Pulsing Gravel Pack Tool

Abstract

Apparatus for use in gravel packing a well includes a pulse producing tool which causes the gravel to be continuously agitated as the gravel is being placed in the well.

Description

BACKGROUND OF THE INVENTION

Gravel packing of wells involves placing a quantity of gravel or sand within a well casing or within a well bore externally of a well screen or liner to prevent the migration of sand particles from the productive formation into the well with the production fluid.

In general, either a perforated or slotted screen or liner is hung from the well casing and extends downwardly into an open or uncased hole or the perforated or slotted screen or liner may be supported beneath a packer which is set in well casing which has been perforated at the production zone. The gravel or sand is pumped down a pipe string in a carrier fluid and passes into the annular space outside of the screen or liner, where the gravel or sand is presumably compacted or packed to filter the well fluid as the well fluid passes into the screen or liner. During placement of the gravel or sand the carrier fluid is circulated through a cross-over tool so as to return to the top of the well by flowing from the annulus being packed, into the screen or liner and then into the annulus between the well casing and the running string of pipe.

Problems are encountered if the gravel or sand does not fill the annular space outside of the screen or liner and perforations or slots remain uncovered or in direct communication with the formation, that is, when the gravel pack is not sufficiently compacted or bridges so that voids remain in the gravel pack.

SUMMARY OF THE INVENTION

The present invention provides novel gravel packing apparatus for use in placing gravel or sand in an annulus outside of a well screen or liner, whereby the gravel is more effectively compacted and fills the annulus.

In accordance with the present invention means are incorporated in the gravel pack apparatus in the path of returning fluid, after the gravel has been placed in the annulus, which causes rapid fluid pulses to agitate the gravel and cause the gravel to settle and become more completely packed in the annulus, than has been heretofore generally possible.

To accomplish the foregoing, shock tube means are provided and define separate flow paths from a fluid inlet to the cross-over in the apparatus, and a valve is rapidly shuttled between positions at which the flow paths are alternately momentarily closed. The valve action results in rapid changes in the velocity of fluid flow, with resultant agitation of the entrained gravel or sand. In addition the energy involved may cause pressure pulses going upstream to assist in agitating the gravel.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of forms in which it may be embodied. These forms are shown in the drawings accompanying and forming part of the present specification. They will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed descriptions are not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in longitudinal section, showing one form of gravel pack apparatus disposed in a well in condition for placement of the gravel in the annulus between a well screen or liner and a perforated section of well casing at a productive earth zone;

FIG. 2 is a view in longitudinal section, showing another form of gravel pack apparatus disposed in a well in condition for placement of the gravel in the annulus between a well screen or liner and an open well bore;

FIG. 3a and 3b, together constitute a longitudinal section, with parts shown partially in elevation, showing the pulse producing tool useful with the apparatus of FIG. 1 or FIG. 2, and showing the valve in one position;

FIG. 4 is a fragmentary longitudinal section, showing the pulse producing tool with the valve in its alternate position;

FIG. 5 is a transverse section, as taken on the line 5--5 of FIG. 4;

FIG. 6 is a transverse section, as taken on the line 6--6 of FIG. 4; and

FIG. 7 is a transverse section, as taken on the line 7--7 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As seen in the drawings, the present invention is adapted to be incorporated in more or less conventional or known types of gravel packing equipment. In FIG. 1, gravel packing apparatus is shown which is more particulary illustrated and described in the pending application for Letters Patent of the U.S. Ser. No. 227,558, filed Feb. 17, 1972, in the name of Rudy B. Callihan et. al. In FIG. 1, the gravel packing apparatus A is connected to a running in string of pipe B and run into a well casing C which has been set in a well bore D and suitably perforated at E to establish communication between the well casing C and a productive earth formation or zone F outside the casing. The invention may also be incorporated in gravel packing apparatus, as generally denoted at A in FIG. 2, which is suspended within the well casing C by liner hanger means generally denoted at G. In this embodiment, the casing C is set within the well bore D, and beneath the lower extremity of the well casing C the well bore D has been under reamed or enlarged at D' to provide a reservoir into which well fluids may flow from the productive formation.

The apparatus of FIG. 1, in general, comprises a setting tool and cross-over assembly generally denoted at 1, adapted to be connected at the lower end of the pipe string B and to initially support a well packer 2 therebelow, with a well screen or liner L extending downwardly from the packer 2.

The setting tool and cross-over assembly 1 comprises an outer tubular body 10 and an inner elongated mandrel 11 which are initially interconnected by suitable frangible means 12. The outer body 10 and the mandrel 11 provide piston and cylinder means generally denoted at 13 to which pressure fluid is applicable through ports 14 to shear the frangible means 12 and then effect setting of the packer 2 when the mandrel 11 and the outer body 10 are initially connected to the relatively shiftable packer components which set the packer 2 as more particularly described in the aforementioned application.

The setting tool and cross-over means 1 includes an outer, tubular cross-over member or conduit 15 adapted to extend downwardly through the packer 2 and into the liner or screen L. An inner, tubular cross-over member 16 extends downwardly within the outer cross-over member 15. The assembly provides an elongated fluid passage 17 extending through the inner cross-over member 16 in which is a ball seating member 18 adapted to initially provide a seat for a ball 19, whereby fluid pressure is diverted to the piston and cylinder means 13 to set the packer 2, the ball thereafter being resiliently deformed and forced through the seat member 18 and falling to the position shown, to allow the circulation of fluid through the passage 17.

The outer cross-over member 15 and the inner cross-over member 16 define therebetween a space or flow path 20 which communicates at its lower end with the well screen or liner L. At the lower end of the inner cross-over member 16, is a cross-over passage 21 which establishes communication between the interior of the inner cross-over member 16 and the annular space between the liner L and the outer cross-over member 15. Extending downwardly in the liner L from the outer cross-over member 15 is an assembly including a wash pipe 22 providing a flow passage 23 for the return flow of fluid during circulating and gravel packing operations, as fluid enters the well screen or liner L from the well. The pulse producing means P of the present invention, as will be later described, is incorporated in the wash pipe 22.

The packer 2, as more particularly described in the aforementioned pending application, comprises suitable normally retracted but expansible well casing engaging anchor means 24, whereby the liner L is adapted to be supported within the well casing, while the cross-over assembly, including the members 15 and 16 is longitudinally moveable relative to the packer 2. The packer 2 also includes a normally retracted but expansible elastomeric sealing or packing member 25 which provides a seal between the packer body 26 and the well casing C, thereby preventing communication between the well bore surrounding the liner L and the well bore above the packer 2.

More particularly the well liner or screen L includes an elongated tubular upper body section 27 having longitudinally and circumferentially spaced ports 28 communicating between the upper body 27 and the annulus defined between the body section 27 and the casing C. Below the upper body section 27 is a tubular sealing receptacle 29 having an inner sealing surface 30, and below the sealing receptacle 29 the liner includes a downwardly extending tubular body 31. Spaced vertically in the body 31 is a well screen section 32 of a desired permeability to allow the transfer of flushing fluids and well fluids between the liner L and the well, but to block out sand and gravel, and a tell-tale screen section 33 spaced above the screen section 32, which causes a change in resistance to flow which is detectible at the top of the well, when the gravel packing operation is completed.

Suitably longitudinally spaced along the outer cross-over member 15 is a number of annular seals 35 adapted for side sealing engagement within the cylindrical sealing surface 30 of the receptacle 29 and within a corresponding cylindrical sealing surface 30a within the body of the packer 2, these seals 35 being selectively positionable by relative longitudinal movement between the setting tool and cross-over assembly 1 and the packer 2 and liner L, after the packer and liner have been anchored in the well bore, as seen in the drawings, and as previously described.

In one stage of operation, i.e., during the placement of gravel, as will be later described, the setting tool and cross-over assembly 1 is moved to the position shown in FIG. 1, so that an upper port 30b, in the outer cross-over member 15, communicates with the casing C, while the lowermost sealing means 35 precludes communication between the space external of the outer cross-over member 15 and the liner L below the sealing receptacle 29. In such position, the wash pipe 22 extends downwardly into the liner L below the sealing receptacle 29, so that fluid may flow into the liner L, into the passage 23, and thence upwardly between the inner and outer cross-over members 15 and 16, as shown by the arrows, outwardly through the ports 30b, and thence in the casing further upwardly. Upward movement of the setting tool and cross-over assembly is limited to the position as shown in FIG. 1 by suitable releasable stop means 36 comprising collet fingers 37 which are deformable to allow ultimate further upward movement of the setting tool and cross-over assembly 1, following completion of the gravel packing operation.

During the gravel packing operation fluid is circulated downwardly through the running in string of pipe B, as shown by the arrows, and passes from the cross-over ports 21 to the space between the outer cross-over member 15 and the upper liner body section 27. Such fluid can then pass through the liner body section 27 into the casing through the ports 28, and then will flow downwardly through the well casing and into the lower liner body section 31 through the screen sections 32 and 33, thence through the tail pipe 22, as previously described, and upwardly through the apparatus, as shown by the arrows and previously described, into the casing for return to the top of the well. During such circulation, the gravel or sand is entrained in the circulated fluid and follows the same path, thereby being placed in and preferably filling the annular space between the casing C and the liner L with gravel or sand, which prevents the intrusion of particles from the productive formation F into the well bore through the casing perforations E during the production of the well.

Typically, during such gravel placement operations, the gravel may not be fully compacted and may contain voids due to bridging between the casing and the liner L, so that the gravel pack may not be fully effective to preclude entry of materials from the formation into the casing. The pulse producing means P, as will be later described assists in assuring proper settling and compaction of the gravel or sand.

Referring to FIG. 2, a different type of gravel packing apparatus is illustrated, with which the invention is useful, wherein the well is produced into the enlarged open hole or well bore D'. In this embodiment the running in string of pipe B is not employed in the setting of the liner L, but instead the liner L, as previously indicated, is suspended by a liner hanger G including normally retracted but expansible anchor members or slips 40 which are expanded into anchoring engagement with the well casing C by setting tool means, not shown, but well known. The liner L depends from the body 41 of the hanger assembly G, and the body 41 incorporates, as is well known, a suitable port collar assembly 42 which provides radial ports 43 which are normally closed by a collar or valve sleeve 44 having ports 45. The liner is hung in the casing C by the hanger G with the ports 43 and 45 out of communication, and the body 41 provides a central bore 46 adapted to receive a combined cross-over and port collar shifting tool generally denoted at 47.

The cross-over and port collar shifting tool 47 is connected to the lower end of the running in pipe string B and includes an elongated body 48, in which is disposed a cross-over flow tube 49. The tube 49 communicates at its upper end with a lateral port 50 in the body 48, and at its lower end the cross-over tube 49 extends downwardly through a barrier 51 into the wash pipe 52, which is in turn connected to the pulse producing means P, hereinafter to be described. The body 48 has laterally opening ports 53 disposed between a pair of opposed packing means 54, 54, these packing means, in the illustrated embodiment, being generally shown as opposing resilient or elastomeric cups adapted to contain fluid under pressure therebetween.

Accordingly, fluid flowing downwardly through the running in string pipe B may pass into the annular space defined between the cross-over tool body 48 and the body 41 of the liner hanger but is confined between the packing cups 54 and by the port collar or valve sleeve 44. The cross-over body 48 carries normally outwardly expanded but inwardly deflectable port collar valve engaging members 56 adapted to automatically engage with an inturned flange 57 on the port collar valve 44 when the body 48 is lowered downwardly on the pipe string B and stabbed into the hanger body 41. When the port collar engaging members 56 are engaged with the port collar 44, the pipe string B is elevated to establish communication, as shown in FIG. 2 between the body ports 53, the port collar ports 45 and the hanger body ports 43. Thus, fluid flowing downwardly through the pipe string B finds access to the well bore, as shown by the arrows, from whence the fluid can flow through the perforated or slotted liner L, and upwardly through the cross-over tube 49, into the casing above the liner hanger G. During such flow of fluid the gravel or sand is placed within the enlarged well bore D' to contain the side walls thereof against sloughing off or otherwise preventing sand from flowing into the well bore with the well production fluid, as is well known.

According to the present invention, the gravel pack apparatus includes means for effecting rapid changes in the fluid flow which tend to agitate the gravel or sand particles so that they become more fully compacted and are less likely to bridge. The changes in fluid flow involved are essentially variations in fluid velocity and depending upon the energy of the pressure pulses due to the geometry of the apparatus, as hereinafter to be described, the changes may also include intermittent reverse pressure pulses traveling from the interior of the liner L through the openigns therein, that is, in a direction opposite to the overall flow direction, essentially, thereby, causing minute and rapid changes in fluid direction.

Referring to FIGS. 3a and 3b, the pulse producing means P of the invention will now be described.

In the illustrative embodiment the pulse producing means P comprises an outer tubular body 60 adapted to be connected as shown in FIG. 1 and FIG. 2 to either the wash pipe 22 of the gravel pack apparatus of FIG. 1 or the wash pipe 52 of the gravel pack apparatus of FIG. 2, by some suitable connection such as a threaded joint requiring no illustration. At its lower end the outer tubular body 60 is threadedly connected as at 61 to a coupling member 62. This coupling member has a lower threaded skirt 63 which supports a slotted or perforated bottom cup 64 through which fluid is adapted to flow after entering the well liner L of either FIGS. 1 or 2. The coupling member 62 also includes an internally threaded upwardly extending neck 65 to which is threadedly connected a tubular valve body member 66 which extends upwardly in inwardly and circumferentially spaced relation to the outer body 60. At its upper end, the valve body 66 is connected at 67 to an upper coupling member 68 which is threadedly connected at 69, to an inner tubular body 70 which extends upwardly in spaced relation within the outer body 60 and is held in spaced relation at its upper end by a suitable spacer members 71. The inner body 70 terminates in an upper free end 72 withn the outer body 60. The upper coupling member 68 has a downwardly extended stem or body section 73 extending downwardly within the valve body 66 and terminating in an abutment member 74 at its lower end.

Two different return fluid flow paths are provided in the pulse producing means as thus far described. First, a flow path extends upwardly through the coupling member 62 and through a lower valve seating tube 75 suitable disposed in a socket 76 in the coupling 62 and having an upper valve seat or stop 77. Adjacent to the upper end of the valve seating member 75, the valve body 66 has lateral ports 78 communicating between the interior of the valve body 66 and the annular space 79 between the valve body 66 on the outer tubular body 60, such annular space extending upwardly to the upper end 72 of the inner tubular body 70. A second annular flow path 80 exists through the pulse producing means which extends upwardly between the downward extension 73 on the coupling 68 and thence through radial ports 81, thence upwardly through coupling 68 and through the tubular body 70.

A valve member 82, shown in FIG. 3b in one position and in FIG. 4 in its alterate position, is adapted to move between the abutment or stop 74 and the valve seat or stop 77 so as to alternately open one of the aforementioned flow paths and close the other of said flow paths at a rapid frequency. The valve member 82 in the illustrative form comprises a cylindrical body 83 slideably disposed within the bore 84 in the valve body 66. The body member 82 has a central flow passage 85 therethrough, having a reduced or restricted central portion 86. At its opposite ends the valve member 83 has a first annular transverse surface 87 adapted to abut with the valve seat 75, at which time communication between the valve seat 75 and the valve body ports 78 is shut-off, and a second annular transverse upper surface 88 adapted to abut with the stop member 74 thereabove, at which time flow through the annulus 80 between the downward extension 73 and the valve body 66 is precluded as seen in FIG. 4, but at which time fluid may flow upwardly through the valve seating member 75 and then outwardly through the ports 78 for upward flow through the annular space 79. Accordingly, it is apparent that reciprocation of the valve member 82 between the two positions shown in FIG. 3b and FIG. 4 will result in the flow of fluid either upwardly within the inner tubular body 70, as shown in FIGS. 3a and 3b, or upwardly through the annular space 79 between the outer tubular body 60 and the inner tubular body 70 as seen in FIG. 4. However, during the transitional stage of valve movement a quantity of fluid may flow through both of the just mentioned paths.

In the operation of the pulse producing means P, during the placement of gravel by either the gravel packing apparatus of FIG. 1 or the gravel packing apparatus of FIG. 2, the returning fluid, after the sand or gravel has been placed within the well bore, enters the liner L and then passes through the slotted lower cup 64 of the pulse producing means P and flows upwardly through the pulse producing means.

Assuming that flow commences and the valve member 82 is on its lower seat or stop 77, and therefore the lateral ports 78 are closed off, then return fluid will pass upwardly through the valve member 82 and into the annular space 80 within the valve body 66, then through the ports 81 and into the inner tubular member 70. As the velocity of fluid flow increases, a pressure drop is developed across the valve member 82 due to the restricted mid-section 86, so that differential fluid pressure will move the valve member 82 towards the upper stop 74, movement of the valve member 82 being accelerated rapidly as it approaches the upper stop 74, until it ultimately impacts against the stop 74 preventing further fluid flow upwardly through the inner tubular body 70. This causes a rarefaction wave to travel up the inner tubular body 70, the wave reflecting back from the upper end of the tube 70 as a high pressure pulse, which travels downwardly in the inner tubular body 70. When this reflected high pressure pulse reaches the valve member 82, the latter is caused to instantaneously shift to the lower seat or stop 77, thereby shutting off flow through the ports 78 into the annular space 79 between the inner tubular body 70 and the outer tubular body 60. Thereupon a rarefaction wave is caused to move up the outer tubular body 60, the wave reflecting back downwardly in the outer tubular body 60 as a high pressure pulse which will shift the valve member 82 again to the upper seat, thereby shutting off flow through the inner tubular body 70 again. This cycling will be repeated during the flow of returning fluid through the pulse producing means, and depending upon the configuration of the pulse producing means, the valve member 82 may be caused to cycle at a very rapid frequency, say, ranging between 1,500 to 3,000 cycles per minute. The shuttling of the valve member 82 results in a variation in the flow of gravel carrying fluid amounting to pressure pulses which are believed to cause minute changes in fluid velocity, and where, due to the geometry of the pulse producing means, the pulse energy is sufficiently large, the pulses may produce minute reversals in the direction of the flow of returning fluid, as the gravel is being placed. The result is that the gravel is more uniformly packed, bridging of the gravel is inhibited and a given weight or quantity of gravel will be caused to occupy less space when the pulse producing means is functioning than would occur in the case of a normal gravel packing operation. Accordingly, the gravel can more effectively prevent the entry of materials from the sub-surface earth formation into the well screen or liner L.

Claims

I claim:

1. In apparatus for gravel packing a well in which casing is set, a liner adapted to be disposed in the well, casing engaging means for supporting the liner in the well, cross-over means for directing fluid containing gravel into the well outside the liner and returning fluid from within the liner, and pulse producing means responsive to the flow of returning fluid to cause pulsing of said fluid and agitation of the gravel.

2. In apparatus as defined in claim 1, said pulse producing means comprising means defining separate flow paths for said returning fluid and valve means for intermittently and alternately closing the respective flow paths.

3. In apparatus as defined in claim 1, said pulse producing means comprising means defining separate flow paths for said returning fluid and valve means for intermittently and alternately closing the respective flow paths and allowing flow through both of said flow paths.

4. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body defining a first flow path for said returning fluid, said inner tubular body being disposed within said outer body and defining with said outer body another flow path for said returning fluid, said inner body terminating in a free end within said outer body, valve means including means providing flow passages leading from said liner to the respective flow paths, and a valve member responsive to fluid flow moveable between positions alternately closing the passages leading to the respective flow paths.

5. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body defining a first flow path for said returning fluid, said inner tubular body being disposed within said outer body and defining, with said outer body another flow path for said returning fluid, said inner body terminating in a free end within said outer body, valve means including means providing flow passages leading from said liner to the respective flow paths, and a valve member responsive to fluid flow movable between positions alternately closing the passages leading to the respective flow paths, said passages communicating with both of said flow paths during movement of said valve member between said positions.

6. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including means providing a return fluid passage leading to said inner tubular body and a return fluid passage leading to said annular space, and a valve member movable between positions alternately opening and closing said return fluid passages, said valve member having a flow passage therethrough providing a restriction to cause movement of said valve member to one of said positions responsive to the flow of return fluid therethrough.

7. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including means providing a return fluid passage leading to said inner tubular body and a return fluid passage leading to said annular space, and a valve member movable between positions alternately opening and closing said return fluid passages, said valve member having a flow passage therethrough providing a restriction to cause movement of said valve member to one of said positions responsive to the flow of return fluid therethrough, and surfaces on said valve member responsive to the rarefaction wave in the fluid in said return fluid passages when closed to shift said valve member to the alternate position.

8. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including a tubular valve body having a return fluid passage communicating with said annular space, means connecting said valve body with said inner tubular body and providing a return fluid passage leading between said inner tubular body and said valve body, longitudinally spaced opposed stops mounted within said tubular valve body, a valve member between said opposed stops, said valve member having means for moving it between said stops responsive to fluid pressure, said valve member also having means for alternately closing said return fluid passages upon engagement with the respective stops.

9. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including a tubular valve body having a return fluid passage communicating with said annular space, means connecting said valve body with said inner tubular body and providing a return fluid passage leading between said inner tubular body and said valve body, longitudinally spaced opposed stops mounted within said tubular valve body, a valve member between said opposed stops, said valve member having means for moving it between said stops responsive to fluid pressure, said valve member also having means for alternately closing said return fluid passages upon engagement with the respective stops, one of said stops having a return fluid passage communicating with said return fluid passage communicating with said annular space and circumscribed by a seating surface, and said valve member having a flow passage aligned with said passage through one of said stops, and said other stop and said valve body having an annular space therebetween leading to said return fluid passage in said inner body, said other stop having a seating surface engageable by said valve member to close said latter annular space.

10. In apparatus as defined in claim 1, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including a tubular valve body having a return fluid passage communicating with said annular space, means connecting said valve body with said inner tubular body and providing a return fluid passage leading between said inner tubular body and said valve body, longitudinally spaced opposed stops mounted within said tubular valve body, a valve member between said opposed stops, said valve member having means for moving it between said stops responsive to fluid pressure, said valve member also having means for alternately closing said return fluid passages upon engagement with the respective stops, one of said stops having a return fluid passage communicating with said return fluid passage communicating with said annular space and circumscribed by a seating surface, and said valve member having a flow passage aligned with said passage through one of said stops, and said other stop and said valve body having an annular space therebetween leading to said return fluid passage in said inner body, said other stop having a seating surface engageable by said valve member to close said latter annular space, and said valve member having a restriction in its flow passage whereby fluid flowing therethrough will shift said valve member into engagement with said other stop.

11. In pulse producing apparatus for use in the return fluid paths from a well screen to the cross-over of gravel packing apparatus for wells: pulse producing means responsive to the flow of returning fluid to cause pulsing of said fluid and agitation of the gravel, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body defining a first flow path for said returning fluid, said inner tubular body being disposed within said outer body and defining with said outer body another flow path for said returning fluid, said inner body terminating in a free end within said outer body, valve means including means providing flow passages leading from said liner to the respective flow paths, and a valve member responsive to fluid flow moveable between positions alternately closing the passages leading to the respective flow paths.

12. In apparatus as defined in claim 11, said passages communicating with both of said flow paths during movement of said valve member between said positions.

13. In pulse producing apparatus for use in the return fluid paths from a well screen to the cross-over of gravel packing apparatus for wells: pulse producing means responsive to the flow of returning fluid to cause pulsing of said fluid and agitation of the gravel, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including means providing a return fluid passage leading to said inner tubular body and a return fluid passage leading to said annular space, and a valve member moveable between positions alternately opening and closing said return fluid passages, said valve member having a flow passage therethrough providing a restriction to cause movement of said valve member to one of said positions responsive to the flow of return fluid therethrough.

14. In pulse producing apparatus for use in the return fluid paths from a well screen to the cross-over of gravel packing apparatus for wells: pulse producing means responsive to the flow of returning fluid to cause pulsing of said fluid and agitation of the gravel, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including means providing a return fluid passage leading to said inner tubular body and a return fluid passage leading to said annular space, and a valve member moveable between positions alternately opening and closing said return fluid passages, said valve member having a flow passage therethrough providing a restriction to cause movement of said valve member to one of said positions responsive to the flow of return fluid therethrough, and surfaces on said valve member responsive to the rarefaction wave in the fluid in said return fluid passages when closed to shift said valve member to the alternate position.

15. In apparatus as defined in claim 11, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including a tubular valve body having a return fluid passage communicating with said annular space, means connecting said valve body with said inner tubular body and providing a return fluid passage leading between said inner tubular body and said valve body, longitudinally spaced opposed stops mounted within said tubular valve body, a valve member between said opposed stops, said valve member having means for moving it between said stops responsive to fluid pressure, said valve member also having means for alternately closing said return fluid passages upon engagement with the respective stops.

16. In pulse producing apparatus for use in the return fluid paths from a well screen to the cross-over of gravel packing apparatus for wells: pulse producing means responsive to the flow of returning fluid to cause pulsing of said fluid and agitation of the gravel, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including a tubular valve body having a return fluid passage communicating with said annular space, means connecting said valve body with said inner tubular body and providing a return fluid passage leading between longitudinally spaced opposed stops mounted within said tubular valve body, a valve member between said opposed stops, said valve member having means for moving it between said stops responsive to fluid pressure, said valve member also having means for alternately closing said return fluid passages upon engagement with the respective stops, one of said stops having a return fluid passage communicating with said return fluid passage communicating with said annular space and circumscribed by a seating surface, and said valve member having a flow passage aligned with said passage through one of said stops, and said other stop and said valve body having an annular space therebetween leading to said return fluid passage in said inner body, said other stop having a seating surface engageable by said valve member to close said latter annular space.

17. In pulse producing apparatus for use in the return fluid paths from a well screen to the cross-over of gravel packing apparatus for wells: pulse producing means responsive to the flow of returning fluid to cause pulsing of said fluid and agitation of the gravel, said pulse producing means comprising an elongated outer tubular body, an elongated inner tubular body disposed within said outer body and defining an annular flow path with said outer body, said inner body terminating in a free end within said outer body, valve means including a tubular valve body having a return fluid passage communicating with said annular space, means connecting said valve body with said inner tubular body and providing a return fluid passage leading between said inner tubular body and said valve body, longitudinally spaced opposed stops mounted within said tubular valve body, a valve member between said opposed stops, said valve member having means for moving it between said stops responsive to fluid pressure, said valve member also having means for alternately closing said return fluid passages upon engagement with the respective stops, one of said stops having a return fluid passage communicating with said return fluid passage communicating with said annular space and circumscribed by a seating surface, and said valve member having a flow passage aligned with said passage through one of said stops, and said other stop and said valve body having an annular space therebetween leading to said return fluid passage in said inner body, said other stop having a seating surface engageable by said valve member to close said latter annular space, and said valve member having a restriction in its flow passage whereby fluid flowing therethrough will shift said valve member into engagement with said other stop.