PERFORATING GUN ASSEMBLY TO CONTROL WELLBORE FLUID DYNAMICS

Abstract

A downhole tool used in the pressure isolation of adjacent subterranean formations. The downhole tool may comprise flow restriction devices along the outer circumference for impeding flow along the length of the tool. The tool may further comprise a perforating gun and an accumulator. Impeding flow along the length of the tool provides a dynamic flow restriction within the wellbore that precludes fluid flowing from one subterranean zone to an adjacent zone.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a perforating system. Yet more specifically, the present invention relates to a perforating gun system capable of regulating wellbore fluid dynamics.

2. Description of Related Art

Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.

Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In FIG. 1 an example of a perforating system 4 is shown. For the sake of clarity, the system 4 depicted comprises a single perforating gun 6 instead of a multitude of guns. The gun 6 is shown disposed within a wellbore 1 on a wireline 5. The perforating system 4 as shown also includes a service truck 7 on the surface 9, where in addition to providing a raising and lowering means, the wireline 5 also provides communication and control connectivity between the truck 7 and the perforating gun 6. As is known, derricks, slips and other similar systems may be used for inserting and retrieving the perforating system into and from a wellbore. Moreover, perforating systems may also be disposed into a wellbore via tubing, drill pipe, slick line, coiled tubing, to mention a few.

Included with the perforating gun 6 are shaped charges 8 that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge 8 at very high velocity in a pattern called a “jet” 12. The jet 12 perforates the casing and the cement and creates a perforation 10 that extends into the surrounding formation 2.

As shown in FIG. 2, subsequent to the perforating step, formation fluid flows from the formation 2, into the wellbore 1, and through the annulus 11 formed by the outer circumference of the perforating gun 6 and the inner diameter of the wellbore 1 (the direction of this fluid flow is illustrated by arrows A). Fluid flows from the formation 2 into the wellbore 1 because the wellbore pressure is exceeded by the formation pressure, this is commonly referred to as an under-balanced situation. Debris 14 from the formation however often travels along with the fluid, this debris 14 can sometimes collect within the annulus 11 and in certain locations thereby resulting in a clog 16 that can effectively lodge the perforating gun 6 within the wellbore 1. The connate fluid is shown flowing from within a first zone Z₁, into the wellbore Tinto zone Z₂. This presents a problem if it is desired to maintain these separate zones Z₁, Z₂ at separate pressures.

BRIEF SUMMARY OF THE INVENTION

The present disclosure discloses examples of a perforating system and a method of perforating. In an example embodiment a perforating system is made up of a perforating string with first and second spaced apart perforating guns. Shaped charges are provided in both guns and a zonal isolation system is included for regulating pressure in a wellbore. The zonal isolation system of this embodiment has axially spaced apart plates that project radially out from the perforating string. The plates define an annulus between the string and a borehole wall, where the annulus restricts fluid flow to cause a pressure drop in the fluid flowing across the plates and along the annular space between the perforating string and wall of the wellbore. This lowers pressure in a fluid flowing from a higher pressure producing zone so that it does not flow into a lower pressure producing zone. In an example embodiment, passages are formed through the plates. Optionally, the diameters of the plates can vary. The zonal isolation system may be disposed on one of the first or second perforating guns. In an example embodiment, the zonal isolation system is disposed between the first and second perforating guns. A sub may optionally be included that connects between the first and second perforating guns. In this example the zonal isolation system is disposed on the sub. In an example embodiment, the zonal isolation system is a first zonal isolation system, and a second zonal isolation system is included with the system.

Also disclosed herein is an alternate perforating system that has a perforating string with shaped charges. The perforating string has a stack of axially spaced apart plates projecting radially outward therefrom that define a restricted flow area between a portion of the perforating string and a wellbore wall. As such, when shaped charges in the perforating string are detonated and perforate formation zones adjacent the wellbore, if the formation zones are at different pressures, fluid communication between the respective formations is impeded by the plates. In an example embodiment, the perforating string includes perforating guns stacked end to end. Optionally, the plates direct fluid from one of the formations along a labyrinthine path for reducing pressure in the fluid. Passages may optionally be included that are formed axially through the plates. Further, the passages in adjacent plates may be offset from one another. Yet further optionally, the diameters of the plates can vary.

A method is described herein for dynamically isolating flow within a wellbore between a first subterranean formation zone and a second subterranean formation zone, where the zones are at different pressures. In an example the method includes inserting a downhole tool in a wellbore, where the downhole tool includes a pressure isolation system that has axially spaced apart plates that extend radially outward from an outer surface of the downhole tool. A restricted flow annulus is defined between the member and the wellbore. Connate fluid flow is induced from within the first and second subterranean formation zones and a dynamic pressure drop is created between the first and second subterranean formation zones by locating the restricted flow annulus between the first and second subterranean formation zones. Directing connate fluid from the higher pressure formation across the restricted flow annulus reduces pressure in the fluid to prevent the fluid from flowing into the lower pressure formation zone. In an example embodiment, the plates are configured to form a labyrinthine path for connate fluid flow along the downhole tool. Alternatively, the labyrinthine path is formed by providing passages through the plates and positioning the passages in each plate to be axially offset from passages in an adjacent plate. Yet further alternatively, the labyrinthine path is formed by varying the diameter of plates that are adjacent.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a partial cutaway side view of a prior art perforating operation.

FIG. 2 is a partial cutaway side view of a prior art perforating operation with formation fluid flowing into a wellbore.

FIG. 3 is a side partial sectional view of a perforating string in accordance with the present disclosure.

FIG. 4 is a side partial sectional view of a perforating string in a deviated wellbore and in accordance with the present disclosure.

FIG. 5 is a side partial sectional view of an embodiment of a downhole tool disposed in a wellbore in accordance with the present disclosure.

FIG. 6 is a partial cut-away side view of a downhole tool disposed in a deviated wellbore in accordance with the present disclosure.

FIG. 7 is a side partial sectional view of an alternate embodiment of a perforating string for regulating wellbore pressure in accordance with the present disclosure.

FIG. 8A is a side perspective view of a portion of the perforating string of FIG. 7 that includes an alternate embodiment of a restriction plate.

FIG. 8B is a side perspective view of a portion of the perforating string of FIG. 7 that includes an alternate embodiment of a restriction plate.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims.

With reference now to FIG. 3 an embodiment of a perforating system 20 in accordance with the present disclosure is illustrated in a side view. The perforating string 20 of FIG. 3 includes a perforating section 22 axially connected to an accumulator section 26. As shown, another perforating section 23 is connected on the end of the accumulator section 26 opposite the perforating section 22. It should be pointed out that the number of perforating sections (or guns) is not limited to the number shown but could be any number of guns included with the perforating string 20 of the present disclosure.

An auger flight 28 is provided along the outer circumference of the perforating string 20. The auger flight 28 is a generally helical member that winds along on the outer circumference of the perforating string 20 along a portion of its length. As shown, the auger flight 28 is disposed primarily along the accumulator section 26 of the perforating string 20. Optionally the auger flight 28 may extend also along one or more of the perforating sections 22, 23 in addition to being along the accumulator section 26. It should be pointed out that the cross section of the auger flight 28 may take one of many different configurations. Typically the base of the auger flight 28 has a wider cross section where it attaches to the perforating string 20 and tapers to a narrower cross section at its outer edge. Other embodiments of the auger flight 28 include a shape where the base and the terminating end have substantially the same thickness with no tapering. However it is well within the scope of those skilled in the art to determine and produce an auger flight suitable for use.

A port 30 is provided on the accumulator section 26 that may be selectively opened or closed. When open, the port 30 provides fluid communication across the side walls of the perforating string 20. Optionally, a reservoir 30 (shown in dashed lines) can be provided within the perforating string 20 and in communication with the port 30. Opening/closing of the port 30 may selectively communicate fluid between the reservoir 30 and outside of the perforating string 20. The reservoir 32 can be disposed solely within the accumulator section 26 or one of the perforation sections 22, 23.

In one non-limiting example of operation, a perforating system 4 having an embodiment of the perforating string 20 herein described is lowered within a wellbore 1 to a predetermined depth wherein perforating operations are to be performed. Initiating detonation of shaped charges 24 shown provided with the perforating system 4 creates perforations 10 in the corresponding formation 2. As previously discussed, in an under-balanced situation, fluid in the higher pressure formation 2 will flow into the lower pressure wellbore 1 through the perforations 10. The ports 30 can be opened, simultaneously with initiation of the shape charges 24 or soon thereafter, so the reservoir 32 can act as a potential sink or accumulator for at least a portion of the formation fluid flowing into the wellbore 1 from the formation 2. The fluid flowing into the reservoir 32 is not limited to wellbore fluid but can also include all flowable matter resident in the wellbore 1, such as drilling mud, drilling fluid, as well as the producing fluid from the formation 2. Accordingly having the accumulator section 26 within the wellbore 1 after perforating provides an open space to absorb potential kinetic energy resulting from the pressure imbalance between the formation 2 and the wellbore 1.

Pressure imbalances between the formation 2 and the wellbore 1 may result from changes in the density of fluid in the wellbore, or by perforating into a formation 2 having a higher pressure than the wellbore 1. Flow into the wellbore 1 from the formation 2 may be induced by perforating into a formation 2 as well as introducing an accumulator within a wellbore 1 having wellbore fluid, wherein the confines of the accumulator are at a lower pressure than the wellbore fluid. Providing fluid communication between the confines of the accumulator and the wellbore 1 can also induce connate fluid flow from the formation 2 into the wellbore 1. As discussed in more detail below, the accumulator in combination with the auger flights can isolate the pressure of one subterranean zone from another.

With reference now to FIG. 4, an additional embodiment of the device of the present disclosure is shown disposed within a deviated portion of a wellbore 1a. In this situation the wellbore 1a is shown intersecting different zones Z₁, Z₂, Z₃, within a formation 2a. Although the embodiment of FIG. 4 is disposed within a deviated portion of the wellbore la, the embodiment shown is operable within wellbore sections that are substantially vertical and/or horizontal. In this configuration, the perforating sections 22a, 23a are proximate to different zones Z₁, Z₃ within the formation 2a. This can be significant when the resident pressure of either Z₁ or Z₃ is sufficiently greater or less than the other zone such that upon perforation the fluid of one zone empties fluid into the wellbore 1a with a sufficiently higher pressure that the fluid back flows into the lower pressure zone. The advantages of the device described herein alleviate such a back flow condition due to its flow restriction and pressure absorption capabilities, i.e. the auger flight 28 and reservoir 32. The auger flight 28 restricts flow by reducing the cross sectional area available for fluid flow thereby causing dynamic pressure losses. The reservoir 32, by virtue of fluid communication of the ports 30, can absorb energy stored in the fluid as pressure thereby further preventing against such a back flow condition. Accordingly, the present device maintains a fluid pressure differential between subterranean zones Z₁, Z₂, Z₃ to zonal isolate the zones Z₁, Z₂, Z₃. The zonal isolation, which typically occurs dynamically (dynamic zonal isolation), can be accomplished by the added pressure surge capabilities of the accumulator section, the pressure drop function of the auger flight, as well as a combination of these two.

The scope of the present disclosure is not limited to perforating systems, but as shown in FIG. 5, can include any tool 38 disposable within a wellbore, such as those used in removing debris from within existing perforations (commonly referred to as a downhole surge assembly). The embodiment of the tool 38 of FIG. 5 includes a flow restrictor section 40 for retarding flow across the length of the tool. The flow restrictor section 40 can include surface elements, such as an auger flight 42, a series of orifice plates 44, some other member for retarding flow, or a combination thereof. Although the flow restrictor section 40 shown in FIG. 5 includes more than one type of member for restricting flow, a single member type may be used on the tool 38 for restricting flow. The flow restrictor section 40 thus may comprise any member (flow restriction member) that restricts or otherwise impedes fluid flow axially through the wellbore 1. Optionally, an accumulator 46 (shown as a dashed line) may be included within the tool 38 formed to receive fluid flow therein. Ports 48 may be provided as shown to enable fluid flow from within the wellbore 1 into the accumulator 46. While operation of the device of FIG. 5 may not include perforating, the tool 38 could be inserted post perforation. The tool 38 as shown could be used to create an underbalanced condition within a wellbore for coaxing connate fluid 52 from a formation Z₁ into the wellbore 1. By flowing fluid from the formation Z₁ into the wellbore, perforations 50, 54 opening formation Z₁, Z₃ to the wellbore 1 can be cleaned free of any debris that may have accumulated while perforating or thereafter. The flow restrictor section 40 impedes fluids axially flowing through the wellbore 1. As discussed above, the flow restrictor and the fluid accumulator, either separately or in combination, impede fluid flow by reducing the available cross sectional area available for flow (in the case of the flow restrictor) or by absorbing fluid potential energy (by using an accumulator). Impeding fluid flow through the wellbore 1 provides dynamic zonal isolation along the body of the tool 38 thereby isolating subterranean zones from one another. As discussed above, the zonal isolation provided by the tool 38 prevents fluid communication between the zones.

Optionally the present device may further allow pressure isolation between various subterranean zones Z₁, Z₂, Z₃. For example, as shown in FIG. 6 an embodiment of a downhole tool 70 disposed in a wellbore 71, wherein the wellbore 71 extends through multiple zones Z₁, Z₂, Z₃ having differing physical and/or pressure properties. The downhole tool 70 is shown equipped with isolation elements 72, that in one example can be an auger flight as described above, disposed at strategic points along its outer surface. The isolation elements 72 include any device extending outward from the surface of the downhole tool 70 for impeding fluid flow in the annulus formed between the inner circumference of the wellbore 71 and the outer circumference of the downhole tool 70. Examples of downhole tools 70 considered include perforating guns (with or without accumulator sections) and perforation surge assemblies. Additionally, the downhole tool 70 could comprise a series of surge assemblies 77, 79, 81 configured to accommodate a particular zone. Optional ports 83 that are selectively opened are shown included to flood the assemblies. The strategic points may correspond to boundaries 74, 75 between zones Z₁, Z₂, Z₃ that are adjacent. Thus strategic placement of the downhole tool 70 within the wellbore 71 may control and manipulate pressure surges between adjacent zones via the wellbore 71. The presence of the isolation elements 72 serves to impede fluid flow through the wellbore 71 along the downhole tool 70. Impeding fluid flow in this manner in turn regulates pressure communication between different zones to zonally isolate these zones Z₁, Z₂, Z₃.

Referring now to FIG. 7, an example embodiment of a perforating string 20B is illustrated deployed in the wellbore 1; where a wellhead assembly 76 is mounted at the entrance to the wellbore 1. A deployment means 77, which can be a wireline, slickline, coiled tubing, or the like, suspends the perforating string 20B downhole. Shaped charges 24 in the perforating string 20B are shown being detonated to create jets 78 that penetrate the formation 2 adjacent the wellbore 1. Initiating the shaped charges 24 may occur from a detonation signal delivered through the deployment means 77. Perforations 50, 80 are created in zones Z₁, Z₂ in the formation 2. Flow restrictor sections 40A are shown provided on the outer circumference of the perforating string 20B. In the embodiment of FIG. 7, the flow restrictor sections 40A include a stack of axially spaced apart plates 81 that circumscribe a body of a perforating gun 82 of the perforating string 20B and a sub 84 attached on an upper end of the gun body 82. The sub 84 can be a connector sub for connecting perforating guns 82 in the perforating string 20B, an accumulator sub as discussed above, or a sub or tool having a different function.

Embodiments of the plates 81 of FIG. 7 include a washer like element having an inner diameter substantially the same as the outer diameter of the portion of the perforating string 20B of where the plate 81 is mounted. An outer diameter of the plates 81 may extend up to the inner diameter of the wellbore 1. Examples of ratios of thickness (or height) to diameter of the plates 81 range from about 1:5 to about 1:30. The outer periphery of the plates 81 is generally circular, but may have different shapes to match the inner surface of the wellbore 1. A gap exists between the outer diameter of the plates 82 and inner surface of the wellbore 1 to define an annulus 86. As discussed above, the plates 82 reduce the area between the perforating string 20B and walls of the wellbore 1 thereby creating a restriction to flow that in turn increases a pressure drop to fluids flowing across the restriction to prevent fluid from a higher pressure to a lower pressure zone Z₁, Z₂.

Shown in a side perspective view in FIG. 8A is a section of the perforating gun 82 or sub 84 of FIG. 7 having an alternate embodiment of the plates 81A that include passages 88 formed through the plates 81A. In this example embodiment, the plates 81A may have a larger diameter thereby urging more fluid radially inward to force the fluid through the passages 88. Further, by staggering the positioning of the passages 88 within adjacent plates 81A, the flow of fluid, as represented by arrows, may follow a labyrinth like path. Pressure in the fluid is lost as the fluid flows through each passage 88 as well as flowing along the longer labyrinthine path. FIG. 8B also illustrates an alternate embodiment of isolating one formation zone Z₁, Z₂ from another. In the example of FIG. 8B, plates 81B have an outer diameter less than other plates 81 on the perforating gun 82 or sub 84. The varying outer diameters of the plates 81, 81B can induce formation of eddy currents in the flow of fluid that can further induce pressure losses in the fluid flow. Optionally, the embodiments of FIGS. 8A and 8B may be combined so that plates of varying dimensions include passages therethrough.

The embodiments described herein, therefore, are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of an invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, instead of an auger flight extending partially between the outer surface of a downhole tool and the inner surface of a casing, other flow path restriction members may be employed. Examples of such members include coaxially disposed plates, plates having orifices therethrough, a partially extended packer, as well as any other member for retarding flow across the length of the tool. Further, the downhole conveyance means used for disposing the above described devices includes casing and drill pipe. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Claims

1. A perforating system comprising: a perforating string;first and second perforating guns that are spaced apart within the perforation string;shaped charges in each of the first and second guns; anda zonal isolation system comprising plates that are axially spaced apart and project radially outward from an outer surface of and around the perforating string for restricting fluid flow in an annular space between the member and a borehole wall and causes a pressure drop in the fluid flow in the annular space so that the pressure in a fluid flowing from a higher pressure producing zone is reduced in the annular space and does not flow into a lower pressure producing zone.

2. The perforating system of claim 1, further comprising passages formed through the plates.

3. The perforating system of claim 1, wherein the diameters of the plates vary.

4. The perforating system of claim 1, wherein the zonal isolation system is disposed on one of the first or second perforating guns.

5. The perforating system of claim 1, wherein the zonal isolation system is disposed between the first and second perforating guns.

6. The perforating system of claim 1, further comprising a sub connected between the first and second perforating guns, wherein the zonal isolation system is disposed on the sub.

7. The perforating system of claim 1, wherein the zonal isolation system comprises a first zonal isolation system, the perforating system further comprising a second zonal isolation system.

8. A perforating system comprising: a. a perforating string;b. shaped charges in the perforating string;c. a stack of axially spaced apart plates that extend radially outward from the perforating string to define a restricted flow area between a portion of the perforating string and a wellbore wall when the perforating string is in a wellbore, so that when shaped charges in the perforating string are detonated and form perforations into formation zones adjacent the wellbore and having different pressures, fluid communication between the respective formations is impeded by the plates.

9. The perforating system of claim 8, wherein the perforating string includes perforating guns stacked end to end.

10. The perforating system of claim 8, wherein the plates are for directing fluid from one of the formations along a labyrinthine path for reducing pressure in the fluid.

11. The perforating system of claim 8, further passages formed axially through the plates.

12. The perforating system of claim 11, wherein the passages in adjacent plates are offset from one another.

13. The perforating system of claim 8, wherein diameters of the plates varies.

14. A method of dynamically isolating flow within a wellbore between a first subterranean formation zone and a second subterranean formation zone that is at a different pressure than the first subterranean formation zone, the method comprising: a. providing a downhole tool in a wellbore that comprises an outer surface, and a pressure isolation system that has axially spaced apart plates that extend radially outward from the outer surface of the downhole tool to define a restricted flow annulus between the member and the wellbore,b. inducing connate fluid flow from within the first subterranean formation zone;c. inducing connate fluid flow from within the second subterranean formation zone; andd. dynamically creating a pressure drop between the first and second subterranean formation zones of different pressures by locating the restricted flow annulus between the first and second subterranean formation zones and reducing pressure in the connate fluid from the subterranean formation zone having a higher pressure, so that flow from the subterranean formation zone having the higher pressure does not flow into the other subterranean formation zone.

15. The method of claim 14, wherein the plates are configured to form a labyrinthine path for connate fluid flow along the downhole tool.

16. The method of claim 15, wherein the labyrinthine path is formed by providing passages through the plates and positioning the passages in each plate to be axially offset from passages in an adjacent plate.

17. The method of claim 15, wherein the labyrinthine path is formed by varying the diameter of plates that are adjacent.