Patent Application
20110067854
1. Field of the Invention
This invention relates generally to perforating well casing, and in particular to an improved apparatus for perforating casing and fracturing multiple formations of highly deviated oil and gas wells in a single trip. More particularly, this invention relates to an improved electronic downhole release tool and actuation circuit therefore that is compatible with multiple select-fire perforating guns.
2. Background Art
Referring to
Perforating guns (14) are often deployed using wireline techniques, in which a wire rope or an armored electrical cable (8) is used to suspend the tool in the well bore. Occasionally, as illustrated in
An improvement over the mechanical weak link is an electrically actuated release tool (10). The release tool (10) is located above the perforating gun (14) (and typically below a casing collar locator (13), sinker bars (12) and the wireline cable head (11)). The release tool (10) has two halves and uses current-activated explosive charges to shear a tension stud (21) to separate its upper portion (10A) from its lower portion (10B). In this manner, the wireline (8) and upper tool string above release tool (10) is, by electrical actuation, severed from the lower portion of the tool string below the release tool (10). The release tool (10) is designed so that when it is parted, the exposed upper end (20) of the lower tool string has a profile that facilitates the fishing process. As electric wireline perforating guns (14) are typically activated by positive DC voltage, the release tool (10) uses a negative DC voltage triggering source. Release tools (10) as described above are available from High Pressure Integrity, Inc. of New Orleans, La., for example.
In many wells it is desirable to perforate casing over greater distances in the wellbore than can be accommodated by one perforating gun. To avoid running perforating guns and withdrawing the spent charges from the wellbore repeatedly, it is advantageous to place a number of perforating charges or groups of charges in the well simultaneously. Select charges are individually fired as the perforating guns are moved along the cased borehole. This technique is called “select-fire,” and it is known in the art.
Examples of apparatus for selectively firing perforating charges are disclosed in U.S. Pat. Nos. 5,531,164 issued to Mosley on Jul. 2, 1996; 5,700,969 issued to Mosley on Dec. 23, 1997; and 7,387,162 issued to Mooney, Jr., et al. on Jun. 17, 2008, which are incorporated herein by reference. The electrical circuits in the devices are designed such that charges are fired sequentially by alternately applying negative and positive electrical voltages to the device.
Although most other electric wireline tools are powered with positive voltage, select fire perforating guns typically use both positive and negative voltage to selectively control the firing process. Thus, select-fire perforating guns have heretofore not been used with negative-voltage actuated electric release tools because of the conflicting operating voltages of the devices. Although additional conductors can be provided within the wireline to remedy conflicting voltages, such a solution is often not cost-effective, particularly given the capital costs in replacing existing wireline cable. As a result, if a select fire perforating gun becomes stuck down hole, wireline retrieval is generally limited to reliance on a weak point built into the system to allow the wireline to be pulled free by breaking the weak point.
However, when down hole tools are deployed in a highly deviated wellbore or a horizontal wellbore it may be extremely difficult to pull directly on the rope socket with sufficient force to part the weak link, because the wireline friction due to contact with the deviated bore hole becomes great. Therefore, as select-fire perforation becomes more prolific, it is desirable to provide the combination of an electric release tool with multiple-charge, select fire, perforating guns to provide for efficient perforation operations, particularly in highly-deviated well bores.
3. Identification of Objects of the Invention
A primary object of the invention is to provide a method and apparatus for performing electric wireline operations, especially select-fire perforating operations, with the ability to activate a release tool using either positive voltage or negative voltage.
Another object of the invention is to provide a method and apparatus for allowing a wireline operator to release a select-fire perforating gun from the wireline by electronic means rather than mechanical pulling on the rope socket.
The objects described above and other advantages and features of the invention are incorporated in a method and a wireline system that allows the wireline operator to release the down hole tools from the wireline on demand by using an electronic release tool as opposed to breaking a weak point by pulling on the wireline, regardless of downhole tool configuration. This ability allows the wireline operator to deploy the tools with a much stronger weak point and allows the tools to be released electronically instead of breaking a weak point, which can be difficult in a highly deviated or horizontal wellbore.
In a preferred embodiment, the system includes a downhole string having an electric release tool and multiple select-fire perforating guns. The release tool employs operating circuitry that allows actuation of the release tool by either a positive or a negative voltage at an absolute magnitude greater than the absolute magnitude of positive or negative voltages used to arm or fire the perforating guns.
The invention is described in detail hereinafter on the basis of the embodiments represented in the accompanying figures, in which:
The perforating gun select fire circuitry 102 preferably consists of a series of blasting caps, squibs, or other ignitors 111, 112, 113, 114, 115 for detonating the perforating charges. Each blasting cap 111, 112, 113, 114, 115 within the series is triggered by a DC voltage of alternating polarity from the adjacent blasting caps in the series. Each blasting cap 111, 112, 113, 114, 115 preferably has an associated arming circuit that typically consists of a magnetic latching relay 121, 122, 123, 124, 125, 126 and a photocell 132, 133, 134, 135, 136, respectively. The magnetic latching relays 121, 122, 123, 124, 125, 126 are connected to form a cascading series, with the arming and triggering control voltages initially passing through each relay in the cascade.
The cascading relays 126 in the select fire circuitry 102 are connected in tandem with two release tool arming relays 201, 202 and to an input node 104. Control voltage from the surface is transmitted by wireline to the input node 104 of release tool actuation circuit 101, which in normal mode of operation is conducted along the cascading series of relays 126, 125, 124, 123, 122, 121.
Normal operation of the select fire circuitry 102 is now described. Select fire circuitry 102 includes an optional ignitor 105 for setting a bridge plug. Because relays 201, 202, 126, 125, 124, 123, 122 and 121 are initially in the unlatched or reset position, a direct signal path connects node 104 to ignitor 105 through the cascade of relays. Setting tool ignitor 105 is fired by applying a voltage of approximately −100 VDC at input node 104. Therefore, there is about a 0.7 volt drop across the forward-biased diode 106, a 10V drop across zener diode 107, and a 89.3V drop across ignitor 105, which causes the setting tool to stroke and set the bridge plug, as is well known in the art.
While setting the bridge plug, no current passes through the coils of the relays. When the −100 VDC bridge plug setting control voltage is applied at node 104, blocking diode 108 prevents current from flowing through the latching coil of arming relay 121. Insufficient current flows through the latching coils to switch any of the arming relays 122, 123, 124, 125, 126, because photocells 132, 133, 134, 135 and 136, which are in darkness, all have a large resistance—on the order of 1 MΩ, for example. Blocking diode 144, which is reverse biased, prevents current from flowing through the latching coil of release tool actuation relay 202. Finally, zener diode 141, which has a breakdown voltage of 500V, prevents current from flowing through the latching coil of release tool actuation relay 201.
After the bridge plug has been set, or if it is not desired to set a bridge plug, the firing circuit for gun number one is armed by applying +100 VDC at node 104. Diode 108 becomes forward-biased, zener diode 109 enters the breakdown region of operation, and current flows through the latching coil of arming relay 121 and through the 1 kΩ resistor to the circuit ground. The latching coil causes the relay contact to switch to the latched position as shown in
Note that the +100 VDC does not actuate ignitor 105 (if it has not been previously actuated to set a bridge plug), because blocking diode 106 is reverse-biased. Likewise, photocells 132, 133, 134, 135, 136 prevent arming relays 122, 123, 124, 125, 126 from latching, zener diode 143 prevents release tool relay 202 from latching, and blocking diode 142 prevents release tool relay 201 from latching.
Once the firing circuit for gun number one is armed (i.e., relay 121 is in the latched position), application of −60 VDC at node 104 will cause diode 151 to become forward-biased, zener diode 161 to enter the breakdown region, and a voltage drop of approximately −49.3V across blasting cap 111. The voltage drop across blasting cap 111 causes gun number one to fire.
As with the previously applied negative bridge plug setting voltage, the negative gun firing voltage does not switch relays 201, 202, because of zener diode 141 and blocking diode 144, respectively. Nor does the −60 VDC gun number one firing control voltage latch arming relays 123, 124, 125, 126, because of the high resistances of photocells 133, 134, 135, and 136, respectively. However, photocell 132 is physically disposed near to blasting cap 111 so that the flash of light from the primer cord of blasting cap 111 will shine upon photocell 132. In this manner, as gun number one fires, illuminated photocell 132 becomes about one thousand times more conductive, for example. Subtracting a breakdown voltage drop of 50V across zener diode 172, there exists a 10V drop across the series combination of photocell 132, a 1 kΩ resistor, and the latching coil of relay 122. When photocell 132 is illuminated, sufficient current flows through the latching coil to switch relay 122 and thereby arm the gun number two firing circuitry, as shown in
Referring to
This process of firing and arming the next gun in the sequence may continue along the cascade for as many guns as are equipped on the down hole tool.
The release tool circuitry 101 is preferably connected at the input to the cascade of gun firing circuitry 102 regardless of how many guns are employed. In normal operation, release tool actuation relays 201 and 202 are never latched. However, if the tool becomes stuck, or it is otherwise necessary to electronically actuate the release tool to sever the wireline connection to the perforating guns, application of either +500 VDC or −500 VDC to node 104 will electrically disconnect the gun firing circuitry 102 from input node 104 and arm the release tool ignitor 145.
In operation, the release tool circuitry 101 works as follows: Referring to
Referring to
Optional reset circuitry may be provided. If after latching either release tool relay 201 or 202 it is desired to resume perforating operations without releasing the tool, voltage may be applied to separate reset coils in relays 201, 202 via reset node 103, which will reset the tool to its previous state without firing release tool ignitor 145 or any of the perforating guns.
In a preferred embodiment, release tool relays 201, 202 are double-pole double-throw high temperature magnetic latching relays such as the 422H relay, available from Teledyne® Relays. However, other suitable relays may be used. As selection of electronic and electrical components that are suitable for downhole use is a known skill of routineers in the art, further detail is not provided herein.
The Abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of the technical disclosure, and it represents solely a preferred embodiment and is not indicative of the nature of the invention as a whole.
While some embodiments of the invention have been illustrated in detail, the invention is not limited to the embodiments shown; modifications and adaptations of the above embodiment may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the invention as set forth herein:
