A single-wire selective perforation system having firing safeguards.

This invention relates to perforating gnns used in well completion operations. More particularly, the présent invention relates to a single-wire sélective gun perforating System capable of selecting and firing in an arbitrary order each gun in a plurality of guns connected in a firing string. Typical prior-art perforating guns generally used m well completion operations consist of a plurality of guns connectée vertically to form an assembly of firing string suitable or lowering into a well borehole. Each gun will contain one or W more shaped charges. Each charge will hâve a detonator or blasting cap connectable to a firing wire for receiving an electrical firing puise to detonate the charges.

It is often désirable in well completion operations to hâve each gun selectable for firing rather than having 15 ail guns firing at the same time. Firing ail guns at the i same time produces perforation spacing detèrmined by the spacing oï the guns in the string, usually in a elosely-spaeed arrangement. On the other hand, individual détonatioïi of tfie charges permits perforations to be made at various e^leàtê-⁴ depths, and in various selected (often widely separated) zones* As each charge is detonated, the string can be repositioned to the next level where another perforation is desired, and another gun fired. This process can continue until the proper perforation spacing is obtained with the 25¹ desired number of shots. A further benefit is obtained from. the single détonation of the — vérification that each gun fired and that the proper number of perforations was obtained.

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However, the sélection and firing of a single gun in the string may involve failures which would prevent the proper firing of the modules. A failure could occur in the gun to be selected that would prevent it from firing; a failure could occur causing the firing of a wrong gun which will be eventually detected; or a failure could occur which caused the undetected firing of a wrong gun. Any one of these failures» especially in many of the prior art devices, would defeat the purposes o£‘ having sélective firing of the guns in the perforation operations.

Many sélective firing Systems and methods hâve been used in the prior art to select a gun for firing from among the plurality of guns in the string. U.S. Patent 4,051,907 discloses one suçh system comprising a surface control unit for controlling the sélection and firing of the guns in a firing string comprised of a subsurface master unit operatively connected to a plurality of identical slave sub units or firing modules that may be armed.' and fired in an arbitrary order under control of the master unit and an operator.

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Sequencing through the firing modules for sélection of a module to be fired is under control of the surface located control unit. The sélection process begins at the uppermost firing module closest to the master unit. Each 5 firing module contains a puise counter which receives puises from the surface via the master slave unit when • that module has been connected to the firing line power.

A predetermined number of puises (8 puises) sequences the counter through nine counts. At selected counts, certain 10 operations are effected in the module. For example, at count 4 a current puise is placed on the firing line, at count 5 a switch is closed to charge a firing capacitor with the voltage currently on the firing line, at count 6 a firing puise whose amplitude is equal to the current 15 voltage on the firing line is applied to a blocking zener diode which is connected to a firing switch (the firing switch is not closed because the voltage on the firing line is not greater than the break over voltage of the zener diode), and at count 9 a pass-through switch is· 20 closed to .pass the firing line power on down to the next lower module in the string.

The above described process is then repeated for, the next module \to be connected to the firing line power. As 25 long as eight puises are issued without a change in the firing line power, the sequencing through the firing modules will continue, one at a time. When the firing module to be selected and fired is reached, only six puises will be issued by the master unit under control of 30. the operator. These six puises take the puise counter in the firing module to be selected to a count of five which closes the switch which connecte the firing line to the firing capacitor. At this point, the operator at the surface activâtes the arm. switch which raises the firing 35 line voltage, and thus the firing capacitor, to a value

-⁴- 0 7480 sufficient to detonate the charge when the capacitor is discharged into the blasting cap. Six puises arm the firing module with one more puise causing a closing of the firing switch to occur since the firing line voltage is now greater than the blocking zener diode voltage to permit the firing switch to be closed. Closure of the firing switch connects the firing capacitor across the blasting cap circuit.

These prior-art sélective perforating Systems, such as that disclosed in 4,051,907, suffer from several disadvantages. One disadvantage is the need for élaborate surface and subsurface circuitry with continuous supervision and interaction required between the surface and subsurface circuitry during the sélection process to effect the sélection and arming of the firing modules. Another disadvantage is that seauencing through the firing modules is solely under control of the surface equipment. Another disadvantage is the lack of any safeguards for de.tecting faults in the firing string which will prohibit the proper firing of a single selected module.

Accordingly, it would be advantageous to provide a single-wire sélective perforating System which provides for the automatic seauencing through the firing modules in a sequence, one at a time, under control of the modules themselves until a module to be selected is receiving power from the firing line.' At that time the module can be^selected and armed for firing. It would also be advantageous to provide a single-wire sélective perforating System which includes safeguards for determining if a single module has been connected in the sequence to the firing line and is operating within predicted power limits thereby insuring that one module is being selected for

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-5SUMMARY OF THE INVENTION

One aspect of the présent invention is directed to in a singleline sélective perforating System having a single firing line for electrically connecting a firing control unit to each of a plurality of shot modules, one at a time in a predetermined sequence, where each module is adapted for connecting the connected control unit to a next module, a method of selecting a module for firing characterized by the step of connecting each module one at a time in the predetermined sequence to the firing line under control of module active time intervals internally generated in the modules, where each module générates «its active time interval in response to being connected to the firing line with the next module in the sequence automatically connected to the firing line at the end of the active time for the last connected module if that module was not selected for firing during its active time interval.

Another aspect of the présent invention is directed to a.singlewire sélective perforating System for selectively detonating the charges in a plurality of firing modules, one at a time, comprising: (a) a control unit operatively connected to the modules by a single firing line which carries both power and control signais between said control unit and the modules; ànd (b) a plurality of selectable firing modules vertically connected one to another for form an elongated assembly suitable for lowering into a well borehole, the assembly including said control unit, and characterized in that each module, (i) containing at least one charge and where each module is automatically connected one at a time to the firing line in a predetermined sequence to receive power therefrom, and (ii) in response to receipt of power on the firing line, internally générâtes a module active time interval during which the module and its charge may be selected for firing by said control unit, each module not selected for firing during its active time interval automatically connecting the firing line to the next module in the sequence.

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BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the présent invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which;

Figure 1 is an illustration of the firing string for the présent invention suspended in a well borehole;

Figure 2 is a functional block diagram of an embodiment of the firing module illustrated in Figure 1;

A ‘ Figure 3 is a timing diagram illustrating operations of the présent invention for selecting, arming and firing a selected module of the type shown in Figure 2;

Figure 4 is a functional block diagram of another embodiment of the firing module illustrated in Figure 1; and

Figure 5 is a timing diagram illustrating operations of the présent invention for selecting, arming and firing a selected module of the type shown in Figure 4.

Similar reference numerals refer^to similar parts throughout the several views of the drawings.

=707480

BRIEF DESCRIPTION OF THE

PREFERRED EMBODIMENT ©F THE INVENTION

Referring now to the figures and-first to Figure 1, a firing string 10 according to the présent invention is shown suspended by a cable 12 in well borehole 1 having â well casing 2. The firing string 10 includes a control unit 14 connected to the cable 12 at the uppermost end. Control unit 14 functions to gene’rate the control signais, and firing line 3 power needed by the firing modules to select and arm their charges for firing. Connected one to another below the control unit 14 is a plurality of identical firing modules 5 to form an elongated assembly suitable for lowering into the well borehole 1.

Control unit 14 contains a current détection means 6 for detecting the amount of current in the firing line 3; a control signal generator 7 for generating control signais to the firing modules to select and arm for firing a module to be selected and to generate a firing puise to détonate the module selected and armed for firing; and, a controllable power supply 8 for generating the voltage and current needed to power the firing modules.

Each of the firing modules 5 contains at least one shaped charged 26 (See Figure 2) with an associated detonator 24 to form a shot or ' gun for blasting a hole through the well casing 2 into the subsurface formations. Also included in each module is a module logic circuit 18 which functions in coopération with the control unit 14 and the signais on

-807480 the firing line 3 generally indicated in Figure 1 by the segmented signal leads 16, 22 contained in each of the modules 5. As will be discussed below, the firing line from the control unit 14 to the various modules 5 consists of a,sériés of segmented leads which are eleçtrically connected together in sequence to form a single firing line 3 as the various modules are connected one at a time in a presser ibed sequence to the .control unit 14. Each module 5, when physically connected to another module in the string 10 makes electrical contact with a portion of the firing line of the module to which it is connected. That is, the portion 16 of the firing line of the module

/.· just connected makes electrical contact with portion.22 of the next higher module to which it is connected.

Still referring tç&gt; Figure 1, each firing module 5 contains a controllable switch.means illustrated as switches 20 and 21, which responds to the module logic circuit 18 to either pass' the input portion 16 of the firing line 3 coming into the firingmodule onto the. output portion 22 of the firing line 3 which passes the firing line power on down to the next module in the string (switch 20), or connects the input portion 16 of the firing line 3 to the detonator 24 of the shaped charge 26 (switch 21). If switch 21 is closed in a module, that module would be the module selected for firing and the., module logic circuit 18 of that selected module would inhibit further sequencing of lower modules in the string 10 by inhibiting switch 20;.from being closed to pass the firing line power on through to the next lower module. In those modules sequenced but not selected during their respective active, time intervals, the pass-thru switch 20 could also include switching to ground their detonator so that accidentai firing cannot occur.

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Sequencing of the selectable firing modules begins with the uppermost module connected to the control unit

14. The uppermost module receives power from the control unit 14 when power is first applied to the firing line 3.' 5 Thereafter, as each firing module complétés its sélection process and is not selected for firing, the next lower module in the string is then connected to the firing line. This*process continues until the lowermost module has executed its sélection sequence.

The sélection sequence for each firing module 5 is best described with reference to Figure 2 which illustrâtes the functional block diagram for a typical firing· module. Referring now to Figure 2, the input portion 16· of the 15 firing lïne 3 is connected to a constant current power supply 29 for regulating the voltage on the firing line 3 to produce the supply voltage for the circuits of the module. The firing line is also connected to a firing line puise detector 37. The output from firing line puise 20 detector 37 is connected to a flip-flop 41. Together, puise detector 37 and flip-flop 41 comprise a stop puise detector 34 for générâting a stop puise to terminate the module active time interval if the module is to be selected and armed for firing. The firing line puise detector 37 25 responds to voltage puises on the firing line to detect when the control unit 14 has issued sélection and,.arming puises on the firing line 3.

i

Also included in each module is a counter circuit means 32 which responds to an internai oscillator clock to produce internally to the module a module active time interval during which the sélection of the module for firing is possible. The oscillator clock 28, in con«“ junction with the number of bits in the binary counter 35 included in the counter means 32, détermines the length of •ίο07480 the module active time interval. A power reset puise generator 30 is also included in each module 5 for generating a resent puise upon the initial receipt of power on the firing line 16. The power resent puise initiâtes the start of the active time interval by resetting counter 35.

The power resent puise has an additional function of generating a current increase puise on the firing line 3 back to the control unit 14 to indicate that a next module has been connected to the firing line_; 3. &gt;This current puise is the identification puise for the module, and muât meet certain requirements. First, the magnitude of the increase in the firing line 3 current must be within a predetermined range to indicate that the just connected module is operating in acceptable limits and that only one module is responding to the firing line power. Second, the occurrence of the . identif ication^/'pulse must be within a predetermined window measured . from the last identification puise on the firing line.

The control means 14 includes (not shown) a means for detecting the amount of current on the firing line. There are several reasons for monitoring this current. First; by counting the number of identification puises generated on the firing line, the control means 14 can détermine which of the modules has just been connected to the firing line. In this manner, the module to be seleeted can be detected as the modules autoroatically sequence through their active times. The control means 14 also includes a means for generating both the sélection and arming signais as well as the firing puise Which will detonate the module which has been seleeted and armed for firing.·’

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Still referring to Figure 2, the stop puise detector 34 is shown comprised of a firing line puise detector 37 which responds to signais on the input portion 16 of the firing line 3, and a flip-flop 41 that, in turn, responds' to the output of the firing line puise detector 37 and the binary counter 35, to generate two control signais. First, •a STOP CLOCK signal is outputted by flip-flop 41 on line 50 to-’one input of an AND gâte 33. Also inputted to AND gâte 33 is the output from oscillator clock 28. AND gâte -.'JO 33, when enabled, outputs the clocking signal to counter

35. The signal STOP CLOCK functions as a disable signal to inhibit further clocking of the counter 35 when the sélection puise is received on the firing line 3.

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When the signal STOP CLOCK. goes to a logic zéro, AND gâte 33 will be inhibited from supplying any further clock signais to the counter 35. At the same time that STOP CLOCK goes to a logic zéro, the signal ARM CONTROL, also outputted by flip-flop&gt;41, goes to a logic one. ARM CON20 TROL appears on signal lead 39 to the firing switch 21. · The signal ARM CONTROL closes the firing switch 21 to connect the cathode of zener diode 43 to the detonator 24 associated with the shaped charge 26 of the module. The anode portion of the zener diode 43 is connected to the input portion 16 of the firing line 3. For this preferred embodiment of the invention, the sélection puise on ...firing line 3 also acts to arm the module for firing.

The improved single-wire sélective perforating System referred to above, has separated the sélection and arming functions to improve the feedback safeguards to avoid failures during firing that resuit in faulty operations.

Specifically, a single puise is used to select a module and a sequence of three arming puises is used to arm the module in a predetermined sequence. The first arming

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puise causes the module to be armed to produce a current increase in the firing line 3 current. This current increase must be within a predetermined range. A second arming puise will remove this current increase. If the value of the current increase is acceptable and the increase was cleared by the second arming puise, then a thitd puise is issued to arm the module for firing. The firing puise to detonate the charge can then be issued with the assurance that one and only one module will be 10 fired.

Still referring to Figure 2, the flip-flop 41 of the

X· stop puise detector 34 functions as a set-reset type flip-flop where the set signal cornes from the firing line’ 15 puise detector 37 and the reset signal cornes from the counter 35. The reset signal to flip-flop 41 is labeled ENABLE and is at a logic one state when the Q11 output from the 12-bit binary counter 35 is true. When the reset input to flip-flop 41 is at a logic one, the flip-flop can 20 be “set to a logic one by a puise on the set input.

Thus, a puise detected by the firing line puise detector 37 will cause flip-flop 41 to change states (logic zéro co logic one) only if the signal ENABLE on signal lead 46 from counter 35 is true. During the first portion of the 25 active time interval Êor the module, the signal ENABLE will not be at a Icgic one. After a certain number of clock puises hâve been counted, ENABLE goes true making the start of the second portion of the module active time interval. ït is during this second portion that the module may be selected and armed.

Also inputted to the AND gâte 33 is another output from the binary counter 35 (Q12) which represents the most significant bit from the 12-bit counter. The signal on 35 the Q12 output, PASS-THROUGH, also controls the passthrough switch 20 which functions to connect the input

-1307480 portion 16 of the firing line 3 to the output portion 22. Additionally, the signal PASS-THROUGH disables clock signais from the oscillator clock 28 from reaching the counter 35. As previously discussed, the flip-flop 41 enables the AND gâte 33 to pass clock puises from oscillator 28 to the counter 35 irrespective of whether any •puises are detected by the firing line puise detector diïring the first portion of the active interval.

The lapsing of the first portion of the time interval is indicated when the signal ENABLE on signal lead 46 goes to a logic one thereby permitting any subséquent puises detected by the firing line puise detector 37 to set the flip-flop 41 and disable AND gâte 33. In the event that no firing line puises are detected by detector 37 during the second portion of the active time interval, then the Q12 output of counter 35 will eventually go true and produce the signal PASS-THROUGH to inhibit further clocking of the counter 35. Simultaneously, the pass-through switch 20 is closed to pass the firing line power on to the next module down the sequence. Closure of the passthrough switch 20 represents the end of the sélection process for the module with the module thereafter connected to the firing line power. Further clocking of the counter 25 is inhibited until the module is reset by removal of power on the firing line 3.

The timing relationships between the signais of the control unit 14 and the plurality of firing modules

30- during the sequencing of the modules is illustrated in Figure 3. Referring now to Figure 3, the voltage and current on the firing line are illustrated for a typical sélection sequence involving three firing modules with the third module representing the module to be selected.

With application of power in the form of voltage and current on the firing line, module No. 1 will begin to

-1407480 internally generate its module active time interval. The active time interval for each module is illustrated in Figure 3 as composed of two portions, a first and second portions T1 and T2, respectively. The first portion T1 represents the time interval from the initial receipt of power in the module to the time when Q11 of binary counter 35 'goes true. The second portion of the time interval T2 represents the remaining portion of the active time interval and represents the time that Q11 from counter 35 is true. In other words, the end of the second portion T2 of each module time interval in indicated when·the Q12 output of the binary counter 35 goes true and Q11 goes false (a true state is represented by a logic one and a false state represented by a logic zéro).

Upon receipt of power by the module No. 1, an identification puise is generated on the firing line 3. The puise is shown as a current increase in the firing line current. The increase indicates to the çontrol unit 14 ' that a module has been connected to the firing line. If the amplitude of the current increase on the firing line for the identification puise does not fall within a predetermined range, the çontrol unit 14 will cease sequencing of the modules because a faulty operation, such as more than one module 5 responding to the application of power on the firing line 3 or that the module just connected is.-not operating within predetermined limit, is indicated. As the signal for the firing line current shown in Figure 3 indi-^!cates, there is an increase in the firing line current ëach time that another module is connected to the- firing line apart from the superimposed current increase puise for the identification puise. These increases in firing line current resuit because each module remains connected to the firing.line current at the end of its module active time interval and continues to draw current until reset by removal of the firing line power.

-1507480

For the example illustrated in Figure 3, at the end of the module active time interval for module t, its pass-thru switch 20 is closed to connect module 2 to the firing line power. As shown 'in Figure 3, module 2 and module 1 are now connected to the firing line cesuitingin a net increase in the amount of current on the firing ¹ line. This is generally illustrated as a step function increase. Superimposed on this step increase is the identification puise for module No. 2.

In addition to the identification puise amplitude falling within a predetermined range, the control unit 14 monitors the time interval as measured from the receipt of the last identification puise to receipt of .the ne&amp;t 15 identification puise, ünless each identification puise falls within a predetermined time window measured from the last puise on the firing line 3, the control unit 14 will terminate further sequencing of the firing modules because a faulty situation is;indicated.

An additional function of the identification puises to the control unit 14 is to function as a clocking puise to enable the control unit 14 to count which of the modules has just been connected to the firing line 3 power. Thus, 25 when the identification puise for module 3 is received' and the identification puise conditions are met, conttQ.l unit ' 14 will know that the module to be selected, module 3, has just been connected to the firing line 3.

M

As previously discussed, any puises occurring on the firing line during the first portion of the time interval will hâve no effect on the sélection and arming of a module. Only during the second portion of the active time interval T₂ will the flip-flop 41 be enabled to receive setting puises detected by the firing line puise detector

-1607480 to select and arm the module. In the example illustrated in Figure 3, since module No. 3 is the module to be selected, the control unit 14 will generate a sélection and arming puise on the firing line indicated as a voltage puise on the firing line voltage .during T2 for module No. 3. When the firing line puise detector 37 detects the voltage pul'se on the firing line voltage during the second portion of the mbdule active time interval, flip-flop 41 will be triggered to terminate further counting of the counter 35 and to generate ARM CONTROL to the firing switch 21. With ARM CONTROL true, firing switch 21 will be closed connecting the· detonator 24 in module No. 3 to the firing fi· line through its zener diode 43.

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Since further clocking of counter 35 has been terminated by receipt of the sélection puise and the setting of flip-flop 41, the module will no longer be in an activé time interval génération operation, but will hâve to be a- selected,; state. Further sélection of lower mèâules ·is terMnated and détonation of moduleNq. ' 3·çatt ^ccur at any time control unit î4 wishes to apply a firing,puise the firing line. Should détonation of the.selected and armed module not be desired, the sélection sequencing process can be repeated by resetting ail of the modules back to the initial state by removing the firing line voltage and current momentarily. When the power is removed, ail the pass-through switches 20 and the firing switch' 21 in module 3 will be switched to their open position so that only the first module connected to the control unit 14 will receive power on the firing line.3 once power is again returned.

-1707480

Summarizing the présent invention, a single-wire sélective perforating gun System is disclosed in which a plurality of identical firing modules are connected, one to another, to form an elongated assembly suitable for 5 lowering into a well borehole. Included in the assembly is a control unit for generating power and firing lme ' signais to each of the firing modules as each module is connédted one at a time in a sequence to the control unit.

Each of the firing modules generates internally an active time interval during which the module can be selected and armed for firing by the control unit. The active time interval begins when power is applied to the module by connection of the module to the firing line'.

Each firing interval has a first and a second portion. During the first portion, the firing module generates an identification puise to the control unit to indicate that a next module has been connected to the firing line. In this way, the control unit counts the modules as they are 20 connected to the firing line to détermine when the module to be selected is generating an active time interval. During the second portion of the module active time interval, the control unit may select a module for firing by issuing a sélection control puise onto the firing line.

Puises on the firing line during the first portion of the active time interval are disregarded by the module since a module may only be selected and armed during the second portion of the time interval.

As a safeguard against attempting to fire a module when conditions of the modules do not permit, each module generates an identification puise on the firing line which the control unit monitors to détermine if the module is

-1807480 operating within acceptable power limite and that the sequencing through the modules has occurred within prescribed time limite. Only when conditions are proper will the control unit select and arm for firing the module to be selected.

The sélection process for each firing module 5 is best described with reference to Figure 2 which illustrâtes the functional block diagram for a typical firing module 5. Referring now to Figure 2, the input portion 16 of the firing line 3 is shown connected to a regulated power -supply 29 which produces the supply voltage for the circuits of the module. For purposes of the following discussion, it is assumed that the firing module shown in Figure 2 has just been connected to the firing line power by the closure of switch 20 in the module immediately above.

The firing line is also shown connected to a control puise detector 34. The control puise detector 34 consiste of a R-C network to shift the DC level of the control puise which is applied directly into the dock input of a 4-bit shift register 38. The shift register’s clock input stage acte as a comparator to detect the control puises.

The control puise detector 34 generates on the Q1 output of shift register 38 the signal STOP CUDCK in response to a sélection control signal on the firing line during the active time interval. The sélection control signal, if received at the proper time during the active

19“

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time interval, selects the module for firing by terminâting the moduie's active time interval which prohibits switch 20 from thereafter closing and passing power to the modules below the seiected module. In addition to detecting a sélection control signal on the firing line, th‘e control puise detector 34 detects the sequence of arming control signais from the control unit 14. This sequence of arming control signais is used as a safeguard détection method for determining if one and only one firing module 5 is responding to the arming sequence.

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Still referring to Figure 2, the last three stages of the 4-bit register 38 comprise an arming circuit which responds to the sequence of arming control signais detected by the control puise detector 34 to generate a feedback current puise to the control unit 14. This feedback current puise on the firing line 3 functions to indicate to the current détection means S in the control unit 14 that one and only one firing module is responding to the sequence of arming. control signais. As will be discussed below, this feedback current puise acts as a safeguard détection method for potential problems which would resuit in the improper firing of the perforation guns.

As mentioned previousiy, the arming sequence feedback current puise on the firing line 3 has a predetermined amplitude of current increase over the firing line steady state current t.o indicate that only a single firing module is responding. The 4-bit shift register 38 opérâtes' to produce this predetermined current puise in the firing line as follows; As long as the signal on line 46 into shift register 38 (the data (D) input) is at a logic 0,

-20any detected control signais or puises on the firing line will sequentially shift logic Os into the various stages of the shift register 38. Logic Os in the stages of the shift register 38 represents the reset condition. Thus, any puises detected by puise detector 34 when the D input to shift .register 38 is at a logic 0 will resuit in no change in the logic state of the shift register, and thus no action by the arming circuit.

When the data input to shift register 38 is at a logic 1 the first control signal detected by the stop puise detector 34 on the firing line will shift a logic 1 into the first stage of _xthe register. As previously discussed, the output of the first stage, Q1, is the signal STOP CLOCK which is applied to signal line 50. The function of STOP CLOCK is to inhibit an oscillator clock 28 which is the internai time base for the logic circuits 18 from generating further clocking signais. The absence of further clocking puises terminâtes the génération of the module*s active time interval and further sequencing of any lower modules. This first received control signal represents the sélection control signal for selecting a module for firing. In other words, if STOP CLOCK goes to a logic 1, this module will be selected for firing. The conditions under which the D input shift register 38 is at a logic 1 are discussed |n more detail below.

Any further control signais detected by the stop puise detector 34 when the D input is at a logic 1 will cause a corresponding logic 1 to be shifted into each of the stages of the shift register 38, with the logic 1 shifted for each control signal detected. Connected between the output of the second stage, Q2, and the third stage, Q3, of the shift register 38 is a resistor R2.

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In accordance with the présent invention, if the module is selected for firing by receipt of a sélection control signal at the proper time, a sériés of arming puises will then be generated by the control unit 14 to 5 the arming circuit of the selected module 5 to generate the arming status feedback current puise indicating that a single module is responding. This sequence of arming control signais consists of three puises on the firing line. The first puise causes the Q2 output of shift 10 register 38 to go to a logic 1. At this time, the Q3 outpu-t of the shift register 38 is at a logic 0 thereby causing the 4-bit register 38 to supply outrent through R2 in the direction Q2 to (13. This results in an increase in the amount of current drain on the power supplied by the 15 firing line in an amount determined by the magnitude of

R2. If a single firing module is responding, a predetermined current increase. results.

With receipt of the second arming puise, a logic 1 will also be shifted into the third stage of the shift register 38 resulting in both sides of resistor R2 being at a logic 1. This logic condition removes the current increase in the firing line current back to the current level for the reset condition of the arming circuit 38.

Thus, if the amplitude of the current puise increase in the firing line current âs a resuit of the first and second arming puises was within acceptable limits, the control unit 14 may then proceed to arm the module for firing.

Arming of the module for firing is accomplished by issuing a third arming control signal on the firing line

3. This results in the fourth stage, Q4, of shift register '38 beconFing a logic 1. The Q4 output of shift register 38

-2207480 is applied to signal line 39 as the signal ABM CONTROL. The signal ARM CONTOOL is supplied to the controllable arming switch 21. For the présent invention arming switch 21 and pass-through switçh 20 are each solid state switches manufactured by international Rectifier as its model IRSC 232. Closure of switch 21 connects the detonator 24 for the shaped charge 26 to the input portion 16 of the firing line 3 thereby arming the module for firing.

As previously discussed, sélection and arming of the module for firing occurs when a control signal is detected by the stop puise detector 34 when the data input, D, to the 4-bit shift register 38 is at a logic 1. The data input to the shift register 38 is at a logic 1 during a portion of the modules active time interval and is generated as follcws: A clock oscillator circuit 28 is provided as the module time base for generating clock puises that will be counted by a 14-bit binary counter 34 to generate the active time interval for the module. The active time interval for each module is divided into two equal portions, Tl and T2 (see Figure 3). During the first portion Tl, the module will perform an identification process whereby the

Z.

module 5 generates a plurality of feedback puise to the control unit

14. The puises are processed by the control unit 14 to uniquely identify which module 5 is currently generating an active time interval.

The D input to shift register 38 is a logic 0 during the first portion Tl of the active time interval and prevents any sélection.of the module for firing. During the second portion T2 of the active time interval, the module is enabled to be selected, armed and fired by the control unit 14. During T2 the D input to shift register 38 is at a logic 1. The D input logic level is controlled by the 14-bit binary counter 35 whose operation is described in more detail below.

As mentioned previously, during the first portion of the module active time interval, a uniquely identifying puise is generated in the control unit 14 to identify which module 5 is currently generating an active time interval. The génération of this uniquely identifying puise occurs as follows: An identification signal generator comprised of the power-up reset circuit 30 and a 4-bit shift register 33 is provided with each firing module 5 for generating a plurality of feedback current puises to the control unit 14 during the first portion of

-23· a module’s active time interval. The power-up reset circuit 30 produces a power reset puise to clear the logic 18 circuits on receipt of power on the input portion 16 of the firing line.

,

The 4-bit shift register 33 functions in a similar way to the shift register 38. That is, if the data input D is at a logic 1, clock puises will cause a logic 1 to be shifted through the various stages of the register.

As shown in Figure 2, the clock source for the shift register 33 is the output of the oscillator clock 28 z The data input for shift register 33 cornes from a 14-bit binary counter 35 which also responds to the clock 28.

The Q6, or the output of the sixth stage of the binary counter 35, is applied as the data D input to the shift register 33. Thus, a .sequence of 1s and Os will be . clocked through the shift register 33 in response to the changes in logic states of the Q6 output of the binary counter 35. A resistor R3 is connected between the Q1 and the Q3 output of the shift register 33 and opérâtes in a manner similar to R2 to create a current increase in the firing line power when there is a différence in the logic states of Q1 and Q3. In accordance with the présent invention, resistors R2 and R3, acting in coopération with the shift registers 38 and 33, respectively, represent a first and a second load connect means for generating current increases on the firing line 3.

The Q13 output of the binary counter 35 is also applied to signal line 48 as the control input to the solid state by-pass switch 20 which responds to the logic state of Q13 to connect the input portion 16 of the firing line to the output portion 22 thereby powering up the next lower module in the string. The stoppina of oscillator

2407480 clock signais on the occurrence of a logic 1 on the Q13 output will thereafter keep the pass-through switch 20 closed until the power on the firing line is removed.

, As previously mentioned, the active time interval for the module will be determined by the time required to count a predetermined number of clock cycles of the clock

28. For the présent invention, the first portion of the module active time interval T1 is measured from the application of the firing line power to the module (the occurrence of the power reset puise) up to the time that the Q12 output' of the binary counter 35 goes to a logic î. The second portion T2 of&gt; the module active time interval is measured by the length of time that Q12 is at a logic 1 (the length of time from when Q12 goes to a logic 1 until when Q13 goes to a logic 1).

As shown in Figure 2, the output Q13 of the binary counter 35 is applied as a second enable input to the oscillator clock 28 to also inhibit the génération of any clock signais when Q13 is at a logic 1. The_i?disabling of the clock 28 when Q13 is true (logic 1) indicates that the module active time interval for this module has been completed without this module being selected for firing., and until the power on the firing line is removed, this module will be in a by-pâssed state. .,·

Having the ability to uniquely identify each module that is generating an active time· interval, the control unit 14 can know precisely if the module currently generating an active time interval is the module to be selected and armed for firing. A faultv module which does not generate downhole an active time interval can be detected from the absence of its uniquely identifying puise envelope

-2507480 in the sequence of envelopes for the modules when ali, the modules are sequenced and none is selected for firing.

'For the preferred embodiment ’of the présent inven,tion, each module générates 64 current puises on the firing line during T1. The control unit 14 will count the puises réceived during Tl of each module's active time interval to' détermine the amount of time reguired by the module to generate the 64 puises. The time interval thus devéloped represents' the envelope of the feedback identification signal from a particular module. Since the oscil.lator clock-circuits will vary somewhat, each module is likêly to’ produce a puise envelope that is unique to the module.

To insure that this is the^- case, each firing module oscillator clock 28 can be slightly altered to produce unique envelope puises; for each module, and this envelope can be measured uphole or downhole to uniquely identify each module. In this way, there is no need to count how many modules hâve been connected to the firing line in the sélection sequence. The uniquely identifying puise détermines when a given module is connected to the firing line and generating an active time interval. Isolated noise puises-on the firing line will not generate an errer condition because 64 puises must be received.

î

While 64 puises is the idéal number, it is possible to permit a small band or variation of total puises rëceived and still result in a unique identification of the module. Thus 64 ί n puises are’permitted and still be able to uniquely identify a given module. ’

Connected to the reset input of the shift register 33 is the Q12 output of the binary counter 35. Thus, the shift register 33, acting in combination with the Q6

-2607480 output of the binary counter 35 and the clock 28, produces a predetermined number of short duration current puises onto the firing line 3 until such time as Q12 go·· te a logic 1. When Q12 goes to a logic 1, the shift register g 33 |s reset and inhibited from further generating any current puises on the firing line. In addition te reset· ting the shift register 33, the Q12 output of binary eounter 35 is also applied as the data D input to the Shift register 38 as the signal labeled SNABL8.

*0

Turning now to Figure 3, a timing diagram of various signais within' the single-wire perforating System accord* ing to the présent invention is shown. For the signais illustrated in Figure 3, the third module down from the 1| control unit 14 is the module to be selected.

Figure 3 illustrâtes 'the first and second portions of each module active time interval, T1 and 72, respectively. During the first portion T1 of each module active time 20 interval, 64 current puises are generated in the current signal on the firing line 3. For;.purposes of illustration* the time interval required to generate the 64 puises by each of the modules is different so that th· width of the resulting envelope puise, labeled tl through t4, ar.e different and each puise uniquely identifies its associated module. The noise puises occurring between module'No. 1 and module No/ 2 results in a narrow puise envelope for an identification puise,’ and because it didn’t contain the correct number of current puises, it will be disregarded 30 by the control unit 14 and reported to the surface for possible action.

-27·

07480

Since module No. 3 is the module to be selected, the çontrol unit 14 will generate the module sélection çontrol signal and the sequence of three arming sélection çontrol signais during the second portion T2 of the module active ,time interval. These çontrol signais are applied as voltage, puises on the power voltage of the firing line. The first çontrol signal received during the second portion of module No. 3’s active time T2 will select the module for firing and thereby terminate further génération of the module active time. This, in turn, prevents further sequencing of any lower modules.

With receipt of a sélection çontrol puise during T2 of the module active time for module No. 3, the module will enter into a selected state during which it can be armed for firing if the safeguard feedback détection sequence détermines that the modules are operating properly. -This safeguard détection sequence begins with receipt of the first arming çontrol signal by the arming circuit. As previously discussed₇·· the arming circuit produces the predetermined current puise increase in the firing line current illustrated in Figure 3 as the arming status puise. The second arming puise will be issued by the çontrol unit 14 to remove the arming status current puise if the proper value for the current increase--was detected. i

If'the proper value for the arming status puise was detected, the çontrol unit 14 proceeds to issue a third arming çontrol signal to cause the arming switch 21 (ses Figure 2) to close connecting the detonator 24 to the firing line 3. With the closure of the arming switch 21, the çontrol unit 14 can then issue a firing puise on the firing line at any time it desires to fire the module. Rather than detonating the module, however, the çontrol

<img file="OA7480A_D0010.tif" />

07480 unit 14 can reset the modules to select a different module by simply removing the power on the firing line without generating a firing puise. This safety feature can be used to sequence through each of the firing modules to détermine if ail modules are operating properly, and to l

further d.efine the unique identifying envelope for each puise as a function of the given operating conditions that the gun is currently experiencing, since température variations encountered downhole may cause fluctuations in the time base in each firing module. À time base variation will change the time required to generate the 64 puises that uniquely identifies the module. &lt;

,z

As a redundant check to the safeguard arming status puise during the arming sequence, the control unit 14 can détermine if the modules are operating as expected by measuring the amount of çurrent increase as each module is added to the firing line. The increase in the firing line current as each module is added to the firing line is illustrated in Figure 3 at the start of each module active time interval as a step function.

Xt is one of the important features of the présent invention that redundant safeguard détection methods are provided for determining faultv conditions or failures in the firing System beforejany attempt to fire the guns is made. These failures may be classified as failures resulting in the firing of a wrong gun which could be noticed or the failures which cause the undetected firing of a wrong gun.

As previously discussed, the response frcm every module during the first portion of the module's active

-2907480 time interval is a train of 64 feedback current puises. The control unit 14 detects these feedback puises and forms the envelope of the puise train to uniquely identify the modules as they are connected to the firing line. To 5 .increase the immunity against noise on the firing line 3, the 6'4.puises generated during the first portion of each module active time interval is recognized as correct if the number of puises detected in the sequence is within a certain number of the correct number. Thus, false puise 10 trains, such as the noise puises illustrated in Figure 3, wiir^-be discarded, and the surface equipment could be informée about their occurrence. '

A safeguard to the détermination that the modules are functioning properly is présent in the active time intervais of the various modules. The envelope of the feedback puises during the first portion of the active time interval is a measurable time interval o-f approximately half the active period of the module. The control unit 14 is built 20 to accept a wide range of active period values and is able to measure them with high resolution. Every module 5 in the gun string 10 can be individualized through a dispersion in their various clock 28 frequencies. Even if the frequencies are not made different, the frequency distri25 bution of the various frequencies represents a random process where the différence between adjacent modules may not alwavs be measurable, but the probability of this condition to leave a failure undetected is sufficiently low. Otherwise, the modules could be trimmed to different values of their active periods and placed sequentially in the string.

Since the présent invention is able to sequence through each of the modules without firing. any module, it

-3007480 is possible to measure, before the guns are fired, the time intervals for each of the modules. These values can form a reference table of active times versus module position which can be used later to verify the sélections dur&gt;ing the perforation operations.

Another safeguard détection System involves the measurement of the line current on the firing line 3. The control unit 14 includes a high resolution measurement of the current supplied to the firing line. After a module is selected, the current on the firing line is proportional to the number of modules connected to the line, and therefore, indicative of the module selected.

The total current drain produced by ail the firing modules connected to the firing line may not be précisé enouah to indicate the number of modules, but the singleaddition or subtraction of a module on the firing line produces.a predictable change in the current. With the perforating string 10 downhole and before firing the guns, reference values of supply current can be measured with sélection cycles of progressive length. In other words, a sélection cycle to select module No. 1 followed by a sélection cycle for module No. 2, etc., can be run to détermine how this increase in firing line current occurs for each module. These Measurements can be made simul-·. taneously with the identification puise measurements.

The vérification of the active time interval and line current is a safeguard in situations where a failure reduces the active period of a module to zéro and the failed module powers up together with the next lower module, and is by-passed without being accounted for.

-3107480

In most perforation Systems where the présent inven~ tion can be applied, the firing of the gun destroys the electrical line passing through it. This situation is inconvénient since it restricts the arbitrary nature of 5 ₍the sélection, but is helpful in finding the position of the last fired gun. This can be accomplished by counting the modules still able to communicate with the control unit 14.

The number of interconnected modules is measured by a sélection cycle of unrestricted length. The control unit 14 will count the feedback puise trains, and there·” fore the number of modulas. As the lasc mocule is bypassed, the measurement of the supply current will indi15 cate the condition of the line below the last unfired gun. The same measurement can locate any failure in the wiring between modules. The .control unit 14 can detect an open or short circuit in the line and détermine up to which gun the string is still opérable.

After the sélection cycle in which a module is selected and armed for firing, only the active module should be able to forward the firing current to the blasting cap. But any of the by-passed modales could b@ defective and remain active'’ after being by-passed. The module with the faulty circuitry could fire in parallel with the selected one, and eventuallv go undetected. As a safeguard against this failure, the selected module is not ready to accept the firing current immediately after the sélection control signal is applied to the firing line

3, but requires an arming sequence of several arming control signais. .

-3207480

As previously discussed, arming is implemented in accordance with the présent invention with three additional control puises on the firing line 3 similar te the one used in the sélection process. Only the seiected modules should be able to receive these puises.

The first arming puise will increase by a fixed amount the supply current drained in the active module with the second puise returning the current to its previous value. If the increase in current was within acceptable limita, a third puise will finallv close the arming switch 21 between the detonator or blasting cap 24' and the firing line 3. JSimultaneously, or sometime after the third arming control puise, the control unit 14 will connect a firing capacitor to the firing line and produce the firing current.

If a defective module is placed in any intermediate arming stage after the sélection, including the state where the switch to the blasting cap is closed, the measurement of the line current before and during the arming sequence will detect this faulty condition.

Summarizing the présent invention, a single-wire sélective perforating gun System is disclosed in which a plurality of identical firing modules are connected, one to another, to form an elongated assembly suitable for lowering into a well borehole. Included in the assembly is a control unit for generating power and firing line signais to each Of the firing modules as each module is connected, one ata time, in a sequence to the control unit.

Each of the firing modules generates internally an active time interval during which the module can be

-3307480 selected and armed for firing by the control unit. The active time interval begins when power is applied to the module by connection of the module to the firing line. Each firing interval has a first and a second portion. During the first portion, a unique identification puise is gerierated in the control unit to indicate that a particular module from among the plurality of modules is connected to the firing line and- is generating an active time interval. In this way, the control unit is able to determine when a particular module is available for sélection.

During the second portion of the module active time interval, the control ur_Kit may select a module for firing by issuing a sélection control puise onto the firing line. Puises on the firing line during the first portion of the active time interval are disregarded by the module since a module may only be selected and armed during the se'cond portion of the time interval.

Once a module is selected, the control unit will issue a sequence of three arming signais to arm the module. The first and second arming control puises will produce a current puise increase on the firing line power of a predetermined amplitude to indicate to the control unit if one and only one module is responding to the arming sequence. If the^current increase is within acceptable limits, the control unit will then issue a third arming control signal to connect the detonator of the charge in the module to the firing line. Once the module is armed for firing, the control unit 14 can issue a firing puise to detonate the charge or can remove the firing line power to reset ail of the modules and permit the sélection process to be repeated to select a different module.·

-3407480

In describing the invention, reference has been made to its preferred embodiment. However, thcse skilled in the'art and familiar with the disclosure of the invention may recognize additions, délétions, substitutions or other modications which would fall within the perview of the invention as defined in the appended daims. For exemple, the invention has been described with reference to a single firing line 3 which carries both power and control signais between the control unit 14 and the plurality of firing modules 5. It will be obvious that the advantages of the présent invention may be obtained by usine more than one signal line to carry power and control signais from the control unit tç the modules. A single line to carry the control signais for sélection and arming seoarate and apart from the firing line power and feedback signais could be employed where the signal Unes are segmented in the same way as disclosed herein.