GB2181663A - Ball catcher for oil wells - Google Patents

Abstract

A ball catcher for incorporation in the flow path of high pressure fluid carrying impact elements such as ball bearings for fracturing the strata in an oil well, comprises a body (2) having coaxially aligned fluid inlet (4) and fluid outlet (6) and a strainer plug (10) whose lower end presents an array of parallel plates with strainer passages between them, through which fluid can flow from inlet (4) to outlet (6) but which are dimensioned to prevent passage therethrough of the impact elements. On abutment with the inclined leading edges 20 of said plates, the impact elements carried by the fluid are deflected into a collection chamber below the plug. The passages are so sized that substantially no restriction to flow is imposed upon the fluid by the strainer plug (10). <IMAGE>

Description

SPECIFICATION Improved ball catcher for oil exploration equipment and the like This invention relates to ball catchers incorporated in equipment associated with the underground recovery of oil and other hydrocarbons.

In the oil exploration industry, underground wells are prepared with a view to extracting oil and other valued carbons from underground sites. These hydrocarbons are commonlytrapped in rocks, and it has become common practice to fracture the strata so that the desired products are released therefrom and subsequently collected for further processing.

Fracture of the strata has heretofore been achieved by pumping a high pressure source of treating fluid typically at a pressure of up to about 20,000 psi down the well and against the strata, said fluid carryingtherein metal ball bearingsorlikeimpactel- ements which serve to fracture the strata and enable release of the oil or other material to be extracted.

The high pressure fluid and ball bearings therein are thereafter returned to the upper regions ofthe fluid circuit and, before the fluid can be recirculated through the pump, it is necessary to remove the bearings and other solid matter therefrom. Such removal enables re-use of the ball bearings and prevents damage to the pump.

It has been proposed to feed the return fluid to a mud-shakerfor purposes of attempting to shake out from the fluid the solid matter therein. However, such mud-shakers have not proved to be totally effective in that not all the solid matter is removed from the fluid.

Recently, it has been proposed to incorporate a ball catcher in the fluid flow circuit in the form of a deflector grid located in the fluid flow path and such asto allow fluid to flow thereth rough but preventing the passage therethrough of the ball bearings. However, such an arrangement suffers from a numberofdis advantages, not the least ofwhich are that the pres- ence ofthe deflector grid severely interrupts and re stricts the normal flow of fluid through the circuit, in that substantial pressure builds up in front ofthe grid, while the substantial forces applied by the ball bearings on impact with the grid put the grid under substantial stress which can result in the destruction thereof.

According to the present invention there is provided a ball catcherfor incorporation in the flow path of high pressure fluid for releasing hydrocarbons from underground strata, the fluid carrying therein a pluralityofimpactelements such as ball bearingsfor fracturing the strata, the ball catcher comprising a body member having a fluid inlet, a fluid outlet and, between said inlet and outlet, an intermediate chamber, the ball catcherfurthercomprising a strainer plug for location in said intermediate chamber, said strainer plug having a plurality of pas sagewaystherein through which fluid can flowfrom the inlet to the outlet but which are dimensioned to prevent passage therethrough of said impact elements, the arrangement being such that, on abutment with said strainer plug, the impact elements carried bythefl uid are deflected into a collecting chamber and substantially no restriction to flow is imposed uponthefluid bythe strainer plug inthe passage of said fluid through the intermediate chamber.

Although it is preferred that the impact elements comprise spherical metal ball bearings, the elements may be other than spherical and may be of materials other than metal providing the necessary strength is present. In all cases it is preferred that the maximum diameter of the elements is of the order of 20mm, with the widths of the passageways being dimensioned accordingly and preferably being of the order of 6m m wide.

Conveniently the intermediate chamber is of generally cylindrical shape with the central longitudinal axis thereof extending perpendicularto the direction of fluid flow along the substantially coaxial inlet and outlet passageways feeding into and from the intermediate chamber respectively.

The strainer plug is of generally part-cylindrical shape the diameter of which is less than that ofthe intermediate chamberwhereby a generally annular space is defined between the outer wall of the plug andtheinnerwall of the chamber, the face of the plug facing the inlet passageway being chamferred in a direction from top to bottom of the plug to define a substantially flat deflector surface on the plug against which the incoming fluid and impactelements impinge.

Conveniently the passageways comprise a series of parallel spaced slots originating in said deflector surface and each extending from top to bottom of said surface and from front to back of the plug considered in the direction of fluid flowthrough the plug.

The areas ofthe slots together with the cross sectional area of the substantially annular space sur- rounding the plug issubstantiallyequaltothecross- sectional area of the inlet passageway, while the cross-sectional area of the outlet passageway is at least equal to that ofthe inlet passageway, whereby fluid flow through the plug issubstantiallyunrestricted and there is no pressure build-up in the intermediate chamber.

Preferably the collection chamber is located below the intermediate chamber such that the impact elements are directed into said collection chamber by said deflector surface of the strainer plug.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is a vertical section through a ball catcher according to the invention, and Figure 2 is a view in the direction of arrow II in Figure 1 ofpartofthe strainer plug.

The illustrated ball catcher is adapted for incorporation in oil exploration systems to enable removal of impact elements, such as spherical metal ball bearings, from the pressurised fluid that is pumped, together with the impact elements, down a well to fracture the oil or hydrocarbon-containing strata at the bottom ofthewell,said removal being effected prior to recirculation of the fluid and impact elements in said system.

Referring to the drawings, the ball catcher com- prises a body member indicated generally at 2 and including an inlet passageway 4 and an outlet passageway 6 coaxial with the passageway 4. The diameter of the passageway 6 is slightly greaterthan thatofthe passageway 4.

Between the passageways 4 and 6 the body member2 defines therein a generally cylindrical intermediate chamber 8 the central longitudinal axis of which is perpendicularto the central axes of the passageways 4 and 6, the chamber 8 being upwardly open and the lower end ofthe chamberfeeding into a collecting chamber (not shown) for reasons which will become apparent.

Located within the chamber8 is a strainer plug in dicated generally at 10, the upper cylindrical portion 12 of said plug seating in the upper regions ofthe chamber8and being secured therein bya hammer lug union incorporating a nut (not shown) screwed onto the threaded flange 14 of the body member2, seals being provided as shown at 16.

The strainer plug 10 further includes a lower portion 18 located between the passageways 4 and 6 and of generally cylindrical shape with a tapered section removed therefrom to define a flat deflector surface 20 facing the inlet passageway 4. The diameter of the portion 18 of the plug 10 is slightly less than that of the chamber8whereby a generally annular space 22 is defined betweenthewall oftheplug l0andthe wall of the chamber 8.

The portion 1 8 of the strainer plug 10 has a plurality of parallel slots 24formed therein, for example by means of a slitting saw, the slots extending from top to bottom andfrontto rearofthe plug to interconnect the inlet and outlet passageways 4,6, the width of said slots, as well as the width of the space 22 shown in Figure 2, being about6mm.

In use ofthe ball catcher, high pressure fluid, typically at a pressure of upto 20,000 psi, containing impact elements such as ball bearingsofupto20mm diameter is fed through the passageway 4 and against the deflector surface 20 of the strainer plug 10. Thefluid flows through and around the portion 18 of the plug 10, by way of the slots 24 and space 22, to the passageway 6, there being little if any restriction to said flow because the combined areas of said slots 24 and space 22 are substantially equal to the crosssectional area ofthe passageway 4 and because of the slightly increased diameter of the passageway 6.

The bearings or impact elements abut the surface 20 and are deflected downwardly into the collecting chamberwhich is sealed in, and forms part of, the fluid flow circuit. Thus the impact elements are availableforremoval and re-use,whilethefluidreturning to the pump isfreeofsolid content.

The strainer plug 10 is removable from the body member 2 and can therefore be replaced when worn, while the impact elements may be other than spherical metal balls, and may be of materials such as ceramic and may be of, for example, polyhedral shape.

Claims (8)

1. A ball catcherfor incorporation in the flow path of high pressure fluid for releasing hydrocarbons from underground strata, the fluid carrying therein a plurality of impact elements forfracturing the strata, the ball catcher comprising a body member having a fluid iniet, afluid outletand, between said inletand outlet, an intermediate chamber, and a strainer plug for location in said intermediate chamber, said strainer plug having a plurality of passageways therein through which fluid can flow in its passage from the inlettothe outlet butwhich aredim ensioned to prevent passage therethrough of said impact elements, the arrangement being such that, on abutment with said strainer plug, the impactelements carried by the fluid are deflected into a collecting chamber and substantially no restriction to flow is imposed upon the fluid by the strainer plug in the passage of said fluid through the intermediate chamber.

2. A ball catcher as claimed in claim 1 for use in fluid carrying ball bearings the maximum diameter of which is of the order or of20mms, the widths ofthe passageways through the strainer plug being of the order of 6m ms.

3. A ball catcher as claimed in claim 1 or claim 2 and including substantially coaxial inlet and outlet passageways feeding into and from the intermediate chamber, said intermediate chamber being of generally cylindrical shape with the central longitudinal axis thereof extending perpendicularto the direction of fluid flow along said inlet and outlet passageways.

4. A ball catcher as claimed in claim 3 in which the strainer plug is of generally part-cylindrical shapethe diameter of which is less than that of the intermediate chamber whereby a generally annular space is defined between the outer wall of the strainer plug and the inner wall ofthe intermediate chamber, the face of the strainer plug facing the inlet passageway being chamferred in a direction from top to bottom of the plug to define a substantially flat deflectorsurface on the strainer plug against which the incoming fluid and impact elements impinge.

5. Aball catcher as claimed in claim 4 in which the passageways in the strainer plug comprise a series of parallel spaced slots originating in said deflector surface and each extending from top to bottom of said surface and from front to back of the plug consi dered in the direction offluid flow through the plug.

6. A ball catcher as claimed in claim Sin which the areas of the slots together with the cross-sectional area of the substantially annular space surrounding the plug is substantially equal to the cross-sectional area of the inlet passageway, whilethe crosssectional area of the outlet passageway is at least equal to that of the inlet passageway, whereby fluid flowthrough the strainer plug is substantially unrestricted and there is no pressure build-up in the intermediate chamber.

7. A ball catcher as claimed in anyone of claims 4 to 6 in which the collection chamber is located below the intermediate chamber such that the impactel- ements are directed into said collection chamber by said deflector surface of the strainer plug.

8. A ball catcher substantially as described with reference to and as illustrated by the accompanying drawings.