DEEP WELL FILTERS

Abstract: A deep well filter comprises a tubular assembly of at least five superimposed roll bonded and sintered wire mesh layers, the aperture size and wire diameter of any one mesh layer being different from the aperture sizes and wire diameter(s) of its neighbouring mesh layer or layers. In a preferred arrangement, seven steel mesh layers are provided, the aperture size and wire diameter of the first and seventh such layers being the same, those of the second, fourth and sixth layers being the same but different from the first and seventh, and those of the third and fifth layers being different from those of the other five layers. The third and fifth layers may be of the same or different aperture size and wire diameters.

Description: DEEP WELL FILTERS This invention relates to deep well filters. Deep well filters are used to remove sand and other granular contaminants during downhole recovery of oil and gas from onshore and offshore reserves. Such filters generally form part of the overall length of the tube through which oil and gas pass from the respective reserve to the well head. They are conventionally positioned at either the tube base or at another position within the bottom third of the tube. Typical filter lengths are between 1 0m and 1 00m with an average length of 30m Recent investigations have been carried out into the use of horizontal tubes which would require longer filter lengths. Conventional filters such as disclosed by US-PS-5004049 include gravelpac filters in which a specially graded gravel typically of 30 to 40 mesh is used in conjunction with a wire wrapped ribbed screen to prevent formation sand from entering the well bore; wire wrapped pipe based welded screens in which a stainless steel wrapping wire is welded to each rib wire of the screen which is in turn welded to a perforated pipe; and wire wrapped rod based welded screens which are similar to pipe-based screens but without a perforated pipe. The wall thickness of these known filters is typically of the order of 0.5 inches. For a given outside diameter there is a smaller inside diameter which limits the gas and oil flow rates obtainable and restricts the diameter of the tooling which can be accommodated in the tube. The limited wall thickness often requires the use of some form of supporting structure whose presence also reduces the available internal space of the tube. Also conventional filters have an open area which equates approximately to 1 0% only of the total filter area. This has the effect of increasing within the filter build-up of scale and from mud residue of the original drilling process. Both of these factors have an effect on service life. The present invention sets out to provide a deep well filter which overcomes or at least alleviates these and other problems present in conventional deep well filters. According to the present invention in one aspect there is provided a deep well filter which comprises a tubular assembly of at least five superimposed roll bonded and sintered wire mesh layers, the aperture size and wire diameter of any one mesh layer being different from the aperture sizes and wire diameter(s) of its neighbouring mesh layer or layers. The layers may each be produced from steel or nickel alloy. The steel is preferably a stainless steel and may be, for example, a 304 or 31 6 stainless steel. In one arrangement the aperture size and wire diameter of the inner and outer mesh layers are the same. The aperture sizes and wire diameters of the mesh layers which lie next to the inner and outer mesh layers may also be the same, although different from those of the inner and outer mesh layers. Seven steel mesh layers may be provided the aperture size and wire diameter of the first and seventh such layers being the same, those of the second fourth and sixth layers being the same but different from the first and seventh, and those of the third and fifth layers being different from those of the other five layers. The third and fifth layers may be of the same or different aperture size and wire diameters. In another aspect the invention provides a method for producing a deep well filter which comprises passing at least five superimposed layers of wire mesh through the nip of a rolling mill at a rolling load sufficient to produce a relatively flat bonded panel substantially free of delaminations, passing the roll bonded panel through a furnace to promote sintering of the superimposed mesh layers, forming the panel into a tube, and welding the adjoining edges of the panel together. The superimposed layers may be passed through a furnace with a reducing atmosphere before entering the nip of the rolling mill to remove any oil residue and to soften the mesh layers. The steel of mesh layers is preferably a stainless steel, especially a stainless steel of 304L specification. Before rolling, the edges of the super imposed mesh sheets are preferably spot welded together. Sintering is preferably effected within a reducing atmosphere. The tubular assembly may be produced by spiral welding of continuous lengths of the steel or nickel alloy layers. After welding, the tubular assembly may be coiled. The invention will now be described with reference to the following example of a deep well filter in accordance with the invention. The exemplified deep well filter comprises seven superimposed sheets of stainless steel or nickel alloy wire mesh. The individual sheet layers are bonded together to form a panel which is free of all delaminations. The abutting panel edges are spot-welded together. Alternatively, the layers may be produced in continuous lengths which are spirally welded into tube form. The continuously formed tube may then be coiled. Individual tubes are typically of 5 feet in length, these tubes being circumferentially welded together as required to produce longer filter lengths. The aperture size and wire diameter of each of the bonded sheets are different from its neighbouring sheet or sheets. A typical arrangement of steel mesh sheets is:- Layer No. Layer Code Aperture (mm) Wire Diameter (mm) 1 A 5.00 2.00 2 B 1 .49 0.63 3 C 0.1 6 0.10 4 B 1 .49 0.63 5 D 0.26 0.1 6 6 B 1 .49 0.63 7 A 5.00 2.00 The outside diameters of filter tubes in accordance with the invention are typically 1 77.8mm and 82.5mm. The arrangement of steel mesh sheets is effected to increase significantly the open area of the filter. Typically the open area of a tubular filter in accordance with the invention is of the order of 45%. This compares with an open area of 1 0% for conventional screen filters. The increased open area has the effect of reducing scale build-up and build-up from mud residue from the original drilling process leading to longer service life. Also, filters in accordance with the invention are both stronger and stiffer than conventional screen filters in terms of resistance to axial compression This is important when additional force is being applied to the tubular filter to overcome obstacles during downhole installation. To produce a deep well filter in accordance with the invention, appropriate sheets of steel mesh conveniently to a 304L stainless steel specification are initially passed through a furnace with a reducing atmosphere to remove any oil residue and to soften the mesh sheets. The sheets are then assembled in the appropriate configuration and the edges of the assembled sheets are spot-welded together The assembled sheets are then passed through a rolling mill at a rolling load sufficient to produce a flat bonded panel free of delaminations. The roll panel is then passed through a furnace with a reducing atmosphere to promote sintering of the vaπous mesh sheets. The panel is then formed into its required tubular shape by a bending operation and the adjoining side edges of the panel are welded to form a welded seam. Individual tubular filters may then be circumferentially welded together to produce a deep well filter of the required length. It will be appreciated that the foregoing is merely exemplary of deep well filters in accordance with the invention and that various modifications may readily be made thereto without departing from the true scope of the invention as set out in the appended claims.

Claims: CLAIMS 1 . A deep well filter which comprises a tubular assembly of at least five superimposed roll bonded and sintered wire mesh layers, the aperture size and wire diameter of any one mesh layer being different from the aperture sizes and wire dιameter(s) of its neighbouring mesh layer or layers. 2. A filter as claimed in Claim 1 wherein each layer is produced from steel 3. A filter as claimed in Claim 2 wherein the steel is a stainless steel. 4. A filter as claimed in Claim 1 wherein each layer is produced from a nickel alloy. 5. A filter as claimed in any one of Claims 1 to 4 wherein the aperture size and wire diameter of the inner and outer mesh layers are the same. 6. A filter as claimed in any one of Claims 1 to 5 wherein the aperture sizes and wire diameters of the mesh layers which lie next to the inner and outer mesh layers are the same, although different from those of the inner and outer mesh layers. 7. A filter as claimed in any one of Claims 1 to 6 wherein seven wire mesh layers are provided the aperture size and wire diameter of the first and seventh such layers being the same, those of the second fourth and sixth layers being the same but different from the first and seventh, and those of the third and fifth layers being different from those of the other five layers. 8. A filter as claimed in Claim 7 wherein the third and fifth layers are of the same aperture size and wire diameters. 9. A method for producing a deep well filter which comprises passing at least five superimposed layers of wire mesh through the nip of a rolling mill at a rolling load sufficient to produce a relatively flat bonded panel substantially free of delaminations, passing the roll bonded panel through a furnace to promote sintering of the superimposed mesh layers, forming the panel into a tube, and welding the adjoining edges of the panel together. 1 0. A method as claimed in Claim 9 wherein the superimposed layers are passed through a furnace with a reducing atmosphere before entering the nip of the rolling mill to remove any oil residue and to soften the mesh layers. 1 1 A method as claimed in Claim 1 0 wherein before rolling, the edges of the superimposed wire mesh sheets are spot welded together. 2. A method as claimed in any one of Claims 9 to 1 1 wherein sintering is effected within a reducing atmosphere. 3. A method as claimed in any one of Claims 9 to 1 2 wherein the tubular assembly is produced by spiral welding of continuous lengths of the steel or nickel alloy layers. 4. A method as claimed in Claim 1 3 wherein after welding, the tubular assembly is coiled.

Inventors: BROOKS NIGEL JOHN, BROOKS, NIGEL, JOHN
Applicants: BROOKS NIGEL JOHN, MIXALLOY LTD, BROOKS, NIGEL, JOHN, MIXALLOY LIMITED
Application year: 1996
Main classification: E21B43
IPC codes: B01D29, B01D39, E21B43