Ammunition and explosives – Igniting devices and systems – Ignition or detonation circuit
Reexamination Certificate
2000-10-12
2002-10-29
Jordan, Charles T. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Ignition or detonation circuit
C102S218000
Reexamination Certificate
active
06470803
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an apparatus and method for remotely activating blasting devices. Such an apparatus and method may be used, for example, in oil and gas well production in other industries in which remote initiation of explosive devices occurs.
BACKGROUND OF THE INVENTION
In the production of oil and gas from underground wells, it is known to convey a perforating gun on a wireline down a bore hole of a well to a position where an oil or gas bearing stratum is located, and then to detonate shaped charges in the perforating gun. The shaped charges penetrate the formation, facilitating the entry of oil or gas into the well.
Safe and reliable initiation of perforating guns or other firing devices in the well-bore, far removed from the surface, has been a continuing source of design challenges. The explosive train in the perforating gun normally comprises a detonator for setting off a detonating cord. The cord in turn detonates a series of connected shaped charges. The detonator is the first element in the explosive train and is normally the most sensitive to external stimulation. Generally speaking, the safety level of the perforating gun is primarily determined by the safety level of the detonator used. Bridge wire electric detonators have been, and are widely used. When an electric current of sufficient strength is applied to its lead wires the bridge wire is heated and ignites the pyrotechnic material surrounding it. This in turns sets off the primary and secondary explosive charges in the detonator.
An inherent problem with bridge wire detonators is the risk of unintentional detonation which may arise from stray currents. A bridge wire detonator does not possess the ability to distinguish between firing current and hazardous electric energy that reaches its lead wires. Typical sources of electrical interference which may cause unintentional detonation are communications equipment, whether cellular telephones or radio, standard 220V, 50 Hz or 110V, 60 Hz line current, electrostatic discharges and lightning. At present when bridge wire detonators are used for perforating jobs, typical safety measures include shutting down electric sources in the well rig environment and turning off communication facilities. It would be advantageous to provide the oil industry a method of initiating perforating guns and a detonator which reduces or eliminates the need to suspend the use of without suspending the electric devices and communication radio in the well rig environment. An additional problem concerns unauthorized use of the detonators. Lost, stolen or mishandled detonators that can be set off by commonly available power sources, whether deliberately or accidentally used, may pose a significant danger. It would be advantageous to have a detonator which will resist detonation except when initiated by an authorized person using a specially designed blasting machine.
A known approach to the problem of unintentional detonation is to add extra resistance in series with the bridge wire, making a “resistorized detonator”. A higher voltage than would otherwise be required is used to fire a resistorized detonator, making it more difficult to set off. However, the magnitude of the electric current needed to initiate the detonator remains the same as non-resistorized detonators.
Another approach is to increase both the voltage and electric current needed to fire the detonator, so that they substantially exceed the upper limit of routine well rig electrical signals like the exploding bridge wire detonator or exploding foil detonator. This kind of exploding bridge wire or exploding foil detonator is disclosed in U.S. Pat. No. 4,777,878 of Johnson et al. issued Oct. 18, 1988 and U.S. Pat. No. 5,505,134 of Brooks et al., issued Apr. 9, 1996. Another approach, as shown in U.S. Pat. No. 4,708,060 of to Bickes et al., issued Nov. 24, 1987 and U.S. Pat. No. 5,503,077 of Motley issued Apr. 2, 1996, employs a semi-conductor bridge wire to achieve improved safety.
Still another method is to isolate the bridge wire, by employing a small transformer in the detonator. The load, generally the bridge wire of the detonator, is connected to the secondary winding of the transformer to form a loop and is electrically isolated from the primary winding of the transformer. The core material of the transformer is chosen to attenuate, or eliminate, spurious electrical power and radiofrequency signals and to respond to firing currents falling within a predetermined range of magnitude and frequency. A blasting machine provides electric current in the predetermined range needed to fire these inductive detonators.
A number of embodiments of transformer based detonators are shown in U.S. Pat. No. 4,273,051 of Stratton, issued Jun. 16, 1981. All of those embodiments employ some form of auxiliary energy dissipation means, whether a series or other leakage inductance, a fusible link, or a resistor in parallel with the primary winding.
Another example of a ferrite core, broad band attenuator is shown in U.S. Pat. No. 4,378,738 of Proctor et al., issued Apr. 5, 1983. U.S. Pat. No. 4,441,427 of Barrett, issued Apr. 10, 1984 discloses an oil well detonator assembly that uses ferrite materials to protect against radio frequency energy.
U.S. Pat. No. 4,544,035 of Voss, issued Oct. 1, 1985 discloses the use of two coils to initiate a detonator in a perforating gun without the coupling of magnetic materials. U.S. Pat. No. 4,806,928 of Veneruso, issued Feb. 21, 1989 discloses the use of coil assemblies arranged on ferrite cores for data transmission between well bore apparatus and the surface and which may also be used to fire perforating guns.
U.S. Pat. No. 3,762,331 to Vlahos, issued Oct. 2, 1973 discloses a firing circuit for detonators that uses a step down transformer having a voltage reduction of roughly 100:1 and a secondary coil having only 1 or 2 turns. It operates at a voltage between 60V and 240V and at a signal frequency of the order of 10 KHz. It is powered by a battery in parallel with a storage capacitor, which discharge through an inverter circuit which includes a solid state oscillator and a transformer for stepping up the resulting a.c. voltage to the desired level. This patent also discloses the use of shunt and series capacitance connected to the primary winding of the detonator, and a large step down at the detonator transformer. U.S. Pat. No. 4,145,968 to Klein, issued Mar. 27, 1979 describes primary and secondary windings and a fixed magnetic screen designed to be saturated in the presence of the magnetic flux generated by the primary winding. U.S. Pat. No. 4,297,947 to Jones et al., issued Nov. 3, 1981 discloses the use of a toroid or a magnetic core with removable parts as transformer cores to couple a relatively short (100 m) firing cable and a number of detonators.
U.S. Pat. No. 4,304,184 to Jones issued Dec. 8, 1981 discloses a transformer circuit whose primary and secondary windings are not completely isolated. Instead, they are coupled not only magnetically but also electrically. While this configuration may provide protection against hazardous electrical currents at low values and low frequencies, the safety features would be more satisfactory if the two windings were completely isolated electrically. None of the transformer-based detonators noted above appear to be suitable for oil well use.
A detonator that can be used in the oil industry at great depth poses special requirements for the coupling transformer. The electric energy supplied from the surface is transmitted along the wireline cable down oil wells as deep as 7,500 m. The cable used for well logging and casing perforation may not be designed for high frequency transmission. The distributed shunt capacitance along the cable is in the order of 0.15 uF/Km. The attenuation for high frequency electrical energy is as high as 3 db/Km (at 20 KHz). Consequently, for effective power transmission along the wireline, a relatively low frequency is preferred. However, electric currents having a frequency lower
Liu Liqing
Lussier Michael Norman
Jordan Charles T.
Matz Daniel
Prime Perforating Systems Limited
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