Patent Grant
7393423
The present invention relates to the use of aluminum in general, and in particular to the chemical reaction between molten aluminum and an oxygen carrier such as water to do useful work in engineering.
Aluminum (“Al”), the most abundant metallic element in the earth's crust, is a light weight, silver metal. Its atomic weight is 26.9815, and its specific gravity is 2.7. The element melts at 660° C. and boils at 2467° C. In today's explosives and ordnance industries, aluminum is used in its powder form in explosives and propellants due to the high heat value it generates when it reacts with oxygen. The heat released by oxidizing 1 gram of aluminum into aluminum oxide is 30.95 KJ, compared to the detonation heat of some most often used high explosives, for example, the tested detonation heat of RDX (Hexogen, Cyclotrimethylenetrinitramine) is 6.32 KJ/gram, and that of HMX (Octogen, Cyclotetramethylenetetranitramine) is 6.19 KJ/gram. Aluminum-oxygen reactions are widely used in metallurgy, fireworks, metal welding and in various other industries. When aluminum powder is mixed with a main explosive such as RDX, TNT (Trinitrotoluene), HMX or ANFO (Ammonium Nitrate Fuel Oil, an explosive used in rock blasting), it reacts with the detonation products from the main explosives such as H2O and CO2, giving off extra heat to do useful work. The addition of aluminum powder in propellants increases the heat generated by combustion of a propellant and helps to stabilize the combustion process.
The present invention uses aluminum's reactivity in its molten form with some commonly seen oxygen-carrying chemicals like water or metal oxides. When Al is heated to above its melting point (660° C.), it reacts with water and gives off a large amount of energy. In such a reaction molten aluminum is fuel, and water functions as an oxidizer. Such a reaction proves to be a hazard in the aluminum casting industry. Known as steam explosion, it is a leading cause of fatalities and serious injuries among workers and of property damage in the metal-casting industry worldwide. It has been reported that from 1980 through 1995, the aluminum industry experienced several hundred explosions during casting operations. Three devastating explosions occurred in 1986 alone. Technologies have been developed to suppress such reactions from happening in the workplace and will not be discussed here. The present invention is concerned with the exploitation of such a reaction to do useful work in engineering. The intentional use of aluminum-water reaction for engineering purposes is rarely seen in today's industries. However, there are some patents that involve the use of such a reaction. For example, U.S. Pat. Nos. 4,280,409 and 4,372,213 to Rozner et al. disclose a molten metal-liquid explosive device and method. The patents teach the use of a pyrotechnic mixture such as a metal-oxidizer mixture that upon ignition heats a solid metal liner that in turn reacts with water to create an explosion event.
There are some patents concerning the use of the aluminum-water reaction to launch projectiles in the ordnance industry. U.S. Pat. No. 5,052,272 to Lee discloses the use of aluminum powder/water reaction to generate hydrogen gas and use it to propel projectiles. U.S. Pat. Nos. 5,712,442 and 5,789,696 to Lee and Ford describe the use of an aluminum (or aluminum-lithium, aluminum-magnesium) wire placed in water and be energized by electrical energy, reacting with water to generate hydrogen gas and to launch a projectile.
Recently, researchers at Oak Ridge National Laboratory in the United States found that the aluminum-water mixture can be used as a propellant to replace commonly used gunpowder. According to Dr. Taleyarkhan, the ORNL program manager, when aluminum mixes with water at high temperatures, the aluminum combines with the oxygen atoms in the water, releasing hydrogen and a great deal of energy, potentially four times greater than TNT. The aluminum-water mixture has been used as a new propellant for a specially made gun by the ORNL. The speed of the bullet launched by this gun is adjustable by controlling the strength of the reaction that launches the bullet, turning from deadly force into minor injury and saving lives. The new weapon fueled by aluminum-water mixture is said to be very suitable for law enforcement and defense, as disclosed in U.S. Pat. No. 6,142,056 to Taleyarkhan.
U.S. Pat. No. 5,859,383 to Davison et al. discloses a method to construct an explosive device such as a shaped charge for oil well casing perforation. The device uses energetic, electrically activated reactive blends such as an aluminum-water blend in place of high explosives, and the said reactive blends are activated by inputting electric energy through electric leads. According to the inventors of that patent, the electrically activated reactive composites such as an aluminum-water blend are potentially safe, energetic, environmentally benign alternatives to conventional explosives. Practical devices will contain filaments, foils, or sintered particles with dimensions of approximately 10 microns. They will be activated by electrical pulses produced by capacitors or by generators driven rapidly rotating devices.
In the oil and gas industry, an explosive device called a shaped charge or oil well perforator is used to establish a communication channel between the oil well and a hydrocarbon bearing formation. Typically, the device comprises three parts, namely a machined steel case, a generally cone-shaped liner and a certain amount of explosives sandwiched between the case and the liner. The liner turns into a high velocity metal jet upon detonation of the explosives, penetrating through the steel casing of the oil well, the concrete lining and into the formation. The perforation created in such a manner bears a layer of material hardened by the perforating process. Often called a “crushed zone”, this layer hinders the flow of hydrocarbons into the oil well. Its permeability is much lower than that of the formation in its virgin state. To improve the oil flow, the crushed zone needs to be broken down using different stimulation techniques, including acidizing, hydraulic fracturing and fracturing using explosives or propellants.
Well stimulation using explosives has a long history. According to Watson, S. C. et al., as early as 1864, E. L. Roberts applied for a patent for increasing oil well productiveness with gun-powder explosions (U.S. Pat. No. 47,485, 1865, details unavailable). The patent also includes the use of NG (nitro-glycerine) because its velocity of detonation was 5˜10 times faster, and its shattering effect was much greater, allowing the creation of more fissures through which the oil flowed into the well. Another purpose of explosives stimulation is to remove the paraffin that would clog the perforations after the well is put into production for some time. The heat generated by the detonation of explosives (or the combustion of propellants) melts the paraffin, removes it and cleans the perforations, increasing production.
A major problem with explosives stimulation is the shattering effects on the well. Due to the high detonation velocity and high percentage of shock wave energy associated with high explosives, a great area is crushed and sloughs into the well. Therefore, it generally needs lengthy cleanout time after the shot to resume production. According to Stoller, H. M., explosive fracturing creates a highly fractured region around the well bore; the gas pressure extends a few of these fractures further into the reservoir. The extremely high pressure results in permanent rock compaction and a very low permeability barrier at the well bore. Due to the shattering effects of an explosive event, explosive fracturing is suitable for uncased wells only. In practical applications, it has been realized that the highly dynamic process of explosive stimulation has an overly rapid pressure rise time, and too much shock energy is transmitted into the formation, creating a large quantity of small cracks.
The other method commonly used in well stimulation is hydraulic fracturing. Compared to the highly dynamic explosive fracturing, the loading process of hydraulic fracturing is much slower and can be regarded as a quasi-static process. It needs lengthy setup time and the operating cost is high. Nevertheless, it generally creates only a single crack into the formation from a perforation. Based on a comparison of the advantages and disadvantages between explosive stimulation and hydraulic fracturing, it is apparent that a process that can be used to create a network of multiple fractures with an operating cost similar to that of explosive stimulation would be most desirable and such a process would be associated with the use of propellants. It is assumed that such a network of multiple fractures is more likely to intersect with far-field natural fractures than the fractures created by explosive or hydraulic fracturing processes.
The original well stimulation technology that uses propellant gas generators to create and extend multiple fractures has been studied and applied in engineering with substantial success. The technology has many names in practical applications, such as tailored pulsed loading, controlled pulse pressurization, high energy gas fracturing, controlled pulse fracturing and dynamic gas pulse loading. When used in oil well stimulation, the basic requirements for the process and the propellant include:
Propellant used in place of high explosives has been found to be the most suitable to create such a network of multiple fractures in the formation. There are numerous patents concerning the use of propellants in stimulating subterranean hydrocarbon bearing formations as well as the efforts to perforate and stimulate a formation in a single operation (to complete perforating and stimulating of a hydrocarbon bearing formation concurrently). Cited below are just some examples.
U.S. Pat. No. 5,775,426 to Snider et al. describes a method to use perforating charges and propellant stimulation simultaneously. Shaped charges are loaded in a perforating gun and a shell, sheath or sleeve of solid propellant material is used to cover the exterior of the gun. Upon detonation of the charges, the high velocity jets penetrate through the gun, the casing and into the formation. At the same time, the jets, high pressure and high temperature ignite the propellant. The high-pressure gas generated by the combustion of the propellant is forced to enter into the perforations created by the jets, creating multiple fractures from each perforation.
U.S. Pat. No. 4,253,523 to Isben discloses the use of shaped charges in a perforating gun which is filled with secondary explosives with lower detonation velocity. According to the inventor, upon detonation of the shaped charge in the gun, it penetrates into the formation, creating a perforation. The shock wave of that secondary explosive will follow the perforation and will continue through the constant diameter perforated cavity.
U.S. Pat. No. 4,391,337 to Ford et al. describes an integrated jet perforation and controlled propellant fracture device and method for enhancing production in oil and gas wells. The device is loaded with perforating charges and fuel packs. Upon detonation of the perforating charges, the fuel packs are ignited. Then the high-velocity penetrating jet is instantaneously followed by a high-pressure gas propellant such that geological fracturing initiated by the action of the penetrating jet is enhanced and propagated by the gas propellant.
U.S. Pat. No. 4,064,935 to Mohaupt provides a gas generating charge that is placed in the oil well bore and activated to generate a controlled surge of gas pressure-volume of a known magnitude-time profile and directed perpendicular to the side of the well bore to flush clogged material away from the well bore and open up clogged passages for the greater flow of the oil into the well bore without damaging the well.
U.S. Pat. No. 5,690,171 to Winch et al. describes a device comprising a pipe having a plurality of weakened portions and containing a propellant material. When the propellant is ignited it produces rapidly expanding gaseous combustion products that puncture the weakened portions of the pipe. The expanding gas fractures the surrounding formation, thereby stimulating the formation to production.
U.S. Pat. No. 5,355,802 to Petitjean describes a method to perforate and fracture a formation in a single operation. The method includes the use of propellant canisters and shaped charges in a perforating tool, and the proper procedures of igniting the propellant and detonating the shaped charges.
U.S. Pat. No. 5,551,344 to Couet et al. discloses the use of propellant or compressed gas along with a liquid column. Upon ignition of the propellant or the activation of the compressed gas, the high-pressure gas released drives the liquid into the formation to propagate the fracture.
U.S. Pat. No. 4,081,031 to Mohaupt describes the use of a chemical gas generating charge activated to provide a controlled surge of gas pressure-volume of a known magnitude-time characteristic and directed to flush away clogged material in the well-bore and open-up clogged passages for the greater flow of oil into well bore without damaging the well.
U.S. Pat. No. 4,683,951 to P. Pathak et al. discloses a method to enhance the effective permeability of subterranean hydrocarbon bearing formations by proceeding the surfactant fluid injection step with creation of multiple formation fractures using tailored pressure pulses generated by propellant canisters disposed in the injection well. Fluid injectivity rates are increased by subsequent fracture extensions provided by repeated steps of generating high-pressure gas pulses at selected intervals.
U.S. Pat. No. 3,747,679 describes the use of a liquid explosive that has a small critical diameter, is safe to handle to fracture well formation for enhancing well productivity.
U.S. Pat. No. 3,797,391 to Cammarata et al. seems to show an example of the use of aluminum as shaped charge liner material in the purpose to project some liner material into the target upon collapse of the liner. Disclosed by Cammarata et al. is a multiple shaped charge bomlet having a plurality of shaped charges. Each charge has a bimetallic liner (the air side being the high density metal such as copper and the explosive side being the pyrophoric metal such as aluminum, magnesium, zirconium). The charges have the capability of penetrating hard structures and propelling incendiary particles through the perforations made in the target by the shaped charge jet. Since the referenced patent is used in an environment without the presence of water, the exothermic reaction of the incendiary particles should be between the said pyrophoric metal such as aluminum with oxygen in air, and obviously not with an oxygen carrying liquid like water.
Due to the relatively high cost associated with the use of a propellant in oil well stimulation, there have also been efforts to find a substitute for it. U.S. Pat. No. 5,083,615 to McLaughlin et al. discloses the use of aluminum alkyls to react with water within a confined space. The gas-generating chemical reaction can build up substantial pressure, and the pressure can be used to fracture rocks around a borehole, and hence stimulate water, oil or gas wells in tight rock formations. According to the inventors, the pressure can also be used to fracture coal seams for enhanced in-situ gasification or methane recovery. The aluminum alkyls are organo-metallic compounds of the general formula AlR3, where R stands for a hydrocarbon radical. These compounds react violently with water to release heat and the hydrocarbon gas. Some aluminum alkyls are available commercially at low cost. However, the tendency of the aluminum alkyls to ignite spontaneously in air would make it very difficult to handle in practical applications, and the pressure increase in the order of 3000 psi (210 bars) seems to be too low to fracture most of the rock formations.
U.S. Pat. No. 4,739,832 to Jennings et al. teaches a method for increasing the permeability of a formation where high impulse fracturing device is used in combination with an inhibited acid. The inhibited acid is directed into a well bore contained in the formation. A two-stage high impulse device is then submerged within the acid. After the high impulse-fracturing device is ignited, activating the retarded acid by the heat generated; then the fractures in the formation are induced and simultaneously forcing said activated acid into the fractures.
Consequently, a first objective of the present invention is to exploit the large amount of energy generated by the oxidation of aluminum from an aluminum-water reaction (or the reaction of aluminum with other oxidizers such as a metal oxide) for engineering applications, an in particular to provide a method to rapidly, economically produce molten aluminum in its free form in large quantities. The molten aluminum should preferably be produced from an explosive detonation process or from a rapid combustion of a fuel-oxidizer mixture so that a “dual-explosion” can be created. The first explosion of such a “dual-explosion” is the detonation of the high explosives or the combustion of the fuel-oxidizer mixture, and the second explosion is the aluminum-water reaction. When such a “dual-explosion” is created in a medium such as water, steel casing or tubing, hydrocarbon bearing formation, rock stratum or concrete etc., the mechanical effects resulting from the first explosion will be greatly enhanced or improved by the second explosion. The mechanical effects in the medium can be the mechanical effects for which an explosive device is designed to achieve, which may include, but is not limited to, one or a combination of the following effects: pressure wave generation and propagation, pressurization and displacement of medium, target penetration and fracturing, crack initialization and propagation, medium disintegration, fragmentation and fragment movement, etc.
A second objective of the present invention is to increase the reactivity between molten aluminum and water so that the minimum temperature required for aluminum for a complete reaction to occur can be lowered and the energy output from the reaction can be increased.
A third objective of the present invention is to make a shaped charge so that it can project some aluminum in molten state into the perforation created by the shaped charge jet. The molten aluminum is then forced to react with water to create an explosion locally within the perforation, fracturing the crushed zone of the perforation and initializing a multitude of cracks.
A fourth objective of the invention is to make a shaped charge that can have a liner made of energetic material. When the collapsed liner is projected toward a target, it carries not only kinetic energy transferred to it by the detonation of the explosives of the shaped charge, but also a substantial amount of thermal energy.
A fifth objective of the invention is to develop a system that uses capsule type shaped charges to concurrently perforate and stimulate a hydrocarbon bearing formation.
A sixth objective of the invention is to develop a system that uses an open-end shaped charge with a tubular perforating gun to concurrently perforate and stimulate a hydrocarbon bearing formation.
A seventh objective of the invention is to provide a method and device using the aluminum-water reaction to stimulate a perforated zone, or to revitalize an old production well, by cleaning the clogged perforations using the pressure and heat generated by the reaction.
An eighth objective of the invention is to provide a method and device to be used in drilled holes filled with water or water solution of some oxygen-rich reagents for rock blasting, pre-splitting, concrete structure blasting, cutting and demolition that can create two consecutive explosions and enhanced mechanical effects.
A ninth objective of the invention is to provide a method and device suitable for in situ gasification of a coal seam. The device should be detonated in the presence of water or a water solution of some oxygen-rich reagents contained in the said coal seam. The device then initializes and extends the cracks far into the coal seam upon its two consecutive explosions.
A tenth objective of the invention is to provide a method to make a torpedo suitable for defense applications. Unlike prior art torpedoes, it creates two consecutive explosions with much more energy output and enhanced mechanical effects when launched and set off underwater.
The above stated and other objectives of the present invention will become apparent upon study of the following detailed specification along with the disclosed drawings and tables.
a) and 8(b) show the collapsing process of a double-layer liner. By controlling the design parameters, all the material in the high-density layer 11 (airside) enters the jet 11′ to penetrate a target and all that in the aluminum layer 12 (explosive side) enters the slug 12′ to create an in-the-target explosion;
I. Methods to Produce Al in Molten State
It is known that aluminum in its molten state reacts violently with water to form aluminum oxide, generating a substantial amount of heat and releasing a large volume of hydrogen gas. The reaction equation of this process is shown as EQ1 in
The huge amount of energy released from the Al—H2O reaction should be harnessed and be used to do useful work. To exploit the engineering use of this reaction, the basic problem is how to achieve aluminum in its molten state in large quantities. U.S. Pat. Nos. 4,280,409 and 4,372,213 to Rozner et al. describe the use of pyrotechnic reactions to heat solid metal (used as container for pyrotechnic mixture) and force the molten metal to react with water. This method may have limited heat transfer efficiency due to the fact that a piece of solid metal has only limited surface area that comes in contact with the pyrotechnic material and the time duration available for such a heat transfer process is very limited once the device is actuated.
In U.S. Pat. No. 5,859,383 to Davison et al. there is disclosed a method of using electric energy to heat the aluminum wires and force the wires to react with water. According to the inventors, the heat needed to activate the reaction is at the level of 1˜10 KJ/gram of reactive mixture. Such a high level of initiation energy would require the use of expensive auxiliaries such as energy transmitting cables, electrical energy generating and storing devices. Such requirements would render the method and process uneconomical and not practical for engineering applications. Similar actuation methods and devices by electrical power can be found in U.S. Pat. Nos. 5,052,272, 5,712,442 and 5,789,696, as referenced previously.
In the present invention, three novel embodiments to effectively, conveniently and economically generate aluminum in its molten state in large quantities for engineering use are disclosed. The molten aluminum produced is normally a “by-product” from a main detonation or combustion event designed to create some required mechanical effects. The method in the first embodiment is to detonate a HE/Al mixture in which the aluminum powder is surplus in stoichiometry. The method in the second embodiment is to initiate an oxidizer/Al mixture in which the aluminum powder is surplus in stoichiometry. The reaction of the mixture may be a detonation or combustion. The method in the third embodiment is to shock Al with an explosive detonation and then heat it with the detonation products. Since the production of molten state aluminum is always associated with the detonation or rapid combustion of an explosive device, the use of the present invention creates a “dual-explosion”. The first explosion is from the reaction of the explosive device, and the second being the Al—H2O reaction. The above embodiments are described below.
When aluminum powder is mixed with a high explosive, upon detonation of the mixture there are two energy sources to heat the reaction products to a high temperature. One is the detonation heat, or the heat released by the detonation decomposition of the high explosive itself; the other is that from the reactions between the detonation products of the said high explosive and the aluminum powder. The high explosive used in the mixture is not necessarily rich in oxygen. As a matter of fact, for some commonly used high explosives like RDX, HMX and TNT, they have negative values in oxygen balance.
For high explosives, the temperature of its detonation products is normally in the order of 3000˜4000° C. In terms of heat generated by the detonation of explosives and the heat needed to melt aluminum, the heat of detonation for typical high explosives is in the order of 4˜6 KJ/gram and that the heat needed to melt 1 gram of aluminum is only 0.396 KJ. This means that the heat generated by 1 unit weight of high explosives should be able to melt a substantial amount of aluminum if the heat is effectively transferred to the latter. In the explosives and ordnance industries, it is not new to add light metal powders like aluminum or magnesium powder to high explosives in the purpose to increase the heat value of the explosives. Generally called “aluminized explosives” in the art when aluminum powder is used, the extra heat value obtained from this category of explosives is from the reaction between aluminum powder with the detonation products of the explosives. Therefore, the aluminum content in the mixture is calculated to maximize the heat that would be generated. In other words, in the prior art of mixing “aluminized explosives”, there is no intent to produce aluminum in its free form Al in molten state, and there is no intent to use the Al—H2O reaction to do useful work.
U.S. Pat. No. 4,376,083 to Ulsteen references some well-known “aluminized explosives” used in the defense industry, such as those known by the names like Torpex, H-6, HBX-1, HBX-3, etc. One grade of the “aluminized explosives”, the TNT/RDX/Al (in the compositions of 60% TNT, 24% RDX and 16% Al, or 60% TNT, 20% RDX and 20% Al) was used very early in torpedoes and maritime bombs for increased power. The aluminum powder mixed in this kind of explosives will all be consumed in the reactions with the detonation products of the high explosives, there will be no aluminum in free form in reaction products. In other words, to utilize the Al—H2O reaction, the aluminum content in the mentioned explosives is not high enough. Except for torpedoes, “aluminized explosives” in the prior art are normally not intended for use in presence of water.
With the method of the present invention, any known explosive can be used to produce molten aluminum by mixing it with aluminum powder. Examples are, but not limited to, RDX (Hexogen, Cyclotrimethylenetrinitramine), HMX (Octogen, Cyclotetramethylenetetranitramine), TNT (Trinitrotoluene), PETN (Pentaerythritol tetranitrate), Picric Acid (2,4,6-trinitrophenol), CE (Tetryl), PYX, HNS (Hexanitrostibene) and some ammonium nitrate based explosives used in rock blasting like ANFO (ammonium nitrate fuel oil) and emulsion explosives. In this method, to produce aluminum in molten state using a high explosive as an energy source, the high explosive is mixed with an amount of aluminum powder that is surplus in stoichiometry. The stoichiometry point for a high explosive-aluminum mixture can be determined assuming complete reaction between aluminum and the detonation products of the said high explosive such as H2O and CO2. In the method of the present invention to produce aluminum in molten state, there are two phases of chemical reactions involved corresponding to the two energy sources to heat the detonation products:
From EQ3 in
The temperature of the final reaction products as a function of Al content can be calculated. Firstly, assume 1 mole of RDX is mixed with x moles of Al (0<=x=<2). EQ6 as seen in
Based on the total amount of heat generated from the said two phases of reactions and the heat capacities of the reaction products and aluminum, the temperature of the final detonation products along with surplus aluminum (if there is any) can be found. Results of a sample calculation of the RDX-aluminum mixture are plotted in
Point B in
Beyond point C in
In
The said two phases of reactions, i.e., detonation of the high explosive and reactions between aluminum powder and the detonation products, are completed within micro seconds and virtually in the original space as was occupied by the high explosive-aluminum mixture. Then the detonation products along with the surplus aluminum in its molten state expand violently and rapidly into the surrounding medium. When this medium is water (the explosive device be detonated in water), the surplus Al in molten state is forced to interact with water, creating a new explosive event that can output even more energy than the said two phases of reactions.
According to some experimental studies, the temperature of molten Al is a critical factor for the Al—H2O interaction. If this temperature is not high enough, the interaction maybe only a physical event, involving intense intermixing and rapid thermal energy transfer between the molten Al and liquid water. Only when the Al temperature is above a critical value will the interaction turn chemical, i.e., the chemical reaction between molten Al and water be “ignited” and the “combustion” will be completed. Theofanous et al. studied the influence of aluminum temperature on the aluminum-water interaction. In their study, gram quantities of molten aluminum droplets at temperatures up to 1973° K are forced to interact with water under sustained pressure pulses of up to 40.8 Mpa in a hydrodynamic shock tube. After examining the morphology of the aluminum debris retrieved, three regimes of interactions were identified: an essential non-chemical “hydrodynamic regime” at low melt temperatures (<1400° C.) which resulted in a few aluminum fragments in the millimeter size range and/or a largely un-fragmented but highly convoluted aluminum mass; a regime of complete aluminum combustion at initial melt temperatures above about 1600° C. which converted almost all of the aluminum mass to a fine powder of oxidic particles in the one to ten microns range and an intermediate or “ignition” regime for melt temperatures in the range 1400˜1600° C. with debris composed of both oxidic powder (10% to 40%) and metallic fragments ranging from hundreds of microns to millimeter sizes. According to this study, for a complete chemical reaction between Al and water to occur, a temperature of aluminum just above the melting point is not high enough; instead, it should preferably be higher than 1600° C. For an RDX/Al mixture, to output surplus Al at a temperature of 1600° C., the corresponding Al content by weight is 77.3%. This point will be termed the Theofanous et al. point in the specifications of the present invention, as indicated by point T* in
In practical applications (as will be seen in the “Examples” section later), the high explosive-aluminum mixture may be contained by the shell of an explosive device, such as the case of a capsule type shaped charge or a torpedo, a container of any proper material such as steel, aluminum, plastic or even water-proof paper, or, a group of such explosive devices are collectively contained in a big container, such as that practiced in the oil well perforating industry where a multitude of shaped charges are contained in a tubular steel perforating gun. To create the said subsequent explosive event, the said charge containers or shells, cases of the charge are submerged in an oxygen carrying liquid such as water. Upon detonation of the explosive charge, the said charge shells or cases are broken into pieces. When the shaped charges are contained in a tubular perforating gun, the gun is punched by the jets, leaving holes on the gun. The surplus aluminum in molten state produced as described above now expands violently and rapidly into the oxygen carrying liquid such as water, forcing the liquid form Al (or even in vapor form, if the Al content for a RDX/Al mixture falls in zone II as shown in
In the second embodiment of the of the present invention to produce Al in molten state, aluminum (preferably in powder form) is mixed with commonly used oxygen carrying reagents and aluminum is surplus in stoichiometry in the mixture. The oxygen carrying reagents, here generally referred as oxidizers, can be a metal oxide, a chlorate, perchlorate or nitrates that are compatible with aluminum powder, or even water or water solution of the said chlorate, perchlorate and nitrate. When such a mixture is used, the thermal energy to heat the reaction products along with the surplus aluminum may come from one or two sources depending on the oxidizer actually used and also the properties of the mixture (detonable or not). If the mixture is not detonable, the thermal energy released from the combustion reaction between aluminum and the oxidizer is the only energy source to heat the reaction products along with the surplus aluminum to a high temperature. However, some oxidizers like nitrates, chlorates and perchlorates, they are by themselves detonable “low explosives”, or when they are mixed with aluminum at a certain ratio, the mixture is detonable. In the case that the said oxidizer/Al mixture is detonable, the thermal energy will come from two sources, from the detonation of the mixture and from the reactions between the detonation products and aluminum powder. The process is similar to the HE/Al mixture, described in embodiment 1 to produce aluminum in molten state of the present invention, except that the detonation of an oxidizer/Al mixture is generally not as powerful as that of a high explosive.
The exothermic reaction of the mixture can be actuated by a proper means such as ohmic heating with an electric wire, by detonating a small high explosive boost charge or by igniting a combustion boost charge. Such an initiation device can be designed by those skilled in the art and will not be detailed in this patent. The said oxidizer that can be used to mix with aluminum in the purpose to produce aluminum in its molten state can be from one of the following groups:
As is known, water is chemically neutral under normal conditions but it does behave like an oxidizer in that it releases its oxygen to react with Al when it encounters aluminum in molten state. In U.S. Pat. No. 5,052,272, water is used and called an oxidizer in a device to launch a projectile. In that patent to Lee, a conducting wire is energized by electrical power so that it melts and is dispersed into a mixture of aluminum powder and water, initiating the reaction between them and using the hydrogen gas released to propel a projectile. However, in the referenced patent, there is no intent to create a dual-explosion and to produce molten aluminum by using a surplus amount of aluminum in the aluminum powder-water mixture. On the contrary, according to the inventor, an excessive amount of water is used in stoichiometry. For the actuation of an aluminum-water mixture, the use of other methods is possible such as by using a boost high explosive charge, by using an Al/metal oxide initiation unit. Such actuation devices can be designed by those skilled in the art and are beyond the scope of the present invention, and therefore will not be discussed in detail.
The temperature of the surplus aluminum as produced by an oxidizer/Al mixture can be calculated similarly as with the HE/Al mixture.
Shown in
In zone i, temperature increases from 0° C. at point P1 (for simplicity, 0° C. ambient temperature was assumed for the calculations) to the maximum of 4150° C. at the stoichiometry point P2 (aluminum 18.4%, CuO 81.6%) by weight. This is different from zone I for the RDX/Al mixture as shown in
In zone ii, defined by points P2(18.4%, 4150° C.) and P3(27.0%, 2447° C.), surplus aluminum produced is in vapor form. The reaction products like Cu and Al2O3 are partly in vapor form (vaporization point of Al2O3 is 2908° C. and that for Cu is 2595° C., the reaction does not release enough heat to vaporize all of them).
Surplus Al experiences a phase change from vapor to liquid form in zone iii. The two points P3(27.0%, 2447° C.), P4(49.3%, 2447° C.) defining this zone have the same temperature of 2447° C., the vaporization point of aluminum. Point P3 (27.0%, 2447° C.) corresponds to a status in which all the surplus aluminum is in vapor form while point P4 (49.3%, 2447° C.) corresponds to all the surplus aluminum in liquid form. The reaction products Cu and Al2O3 are all in liquid form in this zone.
In zone iv defined by points P4(49.3%, 2447° C.) and P5(56.9%, 2045° C.) surplus aluminum as well as Cu and Al2O3 in the reaction products are all in liquid form.
Zone v sees the phase change of Al2O3 at a temperature of 2045° C. (melting point of Al2O3) from liquid form to solid form. Defined by points P5 (56.9%, 2045° C.) and P6 (60.4%, 2045° C.), this zone has the surplus Al and the reaction product Cu in liquid form.
Zone vi defined by points P6(60.4%, 2045° C.), P7(75.7%, 1083° C.), surplus aluminum and the reaction product Cu are all in liquid form but another reaction product Al2O3 is solid. The temperature of molten aluminum at which complete chemical reaction occurs on encountering liquid water as reported by Theofanous et al. falls in this regime. Denoted as T* in
Zone vii is where the reaction product Cu changes phase from liquid to solid at a temperature of 1083° C., the melting point of Cu. In this zone, the other reaction product Al2O3 is in solid form and the surplus Al is in liquid form.
In zone viii defined by points P8 (76.3%, 1083° C.) and P9(82.7%, 660° C.), only surplus aluminum is in liquid form. The reaction products CuO and Al2O3 are all in solid form.
In zone ix defined by points P9(82.7%, 660° C.) and P10(88.6%, 660° C.), liquid and solid forms of surplus aluminum coexist.
In practical applications, a temperature-Al content chart as plotted in
For other aluminum-oxidizer mixtures, a similar Temperature-Al content chart to that shown in
In addition to the two embodiments of chemical methods to produce molten aluminum described, there is still a third embodiment, namely the shock wave along with reaction products heating method. In this method, the aluminum material can be either in solid form, or be compacted aluminum powder. Often the shock wave alone from the detonation of an explosive charge may not have enough energy to melt aluminum, but if the aluminum material comes in contact with the explosive charge, the high temperature detonation products along with the said shock heating will put the aluminum material well above its melting point. Consequently, typical uses of this method can be to make shaped charge liners, cases, charge carriers completely or partly with aluminum. Then upon detonation of the explosive charge, the liner material projected into a perforation, the shaped charge case and carrier heated and broken in a well bore, can all be forced to interact with water and cause a powerful secondary explosion.
It is known in shock physics that once a metallic material like aluminum, copper or iron is shocked, the temperature of the material increases instantly.
For example, when solid aluminum is subjected to a shock wave, it starts to melt at a pressure of 0.6 Mbar and melts completely at 0.9 Mbar. It is known that most high explosives have a detonation pressure in the order of 0.3˜0.4 Mbar (for example, RDX has a detonation pressure of 0.338 Mbar at a density of 1.767 g/cm3, and the detonation pressure for HMX is 0.393 Mbar at a density of 1.90 g/cm3). Obviously, the shock wave alone from the detonation of explosives is not sufficient to melt solid metal. However, when aluminum is used as a component of an explosive device such as a shaped charge liner or case, or charge carrier as will be shown in the embodiments of the present invention, upon detonation of the explosives, it is firstly heated by the shock wave, and then further heated by the high temperature detonation products. When Al is used as a shaped charge liner material, in addition to the first shock by the detonation of the explosive charge, the collision of the liner elements in the centerline of the charge creates another shock. That is, the liner is accelerated to collapse and to collide along the centerline of the shaped charge. This second time shock along with the detonation products heating will further increase the temperature of the collapsed liner. The final temperature will be high enough to melt aluminum and have it ready for the subsequent aluminum-water reaction. Similar to what described previously, to achieve complete reaction when aluminum is at a relatively low temperature, water solution of some oxygen-rich reagents like nitrates, perchlorates can be used in place of plain water. Therefore, it is possible to use the charge case or charge carrier as an energetic material if they are made of aluminum, which upon detonation of the explosive charge can be shocked and be heated to a high temperature and then induce a powerful Al—H2O (water solution of oxygen-rich reagents) reaction.
Numerous other variations based on the above three embodiments to produce molten aluminum in its molten state are possible, without departure from the spirit described above. Theoretically, any detonable or combustible mixture that has an exothermic reaction can be used to mix with Al in an surplus amount in stoichiometry to produce molten aluminum to react with water. Possible variations include but are not limited to:
So far in the specification of this invention, the use of aluminum is preferred as a fuel in the aluminum-water reaction. However, other light metals can also be used in place of aluminum without departure from the spirit of the present invention. Such substitutes include but are not limited to: aluminum in its alloy form with other metals, such as aluminum alloyed with magnesium, aluminum-lithium alloy, magnesium and its alloys, etc. The said substitutes can also be used in a surplus amount in stoichiometry to mix with high explosives or oxidizers in the purpose to produce molten metal and to react with water. Similarly, water solution of oxidizers can also be used in place of plain water so that its reactivity with the said substitute molten metal can be increased, as will be described in the present invention.
II. Method to Increase Al—H2O Reactivity
Aluminum at its high temperature has a tendency to react with oxygen. To free oxygen in water and react with it, aluminum has to be at a very high temperature so that the Al molecules have enough kinetic energy to break the H—O—H bond in water. The minimum temperature for Al to completely react with water is 1600° C., according to Theofanous et al., as described early. However, it is possible to lower the temperature of the molten aluminum needed for a complete chemical reaction if oxygen is easier to obtain, or the reactivity of the oxygen carrier (water) is increased. Disclosed herein is a method to increase the reactivity of water by dissolving oxygen-rich reagents into water.
It is well known that some oxygen-rich reagents like the commonly used nitrates, chlorates and perchlorates have a strong tendency to react with a fuel like Al, they release oxygen much easier than water does. A mixture of aluminum powder with any of these reagents can be detonable or combustible. When such a reagent is dissolved in water to react with molten aluminum, both the oxygen supplier and the “fuel” aluminum are in liquid phase, the reactivity between the water solution of the reagent with liquid Al will be greatly increased compared to the use of plain water. Consequently, the minimum temperature needed for Al to completely react with such a water solution can be greatly decreased. Such a decreased minimum temperature of Al with a specific reagent at a certain concentration can be determined theoretically or experimentally. For example, if molten Al is to be dispersed into a water solution of 10% nitrate, the minimum Al temperature for a complete reaction with the liquid will be significantly lower than 1600° C., the Theofanous et al. point. However, the temperature of Al should preferably be higher than 660° C., the melting point of Al, so that it is in liquid form and can interact and react homogeneously with the water solution of a reagent. As stated in U.S. Pat. No. 5,083,615 to McLaughlin, to produce heat and gas that increases the pressure of a system, homogeneous liquid/liquid reactions are advantageous. Many of the problems of reaction rate prediction and control associated with the heterogeneous solid/liquid reactions can be avoided in homogeneous liquid/liquid reactions.
The oxygen-rich reagents are well known in the art of manufacturing military and commercial explosives, propellants used as gun and rocket fuels, and pyrotechnic materials, like the nitrates, chlorates and perchlorates. Some examples of such materials are tabulated in
III. Classes of Further Embodiments of the Present Invention
Once molten aluminum is produced by an explosive device in the presence of water, an Al—H2O reaction will immediately follow the actuation of the said explosive device. Here the explosive device refers to any device that is designed to detonate, to deflagrate and to output Al in its molten state using one or a combination of the three methods already disclosed. The device can be a detonable or combustible HE/Al or oxidizer/Al mixture in which Al is surplus in stoichiometry. The general purpose of the present invention is to create enhanced mechanical effects in a proper medium. An explosive device of the present invention is always used in presence of an oxygen-carrying liquid, such as water, or water solution of some oxygen-rich reagents. When it is used, it creates a “dual explosion” within the medium where the explosive device is used. The first is the primary reaction of the explosive device, which can be a detonation or a deflagration event, and the second is the powerful reaction between molten aluminum and water, or a water solution of an oxygen-rich reagent if the reactivity is enhanced with the said reagent. This is very different from the use of prior art explosive devices, including high explosive detonating devices, propellant combustion devices, fireworks etc., which create a “one time” event only. In the present invention, the second of the said “dual explosion” can output much more energy than the primary explosion. As described early in the present invention, 1 gram of Al reacting with water can output 3 times as much energy as 1 gram of high explosive like RDX (refer to EQ1 in
The said medium can be any material within which an explosive device of the present invention is used. Examples are water, steel casing or tubing in an oil or gas well, hydrocarbon bearing formation, a rock stratum, a coal seam or concrete etc. The said mechanical effects in the said medium are the mechanical effects for which an explosive device is designed to achieve, which may include, but are not limited to, one or a combination of the following effects, pressure wave generation and propagation, pressurization and displacement of medium, target penetration and fracturing, crack initialization and propagation, medium disintegration, fragmentation and fragment movement, etc.
The present invention is primarily concerned about applications in the design of shaped charges, hydrocarbon bearing formation stimulation devices, explosive devices to be used in rock blasting, coal seam gasification and in defense industry. However, countless embodiments and variations are possible in different application areas without departure from the spirit of the present invention. The preferred embodiments are divided into 6 classes which are set out below.
Class 1: Shaped Charge to Create an Explosion in Target
In the oil and gas industry, the well that is drilled through hydrocarbon bearing formations is often cased with steel tubing, called casing. To establish a communication channel between the formation and the well so that the hydrocarbons can flow into the well and be recovered, an explosive device called a “shaped charge”, or an “oil well perforator”, is used. Generally tubular in appearance and symmetrical to a centerline axis, a shaped charge typically has three parts, namely a conical liner, a case and a certain amount of explosives. When a shaped charge is detonated, the liner collapses into a high velocity metal jet and a relatively low velocity slug traveling behind the jet. A substantial amount of explosive energy is transmitted to the jet and it travels along the centerline of the charge at a velocity in the order of 1000˜9000 meters/per second. The jet is so powerful that it can penetrate through the steel casing, the concrete lining between the casing and the formation and then into the oil-bearing formation, establishing the said communication channel between the well and the formation.
As is known in the art, when a shaped charge is fired into the formation during a perforating operation, having liner materials remain in the perforation is not desired. No matter what the liner material is, either solid metal or powdered metal, it clogs the passage through which the hydrocarbons can run into the well and be recovered. A lot of efforts have been spent to develop a “slug-free” shaped charge. In a research work by Rinehart, J. S. et al., a shaped charge with a low melting point metal liner such as lead is used, the liner melts during collapse, forming a liquid slug which is dispersed. In a work by Delacour et al., the use of bimetallic liner for a shaped charge is used in the purpose to eliminate the slug from a collapsed liner. In the present invention, herein disclosed is a method to turn the “slug” into an energetic material, which does not clog the perforation. Instead, it reacts with water that is forced to enter the perforation and creates a powerful explosion in the perforation, fracturing the crushed zone and cleaning the perforation. The method is to make a shaped charge liner with aluminum, and then fire the charge in presence of water.
As is known in the art of shaped charge design and manufacturing, charge penetration decreases when a decrease in liner density. Due to the low density of aluminum, a liner made of this material will have less penetration into a target than it would with copper and tungsten liners that have a higher density. However, so far as the perforating of a hydrocarbon bearing formation is concerned, perforating with the shaped charge of the present invention disclosed above may have even better results compared to the use of conventional shaped charges with high density liners. This is because of the in-perforation explosion that fractures the crushed zone of the perforation and initializes numerous cracks into the formation, greatly improve the permeability of the perforation. Additionally, the entrance hole of the perforation is bigger than that would be obtained with high-density liners. A big entrance hole makes it easier for the molten aluminum to be projected into the perforation and also easier for water to enter it. After the perforating is completed, it also makes it easier for the hydrocarbons to flow into the well.
However, with the shaped charge of the present invention, if a deeper penetration is required than that would be achieved with pure aluminum liner, a mixture of aluminum powder with other high density metal powders such as iron, tin, copper, lead, tungsten, etc. can be used. When liner 10 shown in
In another embodiment of the present invention as illustrated in
Upon detonation of the charge, a shaped charge liner made of aluminum or aluminum-based materials, in single or multiple layers as described above, is firstly heated by shock wave and by the detonation products to a temperature high enough to melt the liner. Then when it is propelled into the formation, it is further heated by the friction with the formation (kinetic energy carried by the jet is partly turned into thermal energy) and it reaches an even high temperature.
For a shaped charge of the present invention as shown in
Although the molten aluminum 100 may be only in gram quantities for a medium-sized shaped charge, given the fact that 1 gram of Al can give off a few times more energy than the same amount of high explosives, the explosion that it creates in the perforation can substantially improve the permeability of the perforation. The energetic Al—H2O reaction in the small perforation releases a large amount of heat and hydrogen gas, and generate a pressure pulse. After the explosion, the layer of molten aluminum in the perforation is consumed, the crushed zone 90 is pulverized and multiple fractures 120 are created in the formation, as shown in
In addition to the deep penetration type shaped charges that are designed to penetrate a formation as deep as possible, there is another family of shaped charges called big hole charges in oil industry, used particularly in perforating heavy-oil wells and in sand control. The purpose of this kind of charge is to create a big entrance hole on the well casing with only a few inches of penetration into the concrete lining and formation. In the prior art, this family of charges uses a solid metal liner such as brass liner. Unlike powder metal liners, solid liner leaves a slug, or called carrot in the perforation after the shot. The carrot in the perforation clogs the communication channel and it may be flushed back into the well, causing problems for other well operations such as pumping. U.S. Pat. No. 6,012,392 to Norman et al. discloses a method to make shaped charge liner using an alloy of nickel, tin and copper, it is claimed that such a shaped charge liner does not form a slug upon actuation of the charge. In the present invention, herein disclosed is a method to make shaped charge liner so that when the liner collapses, it carries not only kinetic energy but a substantial amount of thermal energy as well. The liner will be made of powder material such as aluminum powder and a metal oxide so that it is reduced to powder again when the liner collapses and it is especially for the big hole type charge but can also be used for deep penetration type charges, too.
As is well known in the art of shaped charge design and manufacturing, for given design parameters such as the type and amount of explosives used, case geometry, liner geometry and test set-up, the size of the entrance hole increases when the density of the liner material decreases (the opposite trend is true for penetration). Aluminum has a density of only 2.7 grams/cm3, much lower than the commonly used metals for deep penetration charge liners, such as Copper (8.96 g/cc), Tungsten (19.5 g/cc) or Lead (11.34 g/cc). So, when aluminum is used for shaped charge liners, the resultant entrance hole size will be significantly larger.
In the use of shaped charges with powder metal liner (either deep penetration type or big hole type), it often happens that a part of liner material is left outside the steel casing surrounding the entrant hole of the perforation. Shown in
As is known in the prior art, a shaped charge liner is always made of inert material. A shaped charge liner by itself does not carry any energy needed to penetrate a target. The energy is imparted to it by the detonation of the high explosive behind the liner. Then, when a shaped charge jet is formed, all the energy available to penetrate a target is the kinetic energy of the jet. In the present invention, a shaped charge liner made of energetic material is used, so that upon detonation of the charge, the collapsed liner (including the jet and slug) carries two parts of energy that can be used to pierce a target. One part is the kinetic energy transferred to the liner upon detonation of the explosive charge, and the other part is the thermal energy derived by the chemical reaction within the liner material that is actuated by the detonation of the explosive charge.
An embodiment of such a method to make an energetic liner is to use a mixture of aluminum powder with some metal oxides, such as copper oxide (CuO), Ferric Oxide (Fe2O3). Called thermite, the mixture of aluminum powder and Ferric Oxide is used to melt some metallic materials like steel. The thermite reaction is listed in EQ11,
When a shaped charge liner is made of Al-based energetic material such as the Al/Fe2O3 mixture, the energy carried by a collapsed liner can be much higher than a conventional, inert liner would carry. The internal energy of the high explosive loaded is the energy source for a prior art shaped charge. Suppose a shaped charge using 30 grams of RDX as main load, the internal energy of this amount of explosives is 189.6 KJ (suppose 6.32 KJ/gram for RDX) and that 50% of the energy is turned into kinetic energy of the collapsed liner (carried by both the jet and the slug), so all the energy available to the collapsed liner is 94.8 KJ in the form of kinetic energy. When a shaped charge of the present invention with Al-based energetic material is built, the energy carried by the collapsed liner can be substantially higher. Suppose the liner is a compacted Al/Fe2O3 mixture at its stoichiometry ratio and the weight of the liner is 40 grams, referring to EQ 11 in
Refer now to
When the shaped charge liner is made by compacting a mixture of Al/metal oxide powder, the collapsed liner will be in liquid form due to the shock by the explosive charge and the heat generated by the chemical reaction within the liner. The actual temperature of the liner upon collapse can be calculated and be adjusted by changing the composition of the liner mixture. By using aluminum that is surplus in stoichiometry or the metal oxide or with the addition of other inert materials into the liner mixture, a temperature of collapsed liner material can be controlled to be below the maximum temperature, which happens at the stoichiometry point. To achieve a high temperature for collapsed liner, it is possible to use other Al/oxidizer mixtures in addition to metal oxides, such as the nitrates, chlorates and perchlorates as described previously in the present invention. However, this is not preferred by the present invention due to the high reactivity of such mixtures (may cause safety problems in operation) and that, unlike an Al/metal oxide mixture, the reaction may be an explosive event and releases gaseous materials. The penetrating power of a shaped charge jet will be questionable if the jet contains gaseous material.
Metal oxides are normally not mixed with high explosives because of compatibility problems under raised temperature. For example, when RDX is mixed with Fe2O3 or CuO, it reacts with the metal oxide to produce unstable products that can be ignited at a temperature as low as 100° C. In the present invention of a shaped charge liner made of energetic materials, although the metal oxide is not directly mixed with the high explosive, as shown in
Referring to
Due to the relatively low density of aluminum and metal oxides, a compacted mixture of Al/metal oxide used as shaped charge liner will have a density significantly lower than that made with other metal powders such as copper, lead and tungsten powders. Therefore, the use of an energetic liner of the present invention is normally associated with large entrant hole of the perforation but limited depth of penetration into the target. However, with another embodiment of the present invention, it is possible to create a big entrant hole and at the same time achieve a deep penetration, if this is needed by an application.
The shaped charge liner in this class of embodiment of the present invention can also be made with an Al/metal oxide mixture in which Al is surplus in stoichiometry, such as a mixture of Al/Fe2O3 with an excessive amount of Al in the composition. Then the collapsed liner has a very high temperature with molten and free Al in it. The method used to produce Al is a combination of method 2 (Al/Oxidizer mixture) and method 3 (shocking and heating) as already disclosed in the present invention. When a shaped charge liner made in this way is fired in presence of water, in addition to penetrating and burning the target, it will also induce an Al—H2O reaction in the perforation and near the entrant hole of the perforation. The effects of such an Al—H2O reaction will be similar to that described in the class 1 embodiments.
Class 3: Capsule Type Shaped Charge to Perforate and Stimulate
In the prior art to make shaped charges, the explosive used is typically a pure high explosive like RDX, HMX mixed with a small amount of phlegmatizers such as wax and some graphite powder as lubricant. As already discussed, for a conventional shaped charge, the portion of the explosive energy that is carried by the jet is the only energy available to do useful work. On the other hand, the perforation created by the high velocity jet in the formation bears a layer of hardened material often called a crushed zone. The crushed zone has a much lower permeability compared to the formation in its virgin state. Therefore, it impedes the flow of hydrocarbons into the well. Also, after firing the charge into the formation, a significant amount of liner material, no matter what the liner is made of solid metal or powder metal, is left in the perforation. For effective communication between the formation and the oil well, the crushed layer of the perforation should be pulverized and the materials remaining in the perforation should be removed. In the prior art, to remove the crushed zone and to clean the perforation, some subsequent procedures are necessary after perforating, like acidizing, flushing, hydraulic fracturing, propellant or explosive stimulation etc. U.S. Pat. No. 5,775,426 to Snider et al. describes a method to perforate and to stimulate simultaneously, the method includes the use of a sleeve of solid propellant wrapping the perforating gun within which the shaped charges are loaded and fired. The propellant sleeve in the prior art can be used with tubular perforating guns only, there is no method known yet in the prior art to complete perforating and stimulating in one trip by using capsule type charges. In the present invention, in addition to example 1, herein disclosed is another novel method to perforate and stimulate simultaneously without using propellants. The method is to create an Al—H2O explosion in the well immediately after the charges are detonated.
Shown in
Shown in
The addition of aluminum powder to high explosives will make the detonation velocity of the high explosives lower than without it. Also, as is described, a substantial amount of the detonation heat is consumed in heating the surplus aluminum. Therefore, explosive 30 which is now actually an HE/Al mixture shown in
The methods to produce surplus aluminum in molten state as disclosed and described already in the present invention can be used individually or in combination in the design of a capsule type charge. In
Shown in
When a capsule type charge as illustrated in
Class 4: Shaped Charge to Perforate and Stimulate with a Perforating Gun
Unlike the capsule type shaped charge that is fluid-tight and can be directly exposed to well fluids, the shaped charges shown in
Similar to the capsule type charge as used in class 3 of the preferred embodiments of the present invention, the three methods used to produce molten aluminum as have been disclosed in the present invention can be used individually or in combination.
In
For a tubular perforating gun system,
The molten Al producing unit 275 uses method 1 or 2 of the present invention to produce molten Al, that is, unit 275 can be a mixture of HE/Al or oxidizer/Al in which Al is surplus in stoichiometry. The unit can be contained in a smaller container made of proper material, such as aluminum, steel, copper or brass, zinc and plastic etc. The container for unit 275 should be fluid-tight so that the well fluid will not enter the unit and the sensitivity of the mixture to jet impaction will not be changed when in the well. The units 275 are attached to the perforating gun 140 using proper means, such as threads, glue or glue tape etc. The initiation mechanism of unit 275 in the present invention is similar to that of the rocket propellant sleeve in U.S. Pat. No. 5,775,426 to Snider et al., it primarily relates to the shaped charge jet impaction, then the high temperature, high pressure detonation products venting through the hole created by the jet on the scallop 210 may also assist the ignition. However, the reaction process of unit 275 in the present invention will be more reliable and stable than the rocket propellant sleeve used in the referenced patent. If unit 275 uses a detonable mixture like HE/Al, a detonation occurs and the reaction is completed and molten Al released instantly; for a combustible mixture like an Al/metal oxide, a combustion is actuated and the process is stable due to a temperature of reaction products higher than most of the propellant combustion temperature. As is known in the art, when Al is involved in the composition of an energetic material, the reaction temperature is high and the process is stable. As a matter of fact, sometimes Al is intentionally added to the composition of a propellant in the purpose to stabilize the combustion process, such as that used in U.S. Pat. No. 4,064,935 to Mohaupt, H. H. In the present invention, for a mixture to produce Al in molten state, the temperature of the reaction products decreases as the Al content in the mixture increases beyond the stoichiometry point. Therefore, in determining the Al percentage for a mixture in a design, the temperature of the reaction products along with the surplus Al should be considered so that the reaction process is stable and reliable. Compared to the use of rocket propellant sleeve in U.S. Pat. No. 5,775,426, the volume or weight of unit 275 can be substantially smaller. This is due to the fact that the Al—H2O reaction has a much higher thermal value than the commonly used high explosives and propellant. Refer to EQ1 in
With the capsule type system in class 3 and the tubular perforating gun method shown in
The use of capsule type charges to perforate and stimulate as disclosed in class 3 embodiments and the tubular perforating gun system (molten Al produced outside gun) shown in
Class 5: Stimulating Method and Device
In this class of preferred embodiments of the present invention, the Al—H2O reaction is induced and used individually to stimulate a formation. This can be the stimulation of a perforated well, or the revitalization of an old production well. For some perforated wells, the hydrocarbon production rate may not be satisfactory. This may be attributed to the decreased permeability of the crushed zone in a perforation, debris remaining in the perforation, or the penetration is not deep enough. Some commonly used stimulating technologies such as acidizing the well to break down crushed zones, well flushing or hydraulic fracturing may not be very helpful. On the other hand, it has been reported that the use of propellants to be very successful (see Watson et al., Liquid Propellant Stimulation of Shallow Appalachian Basin Wells, SPE 13376, 1984). Herein disclosed is a novel method of the present invention for oil well stimulation. Shown in
When a perforated well has been in production for some time, the perforations may become clogged due to the build-up of paraffin. Then the production rate decreases and the well needs to be revitalized by removing the paraffin from the perforations. One common method in the art is to bum some propellants in the well, and then paraffin is melted by the heat released and removed by the high pressure. As noted previously, the combustion of one gram of aluminum in water generates nearly 17.5 KJ of heat, which is 3 or 4 times more than that released by the reaction of 1 gram of high explosives or propel lants. In addition to the high pressure impulse generated upon the actuation of the devices shown in
Class 6: Other Engineering Applications
In addition to oil well uses as embodied in classes 1˜5, the present invention can also be used in numerous other industries where an energetic material should be used. As mentioned previously, aluminum has been used to make “aluminized” explosives in the art of explosive manufacturing, but the aluminum content in the mixture is kept below the stoichiometry point. Therefore, no surplus aluminum in molten state is produced by the detonation of “aluminized” explosives. So it is not possible to utilize the Al—H2O reaction and in fact it is not the intent of using “aluminized” explosives in engineering practice.
An explosive mixture that can output molten aluminum upon detonation of the mixture to induce an Al—H2O reaction is particularly useful for some applications where a secondary explosion event is needed to enhance the mechanical effects created by the primary detonation of the said explosive mixture. In
In
In the applications described above and illustrated by
Explosive devices made using the present invention can also be used in in-situ coal gasification. U.S. Pat. No. 4,109,719 to Martin et al. discloses a method to gasify in situ coal that involves the use of explosives to improve the permeability of coal seams to be gasified. A mixture of an explosive (or an oxidizer) with a surplus amount of aluminum in stoichiometry of the present invention used in presence of water would be particularly suitable for this kind of applications. The Al—H2O reaction releases much more energy than conventional explosives. When used for in situ coal gasification, this part of energy along with the great amount of gas generated would significantly improve the permeability of a coal seam being treated. Similarly, a water solution of oxidizer can be used in place of plain water to increase its reactivity with aluminum.
In another embodiment, the present invention concerns itself about the design of an explosive device used in the defense industry, such as a torpedo to be used underwater. According to the present invention, such an explosive device can be designed to create a “dual explosion” by using an HE/Al mixture as explosive load in which Al is surplus in stoichiometry. The high explosive can be any commonly used military explosive such as RDX, HMX, PETN or TNT etc. The first of the said “dual explosion” is the detonation of the said HE/Al mixture and the second being the Al—H2O reaction. As described previously in the present invention, for such a “dual explosion” event, the second explosion can release much more energy than the first one. When this concept of the present invention is used in the design of an explosive device like a torpedo, to achieve the same energy level the payload of the device that needs to be launched and propelled toward a target can be significantly reduced. With its huge amount of energy release and hydrogen gas generated, the said second explosion will greatly enhance the mechanical effects created by the first explosion in the target. Additionally, similar to the shaped charge designs as described in the class 1 application embodiments, a torpedo can also have a shaped charge capable of projecting molten Al into a perforation created by the first explosion in the target and then inducing an Al—H2O explosion locally within the target, further piercing and fracturing the target that has been penetrated by the said first explosion.
The above description is intended in an illustrative rather than a restrictive sense, and variations to the specific configurations described may be apparent to skilled persons in adapting the present invention to other specific applications. Such variations are intended to form part of the present invention insofar as they are within the spirit and scope of the claims below.
A. U.S. patents
26. U.S. Pat. No. 6,142,056, R. P. Taleyarkhan, Variable Thrust Cartridge, Nov. 7, 2000
B. Publications
Watson, S. C. et al., Liquid Propellant Stimulation: Case Studies in Shallow Appalachian Basin Wells, May 1986, Society of Petroleum Engineers, SPE 13776
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| Number | Date | Country | |
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| 20030037692 A1 | Feb 2003 | US |
