Well perforating tool

A well perforating tool (9) for drilling holes in a well casing substantially from and at right angles to a vertical well bore within which the casing is disposed. The tool (9) includes an elongate housing (15) for insertion within the casing and having a detachable boot (13) at one end thereof for centralizing the longitudinal axis of the tool within the casing. Two motors (53,85) are disposed within the housing (15) for rotating a flexible drill shaft (97), and advancing and retracting the flexible drill shaft (97) with respect to the interior wall of the casing. The entire tool is supported by a cable (19) which also includes power supply and signal lines for independently activating the motors (53,85) from an above-ground control station and ascertaining the depth of drill shaft penetration.

TECHNICAL FIELD OF THE INVENTION 
The invention relates to a tool for use in perforating a well casing and 
associated bore formation materials so that hydrocarbon values can be 
recovered through the well casing. The tool is capable of reliably and 
accurately placing any number of perforations along the entire length of 
the well casing without damaging the well structure. 
BACKGROUND OF THE PRIOR ART 
A well casing is normally disposed within a vertically oriented well bore 
and sealed therein by pumping cement into the annular space between the 
outer surface of the casing and internal wall of the bore. The well casing 
may be made of metal or synthetic plastic material and can extend for 
several miles below the ground surface. 
In order to maximize the extraction of hydrocarbon values from a well, it 
is often necessary to provide a series of lateral perforations through the 
well casing, adjacent casing cement and bore formation material. However, 
the procedure of accurately positioning a perforating tool in the desired 
vicinity of the casing to be perforated, and reliably effecting the 
perforation without damaging the well structure, is often a very critical 
and difficult task to accomplish, particularly if the perforations are to 
be placed thousands of feet below ground level. 
The prior art has sought to accomplish the accurate and reliable 
perforating of well casings through the use of two general types of 
perforating tools. First, it is known to use ignitable charges, such as a 
gun that fires a bullet propelled by an explosive propellant. The gun is 
lowered into the vicinity of the casing that is desired to be perforated 
and, upon actuation of the gun from an above-ground control signal, the 
bullet is fired and caused to penetrate the well casing and adjacent 
cement and bore formation. This type of perforating device may also 
utilize chemical charges, such as thermite or the like, disposed adjacent 
the inner wall of the well casing so that the desired perforation can be 
formed by igniting the charge which burns through the casing wall. Devices 
of this type utilizing an explosive or ignitable composition are basically 
unreliable in actual operation because of variations in charge 
compositions and the unpredictable manner in which bullets penetrate the 
casing and associated formation material. The use of bullets is 
particularly critical since the explosive impact sometimes causes 
unexpected damage to the well assembly that is always extremely expensive 
to repair. 
The second type of perforating tool taught by the prior art comprise 
motor-driven mechanical drills which are normally housed within enclosures 
that are supported by a cable and lowered into the well casing to the 
desired location. A basic design problem inherent in tools of this type is 
the manner in which the dual functions of rotating the drill bit, and 
advancing and retracting the drill bit with respect to the interior wall 
of the casing, are effected. Typically, the tool is lowered and locked 
into position within the well casing and a second cable supporting the 
motor and associated drill bit is lowered and raised to move the bit 
towards and away from the casing wall. The drill bit is normally supported 
at the end of a flexible drill shaft cable that extends from the drive 
shaft of the motor and bends laterally in a direction towards the interior 
wall surface of the casing. This basic structure is also found in similar 
tools utilized for drilling and removing samples from well bore 
formations. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved perforating tool 
which reliably perforates a well casing at any location along the length 
of the casing. 
It is another object of the invention to provide an improved perforating 
tool which quickly and easily perforates well casings made from any 
material without damaging the well assembly. 
It is yet another object of the invention to provide an improved 
perforating tool which is capable of effecting accurately placed single or 
simultaneous multiple perforations at any location along the depth of a 
well casing. 
It is still yet another object of the invention to provide an improved well 
perforating tool which is simple in construction and economical to 
manufacture. 
It is yet still a further object of the present invention to provide an 
improved well perforating tool which is capable of perforating well 
casings of different diameters. 
These and other objects of the present invention are achieved by providing 
a well perforating tool which includes an elongate housing that is 
detachably supported by a cable for raising and lowering the tool within 
the well casing. A first motor disposed within the housing serves to 
rotate a flexible drill shaft provided with a free end for connection to 
an appropriate drill bit. The flexible drill shaft is disposed within a 
guide that directs the bit laterally towards the interior wall surface of 
the well casing. A second motor disposed within the housing is operatively 
connected to the first motor for moving the latter back and forth along 
the longitudinal axis of the housing so that the drill bit may be advanced 
and retracted with respect to the well casing. The lower end of the 
housing is provided with a detachable boot having a diameter that 
corresponds substantially to but is less than that of the well casing to 
be perforated so that the tool is automatically centralized within the 
casing, with the retracted drill bit being disposed directly adjacent the 
portion of the casing to be perforated. A potentiometer having an 
extensible indicator connected to the first motor is also disposed within 
the tool housing for monitoring the drilling operation so that the depth 
of the perforation being produced can be determined. The two motors and 
potentiometer are in electrical communication with a ground level control 
panel through power supply and signal cables associated with the tool 
support cable. 
Other objects and aspects of the invention and the various features of 
construction will become apparent to those skilled in this art upon 
reference to the following specification and the accompanying drawings 
forming a part hereof.

DETAILED DESCRIPTION OF THE INVENTION 
A vertical bore hole formation is generally indicated at 1 in FIG. 1 and 
includes a well casing 3 disposed and sealed therein by means of a cement 
wall 5 disposed in the annular space therebetween. Formation 1 is depicted 
as including a substrata layer 7 providing favorable geological conditions 
for extracting hydrocarbon values, such as oil or gas. 
A perforating tool 9, according to the invention, is shown disposed within 
casing 3 and provided with a cap 11 at its upper end and a detachable boot 
13 at its lower end. The main body of tool 9 is defined by an elongate 
housing 15 having a substantially cylindrical outer configuration. Boot 13 
also preferably has a generally cylindrical outer configuration. As is 
apparent from FIG. 1, the diameter of housing 15 is substantially smaller 
than that of casing 3 in order to facilitate the insertion of tool 9 
therein. However, boot 13 has a maximum diameter which substantially 
corresponds to and is slightly smaller than that of casing 3 so that boot 
13 functions to coaxially orient tool 9 within casing 3. In this manner, 
tool 9 may always be centralized within well casings of different 
diameters merely by selecting a boot 13 having a corresponding diameter 
for attachment to the lower end of housing 15. 
As further seen in FIG. 1, cap 11 encloses a connector 17 disposed between 
tool 9 and a cable assembly 19, the latter including a cable for 
supporting the entire weight of tool 9 and cables for transmitting 
electrical energy and signals between ground level and the interior 
components contained within housing 15. Connector 17 may comprise any such 
type of detachable plug, screw or interlock mechanism well known in the 
art and deemed suitable for the purpose of this invention. An important 
function of connector 17 being that substantially the entire weight of 
tool 9 is supported thereat through cable 19. Cap 11 may also be 
detachably affixed to the upper end of housing 15 by means of a threaded 
engagement, lock screws or any other similar well known attachment 
mechanism. 
Boot 13 is depicted in FIG. 1 as including two substantially 
semi-cylindrical half shells 21 and 22 which are secured together along a 
pair of corresponding peripheral flanges 23 and 25 by means of a plurality 
of screws 27. Boot 13 is provided with a conical-shaped lower end 29 for 
facilitating insertion of tool 9 into casing 3. Boot 13 further includes a 
tapered upper portion 31 which terminates in an upper end 33 that 
substantially corresponds to the outer surface diameter and configuration 
of housing 15. 
Referring now to FIGS. 2 and 3, housing 15 is shown provided with an 
internal component support 35 which is preferably of a semi-cylindrical 
configuration and may be either permanently or detachably secured to the 
internal wall surface of housing 15 through welding, bolting or the like. 
Support 35 carries a lower half 37 of connector 17. A corresponding upper 
half 39 of connector 17 is securely attached to cable assembly 19. All 
electrical and mechanical support connections between cable assembly 19 
and tool 9 are achieved through the interconnection of connector halves 37 
and 39. 
A plurality of electrical signal lines 40 and power supply lines 41 extend 
from the lowermost free end of cable 19 for connection to a terminal block 
43 that is also carried by support 35. Block 43 provides connections for 
transmission of electrical signals between lines 40 to a control line 45 
and transmission of electrical energy between lines 41 and a plurality of 
control lines 47 and 49. The ultimate control of electrical components 
contained within tool 9 may be achieved through a master control panel 
disposed on ground level and provided with known electrical and electronic 
devices for varying and maintaining the transmission of electrical energy 
and signals through lines 40 and 41 and monitoring the operation of the 
individual components being controlled through lines 45, 47 and 49. Such 
known devices may include voltmeters for providing an indication of 
voltage being utilized, variacs for controlling the amount of current 
distributed, digital displays for indicating depth of perforating or 
drilling, and the like. 
Support 35 includes a first fixed plate 51 for supporting a drive motor 53. 
A first movable plate 55 is disposed below plate 51 for movement back and 
forth along the longitudinal axis of support 35. A second fixed plate 57 
is carried by support 35 and disposed below plate 55. A lock disc 59 is 
provided for securing motor 53 to plate 51, preferably through a threaded 
connection. A splined drive shaft 61 extends downwardly from motor 53 
through plate 51 and disc 59 for connection to one end of a coupling 63, 
the latter being preferably flexible in nature. The other end of coupling 
63 is attached to one end of a threaded drive shaft 65 for transmitting 
rotary action imparted by shaft 61. Shaft 65 is passed through a bearing 
cage 67 carried by plate 55 and also through a correspondingly threaded 
aperture 68 in plate 55. The end of shaft 65 is journaled for free 
rotation through an unthreaded guide aperture 69 provided in plate 57. 
A plurality of guide rods 71 are disposed with one set of adjacent ends 
being threaded and secured to plate 55 through apertures 73 by means of a 
plurality of nuts 75. Rods 71 pass downwardly through a plurality of 
apertures 77 in plate 57. The other adjacent ends of rods 71 are also 
threaded and terminate in their connection to a second movable plate 79. 
This is achieved by passing the ends of rods 71 through apertures 81 
provided in plate 79 and attaching the ends thereto by means of a 
plurality of nuts 83. 
A drill motor 85 is supported on plate 79 by a lock disc 87, preferably 
through a threaded connection. A splined drive shaft 89 extends downwardly 
from motor 85 through plate 79 and disc 87 for connection to a collar 91 
for transmitting the rotary motion of shaft 89 to a rigid drill shaft 93 
carried at the lower end of collar 91. The free end of shaft 93 is passed 
into a tubular shaft guide 95 for connection to a flexible drill shaft 97, 
with shafts 93 and 97 being freely rotatable within guide 95. 
As shown in FIG. 3, a sealing plug 99 is disposed within the lower end of 
housing 15, with a portion thereof extending away from the end edge of 
housing 15. This free portion of plug 99 is embraced by upper end 33 of 
boot 13 which is secured thereto by a plurality of screws 101. Plug 99 may 
be made from any material deemed suitable for preventing fluid leakage 
through the end of housing 15 and is attached thereto by a plurality of 
screws 103. A ring gasket 105 may be disposed within plug 99 to bear 
against the internal surface of housing 15 as an additional precaution 
against well fluids from entering upwardly into housing 15. Guide 95 is 
disposed through a passageway 107 formed in plug 99 and sealed therein by 
means of a fluid tight ring gasket 109. The end of guide 95 disposed 
within the interior of housing 15 is threaded and sealed by a 
correspondingly threaded cap 111 having an internal compression gasket 113 
disposed therein for bearing against the upper edge of guide 95 and 
adjacent circumferential surface of shaft 93. In this manner, fluids 
passing upwardly through the annular space defined by the interior surface 
of guide 95 and exterior surfaces of shafts 93 and 97 are prevented from 
flowing into housing 15. The sealing function of cap 111 and gasket 113 
does not impair the free rotational movement of shaft 93 disposed 
therethrough. 
As shown in FIG. 4, guide 95 extends downwardly into boot 13 and curves 
laterally away from the longitudinal axis thereof, terminating in a 
threaded end portion 115 that passes through a correspondingly shaped 
aperture 117 formed in shell half 22 of boot 13. End 115 is rigidly 
secured within aperture 117 by a pair of opposed nuts 119 and 121. The end 
of rigid drive shaft 93 is detachably connected to the upper end of 
flexible drive shaft 97 through an interlock 123 which may include a pin, 
set screw or any other expedient well known in the art for accomplishing 
this function and permitting joint rotative action of shafts 93 and 97. 
The free end of flexible drill shaft 97 is provided with an appropriate 
detachable drill bit 125, the shape and nature of which are well known in 
the art and may be selected for the physical characteristics required to 
accomplish any given perforating operation. 
The orientation of plates 55, 57 and 79 with respect to support member 35, 
threaded shaft 65 and rods 71 is more clearly depicted in FIGS. 5, 6 and 
7. As shown therein, plate 55 is substantially of a flat ring having a 
central opening 68, as shown in FIG. 2, that is coextensive with a central 
passageway 127 in bearing cage 67 through which shaft 65 is passed. The 
peripheral curvature of plate 55 corresponds substantially to the inner 
curvature of support 35, with plate 55 being movable along the 
longitudinal axis of support 35. The outer surface of support 35 is spaced 
from the inner surface of housing 15 and is permanently or detachably 
secured thereto through a plurality of struts 129. Plate 55 also includes 
an aperture 131 through which control line 49 is passed for ultimate 
connection to drill motor 85. Plate 55 further includes a second aperture 
133 through which an indicating member 134, such as a spring or the like, 
may be passed. Member 134 extends downwardly from a perforating depth 
monitoring device 137, as shown in FIG. 2, such as a potentiometer or 
other well known device of this nature. Device 137 is carried by support 
35 with member 134 being extensible and retractable with respect thereto. 
Plate 51 is also provided with a pair of apertures 127 and 129 
therethrough for passage of line 45 and member 134, respectively. Plate 51 
is rigidly secured to support 35 through welding or the like. 
Plate 57, as shown in FIG. 6, may be substantially square in configuration 
and is secured to support 35 by welding a pair of adjacent corners thereto 
as indicated at 137 and 139. As further shown, additional struts 129 may 
be provided adjacent plate 57 for securing support 35 to housing 15 
through welding, bolting or the like. 
Referring to FIG. 7, plate 79 is shown as a ring-shaped disc which supports 
drill motor 85. Member 134 from device 137 is attached to drill motor 85 
through a mechanical connection 141. Plate 79 includes a pair of opposed 
tabs 143 and 145 which support plate 79 for sliding movement along the 
longitudinal edges of support 35. Actuation of motor 85 is achieved from 
current supplied through line 49 which is attached to motor 85 through 
electrical connection 147. 
FIG. 8 depicts a modification of the invention wherein two opposed holes 
may be simultaneously drilled. In this embodiment, drill motor 85 is 
provided with a primary gear 149 attached to the end of splined drive 
shaft 89. A pair of secondary gears 151 and 153 are rotatably secured to a 
pair of extensions 155 and 157 carried by plate 79 and are disposed 
against the toothed periphery of gear 149 in intermeshed engagement 
therewith. Gears 151 and 153 are drivingly connected to a pair of rigid 
drill shafts 159 and 161, the latter being disposed in a pair of 
corresponding guides 163 and 165. A plug 167 is disposed between housing 
15 and boot 13, the latter having a pair of opposed openings 169 and 171 
to accommodate the respective ends of guides 163 and 165. A double pair of 
nuts 173 and 175 secure the ends of guides 163 and 165 in their 
corresponding openings 169 and 171, respectively. As is apparent, rotation 
of primary gear 149 will cause secondary gears 151 and 153 to 
correspondingly rotate and thereby transmit such action through rigid 
shafts 159 and 161 to a pair of corresponding flexible drill shafts (not 
shown) rotatably connected to shafts 159 and 161 and disposed within 
guides 163 and 165. 
Both drive motor 53 and drill motor 85 are preferably electric motors which 
may be any type well known in the art and suitable for performing the 
functions required by the operation of tool 9. Such motors should be 
capable of variable speed control and reversible operation. For example, a 
suitable motor may be a 150 volt DC reversible motor having an operational 
range of 400 to 9000 RPM. 
MODE OF OPERATION 
The manner in which tool 9 of the present invention is utilized in 
perforating a well casing 3 shall now be described with particular 
reference to FIGS. 1-4 of the drawings. At ground level, support cable 19 
is first mechanically and electrically interlocked with tool 9 through 
connector 17 and cap 11 is placed over the corresponding end of housing 
15. Flexible drill shaft 97 is attached to rigid drill shaft 93 through 
interlock 123 and guide 95 is slipped into place through plug 99. Cap 11 
is then threadedly screwed onto the internal end of guide 95 to prevent 
entry of fluids into housing 15. 
A boot 13 having an operative diameter correlating with that of well casing 
3 is selected for assembly onto the other end of housing 15. Shell half 22 
of boot 13 is first interfitted with the lower most end of guide 95 and 
the latter is secured in place through aperture 117 by tightening nuts 119 
and 121. Shell half 21 of boot 13 is then secured against shell half 22 
with screws 27. Boot 13 is then rigidly secured to plug 99 through screws 
101. A suitable drill bit 125 is attached to the free end of flexible 
drill shaft 97, with the working end of drill bit 125 being disposed 
within and substantially flush with the outer surface of shell half 22. 
Tool 9 is then lowered into well casing 3 through cable 19 to the desired 
perforating depth. During this procedure, boot 13 serves to centralize the 
descent of tool 9 so that its longitudinal axis is essentially coaxial 
with that of well casing 3. When tool 9 has arrived at the predetermined 
depth, for example, at a favorable geological substrata 7, it is seen that 
the disposition of boot 13 places open end of drill bit 125 directly 
adjacent the portion of well casing 3 to be perforated. In this manner, 
the time consuming and unreliable procedures for centralizing tools of 
this type are thereby eliminated and highly accurate perforating is 
possible through the use of the present invention by direct location and 
centralization of tool 9 in well casing 3. 
The actual perforating of well casing 3 is initiated by directing current 
to drill motor 85 through control line 49 so that rotation of splined 
drive shaft 89 causes rigid shaft 93, flexible drill shaft 97 and drill 
bit 125 to correspondingly rotate in the same manner. The speed of drill 
bit rotation can be controlled by varying the amount of current being 
supplied to drill motor 85 from ground level. Advancing of drill bit 125 
towards well casing 3 is achieved by supplying current to drive motor 53 
through control line 47. This causes rotation of splined drive shaft 61, 
which in turn transmits rotary action to threaded drive shaft 65 through 
coupling 63. Assuming drive shaft 65 is provided with right hand 
threading, then counterclockwise rotation of shaft 65 within bearing cage 
67 causes plate 55 to move away from motor 53. This in turn causes drill 
motor 85 to also move downwardly with plate 79, the latter sliding along 
the open longitudinal edges of support 35 through tabs 143 and 145. The 
resulting corresponding downward movement of rigid drill shaft 93 advances 
flexible drill shaft 97 and its associated bit 125 into and through well 
casing 3. Continued advancing of drill bit 125 in this manner causes it to 
penetrate the adjacent cement 5 and substrata material 7, thereby 
permitting the hydrocarbon values contained within the latter to enter the 
interior of well casing 3. 
The degree in which drill bit 125 perforates and enters into substrata 7 is 
accurately determined through device 137, which is preferably a 
potentiometer, and associated indicating member 134. Since the latter is 
connected to drill motor 85, advancement of motor 85 during the 
perforating procedure pulls member 134 downwardly, with the degree of 
downward movement being electrically sensed through lines 40 and 41 at 
ground level. When the desired degree of perforating has been 
accomplished, drive motor 53 is reversed in operation, thereby causing a 
clockwise rotation of threaded shaft 65 which in turn pulls plate 55 
towards drive motor 53. Drill bit 125 is then retracted from the drilled 
hole and back into boot 13. Tool 9 may then be either rotated, raised or 
lowered to other desired positions within casing 3 for perforating 
additional holes therethrough. 
With particular reference to FIG. 8, it is seen that by utilizing double 
pairs of rigid and flexible drill shafts, multiple perforations may be 
achieved simultaneously with tool 9 in the same basic manner as described 
for a single perforating operation. 
It is to be understood that the forms of the invention herein shown and 
described are to be taken as preferred examples of the same, and that 
various changes in shape, size and arrangement of parts may be resorted to 
without departing from the spirit of the invention or scope of the 
subjoined claims.