BACKGROUND OF THE INVENTION

Generally, when completing a subterranean well for the production of fluids, minerals, or gases from underground reservoirs, several types of tubulars are placed downhole as part of the drilling, exploration, and completions process. These tubulars can include casing, tubing, pipes, liners, and devices conveyed downhole by tubulars of various types. Each well is unique, so combinations of different tubulars may be lowered into a well for a multitude of purposes.

A subsurface or subterranean well transits one or more formations. The formation is a body of rock or strata that contains one or more compositions. The formation is treated as a continuous body. Within the formation hydrocarbon deposits may exist. Typically a wellbore will be drilled from a surface location, placing a hole into a formation of interest. Completion equipment will be put into place, including casing, tubing, and other downhole equipment as needed. Perforating the casing and the formation with a perforating gun is a well-known method in the art for accessing hydrocarbon deposits within a formation from a wellbore.

Explosively perforating the formation using a shaped charge is a widely known method for completing an oil well. A shaped charge is a term of art for a device that when detonated generates a focused output, high energy output, and/or high velocity jet. This is achieved in part by the geometry of the explosive in conjunction with an adjacent liner. Generally, a shaped charge includes a metal case that contains an explosive material with a concave shape, which has a thin metal liner on the inner surface. Many materials are used for the liner; some of the more common metals include brass, copper, tungsten, and lead. When the explosive detonates, the liner metal is compressed into a super-heated, super pressurized jet that can penetrate metal, concrete, and rock. Perforating charges are typically used in groups. These groups of perforating charges are typically held together in an assembly called a perforating gun. Perforating guns come in many styles, such as strip guns, capsule guns, port plug guns, and expendable hollow carrier guns.

Perforating charges are typically detonated by detonating cord in proximity to a priming hole at the apex of each charge case. Typically, the detonating cord terminates proximate to the ends of the perforating gun. In this arrangement, an initiator at one end of the perforating gun can detonate all of the perforating charges in the gun and continue a ballistic transfer to the opposite end of the gun. In this fashion, numerous perforating guns can be connected end to end with a single initiator detonating all of them.

The detonating cord is typically detonated by an initiator triggered by a firing head. The firing head can be actuated in many ways, including but not limited to electronically, hydraulically, and mechanically.

Expendable hollow carrier perforating guns are typically manufactured from standard sizes of steel pipe with a box end having internal/female threads at each end. Pin ended adapters, or subs, having male/external threads are threaded one or both ends of the gun. These subs can connect perforating guns together, connect perforating guns to other tools such as setting tools and collar locators, and connect firing heads to perforating guns. Subs often house electronic, mechanical, or ballistic components used to activate or otherwise control perforating guns and other components.

Perforating guns typically have a cylindrical gun body and a charge tube, or loading tube that holds the perforating charges. The gun body typically is composed of metal and is cylindrical in shape. Charge tubes can be formed as tubes, strips, or chains. The charge tubes will contain cutouts called charge holes to house the shaped charges.

It is generally preferable to reduce the total length of any tools to be introduced into a wellbore. Among other potential benefits, reduced tool length reduces the length of the lubricator necessary to introduce the tools into a wellbore under pressure. Additionally, reduced tool length is also desirable to accommodate turns in a highly deviated or horizontal well. It is also generally preferable to reduce the tool assembly that must be performed at the well site because the well site is often a harsh environment with numerous distractions and demands on the workers on site.

Electric initiators are commonly used in the oil and gas industry for initiating different energetic devices down hole. Most commonly, 50-ohm resistor initiators are used. Other initiators and electronic switch configurations are common.

Modular or “plug and play” perforating gun systems have become increasingly popular in recent years due to the ease of assembly, efficiencies gained, and reduced human error. Most of the existing plug and play systems either (1) utilize a wired in switch and/or detonator, or (2) require an initiating “cartridge” that houses the detonator, switch, electrical contacts and possibly a pressure bulkhead. The wired in switch/detonator option is less desirable, because the gun assembler must make wire connections which is prone to human error. The initiating cartridge option is less desirable because the cartridge can be a large explosive device—in comparison to a standard detonator—thus takes up additional magazine space at the user facility. There is a need for a modular perforating system in which no wire connections are required by the user AND the switch and pressure bulkhead are in pre-assembled in the gun assembly rather than in the initiating cartridge. The detonator for the proposed system has no wires and allows for simple arming by the user in the field.

SUMMARY OF EXAMPLE EMBODIMENTS

An example embodiment may include a perforating gun system comprising a cylindrical housing with a bottom end and a top end, a prewired loading tube assembly disposed within the cylindrical housing and having a corresponding bottom end and top end, an upper end fitting having a door for receiving a detonator and securing it into a recess coupled to the top end of the prewired loading tube and the top end of the cylindrical housing, a lower end fitting coupled to the bottom end of the prewired loading tube and the bottom end of the cylindrical housing, an upper electrical connections coupled to the upper end fitting, a lower electrical connections coupled to the bottom end fitting, a selective switch coupled to a detonator connector receptacle disposed within the upper end fitting, and a detonator electrically coupled to the selective switch and further disposed within the door of the upped end fitting.

An alternative embodiment may include having the upper end fitting disposed within the pre-wired loading tube houses a selective switch in which the end fitting contains a portion to receive an auto-shunting modular detonator by electrically connecting it to a mating receptacle of a selective switch and affixing the auto-shunting modular detonator proximate to a detonating cord. It may include a means for auto-shunting the detonator. It may include coupling a baffle to the bottom end of the cylindrical housing. The prewired loading tube may further include an insulated wire which is terminated at the selective switch in the upper end and a pressure bulkhead coupled to the lower end. The selective switch may be grounded to the loading tube. The loading tube may be electrically connected to the baffle. It may include having shaped charges installed into the loading tube, in which the shaped charges are held in place by a locking means fixed to the shaped charge. It may include having a detonating cord coupled to the back of the shaped charges with a detonating cord locking means. The detonating cord may be terminated into a detonating cord orifice integral with the end fitting. The detonator may be located adjacent to the detonating cord in an end-to-end configuration. The detonator may have an auto-shunting feature that does not unshunt until a mating receptacle is inserted. The selective switch may have a ribbon pigtail with the un-shunting receptacle attached. The receptacle connected to the switch may be attached to the end of the detonator, disengaging the shunt of the detonator.

An example embodiment may include a pre-wired shaped charge loading tube assembly comprising a cylindrical housing with a bottom end and a top end, an upper end fitting having a door for electrically receiving a detonator and securing it into a recess coupled to the top end of the prewired loading tube and the top end of the cylindrical housing, a lower end fitting coupled to the bottom end of the prewired loading tube and the bottom end of the cylindrical housing, an upper electrical connections coupled to the upper end fitting, lower electrical connections coupled to the bottom end fitting, a selective switch coupled to a detonator connector receptacle disposed within the upper end fitting, and a detonator electrically coupled to the selective switch and further disposed within the door closed into the recess of the upper end fitting.

An example embodiment may include a method of perforating a wellbore comprising coupling a pre-wired first end fitting with a first end of a shaped charge loading tube, coupling a pressure bulkhead at the first end fitting and the first end of the shaped charge loading tube, coupling a pre-wired second end fitting with a second end of a shaped charge loading tube, wherein the second end fitting centers and orients the loading tube and embodies a selective switch, feed through contact and orifices to insert a wireless detonator from the outer end and detonating cord into the inner end, inserting a detonator into a door incorporated into end fitting and closing the door into a recess of the end fitting such that the explosive end of the detonator is adjacent to the detonating cord in an side-by-side configuration, and pre-wiring the loading tube with insulated wire, wherein the wire is terminates at the selective switch in the second end fitting and the pressure bulkhead at the first end fitting.

An alternative embodiment may include centering the loading tube using the first end fitting within a perforating gun body. It may include electrically contacting the pre-installed insulated wire disposed within the loading tube to the pressure bulkhead contact adjacent. It may include pre-installing the baffle in the pin end of the gun carrier. It may include grounding the selective switch to the shaped charge loading tube. It may include inserting the shaped charges into the shaped charge loading tube. It may include locking the shaped charges into place within the shaped charge loading tube. It may include inserting detonating cord into the back of each shaped charge disposed within the shaped charge loading tube via locking features fixed to the shaped charge. It may include inserting the termination of a detonating cord into the end fitting. It may include inserting a wireless detonator into the end fitting from outside of the perforating gun assembly such that the explosive load end of the detonator is adjacent to the detonating cord in an end to end position. The wireless detonator may have an auto-shunting feature that does not un-shunt until a mating receptacle is inserted. The selective switch may have a ribbon pigtail with the un-shunting receptacle attached. It may include inserting the wireless detonator wherein the connector receptacle connected to the switch is attached to the end of the detonator, disengaging the shunt of the detonator. It may include screwing together the loaded perforating modular gun assemblies wherein the top contact makes electrical contact to the bottom contact of the adjacent gun assembly. It may include swaging and threading the outer diameter of a pin end of the perforating gun. It may include installing a pin by pin tandem sub into a box end of perforating gun assembly having a box by box gun body. It may include selectively initiating the detonator of the perforating gun. It may include pre-assembling spring-loaded top contact wires coupled to the selective switch. It may include connecting the through wire of the selective switch to the insulated wire of the loading tube. The output wires of the selective switch may be insulated ribbon or wires which has the detonator connector receptacle affixed to its end. It may include inserting the detonating cord through the inner end of the end fitting and a detonator from the outer end such that the detonator is adjacent to the detonating cord on the horizontal axis of the gun body. It may include overlapping the detonating cord and the detonator to form a side by side explosive coupling. It may include installing the pressure bulkhead into the baffle of the pin end of the gun carrier. It may include coupling the pressure bulkhead into a pin-by-pin tandem sub, wherein the tandem sub is inserted into the first end of the gun carrier. It may include coupling the pressure bulkhead into the second end of the gun carrier. It may include arming the perforating gun by inserting a wireless electric detonator, connector end facing up, into the end fitting detonator orifice. It may include attaching the selective switch to the pre-wired loading tube and wiring the detonator connector receptacle pass through to the upper end fitting. It may include connecting the insulated wire to the switch within the lower end fitting, in which the detonator connector receptacle wire runs the length of the loading tube and the receptacle end passes through the upper end fitting.

