Sand fallback submersible pump protection apparatus

Abstract

A sand fallback tool having an elongate outer housing with proximal end, a distal end, a chamber therebetween surrounding an axis extending from the proximal end through the distal end, a tubular riser supported within the chamber to divide at least a portion of the chamber of the housing into a central passage along the axis and an annular passage radially intermediate an exterior of the tubular riser and an interior of the housing, and an unobstructed axial settling path from the proximal connector into the central passage. One embodiment further includes a tubular extension coupled to the proximal connector and extending along the axis to terminate at a distal end of the tubular extension received within a proximal end of the tubular riser to provide an "S"- shaped flow pathway intermediate the annular passage and the proximal connector of the housing.

Description

SAND FALLBACK SUBMERSIBLE PUMP PROTECTION APPARATUSBACKGROUNDField of the Invention

[0001] The present invention relates to a sand fallback tool that provides protection against damage to or incapacitation of downhole submersible pumps used to recover formation fluids such as, for example, oil from subsurface geologic formations through artificial lift. Sand intrusion into or settling within the submersible pump can damage or disable the submersible pump and / or prevent it from being successfully restarted for continued fluid production to the surface.Background of the Related Art

[0002] Some subsurface geologic formations produce fluids with entrained sand. The sand can cause problems with production equipment. It is preferred to minimize the amount of sand that, with fluid, flows downwardly from the production string, through the proximal connector, through the distal connector and through submersible pumps and other equipment upon interruptions of operation of the submersible pump. Also, it is preferred to prevent large amounts of sand from accumulating near the producing geologic formations from which fluid, such as oil, is produced.

[0003] Sand fallback generally occurs when electrical current to a submersible pump is interrupted or the pump fails due to mechanical issues. Alternately, a pump may be purposely shut down for treating the producing formation or the formation face with chemicals that are pumped into the well.

[0004] Sand fallback tools are generally elongate tools that are coupled to a submersible pump at a distal connector, coupled to the production string at a proximal connector, and positioned within a well in a vertical orientation so that sand separated out of fluid moving up the production string at the time of interruption of the submersible pump is prevented from moving downwardly through an inactive submersible pump coupled to the distal connector.CAVINS-0012.PCT Page 1 of 22SUMMARY

[0005] Embodiments of the sand fallback tool of the present invention include a proximal end with a proximal connector that is adapted to be coupled to a distal end of a tubular production string and positioned in a well in a generally vertical orientation. Embodiments of the sand fallback tool include a distal end with a distal connector adapted for being coupled to a proximal end of a submersible pump, also known as an electrical submersible pump (ESP). Embodiments of the sand fallback tool of the present invention prevent or reduce the amount of sand entering the proximal end of a submersible pump coupled to the distal end of the sand fallback tool during interruptions of operation of the submersible pump.

[0006] Some embodiments of the sand fallback tool of the present invention include movable components that are not physically connected to other movable or immovable components of the tool, but are instead displaceable by fluid flow within a cage, a channel or a chamber in which the movable component can move. Some embodiments of the sand fallback tool of the present invention include check valves that open to allow the flow of fluid through certain portions of the sand fallback tool and upwardly into a production string through which the fluid flows to the surface during operation of a submersible pump. These check valves will later close to prevent and / or to redirect backflow of fluid and sand through certain portions of the sand fallback tool and to promote the accumulation of sand within certain portions of the sand fallback tool.

[0007] Embodiments of the sand fallback tool of the present invention include a proximal end with a threaded proximal connector for threadedly coupling the sand fallback tool to a distal end of a tubular production string that can be stepwise extended into an earthen well to position and to support the sand fallback tool and a submersible pump coupled thereto, and a distal end with a threaded distal connector for threadedly coupling the sand fallback tool to a proximal end (a discharge end) of the submersible pump. “Coupling,” as that term is used herein, means that the production tubing and the sand fallback tool, or the sand fallback tool and the submersible pump, may be directly coupled, and it also means that other tools, including additional sand fallback tools, may be coupled intermediate the proximal end of the sand fallback tool and the production string or between the distal endCAVINS-0012.PCT Page 2 of 22of the sand fallback tool and the submersible pump without loss of benefit and use of the sand fallback tool. More than one sand fallback tool can be included within the same tool string for increased sand storage capacity and enhanced protection against sand entry into the submersible pump.

[0008] One embodiment of the sand fallback tool of the present invention includes an elongate chamber within an outer housing and intermediate the proximal connector end and the distal connector, and an axis extending through the proximal connector, the chamber and the distal connector. The distal connector of embodiments of the sand fallback tool of the present invention has a bore for the passage of fluids entering the chamber of the sand fallback tool from a submersible pump coupled to the distal connector. The proximal connector of embodiments of the sand fallback tool also has a bore for the upward and downward passage of fluids through the sand fallback tool. Embodiments of the sand fallback tool include a riser having a bore that is aligned with the proximal connector and the distal connector of the sand fallback tool and which surrounds the axis. The distal end of the riser is sealably connected to a central passage of a distal passage body that is adjacent to the distal connector. The distal passage body includes the central passage that surrounds the axis of the housing and a plurality of angularly distributed bypass passages that surround the central passage of the distal passage body. Embodiments of the sand fallback tool include an annular passage intermediate the riser and the housing. The bore of the riser is separated from the annular passage by the wall of the tubular riser. Fluid entering the chamber of the housing through the distal connector flows through the central passage of the distal passage body and also through the bypass passages of the distal passage body that surround the central passage. Fluid flowing upwardly into the chamber through the central passage of the distal passage body flows into the bore of the riser. Fluid flowing upwardly into the chamber through the bypass passages of the distal passage body flow into the annular passage that surrounds the tubular riser. The annular passage can receive and store separated sand when the operation of the submersible pump is interrupted. This will be explained in further detail below.

[0009] One embodiment of the sand fallback tool of the present invention includes a proximal assembly and a distal assembly. The proximal assembly includes a descending sleeve, a spin compartment and a proximal check valve, as described in more detail below.CAVINS-0012.PCT Page 3 of 22The distal assembly includes the distal passage body. The distal assembly further includes the tubular riser that surrounds the axis of the housing and that extends upwardly from the central passage of the distal passage body and into the chamber of the housing, thereby creating an annular flow passage that surrounds the riser. During normal operation of the submersible pump, pressurized fluid discharged from the submersible pump coupled to the distal end of the sand fallback tool flows through the distal connector, through the central bore of the distal passage body and upwardly through the tubular riser, and pressurized fluid discharged from the submersible pump also flows through the distal connector, through the angularly spaced bypass passages of the distal passage body to enter and flow through the annular flow passage. As will be seen in the discussion below, flow through the bypass passages and the annular flow passage can be closed or obstructed.

[0010] In one embodiment of the sand fallback tool of the present invention, the distal assembly further includes a distal check valve that can, when closed, obstruct back flow through the plurality of bypass passages. That is, the distal assembly includes a distal check valve that can close to isolate the bypass passages of the distal passage body from fluid and sand within the annular flow passage. In one embodiment, a proximal face of the distal passage body includes an annular seat that surrounds the plurality of proximal ends of the plurality of bypass passages. The distal check valve includes an annular flow stopper that is movable between a closed position, wherein the annular flow stopper sealably engages the annular seat and closes the bypass passages to prevent flow from the annular passage into the bypass passages, and an open position wherein the annular flow stopper is displaced from the annular seat to permit flow through the plurality of bypass passages. The annular flow stopper is in the seated position when fluid flows downwardly from the proximal connector through the chamber towards the distal connector, such as when operation of the submersible pump is interrupted. The annular flow stopper is in the unseated position when fluid flows upwardly from the distal connector, through the passage assembly, through the chamber to the proximal connector. The closure of the annular flow stopper of the distal assembly protects the submersible pump from entry of sand during interruptions of operation of the submersible pump.

[0011] Upon suspension of operation of the submersible pump, the hydrostatic head of fluid with entrained sand in the production string coupled to the proximal connector of theCAVINS-0012.PCT Page 4 of 22sand fallback tool immediately become very large relative to the bottom hole pressure below the submersible pump. This dramatic reversal of the pressure differential across the sand fallback tool and the submersible pump causes the fluid with entrained sand to flow downwardly into the sand fallback tool to immediately close the proximal check valve in the distal section of the descending sleeve of the proximal assembly and the closure of the proximal check valve results in pressurization of the interior cavity of the spin compartment. The dramatic reversal of the pressure differential across the sand fallback tool also causes the distal check valve to close to cover and seal with the annular sealing face to prevent fluid and sand entry into the proximal openings of the plurality of bypass passages in the distal passage body. The closure of the distal check valve generally results in the accumulation of an annular column of sand within the annular flow passage, as explained further below.

[0012] Returning to the proximal assembly of an embodiment of the sand fallback tool of the present invention, the proximal assembly includes the descending sleeve, a spin compartment and a proximal check valve reside. Embodiments of the sand fallback tool of the present invention may include alternate spin compartments, as described below.

[0013] In one embodiment of the sand fallback tool of the present invention, the spin compartment of the proximal assembly is sealably engaged with the proximal connector through a proximal section of the descending sleeve. This embodiment of the spin compartment includes an interior cavity that is sealably engaged with the proximal section and also with a distal section of the descending sleeve of the proximal assembly to receive fluid flow through a proximal check valve in the distal section of the descending sleeve during operation of the submersible pump. The embodiment of the spin compartment further includes at least one spin passage through which fluid may exit the interior cavity of the spin compartment in a radially outwardly direction to enter the chamber of the tubular housing with a spinning flow. In this embodiment, the spin compartment includes at least one spin passage. In some other embodiments, the spin compartment may include a plurality of angularly spaced spin passages. In these embodiments, each spin passage is disposed in the radially outwardly disposed wall of the spin compartment and includes an inlet opening to receive fluid flow from the interior cavity of the spin compartment and an outlet opening through which fluid is discharged to the chamber of the housing. The inletCAVINS-0012.PCT Page 5 of 22opening of each spin passage is angularly offset from the outlet opening of each spin passage to impart a tangentially directed flow component to the directional flow of fluid discharged from the at least one spin passage as the discharged fluid enters the portion of the chamber intermediate the tubular housing and the spin compartment. This arrangement results in a spinning fluid pattern intermediate the housing and the spin compartment that causes more dense materials entrained in the fluid, such as, for example, sand, to move to the interior wall of the tubular housing and, subsequently, to separate from the spinning fluid component and settle into the annular passage intermediate the riser and the housing instead of settling in the bore of the riser. The accumulation of sand in the distal portion of the annular passage prevents sand from entering the intermediate passage disposed intermediate the distal end of the descending sleeve of the proximal assembly and the proximal end of the riser of the distal assembly. The result is that fluid passing downwardly through the sand fallback tool upon suspension of operation of the submersible pump is substantially free of entrained sand as it flows through the intermediate passage and then into the bore of the tubular riser and downwardly through the tubular riser, through the central bore of the distal passage body and from the sand fallback tool through the distal connector to the submersible pump. There is no flow of fluid from the annular flow passage into the plurality of angularly distributed bypass passages surrounding the central passage of the distal passage body because the bypass passages are isolated by closure of the distal flow stopper due to engagement with the seat on the distal passage body.

[0014] In another embodiment of the present invention, one or more spiraling vanes is / are supported within the annulus intermediate the descending sleeve and the housing. In this embodiment, the fluid entering the proximal connector into the spin compartment is discharged from the spin compartment and radially outwardly through the spin passages, which may or may not be circumferentially angled to induce spinning, and the fluid flows rapidly downwardly through the annulus intermediate the descending sleeve and the housing and the one or more spiraling vanes impart the spinning motion that separates the sand particles from the fluid. In other embodiments of the present invention, both circumferentially angled spin passages and one or more spiraling vanes may be used together to induce spinning in the fluid. The phrase “spin compartment,” as that phrase is used herein, may refer, in some embodiments, to the spin compartment andCAVINS-0012.PCT Page 6 of 22circumferentially angled spin passages, in other embodiments, the section of the tool with one or more vanes supported within the annulus intermediate the descending sleeve and the housing, and in still other embodiments, the phrase may refer to the section of the tool having having a spin compartment with angled spin passages and with one or more vanes supported within the annulus intermediate the descending sleeve and the housing.

[0015] Upon resumption of operation of the submersible pump, flow resumes from the pump through the distal connector, through the central bore of the distal passage body, but flow is obstructed, in whole or in part, by the annular flow stopper and the accumulated annular column of sand within the annular flow passage atop the annular flow stopper. Continued operation of the pump results in pressurized fluid displacing the annular flow stopper from the annular seat on the central passage body. The pressurized fluid increasingly fluidizes the accumulated annular column of sand that accumulates on top of the annular flow stopper and the accumulated annular column of sand is removed from the annular flow passage into the intermediate passage and upwardly through the descending sleeve, through the opened check valve and from the sand fallback tool through the proximal connector. Some of the accumulated annular column of sand may enter the spin compartment through the spin passages and exit the descending sleeve through the proximal connector.

[0016] In an alternative embodiment of the sand fallback tool of the present invention, the spin compartment includes a cylindrical wall that surrounds the axis and resides in the descending sleeve of the proximal assembly intermediate the proximal check valve and the proximal connector. The cylindrical wall includes at least one passage that allows pressurized fluid and entrained sand to flow from the proximal connector into the walled portion of the spin compartment and radially outwardly through the at least one passage in the walled portion of the spin compartment. The alternative embodiment of the sand fallback tool of the present invention further includes at least one spiraling vane disposed within the annular passage intermediate the descending sleeve and the housing, the at least one spiraling vane imparting a spinning flow to the fluid and entrained sand that flows downwardly from the walled portion of the spin compartment and through the annular passage upon termination of operation of the submersible pump. In one embodiment of the sand fallback tool of the present invention having the alternate spin compartmentCAVINS-0012.PCT Page 7 of 22structure, the at least one vane includes a plurality of spiraling vanes disposed within the annular passage to promote spinning flow to the fluid and entrained sand entering the sand fallback tool from the production string and through the proximal connector.

[0017] Operation of embodiments of the sand fallback tool of the present invention will be understood by the detailed disclosure of an embodiment of the tool that follows.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0018] FIG. 1 is a sectional elevation view of an embodiment of the sand fallback tool of the present invention during sustained operation of a submersible pump (not shown) coupled to the distal connector of the sand fallback tool.

[0019] FIG. 2 is a sectional plan view of the distal passage body of the distal assembly of the sand fallback tool of FIG. 1.

[0020] FIG. 3 is the sectional elevation view of FIG. 1 after interruption of the power supplied to the submersible pump (not shown) and after sand separated from fluid in the production string (not shown) coupled to the proximal connector of the sand fallback tool at the time of suspension of operation of the submersible pump settled into the annular flow passage.

[0021] FIG. 4 is the sectional plan view of the spin compartment of the proximal assembly of the sand fallback tool of FIGs. 1 and 3 illustrating fluid flow from the interior cavity of the spin compartment to the chamber of the outer tubular housing during unloading of the column of fluid from the production string back through the sand fallback tool.

[0022] FIG. 5 is the sectional elevation view of sand fallback tool of FIGs. 1 and 3 after restoration of operation of the submersible pump and resumption of fluid flow upwardly through the sand fallback tool.

[0023] FIG. 6 is a sectional perspective view of an embodiment of the sand fallback tool of the present invention having a spin compartment that includes one or more vanes supported within the annulus intermediate the descending sleeve and the housing (outer housing).CAVINS-0012.PCT Page 8 of 22DETAILED DESCRIPTION

[0024] Embodiments of the sand fallback tool of the present invention provide a substantial amount of storage space for separated sand so that the separated sand does not enter and possibly clog or otherwise disable a submersible pump coupled to the distal connector of the sand fallback tool.

[0025] FIG. 1 is a sectional elevation view of an embodiment of the sand fallback tool 10 of the present invention during sustained operation of a submersible pump (not shown) coupled to the distal connector 14 of the sand fallback tool 10. The sand fallback tool 10 of FIG. 1 includes an elongate outer housing 16 with a proximal connector 12 for coupling the sand fallback tool 10 to a tubular production string (not shown) through which fluid moved by the submersible pump (not shown) through the sand fallback tool 10 is delivered to the surface. The distal connector 14 and the proximal connector 12 may include threads for coupling to the submersible pump and the production string, respectively.

[0026] The sand fallback tool 10 of FIG. 1 further includes a distal assembly 20 and a proximal assembly 60. The distal assembly 20 comprises a distal passage body 22 that includes a central passage 25 and a plurality of bypass passages 24 that surround the central passage 25 of the distal passage body 22. The distal assembly 20 further includes a tubular riser 29 having a proximal end 30 and a distal end 31 sealably engaging the central passage 25 of the distal passage body 22. The tubular riser 29 divides an annular passage 32, formed intermediate the tubular riser 29 and the housing 16, from the bore 33 of the riser 29. The fluid flow entering the sand fallback tool 10 from the submersible pump (not shown) through the distal connector 14, as indicated by arrow 50, is divided by the distal passage body 22 into a stream of fluid passing through the central passage 25 of the distal passage body 22, and then into the bore 33 of the tubular riser 29, and a plurality of streams of fluid passing through the plurality of bypass passages 24 in the distal passage body 22 and then into the annular passage 32.

[0027] The distal assembly 20 of the sand fallback tool 10 of FIG. 1 further includes an annular flow stopper 28 surrounding the tubular riser 29 that is shown in FIG. 1 as being displaced from a seat 26 that is formed on the distal passage body 22 and correspondingly shaped to sealably engage the annular flow stopper 28. The annular flow stopper 28 isCAVINS-0012.PCT Page 9 of 22shown in the open position displaced from the seat 26 by the pressure of fluid emerging from the bypass passages 24 of the distal passage body 22. The displacement of the annular flow stopper 28 from the seat 26 allows fluid to flow upwardly through the bypass passages 24 and around the annular flow stopper 28 as indicated by the arrows 54. Fluid emerging from the central passage 25 of the distal passage body 22 flows upwardly through the bore 33 of the tubular riser 29 as indicated by the arrow 56.

[0028] The sand fallback tool 10 of FIG. 1 further includes a proximal assembly 60 having a descending sleeve 62 with a proximal end 63 sealably engaging the proximal connector 12 of the sand fallback tool 10 and a distal end 64 disposed within the annular passage 32 surrounding the proximal end 30 of the riser 29. The distal end 64 of the descending sleeve 62 surrounds the proximal end 30 of the tubular riser 29 to create an annular intermediate passage 34 intermediate the descending sleeve 62 and the tubular riser 29. The proximal assembly 60 further includes a proximal check valve having a ball 69 movably captured within a cage 68 and a seat 66 shaped to sealably engage the ball 69. In FIG. 1sthe ball 69 is shown in the open position with the ball 69 displaced from its seat 66 by the pressurized fluid emerging from the bore 33 of the tubular riser 29 and a portion of the fluid emerging from the annular passage 32. Displacement of the ball 69 from the seat 66 allows fluid to flow upwardly within the descending sleeve 62 and around the ball 69 as indicated by the arrows 67.

[0029] The proximal assembly 60 of the sand fallback tool 10 of FIG. 1 further includes a spin compartment 65 disposed intermediate the cage 68, in which the ball 69 is movably captured, and the proximal end 63 of the descending sleeve 62. The spin compartment 65 receives fluid flowing into the distal end 64 of the descending sleeve 62 and around the displaced ball 69 as indicated by the arrows 67, and the fluid flows through the spin compartment 65, through the proximal end 63 of the descending sleeve 62 and from the sand fallback tool 10 through the proximal connector 12 to the connected production string (not shown) for delivery to the surface. The spin compartment 65 and its function are described in greater detail below.

[0030] FIG. 2 is a sectional plan view of the distal passage body 22 of the distal assembly 20 of the sand fallback tool 10 of FIG. 1 showing the central passage 25 and the pluralityCAVINS-0012.PCT Page 10 of 22of bypass passages 24 through which fluid flows upwardly from a submersible pump (not shown) coupled to the distal connector 14.

[0031] FIG. 3 is the sectional elevation view of the sand fallback tool 10 of FIG. 1 after interruption of the power supply to the submersible pump (not shown), and after sand 39 that was entrained in fluid moving up the production string (not shown) prior to the interruption of operation to the submersible pump has been centrifugally separated from liquid discharged from the spin compartment 65 and allowed to settle within the annular passage 32.

[0032] Submersible pumps used in artificial lift operations implemented to recover oil from drilled wells are designed to produce a large amount of discharge pressure to move fluids with entrained sand through the sand fallback tool 10 and the production string to the surface. The hydrostatic head resulting from the column of fluid with entrained sand in the production string and bearing on the sand fallback tool 10 at the time of interruption of submersible pump operation is very large. This results in a substantial differential pressure forcing fluid flow from the production string and downwardly through the sand fallback tool 10. The sudden and dramatic reversal of the direction of fluid flow resulting from interruption of submersible pump operation immediately closes the proximal check valve (that is, it displaces the ball 69 onto its seat 66) and it immediately closes the distal check valve (that is, it displaces the annular flow stopper 28 onto its seat 26 to close the bypass passages 24 of the distal passage body 22). The result is that fluid entering the proximal connector 12 at a large rate of flow enters the spin compartment 65 and exits the spin compartment 65 through the one or more spin passages 70.

[0033] FIG. 4 is the sectional plan view of the spin compartment 65 of the sand fallback tool 10 of FIGs. 1 and 3 illustrating fluid flow from the interior 61 of the spin compartment 65 to the housing 16. The proximal check valve including the ball 69 and its seat 66 can be seen below the spin compartment 65. FIG. 4 illustrates how the closure of the proximal check valve in the manner described above forces fluid through the interior 61 of the spin compartment 65 and laterally from the interior 61 of the spin compartment 65 through the spin passages 70 as indicated by the arrows 71. The fluid with entrained sand flows through the spin compartment 65 at a dramatic rate. FIG. 4 shows a spin compartment 65 with four spin passages 70. Other embodiments may have as few as one, or it may have two, threeCAVINS-0012.PCT Page 11 of 22or more than four. The one or more spin passages 70 of the spin compartment 65 are formed at an angle (circumferentially angled) to provide a substantial tangential velocity component. The spin passages 70 are formed at such an angle as to generate a spinning flow within the portion 18 of the annular passage 32 formed intermediate the spin compartment 65 and the interior wall 17 of the housing 16. The result is a substantial swirling flow of the fluid that causes the sand entrained in the fluid, which is denser than the fluid, to be directed radially outwardly and against the interior wall 17 of the housing 16. The sand will then settle or descend due to its high density from the portion 18 of the annular passage 32 formed intermediate the spin compartment 65 and the interior wall 17 of the housing 16 downwardly within the annular passage 32 to the portion of the annular passage 32 that is intermediate the tubular riser 29 and the housing 16 as illustrated in FIG. 3. The sand will settle and accumulate in the annular passage 32 atop the closed annular flow stopper 28, which is engaged with its seat 26, and intermediate the tubular riser 29 and the housing 16 in an annular column 39 as shown in FIG. 3. As shown in FIG. 3, the fluid component, from which the accumulated sand column 39 has been substantially removed, can turn at the distal end 64 of the descending sleeve 62 and flow upwardly into the intermediate annular passage 34, then turn again at the proximal end 30 of the tubular riser 29 and flow downwardly through the bore 33 of the tubular riser 29 and the central passage 25 of the distal passage body 22. This fluid path is illustrated by arrows 57. The fluid is then discharged from the sand fallback tool 10 through the distal connector 14 to flow through the inactive submersible pump to the portion of the wellbore proximal to the geologic formation from which the fluid was originally extracted.

[0034] Returning to FIG. 3, this figure illustrates two of the benefits provided by embodiments of the sand fallback tool 10 of the present invention. First, the capacity of the sand fallback tool 10 to separate entrained sand from the fluid residing in the production string at the time of interruption of operation of the submersible pump enables the sand to be stored within the sand fallback tool 10. The storage of the sand in the sand fallback tool 10 thereby protects the submersible pump from becoming packed with or otherwise disabled by large amounts of sand settling in or passing through the pump. Second, as indicated by the arrows 57 in FIG. 3, chemical agents can be pumped during inactivity of the submersible pump into the production string at the surface, down through theCAVINS-0012.PCT Page 12 of 22production string, through the sand fallback tool 10 and to the geologic formation that is in fluid communication with the wellbore in which the sand fallback tool 10 and the submersible pump are installed. This feature enables how chemical agents such as, but not by way of limitation, acids used to stimulate the geologic formation and the formation face, oxygen scavengers, biocides, corrosion inhibitors and other agents, can be introduced into the well and pumped to the desired targeted formation or equipment during an interruption in operation of the submersible pump.

[0035] FIG. 5 illustrates the fluid flow within the sand fallback tool 10 of FIGs. 1 and 3 upon reactivation of the submersible pump (not shown) after an interruption of the operation of the pump and accumulation of sand in the annular passage as shown in FIG. 3. The fluid flow enters the distal connector 14 as indicated by arrow 50 and approaches the distal passage body 22. Fluid flows through the central passage 25 of the distal passage body 22 and up through the bore 33 of the tubular riser 29 as indicated by arrow 56. The flow of fluid through the bypass passages 24 of the distal passage body 22 is reduced immediately after reactivation of the submersible pump due to the accumulated annular sand column 39 resting atop the annular flow stopper 28 in the closed position engaging the seat 26 as illustrated in FIG. 3. However, sustained fluid pressure applied through the bypass passages 24 against the annular flow stopper 28 will displace the annular flow stopper 28 from the seat 26 and begin to fluidize the accumulated annular column of sand 39 in the annular passage 32 as illustrated in FIG. 5. Sustained operation of the submersible pump will fluidize, diminish and remove the accumulated annular column of sand 39 and the sand will once again become entrained in the fluid flow and will be carried upwardly through the sand fallback tool 10, into the production string and to the surface.

[0036] It will be understood that the ball 69 and seat 66 of the proximal check valve (in the descending sleeve) may, in some embodiments of the sand fallback tool 10 of the present invention, include other components known for their use in check valves such as, for example, but not by way of limitation, flapper check valves, butterfly check valves, spring-loaded check valves and others. Similarly, other types of check valves could be substituted for the distal check valve disclosed in connection with the embodiment shown in the appended drawings. The number and configuration of the spin passages in the spin compartment may vary. The overlap in the proximal portion of the riser and the distalCAVINS-0012.PCT Page 13 of 22portion of the descending sleeve may vary in axial length and clearance therebetween in different embodiments.

[0037] FIG. 6 is a sectional perspective view of an embodiment of the sand fallback tool 10 of the present invention having a spin compartment 65 that includes one or more vanes 72 supported within the annulus intermediate the descending sleeve 62 and the interior surface 17 of the housing 16. Upon interruption of operation of the sand fall back tool 10, fluid from above flows briskly downwardly into the tool 10,outwardly through the spin passages 70 (which may or may not be circumferentially angled to produce spin), and downwardly within the annulus 32 and across the vanes 72 which produce the desired spinning flow that separates the sand from the fluid.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and / or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0039] The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.CAVINS-0012.PCT Page 14 of 22

Claims

We claim:

1. A sand fallback tool, comprising: an elongate outer housing having a proximal end with a proximal connector for coupling to a production string, a distal end with a distal connector for coupling to a submersible pump, an elongate chamber within the housing and intermediate the proximal end and the distal end, and an axis extending through the proximal connector and the distal connector; a distal assembly, including: a riser with a bore surrounding the axis, the riser having a proximal end and a distal end, the riser separating the bore from a portion of an annular flow passage disposed radially intermediate the riser and the housing; a distal passage body sealably engaging the distal connector, the distal passage body having a central passage sealably engaging the distal end of the riser, the central passage surrounded by a plurality of angularly distributed bypass passages, the plurality of bypass passages having proximal openings in fluid communication with the chamber, each of the proximal openings forming a portion of an annular seat that surrounds the central passage; and an annular flow stopper having a hole with a diameter larger than an outer diameter of the riser and a distal face shaped for sealing engagement with the annular seat of the distal passage body, the flow stopper being movable between a closed position with the distal face of the annular flow stopper sealingly engaged with the correspondingly shaped annular seat to close the plurality of bypass passages, and a displaced position with the distal face of the flow stopper disengaged from the annular seat to open the plurality of bypass passages and to enable fluid flow from the submersible pump that is connected to the distal connector through the plurality of bypass passages and into the elongate chamber; and a proximal assembly, having: a descending sleeve with a proximal end sealably engaging the proximal connector, a distal end extending downwardly into the chamber and terminatingCAVINS-0012.PCT Page 15 of 22within the portion of the annular passage surrounding a proximal portion of the riser, thereby creating an intermediate flow passage disposed intermediate the proximal portion of the riser and a distal portion of the descending sleeve; a spin compartment disposed intermediate the distal end of the descending sleeve and the proximal end of the descending sleeve, the spin compartment having a wall surrounding the axis of the chamber and at least one spin passage in the wall, the at least one spin passage having an outer opening of the at least one spin passage that is angularly offset from an inner opening of the at least one spin passage to induce a spinning flow within the chamber adjacent to the spin compartment resulting from fluid flowing from the production string coupled to the proximal connector of the sand fallback tool, downwardly into the proximal end of the descending sleeve and into the spin compartment, into the inner opening of the at least one spin passage of the spin compartment and out through the outer opening of the at least one spin passage of the spin compartment to enter the chamber; and a check valve disposed within the descending sleeve and intermediate the spin compartment and the distal end of the descending sleeve, the check valve including a ball seat and a ball movable between a closed position with the ball engaging the ball seat to prevent fluid flow from the proximal connector to the distal end of the descending sleeve and an open position with the ball displaced upwardly and away from the ball seat to allow fluid flow upwardly from the distal end of the descending sleeve, through the descending sleeve, through the spin compartment and to the proximal connector; wherein during normal flow operation of the submersible pump coupled to the distal connector of the sand fallback tool, pressurized fluid flows from the pump through the central passage, through the bore of the tubular riser and also through the plurality of bypass passages to displace the annular flow stopper from the closed position to permit flow into the annular passage, the fluid also flowing into the distal end of the descending sleeve to displace the ball from its seat to permit flow around the ball to the spin compartment; wherein upon interruptions in operation to the submersible pump, fluid with entrained sand in the production string flows downwardly through the proximal connector,CAVINS-0012.PCT Page 16 of 22into the spin compartment and radially outwardly through the one or more spin passages in a spinning flow pattern to centrifugally separate; and wherein the sand separated from the fluid resulting from interruption of the operation of the submersible pump accumulates within the annular passage atop the closed annular flow stopper.

2. The sand fallback tool of claim 1, wherein the one or more spin passages comprise a plurality of angularly spaced spin passages.

3. The sand fallback tool of claim 1, further comprising: a cage surrounding the ball to limit a range of movement of the ball within the descending sleeve of the proximal assembly.

4. A sand fallback tool, comprising: an elongate outer housing having a proximal end with a proximal connector to couple to a production string, a distal end with a distal connector for coupling to a submersible pump, an axis extending from the proximal connector to the distal connector, and an elongate chamber intermediate the proximal end and the distal end of the housing; a passage assembly sealably engaging the distal connector, the passage assembly having a central passage and a plurality of bypass passages surrounding the central passage, each bypass passage having a proximal opening through which fluid entering the distal connector flows into the chamber; a tubular riser having a proximal end and a distal end sealably engaging the central passage of the passage assembly, the tubular riser supported within the chamber to surround the axis and to divide a bore of the riser from an annular passage disposed radially intermediate the riser and the housing; an annular flow stopper having a central hole surrounding the riser and a distal face, the annular flow stopper movable between a closed position with the distal face engaging the plurality of proximal openings of the plurality of bypass passages and an open position with the distal face displaced from engagement with the plurality of proximal openings; a descending sleeve having a proximal end sealably engaging the proximal connector and a distal end disposed within the annular passage;CAVINS-0012.PCT Page 17 of 22a spin compartment disposed within the descending sleeve, the spin compartment having a wall surrounding the axis and at least one of a spin passage in the wall, the at least one spin passage having an outlet that is angularly spaced from an inlet of the spin passage, and one or more vanes supported within the annulus intermediate the descending sleeve and the housing; and a check valve disposed within the descending sleeve intermediate the proximal end and the distal end, the check valve having a ball movable from a closed position with the ball engaging a ball seat to prevent fluid flow from the spin compartment to the distal end of the descending sleeve and an open position with the ball displaced from the ball seat to allow fluid flow from the distal end of the descending sleeve to the spin compartment; wherein upon an interruption in operation of the submersible pump, sand entrained in fluid residing in a production string coupled to the proximal connector will flow into the sand fallback tool through the proximal connector and through a portion of the descending sleeve to the spin compartment, from the spin compartment through the at least one spin passage and into the portion of the annular passage radially intermediate the spin compartment and the outer body in a spinning flow patter that centrifugally separates the sand from the fluid; and wherein sand separated from fluid entering the sand fallback tool after an interruption in operation of the submersible pump can accumulate in the portion of the annular passage radially intermediate the riser and the outer body.

5. The sand fallback tool of claim 4, further comprising: a distal check valve disposed within the chamber and proximal to the distal connector, the distal check valve having a closed position to prevent fluid flow from the chamber through the distal connector and an open position to allow fluid flow from a submersible pump coupled to the distal connector into the chamber.

6. The sand fallback tool of claim 4, wherein the tubular riser is supported within the chamber from at least one of the proximal end and the distal end.CAVINS-0012.PCT Page 18 of 227. The sand fallback tool of claim 4, further comprising a cage proximal to the distal connector to limit movement of the annular flow stopper from the closed position to the open position.

8. A sand fallback tool, comprising: an elongate outer housing having a proximal end with a proximal connector for coupling to a production string, a distal end with a distal connector for coupling to a submersible pump, an elongate chamber within the housing and intermediate the proximal end and the distal end, and an axis extending through the proximal connector and the distal connector; a distal assembly, including: a riser with a bore surrounding the axis, the riser having a proximal end and a distal end, the riser separating the bore from a portion of an annular flow passage disposed radially intermediate the riser and the housing; a distal passage body sealably engaging the distal connector, the distal passage body having a central passage sealably engaging the distal end of the riser, the central passage surrounded by a plurality of angularly distributed bypass passages, the plurality of bypass passages having proximal openings in fluid communication with the chamber, each of the proximal openings forming a portion of an annular seat that surrounds the central passage; and an annular flow stopper having a hole with a diameter larger than an outer diameter of the riser and a distal face shaped for sealing engagement with the annular seat of the distal passage body, the flow stopper being movable between a closed position with the distal face of the annular flow stopper sealingly engaged with the correspondingly shaped annular seat to close the plurality of bypass passages, and a displaced position with the distal face of the flow stopper disengaged from the annular seat to open the plurality of bypass passages and to enable fluid flow from the submersible pump that is connected to the distal connector through the plurality of bypass passages and into the elongate chamber; and a proximal assembly, having:CAVINS-0012.PCT Page 19 of 22a descending sleeve with a proximal end sealably engaging the proximal connector, a distal end extending downwardly into the chamber and terminating within the portion of the annular passage surrounding a proximal portion of the riser, thereby creating an intermediate flow passage disposed intermediate the proximal portion of the riser and a distal portion of the descending sleeve; a spin compartment disposed intermediate the distal end of the descending sleeve and the proximal end of the descending sleeve, the spin compartment having a walled portion surrounding the axis of the chamber, the walled portion having at least one aperture in the wall to allow fluid flow from the production string, through the proximal connector and into the annular passage intermediate the descending sleeve and the housing during interruptions in operation of the submersible pump, the spin compartment further including at least one spiraling vane disposed within the annular passage intermediate the descending sleeve and the housing to impart spinning of the fluid as it flows from the aperture in the wall and downwardly along the descending sleeve towards the distal passage body; and a check valve disposed within the descending sleeve and intermediate the spin compartment and the distal end of the descending sleeve, the check valve including a ball seat and a ball movable between a closed position with the ball engaging the ball seat to prevent fluid flow from the proximal connector to the distal end of the descending sleeve and an open position with the ball displaced upwardly and away from the ball seat to allow fluid flow upwardly from the distal end of the descending sleeve, through the descending sleeve, through the spin compartment and to the proximal connector; wherein during normal flow operation of the submersible pump coupled to the distal connector of the sand fallback tool, pressurized fluid flows from the pump through the central passage, through the bore of the tubular riser and also through the plurality of bypass passages to displace the annular flow stopper from the closed position to permit flow into the annular passage, the fluid also flowing into the distal end of the descending sleeve to displace the ball from its seat to permit flow around the ball, past the one or more apertures in the wall and to the proximal connector and into the production string;CAVINS-0012.PCT Page 20 of 22wherein upon interruptions in operation to the submersible pump, fluid with entrained sand in the production string flows downwardly through the proximal connector, into the aperture in the wall of the spin compartment, radially outwardly through the one or more apertures in the wall and downwardly through the annular passage intermediate the descending sleeve and the housing as the at least one vane imparts a spinning flow pattern to centrifugally separate sand from the fluid flow; and wherein the sand separated from the fluid resulting from interruption of the operation of the submersible pump accumulates within the annular passage atop the closed annular flow stopper.

9. The sand fallback tool of claim 8, wherein the one or more apertures in the wall portion of the spin compartment comprises a plurality of angularly spaced apertures.

10. The sand fallback tool of claim 1, further comprising: a cage surrounding the ball to limit a range of movement of the ball within the descending sleeve of the proximal assembly.CAVINS-0012.PCT Page 21 of 22

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