SELF ORIENTING, SWITCH MODULE OPERATED PERFORATING TOOL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is a non-provisional patent application which claims benefit of U.S. provisional Ser. No. 63/741,354 filed Jan. 2, 2025, and entitled “Self-Orienting, Switch Module Operated Perforating Gun,” which is hereby incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002]Not applicable.

BACKGROUND

[0003]In a project for drilling a hydrocarbon-producing well and bringing the well online and into production, the process of perforating the wellbore and fracking those perforations is a multi-day effort requiring a lot of equipment and personnel. As such, an efficient but effective perforating and fracking operation is a considerable concern for the investors and operators of such new wells. The total number of perforations needed to be created and fracked is an important and financially weighty decision recognizing that too few perforations may limit the productivity of the well while too many perforations adds significant costs. Another aspect for efficiently creating a highly productive well is the orientation that the perforations are directed from inside a generally horizontal wellbore radially outwardly through the casing and into the formation. Some believe that having all the perforations oriented in a vertically upward direction is best, while others believe that horizontal perforations directed outward on opposite sides is best, while others want both up and down and others may have an entirely different paradigm. Whatever the belief, providing a perforating tool design that may be designed to consistently orient the trajectory of shaped charges is no simple feat. Designs that include movement inside a perforating tool are inherently more vulnerable to communication and reliability issues. When hundreds or thousands of perforations are intended to be created in a single well and there is much money expended and at stake, there must be no doubt about perforating tool reliability.

[0004]In long horizontal wells, it is impractical to puncture all of the perforations in one quick process and then frack all of the perforations in a single following step. Perfing and fracking is done in bite size segments limited mostly by the number of tools that will fit in a single tool string. Tool strings are generally limited by the length of the wireline lubricator brought to the site and that tends to be between 40 and 60 feet.

[0005]The casing is perforated very far down hole such that getting a tool string from the surface to the operative position within the casing commonly takes a couple of hours. A round trip is typically at least three hours and, if all goes smoothly, takes up to about five or six hours. Considering the costs at the wellsite on a per hour basis, it is very important that the tools fire when signaled. Unfortunately, while most current tool designs provide better than 99% reliability, anything less than 100% is disappointing and expensive.

[0006]Failures to detonate seem to most commonly occur in the electric system. The same electric system through the wireline serves as both the electronic signaling and the electric power to drive the detonator to detonate, so it needs to be designed to avoid multiple types of failure. On the electronic side, the communications must be perfectly continuous. Any momentary loss of continuous electric signal causes a reset on digital switches and requires a reprogramming process where all of the switches are provided their individual mission protocol. The overall mission protocol is for each switch to individually open an electric path to its individual and respective detonator to activate in sequence from bottom to top and as signaled. When a reset occurs, the switches need to be reprogrammed to know where each is in the firing order so that only the designated detonator is detonated and that designated detonator is actually detonated when signaled. Essentially, a brief loss of signal continuity causes the switches to forget where they are in the order. As long as the brief loss of continuity is not associated with a larger problem and is discovered at a time when the tools are not intended to be fired such as near the top of the hole when being pumped down, reprogramming is not a significant cause for concern. But it is certainly disconcerting and preferably avoided. Such brief discontinuities can be caused or associated with the banging of the tool string progressing down hole at casing joints or the impulse forces when the plug is set or other tools are fired where a spring connector is compressed and slackened quickly and briefly lifts off its terminal. Wire connections tend to be slightly more fragile at their junctions then is desirable.

[0007]Turning to failures for the electric conduction system, there is a risk of failing when higher voltage power is delivered for detonation of a tool if any kind of conductive dust or debris gets loosened after the tools string is assembled at the surface. This debris seems to work its way into gaps between the positive and negative sides of the circuit when the two sides are in closer proximity to one another. With conductive dust not necessarily connecting the two sides, but reducing the effective spacing between the positive and negative, a shortened arc path is created for an electric short to occur. This short deprives the detonator of the power needed to detonate.

[0008]For perforating tools with orientating movement inside the carrier or housing, robust design is paramount as shots from other tools, blasts from plug setting tools and the rattling, bumping, vibration endured while being conducted miles down the casing jars dust and debris loose. And, it is unlikely that harsh impulses and G-forces can be much mitigated. What is apparently needed are orienting perforating tools with more robust design including emphasis with their electric systems that improve overall reliability in a perforating string.

SUMMARY OF THE DISCLOSURE

[0009]An embodiment of a downhole assembly deployable into a wellbore extending through a subsurface region comprises a self-orienting perforating tool comprising a tool housing, and a charge carrier positioned in the tool housing and comprising one or more charge receptacles for receiving one or more shaped charges, a plurality of bearings facilitating relative rotation between the charge carrier and the tool housing, and a signal pod connectable to the perforating tool and comprising an electrical switch electrically connectable to the perforating tool, wherein the signal pod is connectable to the perforating tool such that relative rotation is permitted by the plurality of bearings between the signal pod and the charge carrier while also permitting electrical connectivity between the electrical switch and the perforating tool. In some embodiments, relative rotation between the tool housing and the signal pod is restricted. In some embodiments, the signal pod comprises a biasing element that restricts relative rotation between the tool housing and the signal pod. In certain embodiments, the biasing element of the signal pod is electrically conductive to electrically ground the signal pod to the tool housing when the signal pod is connected to the perforating tool. In certain embodiments, the downhole assembly comprises an electrical connector connectable between the signal pod and the perforating tool to electrically connect the signal pod with the perforating tool while permitting relative rotation therebetween. In some embodiments, the downhole assembly comprises a pressure bulkhead that includes the electrical connector. In some embodiments, a first bearing of the plurality of bearings is coupled at a first end of the charge carrier and a second bearing of the plurality of bearings is coupled at a longitudinally opposed second end of the charge carrier where both the first and second bearings are configured to allow for rotation of the charge carrier, and wherein a maximum outer diameter of the second bearing is greater than a maximum outer diameter of the first bearing. In certain embodiments, a first bearing of the plurality of bearings is coupled at a first end of the charge carrier and a second bearing of the plurality of bearings is coupled at a longitudinally opposed second end of the charge carrier where both the first and second bearings allow for rotation of the charge carrier, and wherein a minimum inner diameter of the second bearing is greater than a minimum inner diameter of the first bearing. In certain embodiments, each of the plurality of bearings comprises a plurality of circumferentially spaced bearing elements, a first bearing of the plurality of bearings is coupled at a first end of the charge carrier, a second bearing of the plurality of bearings is coupled at a longitudinally opposed second end of the charge carrier, and an outer diameter of each of the plurality of bearing elements of the second bearing is greater than an outer diameter of each of the plurality of bearing elements of the second bearing. In some embodiments, the downhole assembly comprises a pair of tandem subs coupled to longitudinally opposed ends of the tool housing, and wherein a pair of the plurality of bearings are coupled to endfaces of the pair of tandem subs. In some embodiments, the perforating tool comprises a pair of endplates coupled to longitudinally opposed ends of the charge carrier and are coupled to the pair of the plurality of bearings. In certain embodiments, the downhole assembly comprises a tandem sub comprising an opening configured to at least partially receive the signal pod, wherein the tandem sub is connectable to the perforating tool such that one of the plurality of bearings is connected between the charge carrier and the tandem sub for permitting relative rotation between the charge carrier and tandem sub. In certain embodiments, a first bearing of the plurality of bearings is coupled at a first end of the charge carrier adjacent the tandem sub, a second bearing of the plurality of bearings is coupled to a longitudinally opposed second end of the charge carrier and coupled between the charge carrier and a second tandem sub, and a maximum outer diameter of the second bearing is greater than a maximum outer diameter of the first bearing. In some embodiments, the downhole assembly comprises a detonator electrically connected to the electrical switch and ballistically connectable to the perforating tool, and a detonating cord ballistically connecting the detonator to the one or more shaped charges when the one or more shaped charges are received in the one or more charge receptacles and the signal pod is connected to the perforating tool with the detonating cord extending through one of the plurality of bearings. In some embodiments, wherein the signal pod comprises a pod chassis coupled to the electrical switch. In certain embodiments, the signal pod comprises a detonator electrically connected to the electrical switch and ballistically connectable to the perforating tool, wherein the detonator is received within the pod chassis. In certain embodiments, in response to coupling the signal pod with the perforating tool, the signal pod is positioned at least partially within one of the plurality of bearings. In some embodiments, the downhole assembly comprises a tandem sub having an opening configured to receive the signal pod and wherein the signal pod has a maximum outer diameter that is less than a minimum inner diameter of at least one of the plurality of bearings to permit insertion of the signal pod through the at least one of the plurality of bearings and into the opening of the tandem sub. In some embodiments, the downhole assembly comprises a tandem sub comprising an opening configured to at least partially receive the signal pod and a plurality of circumferentially spaced threaded apertures, wherein the tandem sub is connectable to the perforating tool such that a first bearing of the plurality of bearings is connected by one or more threaded fasteners between the charge carrier and the tandem sub, and wherein the first bearing comprises an annular bearing race having a plurality of circumferentially spaced openings for receiving fasteners extendable through the openings and into the threaded apertures of the tandem sub to couple the first bearing to the tandem sub, and wherein the number of threaded apertures of the tandem sub is greater than the number of openings of the bearing race.

[0010]An embodiment of a downhole assembly deployable into a wellbore extending through a subsurface region comprises a self-orienting perforating tool comprising a tool housing, and a charge carrier positioned in the tool housing and comprising one or more charge receptacles for receiving one or more shaped charges, a plurality of bearings coupled to the charge carrier facilitating relative rotation between the charge carrier and the tool housing, and one or more eccentric weights coupled to the charge carrier applying an off axis orienting force to the charge carrier, and a signal pod connectable to the perforating tool and comprising an electrical switch electrically connectable to the perforating tool external the charge carrier. In certain embodiments, the one or more eccentric weights each comprising one or more receptacles for at least partially receiving the one or more shaped charges and wherein the one or more receptacles are at least partially received within an interior of the charge carrier. In certain embodiments, the one or more receptacles of each of the one or more eccentric weights are axially aligned with the one or more charge receptacles of the charge carrier. In some embodiments, an opening is formed in the one or more receptacles of the one or more eccentric weights for at least partially receiving the one or more shaped charges. In some embodiments, the opening of each of the one or more receptacles of the one or more eccentric weights is positioned centrally in the receptacle. In certain embodiments, the opening of each of the one or more receptacles of the one or more eccentric weights is elongate to facilitate passage of a detonating cord through the interior of the charge carrier. In certain embodiments, the downhole assembly comprises a plurality of the eccentric weights and one or more support rods coupled longitudinally between the plurality of eccentric weights configured to resist sagging of the charge carrier. In some embodiments, the downhole assembly comprises a plurality of the eccentric weights and one or more support shims positioned between the plurality of eccentric weights to reduce sagging of the charge carrier. In some embodiments, the one or more support shims are wedge-shaped to resist pivoting of the plurality of eccentric weights relative to each other.

[0011]An embodiment of a downhole assembly deployable into a wellbore extending through a subsurface region comprises a self-orienting perforating tool comprising a tool housing, a detonating cord housing configured to partially receive a detonating cord, and a charge carrier positioned in the tool housing and comprising one or more charge receptacles for receiving one or more shaped charges, a plurality of bearings coupled to the charge carrier facilitating relative rotation between the charge carrier and the tool housing, a signal pod connectable to the perforating tool and comprising a biasing element, and an electrical switch electrically connectable to the perforating tool external the charge carrier, a tandem sub comprising an opening configured to at least partially receive the signal pod, wherein the tandem sub is connectable to the perforating tool such that one of the plurality of bearings is connected between the charge carrier and the tandem sub, and wherein the biasing element is configured to resist angular misalignment between a longitudinal axis of the signal pod and a longitudinal axis of the detonating cord housing. In certain embodiments, the biasing element is configured to resist angular misalignment in a plurality of circumferentially spaced directions between the longitudinal axis of the signal pod and the longitudinal axis of the detonating cord housing. In certain embodiments, the signal pod comprises detonating cord housing configured to receive a terminal end of a detonating cord from the perforating tool, and wherein the biasing element is configured to resist angular misalignment between a longitudinal axis of the detonating cord housing and the longitudinal axis of the detonating cord housing. In some embodiments, the biasing element is electrically conductive to electrically connect the detonating cord housing with the switch. In some embodiments, the biasing element extends arcuately along an outer surface of the detonating cord housing and about the longitudinal axis of the detonating cord housing. In certain embodiments, the biasing element comprises a continuously extending coil spring. In certain embodiments, the biasing element is annular and extends around an outer surface of the detonating cord housing and about the longitudinal axis of the detonating cord housing. In some embodiments, the biasing element comprises a plurality of circumferentially spaced, flexible fingers in sliding contact with the outer surface of the detonating cord housing. In some embodiments, a terminal end of each of the plurality of fingers flares radially outwards away from the outer surface of the detonating cord housing.

[0012]An embodiment of a downhole assembly deployable into a wellbore extending through a subsurface region comprises a self-orienting perforating tool comprising a tool housing, and a charge carrier positioned in the tool housing and comprising one or more charge receptacles for receiving one or more shaped charges, a plurality of bearings facilitating relative rotation between the charge carrier and the tool housing, and an electrical switch electrically connectable to the perforating tool whereby relative rotation is permitted by the plurality of bearings between the electrical switch and the charge carrier while also permitting electrical connectivity between the electrical switch and the perforating tool. In certain embodiments, the downhole assembly comprises a detonator electrically connectable to the electrical switch and ballistically connectable to the perforating tool. In certain embodiments, relative rotation is restricted between the detonator and the electrical switch. In some embodiments, the detonator is ballistically connectable to the perforating tool external the charge carrier. In some embodiments, the electrical switch is electrically connectable to the perforating tool external the charge carrier. In certain embodiments, the downhole assembly comprises a signal pod comprising a pod chassis and the electrical switch supported by the pod chassis. In certain embodiments, relative rotation is restricted between the electrical switch and the tool housing.

[0013]An embodiment of a downhole assembly deployable into a wellbore extending through a subsurface region comprises a self-orienting perforating tool comprising a tool housing, and a charge carrier positioned in the tool housing and comprising one or more charge receptacles for receiving one or more shaped charges, a plurality of bearings facilitating relative rotation between the charge carrier and the tool housing, and a detonator ballistically connectable to the perforating tool whereby relative rotation is permitted by the plurality of bearings between the detonator and the charge carrier while also permitting ballistic connectivity between the detonator and the perforating tool. In some embodiments, the downhole assembly comprises a signal pod comprising a pod chassis and the detonator supported by the pod chassis. In certain embodiments, relative rotation is restricted between the detonator and the tool housing. In some embodiments, the perforating tool comprises a detonating cord ballistically connectable to the one or more shaped charges, and wherein relative rotation is permitted by the plurality of bearings between the detonator and the detonating cord. In some embodiments, the downhole assembly comprises a detonating cord housing ballistically connectable between the detonator and the detonating cord that permits relative rotation between the detonating cord and the detonator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]A more complete understanding of the present disclosure may be obtained from the following detailed description with reference to the attached drawing figures as summarized below, in which:

[0015]FIG. 1 is an elevation view of a wellsite with a crane lifting a wireline lubricator with a tool string suspended below about to be pulled into the wireline lubricator so that that after the lubricator is re-attached to the wellhead, the tool string may be inserted into a wellbore;

[0016]FIG. 2 is a schematic view of an exemplary system for perforating a hydrocarbon-producing wellbore including a tool string deployed by a wireline system;

[0017]FIG. 3 is a schematic elevation view of the well with the plug and perf tool string in the extended horizontal segment;

[0018]FIG. 4 is perspective view of two perforating tools connected end to end;

[0019]FIG. 5 is an elevation cross-section view of an embodiment of a self-orienting perforating tool view according to principles disclosed herein;

[0020]FIG. 6 is a perspective view of the charge assembly of the self-orienting perforating tool view of FIG. 5;

[0021]FIG. 7 is a perspective view of the eccentric weight that is to be attached to the charge assembly for the self-orienting perforating tool view of FIG. 5;

[0022]FIG. 8 is perspective view of the underside of charge assembly including the eccentric weight for the self-orienting perforating tool view of FIG. 5;

[0023]FIG. 9 is a perspective view of a tandem sub used to connect perforating tools together end to end to assemble a tool string;

[0024]FIG. 10 is a perspective view of an eccentric weight in an alternative embodiment of the present disclosure;

[0025]FIG. 11 is a cross-section elevation view of the charge carrier and eccentric weight of the alternative embodiment shown in FIG. 10;

[0026]FIG. 12 is a perspective view of the underside of the charge carrier for the alternative embodiment shown in FIG. 11;

[0027]FIG. 13 is a cross-section view of another alternative embodiment of the charge carrier and eccentric weight;

[0028]FIG. 14 is an exploded perspective view of the embodiment shown in FIG. 13;

[0029]FIG. 15 is an enlarged perspective view of one of the modular eccentric weights in FIG. 14;

[0030]FIG. 16 is a top view of two modular weights positioned together in the same relationship as intended when attached to the charge carrier;

[0031]FIG. 17 is a bottom view of the two modular weights in FIG. 16;

[0032]FIG. 18 is a side view of two modular weights positioned together;

[0033]FIG. 19 is a side view of an embodiment of a charge carrier and modular weights;

[0034]FIG. 20 is a cross-sectional view along line 20-20 of FIG. 19;

[0035]FIG. 21 is a cross-sectional view along line 21-21 of FIG. 19;

[0036]FIG. 22 is a cross-sectional view along line 22-22 of FIG. 19;

[0037]FIG. 23 is a cross-sectional view along line 23-23 of FIG. 19;

[0038]FIG. 24 is a perspective of shaped charges, a pair of modular weights, and a pair of endplates of an embodiment of a perforating tool;

[0039]FIG. 25 is another side view of two modular weights positioned together;

[0040]FIG. 26 is an elevation view of two modular weights positioned together but having undertaken a bent alignment when the charge carrier is overweighted and yields revealing a concern where the eccentric weights drag along the inside of the outer housing;

[0041]FIG. 27 is a perspective view showing a first solution to resist charge carrier bending;

[0042]FIG. 28 is a perspective view of another alternative solution to charge carrier bending;

[0043]FIG. 29 is a side view of the solution illustrated in FIG. 28;

[0044]FIG. 30 is a side view of another alternative solution to charge carrier bending;

[0045]FIG. 31 is an end view of the solution to charge carrier bending shown in FIG. 30;

[0046]FIG. 32 is a side view of a fourth alternative solution to charge carrier bending;

[0047]FIG. 33 is a side cross-sectional view of a pair of bearings of an embodiment of a downhole assembly;

[0048]FIG. 34 is an exploded perspective view of a reusable tandem sub showing alternative mounting positions for a face mounted bearing assembly ;

[0049]FIG. 35 is a fragmentary cross-section of a tandem sub showing an alternative mounting configuration for a bearing assembly;

[0050]FIG. 36 is a cut away perspective view of a tandem sub and a fragmentary charge carrier attached showing the two bearing assemblies;

[0051]FIG. 37 is an enlarged fragmentary cross-section of the perforation tool shown in FIG. 28 with a reduced rotation friction electrical connection at the top end of the charge carrier;

[0052]FIG. 38 is an enlarged fragmentary cross-section of a perforation tool similar to FIG. 37 with another alternative reduced rotation friction electrical connection at the top end of the charge carrier;

[0053]FIG. 39 is an enlarged fragmentary cross-section similar to FIGS. 37 and 38 of another reduced rotation friction electrical connection at the top end of the charge carrier;

[0054]FIG. 40 is an enlarged fragmentary cross-section of another reduced friction electrical connection;

[0055]FIG. 41 is an enlarged fragmentary cross-section of another reduced friction electrical connection;

[0056]FIG. 42 is a perspective view of the detonating cord housing with a reduced rotation friction electrical connector;

[0057]FIG. 43 is a cross-sectional end view of the reduced rotation friction electrical connector shown in FIG. 42,

[0058]FIG. 44 is a side elevation view of a third alternative embodiment for a reduced rotation friction electrical connector;

[0059]FIG. 45 is an end view of the low friction electrical connector engaging with the detonating cord housing;

[0060]FIG. 46 is a perspective view of the low friction electrical shown with one spring separated and spaced away from its mount for clarity;

[0061]FIG. 47 is a perspective of a low friction electrical connector for a downhole assembly;

[0062]FIG. 48 is a cross-sectional view of a downhole assembly including a detonator and the electrical connector of FIG. 47;

[0063]FIG. 49 is a side cross-sectional view of the downhole assembly of FIG. 48; and

[0064]FIG. 50 is a perspective view of a signal pod of a downhole assembly.

DETAILED DESCRIPTION

[0065]The following discussion is directed to various exemplary embodiments of the present disclosure. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0066]In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. Further, the term “fluid,” as used herein, is intended to encompass both fluids and gasses.

[0067]Referring now to FIG. 1, a wireline system 5 is shown for deploying a “plug and perf” tool string 30 into a wellbore 10 in which casing 15 (commonly called a casing string) is installed. The view shown in FIG. 1 is near the surface 7 with the wellbore 10 extending far into the earth and into an extended generally horizontal run within a prospective hydrocarbon bearing formation 3 (see FIG. 3) deep in the ground. A crane 11 is positioned adjacent the cased wellbore 10 for lifting a wireline lubricator 20 off the top of the valve tree 12 in preparation for lifting a tool string 30 up inside the wireline lubricator 20. Wireline 28 of the wireline system 5 is fed through a wireline sealing element 22 and down through the wireline lubricator 20 to pull the tool string 30 up into the wireline lubricator 20 whereupon the wireline lubricator 20 is then attached onto the top of a valve tree 12. A bottom coupling 21 sealingly connects the lubricator 20 to a coupling 14 at the top of the valve tree 12.

[0068]In the configuration shown in FIG. 1, the wellbore 10 is sealed by one or more valves of the valve tree 12. As is well known, pressure within cased wellbore 10 must be maintained in a pressure-controlled state at all times so that before any valve is opened, others are closed in a manner that maintains well pressure control. The position of wireline lubricator 20 is controlled by an operator of the crane 11 using a bridle 25 attached to an upper end of the wireline lubricator 20, while the position of tool string 30 is controlled by an operator of a wireline truck (not shown) via the wireline 28. In FIG. 1, the wireline operator has reeled in the wireline 28 to lift the tool string 30 off of the surface 7 into a vertical orientation such that an upper end of the tool string 30 is proximal to the bottom of the wireline sealing element 22 at the bottom end of the wireline lubricator 20. The entire length of tool string 30 must fit fully into the wireline lubricator 20 to allow the bottom coupling 21 of wireline lubricator 20 to sealingly connect to the coupling 14 of valve tree 12 to maintain well pressure control prior to insertion of the tool string 30 into the cased wellbore 10 through the valve tree 12.

[0069]The tool string 30 includes a number of tools that are selected by an operator of the cased wellbore 10 and which, in this example, includes a plug 31 at the bottom thereof, an adapter kit 32 and a setting tool 33 where the adapter kit 32 is connected between the plug 31 and setting tool 33. Above the setting tool 33 are a number of perforating tools or “perf guns” 35 along with other tools that include electronic communication with the setting tool 33 and the perforation tools 35 and other tools of tool string 30 that provide the wellbore location of the tool string 30 as well as other known functions. A tandem sub 50 may be coupled between the perforating tools 35 to provide pressure isolation therebetween. At the top of the tool string 30 is a wireline coupling device 36 that attaches to the wireline 28. The wireline 28 extends from the wireline truck, over a pair of sheaves 26 and 27, and is typically quite long to permit the tool string 30 to run potentially miles down into the cased wellbore 10. It may be generally understood that wellbores, including cased wellbore 10, extend vertically downwards from the surface 7 and then turns along a broad curve to a more horizontal path or portion that is typically a great length (e.g., a mile or more) horizontally through a probable hydrocarbon bearing zone.

[0070]Turning to FIG. 2, the tool string 30 is shown within the well 10 below and past the valves in the valve tree 12 such that the tool string 30 is on its decent within a first vertical section where the well is sealed from outside environment by the wireline sealing element 22 at the top of the wireline lubricator 20 (both shown only in FIG. 2). The tool string 30 is lowered into the vertical section and typically pumped down to a generally horizontal section shown in FIG. 3 where the wellbore 10 extends a significant distance along and within a prospective hydrocarbon bearing formation 3.

[0071]In FIG. 3, a prior perfing and fracking operation has been conducted including the setting of a prior plug 17 and puncturing of prior perforations 69 that have been fracked by high pressure hydraulic fluid to enlarge the perforations. So, just above the existing perforations 69, the plug 31 at the end of the plug and perf tool string is set or deployed to seal against the inside of the casing to isolate the upper portion of the wellbore 10 from a lower portion below the plug 31. The plug 31, once set, prevents fluid that will be pumped down from the surface 7 and is intended to frack newly created perforations from escaping into the existing perforations 69 and preventing the needed build in fluid pressure. It takes significant hydraulic pressure to enlarge and extend new perforations so any plug and perf operation begins with plugging off the lower existing perforations such as those shown at 69, separating the set plug from the remainder of the plug and perf tool string so that new perforations may be created in the casing 15 above the set plug 31. Once the plug 31 is disengaged from the tool string 30, the plug and perf tool string lays on the bottom of the horizontal run of the casing 15 and is pulled upwardly toward the surface while each of a number of perforating tools 35 are detonated at predetermined positions to shoot or discharge shaped explosive charges 125 (see FIGS. 5 and 6) which puncture the casing 15 thereby creating a perforation.

[0072]Turning to FIG. 4, two perforating tools 35A and 35B are shown as connected both physically and electrically. Specifically, an uphole perforating tool 35A is connected to a downhole perforating tool 35B where the two tools are essentially identical but for their order in a tool string 30. It should be understood that adjacent tools need not be identical in that some adjacent tools may have more or less shots than other tools in the tool string 30 or those shots may be directed into the casing 15 at differing directions, as desired. For the purposes of this embodiment and disclosure, uphole and downhole tools have a common design and construction and the components of the tools will be described with the same referenced numerals. The tools 35A and 35B are part of a tool string 30 where the uphole tool 35A is connected at its top end by a tandem sub 50A revealing a free pin thread end extending to the left in the uphole direction. A second tandem sub 50B (downhole tandem sub) connects the two tools 35A and 35B together by screw threads. In this embodiment, the tandem subs 50A and 50B have double ended pin threads 58 that secure to box threads 38 at the ends of each tool.

[0073]Referring now to FIGS. 5-9, an exemplary embodiment of a self-orienting perforating tool 100 along with exemplary embodiments of a pair of tandem sub 400 (shown as tandem subs 400A and 400B in FIG. 5) are shown where the uphole end of perforating tool 100 and each tandem sub 400A and 400B is to the left in FIG. 5 and the downhole end of perforating tool 100 and each tandem sub 400A and 400B is oriented to the right in FIG. 5. The assembly formed from perforating tool 100 and tandem subs 400A and/or 400B may be referred to herein as a downhole assembly 101 deployable with a tool string into a wellbore penetrating a subterranean formation.

[0074]Perforating tool 100 generally includes a tubular outer tool housing 150 and a charge assembly 200 receivable in the tool housing 150. The tool housing 150 of perforating tool 100 is connected (e.g., threadably coupled such as by screw threads) at either end to an uphole tandem sub 400A at the uphole end thereof and a downhole tandem sub 400B at the downhole end thereof. In some embodiments, the perforating tool 100 of FIG. 5 may comprise an embodiment of the perforating tools 35A and 35B of the wireline system 5 shown in FIGS. 1-3. However, perforating tool 100 may be utilized in systems other than the wireline system 5 shown in FIGS. 1-3. Similarly, the tandem subs 400A and 400B of FIG. 5 may comprise embodiments of the tandem subs 400A and 400B of the wireline system 5. However, tandem subs 400A and 400B may be utilized in systems other than the wireline system 5.

[0075]Both the uphole and downhole ends of perforating tool 100 are sealed by annular seals (e.g., O-rings) defining an air-filled sealed interior or chamber 160 within the tool housing 150 for an orienting charge assembly 200. The charge assembly 200 includes a charge carrier 210 which physically support combustible shaped charges 260 via charge receptacles 211 formed in the charge carrier 210. In this exemplary embodiment, shaped charges are generally conical or frustoconical in shape having an enlarged outer end from which an explosive charge or jet may be emitted in response to the detonation of shaped charge 260, and an opposed inner end or base defining a ballistic connector 264 for ballistically connecting the shaped charge 260 to a detonating cord 270 of the perforating tool 100.

[0076]Charge carrier 210 is generally tubular in this exemplary embodiment with an interior 213 and having a longitudinal or rotational axis 215; however, the shape or configuration of charge carrier 210 may vary in other embodiments. In this example, three shaped charges 260 are shown as received in three corresponding charge receptacles 211 but the number of shaped charges 260 may vary from three in other embodiments. For instance, perforating tools with fewer than six shaped charges 260 are fairly standard and some perforating tools can include upwards of 200 and higher shaped charges 260. In this exemplary embodiment, charge assembly 200 additionally includes a pair of endplates 220 and 240 coupled to the charge carrier 210 at opposing longitudinal end thereof. Particularly, an uphole endplate 220 is coupled to the uphole end of the charge carrier 210 such as by one or more fasteners (e.g., threaded fasteners, rivets, and the like). Similarly, a downhole endplate 240 is secured to the downhole end (toward the right of FIG. 5) of the charge carrier 210.

[0077]In some embodiments, charge carrier 210 comprises an electrically conductive material while both endplates 220 and 240 comprise electrically insulating materials. Additionally, in this exemplary embodiment, a detonating cord housing 290 is coupled to the downhole endplate 240 and projects externally and longitudinally therefrom. The detonating cord housing 290 may receive a terminal end of the detonating cord 270 and may comprise an electrically conductive material whereby the detonating cord housing 290, with the detonating cord 270 received therein, may form both a ballistic and an electrical connection with the signal pod 420 when the perforating tool 100 is coupled to the signal pod 420.

[0078]Downhole assembly 101 comprises a plurality of bearings 440. In this exemplary embodiment, bearings 440 are face-mounted to tandem subs 400A and 400B at each longitudinal end thereof for supporting the charge assembly 200 within the sealed chamber 160 of tool housing 150. In particular, the face mounted bearings 440 each comprise an annular outer race 442 attached to the tandem subs 400A, 400B by fasteners 450 (e.g., threaded fasteners such as screws, bolts, and the like) and a corresponding annular inner race 446 that is allowed to freely rotate within the outer race 442, such as by one or more roller or bearing elements 448 (e.g., ball bearings and the like) positioned radially between the outer race 442 and inner race 446 to facilitate relative rotation therebetween about the rotational axis 215.

[0079]In this exemplary embodiment, uphole endplate 220 comprises an annular uphole collar 230 and the downhole endplate 240 comprises an annular downhole collar 250. An outer diameter of the uphole collar 230 corresponds to an inner diameter of the inner race 446 of the ball bearing 440 located at the downhole end of the uphole tandem sub 400A, while an outer diameter of the downhole collar 250 corresponds to an inner diameter of the inner race 446 of the bearing 440 mounted to the uphole end of downhole tandem sub 400B. In this exemplary embodiment, the uphole and downhole collars 230 and 250 of endplates 220 and 240 are sized and shaped to be slidably inserted within the inner races 446 of the respective bearings 440 such that the entire charge assembly 200 may freely rotate within the sealed chamber 160 relative to tool housing 150 (e.g., about rotational axis 215). While the respective collars 230 and 250 and associated bearings 440 may be different dimensions, in at least some embodiments each end-use common parts for simplicity in manufacturing.

[0080]In this exemplary embodiment, charge assembly 200 further includes one or more eccentric weights 280 for controlling an angular position of the charge assembly 200 about the rotational axis 215. Eccentric weight 280 may apply an off-axis orienting force or torque to the charge carrier 210 urging the charge carrier 210 towards a desired angular orientation (e.g., relative to the direction of gravity). Particularly, eccentric weight 280 is coupled to the charge carrier 210 in a manner to orient or bias the assembly 200 towards a preferred angular orientation relative the rotational axis 215 while the perforating tool 100 is laying in a generally horizontal run (relative to the direction of gravity) of a hydrocarbon wellbore. In FIG. 5, an exemplary preferred orientation of charge assembly 200 is shown that corresponds to a position in which each of the shaped charges 260 are aimed vertically upwards. However, by positioning the eccentric weight 280, any preferred orientation of shaped charges 260 may be created.

[0081]In another aspect of the presently described embodiment is that the perforating tool 100 is operated by a control module or signal pod 420 of one of the adjoining tandem subs 400A and 400B. The signal pod 420 may form part of the downhole assembly 101 along with the perforating tool 100 and tandem sub 400. In some embodiments, the downhole assembly 101 may include a perforating tool 100 and a signal pod 420 for controlling the operation of the perforating tool 100 (e.g., for controlling the detonation of shaped charges 260 of the perforating tool 100) but not a tandem sub 400. Instead, for example, the signal pod 420 may instead be located in the tool housing 150 of perforating tool 100 or another container besides the tandem sub 400.

[0082]In this exemplary embodiment, downhole assembly 101 comprises a first or uphole signal pod 420A is positioned within an internal cavity or opening 402 (e.g., a cylindrical opening) of the uphole tandem sub 400A at the uphole or left end thereof and a second or downhole signal pod 420A is similarly positioned in an opening 402 of downhole tandem sub 400B. Additionally, in this exemplary embodiment, each signal pod 420 is a self-contained pod including an electrical switch 422 and a detonator 424 positioned adjacent to the detonating cord housing 290 (coupled to downhole endplate 240) having detonating cord 270 (shown in dotted lines) received therein. The detonator 424 may be ballistically connected to the shaped charges 260 of perforating tool 100 through the intervening detonating cord 270. In some embodiments, downhole assembly 101 may not include signal pod 420. Instead, the downhole assembly 101 may, for example, only include an electrical switch 422 and/or detonator 424.

[0083]As will be described further herein, detonator 424 may be electrically connected to the electrical switch 422 whereby the electrical switch 422 may control the detonation of detonator 424. In some embodiments, switch 422 comprises a computing system including one or more processors, one or memory devices, and the like positioned on a printed circuit board (PCB). However, in other embodiments, the configuration of switch 422 may vary. In some embodiments, each signal pod 420 also includes a pod chassis 426 for physically supporting the switch 422 and detonator 424. In other embodiments, signal pods 420 may not include a pod chassis 426. Further, although only the switch 422 and detonator 424 of downhole signal pod 420B is shown in FIG. 5, in some embodiments, uphole signal pod 420A may be configured similarly as downhole signal pod 420B and thus may similarly include a switch 422 and detonator 424. The detonator 424 of downhole signal pod 420B is arranged to deliver, an electric signal is delivered to the switch 422 with sufficient power to detonate the detonator 424, an explosive blast to combust or detonate the detonating cord received in detonating cord housing 290 via holes or windows formed in the detonating cord housing 290. Additionally, the downhole signal pod 420B includes minimal wiring connections to minimize probabilities for a non-fire or mis-fire.

[0084]With the signal pods 420A and 420B positioned within their respective openings 402, the longitudinal length of the assembly formed from perforating tool 100 and tandem subs 400A and 400B may be minimized. Generally, one of the more expensive components of the perforating tool 100 is typically the housing 150 due primarily to the high physical demands of the tool housing 150. Particularly, tool housing 150 must be sufficiently strong to withstand the immense hydrostatic pressures downhole especially when other perforating tools are being fired so as to maintain the integrity (e.g., prevent leaks) in the sealed chamber 160 thereof. Specifically, a leak within the sealed chamber 160 of tool housing 150 will almost certainly cause an electrical short in the limited wiring and electronics within the sealed chamber 160. But the job of the housing 150 is only half done until the shaped charges 260 are fired when the pressures reverse and an immense pressure pulse occurs from within. High strength is not helpful when the perforating tool 100 is fired but rather great toughness is needed to hold the fired perforating tool 100 together without letting it break up, shatter or fragment or just get distorted to a point where it will be tough to drag out of the well past each of the connections and distortions of the casing of the wellbore. Generally, high strength and high toughness is expensive (e.g., due to the requirement of using thicker and/or more exotic materials) such that, among other reasons, minimizing the longitudinal length of the tool housing 150 is very desirable. Note that the longitudinal length of the of the housing 150 is shown by arrow 810 in FIG. 5. In addition, the length of the arrow 810 is the minimal length for the number of shaped charges 260 and the endplate and bearing 440 plus the threads of tool housing 150 and accompanying annular seals. These extra length dimensions are shown by arrows 820 and 830. Conventional perforating tools typically include a longer housing to accommodate a long switch received therein. In some embodiments, downhole assembly 101 may facilitate a length reduction of between about five and seven inches in housing length in some embodiments which amounts to savings between one and three dollars per inch.

[0085]As described above, in this exemplary embodiment, charge assembly 200 includes eccentric weight 280 that fits externally onto an outer surface or profile of the charge carrier 210 and may extend arcuately up to 180 degrees of what is intended to be the bottom of the charge assembly 200 (when charge assembly 200 is disposed in its preferred angular orientation about rotational axis 215) while having an outside shape to be closely space within the housing 150. Additionally, although eccentric weight 280 is shown in FIG. 5 as comprising a single integral or monolithically formed member or body, in other embodiments, the shape or configuration of eccentric weight 280 may vary.

[0086]As show particularly in FIGS. 7 and 8, in this exemplary embodiment, eccentric weight 280 includes one or more openings 282 positioned equidistantly between opposing lateral sides of the eccentric weight 280 and centrally aligned with a corresponding detonator 424 for at least partially receiving the ballistic connector 264 of a shaped charge. Additionally, in this exemplary embodiment, eccentric weight 280 includes one or more elongate openings or slots 284 extending longitudinally and contiguously from the central openings 282 for at least partially receiving to provide space for the detonating cord 270 (shown only in dotted lines in FIG. 4) to be run lengthwise within the charge carrier 210 and follow a serpentine path in and out of the charge carrier 210 so as to feed through a detonating cord groove (located external the charge carrier 210) at the base of each shaped charge 260 (e.g., at ballistic connector 264) to be in proximity of the explosive primer within a corresponding shaped charge 260 proximal to the ballistic connector 264.

[0087]Referring to FIGS. 10-12, another embodiment of a eccentric weight 300 is shown. Eccentric weight 300 includes some features in common with eccentric weight 280 described above, and shared features are labeled similarly. In some embodiments, eccentric weight 300 may be incorporated into perforating tool 100 in lieu of eccentric weight 280; however, in other embodiments, eccentric weight 300 may be incorporated in perforating tools that vary in configuration from perforating tool 100.

[0088]The amount of righting or off-axis force may be augmented by eccentric weight 300 shown in FIG. 9 without needing to increase the arcuate width of the eccentric weight 300. Particularly, in this exemplary embodiment, eccentric weight comprises one or more inner lobes 302 of additional dense material (e.g., a low cost but dense steel) that project from an inner surface 301 of eccentric weight 300 which is positioned directly adjacent or contacting an outer surface of the charge carrier 210. Lobes 302 may be received at least partially within the interior 213 of charge carrier 210 with lobes 302 extending inwardly through openings 214 formed in the charge carrier 210. Charge carrier 210 may include additional openings to permit ballistic connectors 264 of shaped charges 260 to project externally from the interior 213 of charge carrier 210 along with portions of the detonating cord 270 as the detonating cord 270 snakes or extends through the ballistic connectors 264 of shaped charges 260. Thus, in this exemplary embodiment, a portion of eccentric weight 300 is positioned external the interior 213 of charge carrier 210 while another portion of the eccentric weight 300 (e.g., lobes 302) are positioned instead within the interior 213 of charge carrier 210.

[0089]Adding additional weight outside the charge carrier 210 becomes limited by the minimal space within the sealed chamber 160 outside the charge carrier 210. Ideally, all of the weight of the eccentric weight would be at the six o'clock position (maximizing the lever arm extending between the rotational axis 215 and the center of mass of the eccentric weight) looking at a cross-section view but after that peripheral volume is fully occupied by the sculpted body of the eccentric weight, an ever broadening curve of steel leads to diminishing additional righting force as the curve passes the bottom 90 degrees and approaches the bottom 180 degrees, as shown particularly in FIG. 11. Reducing the widthwise extent or sweep of the eccentric weight extending between opposing lateral sides 202 of eccentric weight 300 (generally indicated by the dotted line angle), additional weight may be infilled by lobes 302 projected into the hollow core of the charge carrier 210 in available space around the shaped charges 260, wiring and detonating cord 270. Configuring the eccentric weight 300 to have dense lobes 302 shaped to reside within the charge carrier 210 increases the total weight of the eccentric weight 320 without expanding the sweep of the eccentric weight 300 to provide higher aiming accuracy for the shaped charges 260. As used herein, “aiming accuracy” refers to the angular or circumferential variation of the shots made by shaped charges 260 about rotational axis 215 from the idealized orientation about rotational axis 215. For example, even when all rotational friction is minimized as much as practical, a slight amount of friction could potentially cease rotation of the charge carrier 210 with shaped charges 260 out of the preferred orientation about rotational axis 215 such that the actual orientation may be off by 5 or 10 degrees, as an example. Thus, more weight precisely positioned could tighten the rotational accuracy. In some embodiments, the rotational accuracy of shaped charges 260 and perforating tool 100 generally can be as little as +/−3 to 5 degrees, while in other embodiments the aiming accuracy may be less.

[0090]Turning now to FIGS. 13-16, another embodiment of a downhole assembly 1011 is shown. Downhole assembly 1011 may include features in common with downhole assembly 101 shown in FIG. 5, and shared features are labeled similarly. In this exemplary embodiment, downhole assembly 1011 includes a perforating tool 1000, one or more tandem subs 400 (shown as tandem subs 400A and 400B in FIG. 13), one or more signal pods 420 (shown as signal pods 420A and 420B in FIG. 13), a first bearing 1440, and a second bearing 1450. Additionally, perforating tool 1000 generally includes tool housing 150, a charge carrier 1210, and one or more eccentric weights 1280. Prior to being deployed downhole in a wellbore, one or more shaped charges 260 may be installed in the charge carrier 1210. Generally, perforating tool 1000 features alternative bearing arrangements, enhanced sculpture of the eccentric weights, and friction reducing aspects to portions that may be otherwise prone to frictional contact. Reduced rotational friction permits the charge carrier 1210 of the perforating tool 1000 rotate more freely about a rotational axis 1215 and attain and maintain a higher fidelity to a desired angular orientation (e.g., a 12 o'clock orientation in this example).

[0091]In this exemplary embodiment, perforating tool 1000 includes a single-shot eccentric weight 1280S and a double-shot eccentric weight 1280D where eccentric weight 1280S is configured to interface with a single shaped charge 260 while eccentric weight 1280D (having a greater longitudinal length than eccentric weight 1280S) is configured to interface with a pair of shaped charges 260. The eccentric weights 1280S and 1280D are sculpted to fit snugly around outer convex surfaces of shaped charges 260 extending from the ballistic connector 264 to the opposing outer end of the shaped charge 260. In addition, eccentric weights 1280 are modular in that they may be configured to fit a single shaped charge 260 (e.g., eccentric weight 1280S), a pair of shaped charges 260 (e.g., eccentric weight 1280D) or more than a pair of shaped charges. Particularly, eccentric weight 1280 includes a single concave receptacle 1282 defined by one or more concave surfaces configured to partially receive a single shaped charge 260, while eccentric weight 1280D includes a pair of concave receptacles 1282 for at least partially receiving a pair of shaped charges 260. In this exemplary embodiment, central openings 282 and slots 284 are centrally located or formed in each concave receptacle 1282 to permit the passage of the ballistic connector 264 and detonating cord 270 therethrough. In other embodiments, concave receptacles 1282 may not include central openings 282 and/or slots 284. In a two-shot perforating tool, on double-shot eccentric weight 1280D may be used (or a pair of eccentric weights 1280S) and in a four-shot perforating tool, different permutations of single-shot, double-shot, or quadruple-shot eccentric weights 1280 may be used. As an example, and referring briefly to FIGS. 17 and 18, an example is provided showing a pair of eccentric weights 1280D that may form part of a charge carrier configured to carry four separate shaped charges 260.

[0092]Referring again to FIGS. 13-17, as compared with other eccentric weights, eccentric weights 1280 concentrate more of the mass of eccentric weights 1280 nearer the 6 o'clock position (circumferentially opposite the desired 12 o'clock shot direction in this exemplary embodiment), maximizing the righting or off-axial force applied by eccentric weights 1280 to the charge carrier 1210. Additionally, the amount of the overall volume or mass of eccentric weights 1280 received within an interior 1213 of charge carrier 1210 to increase the overall volume or mass of each eccentric weight 1280 per unit length of eccentric weights 1280 and a given sweep (e.g., sweep angle extending between opposing lateral sides 1281 of eccentric weights 1280). This expands on the design effort that includes the inner lobes 302 in FIG. 10 including more volume of high density material (e.g., cast steel) inside the radius of the tubular charge carrier 210.

[0093]A second aspect to the concave receptacle 1282 is that it seems to provide additional resistance to movement or more properly, resistance to acceleration of the detonation of the shaped charge 1260. In effect, it appears that the explosive energy collapsing inside the cone of the shaped charge and projecting out the top bleeds a small amount of energy pressing the dense metal of the shaped charge body downwardly. And the close proximity of a higher amount of dense material (the concave eccentric weights 1280S and 1280D) underneath the shaped charge 1260 resists this downward movement or acceleration effectively redirecting at least of portion of the energy back toward the top and further out of the perforating tool and into the perforation of the casing and formation. This may not be a huge redirection of the blast energy, but any little extra would be at least helpful or may allow the use of a slightly reduced explosive charge with the same net effect.

[0094]Referring to FIGS. 19-24, in this exemplary embodiment, charge carrier 1210 includes a plurality of longitudinally spaced weight openings 1217 separated by arcuately extending ribs 1219. Ribs 1219 are received snugly in the concave receptacles 1282 of eccentric weights 1280 while weight openings 1217 permit the passage of a portion of eccentric weights 1280 into the interior 1213 of charge carrier 1210 as shown particularly in FIGS. 20-23. By utilizing the space afforded by the interior 1213, and particularly by maximizing the volume of eccentric weights 1280 received in the interior 1213 of charge carrier 1210 proximal the 6 o'clock position, the off-axis force applied by the eccentric weights 1280 to the charge carrier 1210 may be maximized to maintain the charge carrier 1210 in the desired angular orientation. This maximization of the volume of eccentric weights 1280 within the interior 1213 of charge carrier 1210 may be achieved via weight openings 1217 in charge carrier 1210 and the concave receptacles 1282 of weights 1280 which cradle the shaped charges 260 as shown particularly in FIG. 24.

[0095]Turning now to FIGS. 25 and 26, one concern for a perforating tool design including charge carriers having numerous openings formed therein, such as weight openings 1217 of charge carrier 1210, is that after many bumps and knocks moving miles down a wellbore that the heavy right weights 1280S and 1280D may cause the charge carrier 1210 to deform or sag from the intended relative orientation of the eccentric weights 1280S and 1280D shown in FIG. 25 to a sagged configuration shown in FIG. 26, resulting in concomitant sagging or bending of the rotational axis 1215. Such sagging may be of particular concern should it result in the outer periphery of eccentric weights 1280 physically contacting and frictionally dragging against an inner surface of the tool housing 150, likely reducing the aiming accuracy of the perforating tool 1000.

[0096]Turning to FIG. 27, an exemplary solution to this issue is shown where the modular eccentric weight 1280S includes longitudinal openings or blind holes 1285 suited to receive corresponding elongate members or stiffening pins 1283. The stiffening pins 1283 are shown in FIG. 27 as having a circular cross-section but the cross-section of stiffening pins 1283 may vary. For instance, in other embodiments, the cross-section of stiffening pins may be square, rectangular, triangular, other polygons, elliptical and star shapes are optional. It should be understood that the stiffening pins are double ended where the opposite end is arranged to extend into a similar blind hole 1285 in the other modular eccentric weight such as eccentric weight 1280D. If either eccentric weight 1280 is used alone without a second weight such as in a single shot or double shot perforating tool, a single end stiffening pin may be inserted into the blind hole to preserve the total mass of steel for the eccentric weight rather than have the small void space being empty.

[0097]Referring to FIGS. 28 and 29, a second stiffening arrangement is shown including an externally threaded rod or fastener 1287 arranged to extend longitudinally or lengthwise through a corresponding aperture or throughhole 1286 formed in each of the eccentric weights 1280S and 1280D. The threaded rod 1287 may be all-thread or simply threaded at the ends and secured by an external fastener 1289 (e.g., a nut and washer) as shown particularly in FIG. 29. However, threaded rod 1287 may be secured to eccentric weights 1280S and 1280D via a variety of mechanisms other than external fasteners such as fasteners 1289. As shown particularly in FIG. 29, elongate members such as threaded rod 1287 (and/or stiffening pins 1283) maintains the rectilinearity of rotational axis 1215.

[0098]Referring to FIGS. 30 and 31, resisting flexion between two eccentric weights 1280 may also be accomplished by filling the small gap 1290 formed longitudinally between the pair of eccentric weights 1280S and 1280D as the perforating tool 1000 is assembled. As an example, a thin plate or washer 1292 may be inserted into the gap 1290 directly between the eccentric weights 1280S and 1280D to restrict the eccentric weights 1280S and 1280D from pivoting or bending relative to each other which would otherwise result in a closing of the gap 1290 as shown in FIG. 26. Thus, a width of the washer 1292 may be similar to but slightly less than the width of gap 1290 to permit the insertion of washer 1292 into gap 1290. Additionally, in this exemplary embodiment, an outer periphery of the washer 1292 is curved to conform to the outer periphery of eccentric weights 1280S and 1280D. Further, washer 1292 is provided with a slotted opening 1294 to permit the passage of the detonating cord 270 therethrough. However, the shape or configuration of washer 1292 may vary in other embodiments.

[0099]Referring to FIG. 32, another embodiment of a thin plate or washer 1296 is shown for insertion into the gap 1290. In this exemplary embodiment, washer 1296 is wedge-shaped having a thickness that varies along the length of washer 1296 such that washer 1296 has a maximum thickness at an outer end 1297 thereof. In this configuration, washer 1296 may be wedged into the gap 1290 to prevent eccentric weights 1280S and 1280D from sagging or pivoting relative to one another. The washers 1292 and 1296 shown in FIGS. 30-32 may be inserted into gap 1290 from a variety of directions including from vertically below (shown in FIG. 30) and from vertically above (shown in FIG. 32).

[0100]Referring to FIG. 33, bearings 1440 and 1450 of a downhole assembly 1401 are shown in isolation to facilitate the discussion of features thereof. In this exemplary embodiment, first bearing 1440 of downhole assembly 1401 includes a radially outer race 1442, a radially inner race 1444, and a plurality of roller or bearing elements 1448 (e.g., ball bearings, rollers, and the like) positioned therebetween that facilitate relative rotation between the outer race 1442 and inner race 1454. The outer bearing race 1442 of first bearing 1440 has a minimum inner diameter 1443 and a maximum outer diameter 1445. Additionally, the inner bearing race 1446 of first bearing 1440 has a minimum inner diameter 1447 and a maximum outer diameter 1449.

[0101]Similarly, the second bearing 1450 of downhole assembly 1401 includes a radially outer race 1452, a radially inner race 1454, and a plurality of roller or bearing elements 1456 (e.g., ball bearings, rollers, and the like) positioned therebetween that facilitate relative rotation between the outer race 1452 and inner race 1454. The outer bearing race 1452 of first bearing 1450 has a minimum inner diameter 1453 and a maximum outer diameter 1455. Additionally, the inner bearing race 1456 of second bearing 1450 has a minimum inner diameter 1457 and a maximum outer diameter 1459. In this exemplary embodiment, the minimum inner diameters 1453 and 1457 of second bearing 1450 are greater than the corresponding inner diameters 1443 and 1447, respectively, of first bearing 1440. Similarly, the maximum outer diameters 1455 and 1459 of second bearing 1450 are greater than the corresponding maximum outer diameters 1445 and 1449 of first bearing 1440. In this configuration, a central opening of the second bearing 1450 is enlarged relative to a central opening of the first bearing 1440 facilitating the passage of signal pod 420 through the central opening of second bearing 1450 and the axial overlapping of signal pod 420 with second bearing 1450 to minimize the overall longitudinal length of downhole assembly 1401.

[0102]Referring to FIG. 34, another embodiment of a tandem sub 1300 is shown along with an annular bearing 1310 for coupling with the tandem sub 1300. In this exemplary embodiment, an endface of the tandem sub 1300 includes a first plurality of circumferentially spaced openings 1302 (e.g., internally threaded apertures). Additionally, an outer race 1312 of the bearing 1310 includes a second plurality of circumferentially spaced openings 1314 that are fewer in number than the first plurality of openings 1302. A plurality of fasteners (e.g., equal in number to the second plurality of openings 1314) may be inserted through openings 1314 and inserted into (e.g., threaded into) the first plurality of openings 1302 formed in tandem sub 1300 to couple the bearing 1310 to the tandem sub 1300. The number of first openings 1302 may be greater than the number of second openings 1314 to provide redundancy as the specific first openings 1302 used to fasten the bearing 1310 to the tandem sub 1300 may become damaged during operation of the downhole assembly in the wellbore. In some embodiments, the number of first openings 1302 may be a multiple of the number of second openings 1314 (e.g., twice as many, three times as many, and the like). Similarly, the circumferential spacing of second openings 1314 may be a multiple of the circumferential spacing of first openings 1302.

[0103]Detonation of shaped charges (e.g., shaped charges 260) of the downhole assembly may result in the fasteners becoming stuck or otherwise damaging the first openings 1302 such that the fastener may need to be drilled out. By including a greater number of first openings 1302 than second openings 1314, other, undamaged first openings 1302 of tandem sub 1300 may be used in a subsequent operation such that the tandem sub 1300 may be reused in multiple downhole operations even if some of the first openings 1302 thereof have become damaged or unusable. Thus, the greater number of first openings 1302 relative to second openings 1314 may increase the reusability of tandem sub 1300 such that the tandem sub 1300 need not be replaced should damage occur to some of the first openings 1302 rendering them unusable for future downhole operations.

[0104]Referring to FIG. 35, another embodiment of a downhole assembly 1320 is shown that includes a tandem sub 1330 and an annular bearing 1340 connectable to the tandem sub 1300 for facilitating relative rotation between the tandem sub (and a signal pod coupled to the tandem sub 1330) and a charge carrier of a perforating tool coupled to the bearing 1340. In this exemplary embodiment, the tandem sub 1330 has an opening 1332 for receiving a signal pod 420 and an annular groove 1334 for at least partially receiving the bearing 1340. Additionally, bearing 1340 generally includes a radially outer bearing race 1342, a radially inner bearing race 1346, and a plurality of circumferentially spaced roller or bearing elements 1348 received therebetween that facilitate relative rotation between bearing races 1342 and 1346. In some embodiments, the inner bearing race 1346 may rotatably support a charge carrier of a perforating tool to permit relative rotation between the charge carrier and a signal pod received in the opening 1332 of tandem sub 1330.

[0105]In this exemplary embodiment, the outer bearing race 1342 of bearing 1340 includes an externally threaded outer shoulder that is threadably insertable into a corresponding threaded inner surface of the groove 1334 of tandem sub 1330 to threadably couple the outer bearing race 1342 to the tandem sub 1330. Thus, in this exemplary embodiment, bearing 1340 is threadably coupled to the tandem sub 1330 rather than being press fit. Threadably coupling the bearing 1340 to tandem sub 1330 may be advantageous in some applications where press fitting the bearing 1340 to the tandem sub 1330 may be difficult or impractical.

[0106]Referring to FIGS. 36 and 37, additional views of a tandem sub 400, a second bearings 1450, and an electrical connector 1480 of the downhole assembly 1001 are shown. Tandem sub 1400 includes an opening or receptacle 1402 for receiving a signal pod 420 of downhole assembly 1001. In this exemplary embodiment, second bearing 1450 includes a radially outer race 1452 secured to the tandem sub 1400, a radially inner race 1454, and a plurality of roller or bearing elements 1456 (e.g., ball bearings, rollers, and the like) positioned therebetween that facilitate relative rotation between the outer race 1452 and inner race 1454. In this exemplary embodiment, the outer race 1452 of second bearing 1450 is press fit into an annular groove 1404 formed in the tandem sub 1400 (e.g., into an endface thereof). Additionally, an annular friction element 1406 (e.g., an elastomeric O-ring) may be received in annular groove 1404 to seal the annular interface formed between outer race 1452 and an inner surface of the groove 1404 of tandem sub 1400 to increase friction resistance therebetween. Press fitting the outer race 1452 of second bearing 1450 to the tandem sub 1400 may minimize the labor required in assembling the second bearing 1450 with the tandem sub 1400 in at least some applications. Additionally, press fitting the outer race 1452 to tandem sub 1400 may permit the diameter of second bearing 1450 to be maximized, facilitating access to the opening 1402 of tandem sub 1400. However, outer race 1452 may be attached to tandem sub 1400 using various means beyond press fitting into groove 1404.

[0107]Electrical connector 1480 is receivable in a corresponding receptacle formed in the tandem sub 1400 and is generally configured to electrically connect the signal pod 420 of a first downhole assembly 1001 (shown as downhole assembly 1001A in FIG. 36) with the perforating tool 1001 of another downhole assembly 1001 (shown as downhole assembly 1001B in FIG. 36) while restricting the communication of fluid pressure between the pair of downhole assemblies 1000A and 1000B. In some embodiments, the pair of bearings 1440, 1450, signal pod 420, tandem sub 1400, pair of perforating tools 1000, and electrical connector 1480 may comprise a single downhole assembly 1001.

[0108]As shown particularly in FIG. 37, the electrical connector 1480 of downhole assembly 1001 generally includes a first electrical contact 1482, a second electrical contact 1484, and a biasing element 1490 for maintaining electrical contact and connectivity between electrical contacts 1482 and 1484. In some embodiments, first electrical contact 1482 is coupled to the tandem sub 1400 whereby relative longitudinal movement is restricted between first electrical contact 1482 and tandem sub 1400. For example, first electrical contact 1482 may be sealingly received in a receptacle of tandem sub 1400 and locked therein by a threaded collar or hub 1410 that supports the second bearing 1450. However, the manner in which the first electrical contact 1482 is sealingly coupled with tandem sub 1400 via a variety of mechanisms.

[0109]The second electrical contact 1484 is coupled to the uphole endplate 220 (formed from an electrically insulative material) of a corresponding perforating tool 1000 whereby relative longitudinal movement between the second electrical contact 1484 and the uphole endplate 220 is restricted. In this arrangement, the first electrical contact 1482 may be electrically connected to the second electrical contact 1484 by axially sliding and physically abutting the electrical contacts 1482 and 1484 together. However, the downhole assembly 1001 may be subject to substantial vibration in the downhole environment (e.g., following detonation of shaped charges 260) which could result in electrical contacts 1482 and 1484 inadvertently chattering against one another such that electrical connectivity is interrupted between electrical contacts 1482 and 1484.

[0110]To avoid potential disruptions to the electrical connection formed between electrical contacts 1482 and 1484, the biasing element 1490 of electrical connector 1480 biases the second electrical contact 1484 longitudinally towards and against the first electrical contact 1482 to prevent a loss of physical and electrical contact between electrical contacts 1482 and 1484 as the downhole assembly 1001 is exposed to downhole vibration. In this exemplary embodiment, the biasing element 1490 comprises a mechanical spring (e.g., a coil spring) that extends between an internal shoulder of the uphole endplate 220 and an external shoulder 1486 of the second electrical contact 1484 to apply a biasing force to the second electrical contact 1484 in the longitudinal direction of first electrical contact 1482.

[0111]Referring to FIGS. 38 and 39, another embodiment of a downhole assembly 1500 is shown that includes tandem sub 1400, bearings 1440 and 1450, perforating tool 1000, and an electrical connector 1510 for providing electrical connectivity and pressure isolation between the perforating tool 1000 and a signal pod received in the opening 1402 of tandem sub 1400. Electrical connector 1510 includes features in common with electrical connector 1480 shown in FIGS. 36 and 37, and shared features are labeled similarly. As shown particularly in FIG. 39, in this exemplary embodiment, electrical connector 1510 includes first electrical contact 1482, and a second electrical contact 1520 coupled to the uphole endplate 220 of perforating tool 1000.

[0112]The second electrical contact 1520 of electrical connector 1510 comprises an electrically conductive base member 1522 coupled to the uphole endplate 220 such that relative longitudinal movement is restricted therebetween. Additionally, second electrical contact 1520 comprises an electrically conductive sliding member 1524 and an electrically conductive biasing element 1526 (e.g., a mechanical spring such as a coil spring) coupled between the sliding member 1524 and the base member 1522. Sliding member 1524 is slidably received in an opening formed in the base member 1522 along with biasing element 1526 and is permitted to slide or travel longitudinally relative to base member 1522. Additionally, biasing element 1526 biases or applies a biasing force against the sliding member 1524 longitudinally towards the first electrical contact 1482 to maintain electrical connectivity between electrical contacts 1482 and 1520 even when electrical connector 1510 is subjected to substantial vibration in the downhole environment.

[0113]Referring to FIG. 40, another embodiment of a downhole assembly 1550 is shown that includes tandem sub 1400, bearings 1440 and 1450, perforating tool 1000, and an electrical connector 1560 for providing electrical connectivity and pressure isolation between the perforating tool 1000 and a signal pod received in the opening 1402 of tandem sub 1400. Electrical connector 1560 includes features in common with electrical connector 1480 shown in FIGS. 36 and 37, and shared features are labeled similarly. In this exemplary embodiment, electrical connector 1560 includes first electrical contact 1482, and a second electrical contact 1570 coupled to the uphole endplate 220 of perforating tool 1000.

[0115]Referring to FIG. 41, another embodiment of a downhole assembly 1580 is shown that includes tandem sub 1400, bearings 1440 and 1450, perforating tool 1000, and an electrical connector 1582 for providing electrical connectivity and pressure isolation between the perforating tool 1000 and a signal pod received in the opening 1402 of tandem sub 1400. Electrical connector 1582 generally includes first electrical contact 1482 and a second electrical contact 1590 that includes a base member 1592, a floating member 1594, biasing element 1578, and an annular biasing element 1596 (e.g., a garter spring). Second electrical contact 1590 is similar to the second electrical contact 1570 shown in FIG. 40 except that, in this exemplary embodiment, base member 1572 and biasing element 1596 are both at least partially received in an opening formed in the floating member 1574.

[0116]Referring to FIGS. 42 and 43, another embodiment of a downhole assembly 1600 is shown that detonating cord housing 290 and an electrical connector 1610 for electrically connecting the detonating cord housing 290 with a switch (e.g., 422) of a signal pod (e.g., signal pod 420). In this exemplary embodiment, electrical connector 1610 comprises an electrically conductive base member 1612 coupled to the switch (e.g., a PCB of the switch) and a biasing element 1620 biased into contact with the base member 1612 and the detonating cord housing 290 to maintain electrical connectivity between the base member 1612 and the detonating cord housing 290 even as the downhole assembly 1600 is subjected to substantial vibration in the downhole environment.

[0117]In this exemplary embodiment, base member 1612 comprises one or more first fingers 1614 coupled directly to the switch and one or more second fingers 1616 opposite the first fingers 1614. In this exemplary embodiment, biasing element 1620 comprises a continuous coil spring (e.g., a garter spring) that extends around or hooks onto the second fingers 1616 to retain the biasing element 1620 to the base member 1612. Additionally, the biasing element 1620 extends partially or arcuately about an outer cylindrical surface of the detonating cord housing 290 such that the biasing element 1620 is in sliding contact with the detonating cord housing 290. In this arrangement, detonating cord housing 290 may rotate relative to the electrical connector 1610 with electrical connectivity maintained therebetween via sliding contact between biasing element 1620 and the outer surface of detonating cord housing 290. The coils of biasing element 1620 may maintain electrical connectivity between electrical connector 1610 and detonating cord housing 290 without producing excessive friction therebetween.

[0118]Referring to FIGS. 44-46, another embodiment of a downhole assembly 1650 is shown that detonating cord housing 290 and an electrical connector 1660 for electrically connecting the detonating cord housing 290 with a switch (e.g., 422) of a signal pod (e.g., signal pod 420). In this exemplary embodiment, electrical connector 1660 comprises an electrically conductive base member 1662 coupled to the switch (e.g., a PCB of the switch) and a plurality of biasing elements 1670 biased into contact with the base member 1662 and the detonating cord housing 290 to maintain electrical connectivity between the base member 1662 and the detonating cord housing 290 even as the downhole assembly 1650 is subjected to substantial vibration in the downhole environment.

[0119]In this exemplary embodiment, base member 1662 comprises one or more first fingers 1664 coupled directly to the switch and a plurality of second fingers 1666 opposite the first fingers 1614. In this exemplary embodiment, each biasing element 1670 comprises an elongate (rather than continuous) coil spring (e.g., a garter spring) having a first or fixed end coupled to a corresponding second finger 1666 and a longitudinally opposed free end spaced from the base member 1662. In this configuration, the biasing elements 1670 straddle the detonating cord housing 290 to permit relative rotation between the detonating cord housing 290 and the electrical connector 1660 while maintaining electrical connectivity therebetween. Additionally, by straddling the detonating cord housing 290, the biasing elements 1670 apply an aligning force to the detonating cord housing 290 to resist angular misalignment between a longitudinal axis of the detonating cord housing 290 and a longitudinal axis of the signal pod coupled to the electrical connector 1660. Indeed, biasing elements 1670 may resist angular misalignment between these longitudinal axes in a plurality of circumferentially spaced directions. Reducing such angular misalignment may enhance the operability of downhole assembly 1650 such as by maintaining a proper lateral spacing between the detonating cord housing 290 and a corresponding detonator of the signal pod.

[0120]Referring to FIGS. 47-49, another embodiment of a downhole assembly 1700 is shown that detonating cord housing 290 and an electrical connector 1710 for electrically connecting the detonating cord housing 290 with a switch (e.g., 422) of a signal pod (e.g., signal pod 420). In this exemplary embodiment, electrical connector 1710 comprises an electrically conductive, annular base member 1712 defining a central opening 1711 of the electrical connector 1710, and a plurality of electrically conductive fingers 1714 that project radially inwards into the opening 1711.

[0121]The base member 1712 of electrical connector 1710 may couple to the switch (e.g., to a PCB of the switch) of the signal pod to electrically connect electrical connector 1710 to the switch. Additionally, the detonating cord housing 290 is slidably insertable into and through the central opening 1711 of electrical connector 1710. The plurality of fingers 1714 are in sliding contact with and biased against the outer surface of detonating cord housing 290 to maintain electrical connectivity between the electrical connector 1710 and the detonating cord housing 290. Additionally, the biasing forces applied by fingers 1714 act to minimize any angular misalignment between the longitudinal axis of the detonating cord housing 290 and the signal pod. Additionally, in this exemplary embodiment, a terminal end 1716 of each finger 1714 is curved convexly such that is flares radially outwards to prevent the terminal ends 1716 of fingers 1714 from inadvertently catching against the outer surface of signal pod 420 which could prevent removal of the detonating cord housing 290 from the opening 1711 of electrical connector 1710.

[0122]Referring to FIG. 50, an embodiment of a signal pod 1800 is shown. In some embodiments, the signal pod 420 shown in FIG. 5 may be configured similarly as signal pod 1800; however, in other embodiments, signal pod 420 of FIG. 5 may vary in configuration from signal pod 1800. Additionally, signal pod 1800 shares features in common with signal pod 420, and shared features are labeled similarly. Particularly, in this exemplary embodiment, signal pod 1800 generally includes a pod chassis 1802, electrical switch 422, a first electrical connector 1810, a second electrical connector 1820, and a third electrical connector 1830. In some embodiments, signal pod 1800 may also include a detonator while in other embodiments a detonator may be separate from and external to the signal pod 1800.

[0123]The pod chassis 1802 physically supports the electrical switch 422 and electrical connectors 1810, 1820, and 1830. The first electrical connector 1810 may comprise a receptacle for receiving the detonator cord housing 290 of a perforating tool to electrically connect the signal pod 1800 with the perforating tool. Additionally, the second electrical connector 1820 may electrically connect to another perforating tool. In this manner, electrical switch 422 may control the operation of either perforating tool electrically connected to the signal pod 1800 via electrical connectors 1810 and 1820. The third electrical connector 1830 may comprise a ground connector for electrically grounding the signal pod 1800 to a tool housing of either perforating tool. Additionally, the third electrical connector 1830 may be configured to provide greater frictional resistance to rotation (e.g., when in sliding contact with an inner surface of a corresponding tandem sub) than either electrical connectors 1810 and 1820 to permit relative rotation between the signal pod 1800 (including electrical switch 422) and the charge carriers of either perforating tool while restricting relative rotation between the signal pod 1800 (held stationary within a corresponding tandem sub) and the tool housing of either perforating tool (coupled to the tandem sub and rotationally locked thereto).

[0124]The relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.