Electro-hydraulically Controlled Perforator

Abstract

A plurality of explosive charges are positioned in an instrument to be lowered into a well. An electrical detonation system is connected to each explosive charge. A hydraulic system controls switches in the electrical system.

Description

BACKGROUND OF THE INVENTION

This invention relates to the art of producing oil and gas and more specifically to a switching system for well tools. The invention has specific utility as a detonating device for actuating a perforator used in the oil well art but may be used as an actuator in other systems.

It is common practice in the completion of oil and gas wells in the petroleum industry to perforate the well casing to bring the well into production or to establish communication with formations behind the casing through these perforations for remedial work on the well. These perforations are normally made with either a shaped charge perforator or a bullet perforator. The shaped charge perforator can be either a hollow carrier type perforator or a capsule type perforator. The hollow carrier gun consists of a hollow tube containing one or more shaped charges. This hollow carrier is retrievable after the shaped charges have been fired and may either be reusable or expendable. The capsule type shaped charge gun consists of individual shaped charges encased in their own pressure containers. These capsule charges are mounted in a carrier or attached together by other means and lowered into the well to perforate the well casing. The bullet type perforator consists of either a solid gun body machined to allow bullet loads to be inserted into it at intervals or a multiplicity of individual guns attached together to form a longer gun.

There are many advantages in maintaining simplicity in a perforator. Probably one of the most important factors is safety. The dangers inherent in handling explosive charges are reduced by maintaining a system that can be understood by the personnel handling them. In addition, by reducing the number of elements in a perforator there is less chance that any one element will be defective. Other than safety to the operating personnel, it is important that the perforator be fired only at the desired location in a well and that accidental firing be avoided. Somewhat paralleling the safety factor is the reliability factor. It is believed that by reducing the number of elements in a perforating system the reliability of the overall perforator is increased. The cost factor should not be overlooked and in that regard simplicity is a key in reducing expenses. Another extremely important factor is size. Many of the perforating tools must be compact and by reducing the number of elements involved, this compactness is obtained.

The present invention provides an electrohydraulic arming and timing device that will provide a means of selectively arming and timing perforators so that they may be fired individually or collectively. The invention provides a perforating system that has the advantages of simplicity, safety, reliability, economy, size and few separate elements. The present invention may also be used as a timing and actuating device in other well tools.

Description of the Prior Art

It is well known in the oil and gas well art that either of the three types of perforators; hollow carrier shaped charge, capsule shaped charge or bullet perforators may be selectively fired as individual shots and also selectively fired as individual guns or banks of shots. It is also well known that shaped charges and bullet guns be combined into one tool and that both a shaped charge and a bullet gun may be fired from each individual tool body in order to have a combination of each in one shot.

Detonation of prior art perforators has generally been controlled by either mechanical or electrical systems. The mechanical systems of detonation control are illustrated by the conventional "Go-Devil" which is a weight that is designed to be dropped down the well guided by the tool suspending line to operate the trigger mechanism of the perforator. The electrical systems are represented by perforators using a control device such as an electrically operated solenoid to actuate a switch or series of switches thereby conducting current to blasting caps which detonate the individual explosive charges, perforators that use an electrical motor drive to actuate a switch in order to set off the explosive charges, the use of electrical resistors to direct an electrical current directly to the various blasting caps, or the use of diodes to direct the electrical current to combinations of charges. Some of these systems also use positive and reverse polarity of the electrical circuit in conjunction with their individual system.

The prior art systems have their particular advantages and limitations. Some of the prior art devices require a multiplicity of electrical cables. Other prior art devices require somewhat complicated electrical systems that are unreliable, expensive and are a burden to the field people in charge of carrying out the perforating operation. The mechanical systems also suffer from the disadvantage of being somewhat complicated and unreliable. Many of the prior art devices run into difficulties when operated in high temperature and high pressure environments.

The present invention provides a hydraulic arming and timing device that can be used between any of the above-mentioned guns to provide a means of selectively arming and timing any of the above type perforators so that they may be fired individually or collectively.

The present invention may also be used as an actuator in other systems by building up pressure to rupture a bulkhead or seal and provide a path of communication for this pressure thereby actuating the hydraulic timing and switching device. This could either be a fluid pressure or gas pressure to actuate the hydraulic timing and switching device and may be accomplished by the timing device having its own hydraulic fluid reservoir.

SUMMARY OF THE INVENTION

The present invention utilizes an electrohydraulic switching and timing system that eliminates the need for electrical or mechanical control devices for selectively firing the charges of a perforator. The electrohydraulic arming and timing system also provides a device using only one electrical conductor in a selective firing system. The present invention eliminates the need for delayed detonators or other timing devices in the select fire system. In small diameter tools the present invention makes more efficient use of available space. In larger perforating devices the complicated electrical and mechanical devices can be eliminated. One embodiment of the present invention utilizes a single hot thru-wire from the control unit located at the surface to the downhole instrument. Hydraulic units in the subsurface instrument time and actuate the explosive charges. Another embodiment is self contained with the electrical power source provided in the tool housing. The invention may also be used as a timing and actuating device in other well tools.

It is, therefore, an object of the present invention to provide a perforating system that includes an improved switching system for arming and firing of the explosive charges. It is a still further object of the present invention to provide a perforating system that includes an electrohydraulic means of arming and firing the explosive charges.

It is a still further object of the present invention to provide a perforator that can be used in small diameter wells. It is a still further object of the present invention to provide a perforating system that can be used in environmental conditions that have been considered difficult for selective firing systems of the prior art.

It is a still further object of the present invention to provide a perforating system that utilizes either the hydrostatic head of the well fluid or the pressure of formation fluids or gases to fire the explosive charges.

It is still a further object of the present invention to provide a hydraulic timing device that can be used with a perforating system or any other system that requires delayed actuation.

The above and other objects and advantages will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a perforator of the present invention suspended in a well.

FIG. 2 shows one of the hydraulic means for arming and timing the explosive charges.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, the downhole instrument 11 is shown suspended in a well 12 by cable 13. A surface control section 14 is provided in a conventional manner. A conventional means 15 of positioning the downhole instrument in the well is also provided. Cable 13 supports the downhole instrument and includes a conductor from the surface control section 14. Explosive charges 16, 17, and 18 are provided in the downhole instrument and may be any of the conventional explosive charges used in perforators. It is to be understood that three charges are shown for illustration purposes but that any number of charges may be used without departing from the invention. It is also to be understood that other forms of perforators such as bullet or jet perforators could also be used in place of explosive charges 16, 17 and 18 without departing from the scope of this invention. A bull plug 19 is provided in the downhole instrument 11 to seal the bottom of the hollow carrier gun shown.

A means of detonating the various explosive charges 16, 17, and 18, either collectively or individually, is provided in the downhole instrument. This means includes electrical blasting caps 20, 21 and 22 connected to each individual explosive charge 16, 17 and 18. A thru-wire 23 extends from cable 13 to each individual blasting cap 20, 21 and 22. Blasting cap 22 is directly grounded to the subsurface instrument 11 by ground 24. Ground wires 25 and 26 are connected to the subsurface instrument 11 and may be switched into connection with blasting caps 20 and 21 by means of the hydraulically operated switches 27 and 28.

Referring now to FIG. 2, one of the electro-hydraulically controlled arming and timing devices is shown in greater detail connected to a blasting cap through the normally open switch 27 and the thru-wire 23. The ground wire 29 of the blasting cap is connected to the normally open switch 27. The hot wire of the blasting cap is connected to thru-wire 23. It can be seen that movement of piston 30 in an upward direction will close the normally open switch thereby arming the blasting cap and explosive charge. The cap and charge may then be fired from the surface control section by energizing thru-wire 23.

Movement of piston 30 is controlled hydraulically. The bottom explosive charge 22 is detonated by control from the control section 14. After explosive charge 22 is fired, the hydrostatic head of the well fluid is transmitted to the hydraulically operated switch 27. The hydrostatic head or gas pressure is transmitted to piston 31 through an opening in the bottom of electrohydraulic arming and timing device 40. The hydrostatic head or gas pressure is transmitted to piston 31 by movement of primary piston 32. It should be noted that an orifice and/or a filter element could be substituted for primary piston 32. As piston 31 is moved upward, fluid in reservoir 33 is forced through orifice 34 in timing element 35. The fluid exerts pressure on piston 36 and actuator 30 forcing it upward thus closing the normally open switch 27.

Orifice 37 connected to orifice 34 provides room for fluid expansion or fluid movement during firing. More room for fluid expansion or fluid movement during firing is also provided in the void directly below piston 36. Orifice 37 also is used to provide a means of bleeding the hydraulic system should a buildup of pressure occur. This is accomplished by unscrewing cap 42 so that the entrapped pressure may be bled off. This same orifice 37 can also be used to either add or remove fluid from the hydraulic reservoir 33 after determining exactly what temperature the tool is to be run. By knowing what fluid is being used in the hydraulic reservoir it is possible to determine how much fluid expansion can be expected at a given temperature. It is to be understood that orifice 37 could also be located to connect reservoir 33. Springs 38 and 39 prevent shock of detonation from the lower explosive charge from moving the pistons and thus closing the normally open switch.

Timing element 35 is easily removed and may be replaced with a timing element having a different size orifice thus requiring a different length of time for the fluid to be forced from reservoir 33 and move piston 36 upward. By choosing different timing elements 35, it is possible to regulate the time required to close the normally open switch 27. This feature makes it possible to regulate the timing of the switch so that the time can be chosen for either high or low pressure wells and high or low hydrostatic head.

It can be seen from the above description of the invention that a perforating tool may be selectively fired using this invention. Using FIG. 1 as an example, the bottom charge 18 would first be detonated from control section 14 because the bottom blasting cap 22 is connected directly to thru-wire 23 and the ground wire of blasting cap 22 is connected directly to ground. The bottom charge 18 could then be detonated when desired from control section 14 by pressing the firing switch in control section 14. After the charge fired and penetrated the subsurface instrument housing 11, the hydrostatic head of the well fluid or gas pressure in the well would then work on the electro-hydraulically controlled arming and timing device 40 and move piston 30 upwards, arming blasting cap 21. When this occurs, charge 17 may be detonated from control section 14.

It can also be seen that any downhole tool can also be operated with the same principle used to fire the perforating tool.

The electrohydraulic switch 40 shown in FIG. 2 could also be incorporated in a downhole tool other than a perforator to allow the different operations of the tool to be timed by proper selection of timing elements 35. In this embodiment, the thru-wire 23 (shown in FIG. 2) is connected to a power source in the well tool. The blasting cap 21 is replaced by the appropriate actuating device for the well tool. When piston 30 closes the normally open switch 27, the actuating device is energized and the desired performance of the well tool obtained.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A well tool comprising:

a housing that can be lowered into a well;

a multiplicity of operating means in said housing for creating a preselected operation on the well;

a multiplicity of actuating means in said housing for actuating said operating means, each of said actuating means including

an electrical circuit with a normally open switch that actuates said operating means when closed;

a first piston slidably received in said housing capable of closing said normally open switch;

a second piston slidably received in said housing responsive to fluid pressure;

passage means between said first piston and said second piston for providing fluid communication from said second piston to said first piston; and

an interchangeable timing element positioned in said passage means, said timing element having an orifice that regulates the length of time required for fluid to move in said passage means and act upon said first piston to close said normally open switch.

2. The well tool of claim 1 including a second orifice in fluid communication with said orifice to prevent premature closure of said normally open switch.

3. The well tool of claim 2 including springs connected to said first and second pistons to prevent premature closure of said normally open switch.

4. A hydraulically controlled detonator for a well perforator, comprising:

a housing;

a normally open switch in said housing;

a first piston slidably received in said housing capable of closing said normally open switch;

a second piston slidably received in said housing, responsive to fluid pressure;

passage means between said first piston and said second piston for providing fluid communication from said second piston to said first piston; and

an interchangeable element in said passage means between said first and second piston with an orifice therethrough.

5. The hydraulically controlled detonator of claim 4 including a second orifice in fluid communication with said orifice to prevent premature closure of said normally open switch.

6. The hydraulically controlled detonator of claim 5 including springs connected to said first and second pistons to prevent premature closure of said normally open switch.