|
|US8616279||Jan 7, 2010||Dec 31, 2013||Exxonmobil Upstream Research Company||Water treatment following shale oil production by in situ heating|
|US8616280||Jun 17, 2011||Dec 31, 2013||Exxonmobil Upstream Research Company||Wellbore mechanical integrity for in situ pyrolysis|
|US8622127||Jun 17, 2011||Jan 7, 2014||Exxonmobil Upstream Research Company||Olefin reduction for in situ pyrolysis oil generation|
|US8622133||Mar 7, 2008||Jan 7, 2014||Exxonmobil Upstream Research Company||Resistive heater for in situ formation heating|
|US8641150||Dec 11, 2009||Feb 4, 2014||Exxonmobil Upstream Research Company||In situ co-development of oil shale with mineral recovery|
|US8770284||Apr 19, 2013||Jul 8, 2014||Exxonmobil Upstream Research Company||Systems and methods of detecting an intersection between a wellbore and a subterranean structure that includes a marker material|
|US8863839||Nov 15, 2010||Oct 21, 2014||Exxonmobil Upstream Research Company||Enhanced convection for in situ pyrolysis of organic-rich rock formations|
|US8875789||Aug 8, 2011||Nov 4, 2014||Exxonmobil Upstream Research Company||Process for producing hydrocarbon fluids combining in situ heating, a power plant and a gas plant|
|US9080441||Oct 26, 2012||Jul 14, 2015||Exxonmobil Upstream Research Company||Multiple electrical connections to optimize heating for in situ pyrolysis|
|US9347302||Nov 12, 2013||May 24, 2016||Exxonmobil Upstream Research Company||Resistive heater for in situ formation heating|
|US20100078169 *||Apr 1, 2010||Symington William A||Methods of Treating Suberranean Formation To Convert Organic Matter Into Producible Hydrocarbons|
|USRE29553 *||Jul 18, 1977||Feb 28, 1978||Occidental Oil Shale, Inc.||Oil shale retort flue gas cooling and cleaning|
|U.S. Classification||166/256, 166/57|
|Cooperative Classification||E21B36/006, E21B36/00, E21B36/001|
|European Classification||E21B36/00, E21B36/00F, E21B36/00B|