WO1994028284A1

WO1994028284A1 - Sand screen structure

Info

Publication number: WO1994028284A1
Application number: PCT/US1994/005720
Authority: WO
Inventors: Paul C. Koehler; Stephen A. Geibel; Michael B. Whitlock; Reza Hashemi
Original assignee: Pall Corporation
Priority date: 1993-05-25
Filing date: 1994-05-17
Publication date: 1994-12-08
Also published as: EP0699271A1; NO954746D0; AU679081B2; CA2163754A1; EP0699271A4; CN1124517A; AU7042194A; NO954746L

Abstract

A damage resistant sand screen assembly has at least one layer of a sintered porous medium (10, 11, 12), preferably a sintered metal membrane, coaxially disposed about and secured to a perforated core (1). The assembly may also include a woven wire mesh drainage layer (9) disposed between the perforated production tube (1) and the sintered porous medium (10, 11, 12), and a protective covering (13), preferably a woven wire mesh. The assembly is suitable for use in gravel pack (4), or it may be installed outside of agravel pack (4), such as on the end of a production pipe (17) or on a down-hole pump (18).

Description

SAND SCREEN STRUCTURE

Field of the Invention

This invention relates generally to structures for use in hydrocarbon well completion and workover applications, and, in particular, to sand screens for limiting the intrusion of particulate matter into the well production fluid.

Background of the Invention

Unconsolidated particulate matter, hereinafter referred to as "formation sand," is often associated with subterranean hydrocarbon formations. A major problem in producing hydrocarbon fluids from unconsolidated formations is the intrusion of formation sand, which is typically very fine, into the production fluid and equipment. The presence of sand in the production fluid often leads to-the rapid erosion of expensive well machinery and hardware. Furthermore, the shifting of sand in an unconsolidated formation may result in the collapse of perforations purposefully blasted in the formation, thereby reducing or even halting production. In order to prevent the shifting of formation sand, such formations are typically "gravel packed." The gravel packing also acts as a filter, preventing the fine sand from entering the production fluid. Gravel packing involves the introduction of a particular grade of sand into the well bore, often by pumping it down as a dense slurry, into the annulus defined by the inner circumference of the casing wall and the outer circumference of the work string. The gravel pack is often forced through the perforations in the casing wall and incorporated into the formation perforations, thereby stabilizing the formation.

Since the gravel pack itself comprises sand, sand screen assemblies are utilized to prevent the intrusion of gravel pack sand into the well production fluid, as well as to prevent the intrusion of fine formation sand ( which often initially passes through the gravel pack) into the production fluid. If too much formation sand passes through the gravel pack a collapse of the formation perforations can occur. In such instances the well may need to be re-perforated and repacked, usually at substantial expense.

The production of hydrocarbon fluids from horizontal wells is highly desirable in that multiple bores may be drilled radially from one central vertical bore, thereby increasing production efficiency from a particular formation. However, horizontal well completion involves several technical impediments, and as a result, has, heretofore, not been extensively practiced. Placing a production pipe deep into the earth and then attempting to snake the pipe at an angle approaching ninety degrees requires pipe made from a material which combines mechanical strength with flexibility and ductility. The problem of placing production pipe in the well is often exacerbated by the fact that many horizontal wells are of an unconsolidated nature. Gravel packing and sand screen use are very difficult under such circumstances. With regard to the problem of sand intrusion in unconsolidated formations, several sand screens structures have been designed. Exemplary designs include a wire-wrapped screen assembly (see, for example, U.S. Patent Number 3,958,634), a wire- wrapped screen and prepacked gravel assembly (see, for example, U.S. Patent Number 5,050,678) and a sintered metal unitary body assembly (see, for example, U.S. Patent Number 5,088,554). Wire- wrapped screen assemblies exhibit several undesirable tendencies: erosion induced by fine sand that initially flows past the wire/gravel pack interface; plugging with carbonaceous, siliceous or organic solids; and collapse or gaping of the wire screen due to the effects of formation and geo- pressure.

Prepacked wire-wrapped screen assemblies also suffer, to varying degrees, from plugging and the effects of well bore stresses. Furthermore, many prepacked screens have a substantially larger outer diameter than the production pipes around which they are disposed, making initial placement and retrieval difficult.

Wire-wrapped, and to some degree prepacked, sand screen structures are not particularly damage resistant; they require very careful handling on the well rig floor and during placement in the well bore. Even a slight bump from the casing wall may create a gap in the wire spacing which could lead to erosion and failure of the screen. Furthermore, conventional wire-wrapped screens and prepacked screens can develop gaps in the wire spacings during placement in a horizontal well which can lead to a failure in the screen.

Sintered metal unitary sand screen structures are cost prohibitive for use in all but the most critical situations- Further, the assemblies lack an integral support, and are not damage resistant. Homogeneous, or monolithic constructions allow a crack to propagate, via stress concentration effects and low ductility, through the entire unitary body thickness. Sintered metal unitary assemblies also have a tendency to plug from fines entrained in the formation fluid. To enhance their performance, sintered metal unitary sand screens may need to be electropolished which adds to their cost.

While sintered metal unitary sand screen assemblies exhibit an effective open area (voids volume) , they lack a mechanism to facilitate uniform flow distribution between the unitary body and the perforated pipe. Poor downstream flow distribution (drainage capability) will, in effect, create flow channels, resulting in higher flow velocity areas, higher pressure drops, and early plugging. Wire wrapped and prepacked wire screens, on the other hand, have an efficient use of flow area and flow distribution, but exhibit very low effective open area (voids volume) , which may cause a reduced production rate.

Summary of the Invention In accordance with the present invention a structure is provided that in large measure overcomes the substantial problems described above. The present invention comprises a damage resistant sand screen structure for use in hydrocarbon wells which is particularly suited for applications involving unconsolidated and horizontal formations.

In one embodiment the invention comprises multiple layers of supported porous media, coaxially disposed about a perforated production pipe. In a method of forming such a structure, a sheet or strip of supported porous media is wrapped around a production pipe and secured in place. In a preferred method of forming such a structure, an end portion of the porous media is secured to the production pipe, by, for example, spot welding, and the porous media is then wrapped around the pipe in either a spiral or helical fashion, and secured.

In another embodiment, the invention comprises, in combination, a cylindrical inner drainage layer, a cylindrical porous outer protective layer, and disposed between the inner and outer layers, multiple layers of a supported porous membrane. Still another embodiment of the invention comprises a module or sleeve comprising multiple layers of supported porous membrane which is designed to slip over and be secured to a perforated production pipe.

A sand screen structure according to the present invention can be employed in a variety of manners within a well. For example, it can be installed within a gravel pack inside a well bore, it can be installed on the end of production pipe, and it can be installed at the inlet of a down-hole pump to prevent particulate matter from entering the pump.

The sand screen structures of the present invention exhibit excellent damage resistance, have a high voids volume, and provide uniform flow distribution. The preferred media used in the present invention are supported or reinforced, and are preferably helically wrapped with abutting edges.

Brief Description Of The Drawings

Figure 1 shows a well bore containing a partially cut away elevation view of a sand screen assembly embodying the present invention.

Figure 2 is an enlarged view of the cut away section of the sand screen assembly of Figure 1. Figure 3 is a partially cross-sectional schematic elevation of an embodiment of the present invention installed on the lower end of production pipe.

Figure 4 is a transverse cross-sectional view of a seam of the assembly of Figure 3.

Figure 5 is a partially cross-sectional schematic elevation of another embodiment of the present invention installed on the inlet of a down- hole pump. Figure 6 is a transverse cross-sectional view of a portion of an embodiment of the present invention including a pleated composite.

Detailed Description Of Embodiments

The subject invention is directed to a sand screen structure exhibiting damage resistance to forces encountered in well completion applications and having particular application in unconsolidated and horizontal well formations. For purposes of the present invention, "damage resistance" refers to a sand screen structure's ability to substantially maintain its "integrity" when collapsed from about 1/3 to about 1/2 its original diameter, i.e., the structure has at least 90%, more preferably at least 95%, of its original integrity. As used herein, "integrity" refers to the stated removal efficiency. The structures of the present invention include sand screen assemblies, wherein a section of perforated production pipe is part of the structure, and sand screen modules, wherein the structure is designed to be slipped over and secured to a section of perforated production pipe.

The invention may further comprise multiple layers of a porous media coaxially wrapped around a small diameter perforated pipe that is introduced into the work string via a continuous coiled tube of the type used in workover applications (where a sand screen has been damaged) . In this manner the onstream life of a well can be extended by producing through a damaged sand screen.

Referring now to the drawings, Figure l shows an exemplary sand screen assembly in a well formation application, with the production zone, gravel pack and casing in cross section and a sand screen assembly partially cut away. In Figure 1 a perforated production pipe 1 is positioned inside a well bore casing 2 showing a perforation 3 in the casing wall, with the gravel pack 4 in the annular space between the production pipe l and the casing 2. The production pipe 1 may be threaded at its ends or along its entire length. The assembly in Figure 1 also includes centralizers 5, which prevent the assembly from bumping against the casing wall. Figure 2, discussed in more detail below, is an expanded cross-sectional view of the sand screen assembly in Figure 1 showing in cross section the layers of the sand screen assembly.

The supported porous materials utilized in the present invention produce a damage resistant sand screen structure when coaxially disposed about a perforated production pipe. This is surprising, in that, under typical well completion stresses, the materials useful for the present invention would normally be expected to be susceptible to point loading, erosion and shearing. Preferred for use as the supported porous media, to limit the intrusion of particulate matter into the well production fluids, are supported porous metal sheet materials. Typically, the porous media will have a high degree of flexibility. Flexibility, as used herein, refers to the ability of a material to bend about a small radius while maintaining its integrity. Preferred materials for the present invention are those capable of bending about a radius five times the thickness of the material, or less, while still maintaining the integrity of the material. Particularly preferred are materials which can bend about a radius three times their thickness, or less, while maintaining their integrity. Preferred flexible materials for use in the present invention are supported porous metal sheet materials. Particularly preferred are supported sintered porous metal sheet materials such as those disclosed in U.S. Patent No. 4,613,369, which is incorporated herein by reference, and which are referred to herein as supported porous membranes. These membranes comprise a foraminate metal support, e.g., a woven wire mesh, and metal particulate contained within the openings in the support, the individual particles of the metal particulate being bonded to each other and to the support by sintering. Especially preferred are supported sintered metal membranes wherein the metal particles are no more than one-fifth the size of the smallest dimension of the openings of the foraminate support. These materials are available from Pall Corporation under the trademark PM ®.

The metal particulate and foraminate metal support can be of any of a variety of metals, such as nickel, iron, chromium, copper, molybdenum. tungsten, zinc, tin, aluminum, cobalt, iron, and magnesium, as well as combinations of metals and metal alloys including boron-containing alloys. Nickel/chromium alloys are preferred. Of these the AISI designated stainless steels which contain nickel, chromium and iron are most preferred.

Examples of suitable woven mesh screens, useful as the foraminate support, include stainless steel mesh screens with a mesh weave of from about 20 x 20 to about 100 x 100 with a wire diameter range from about 0.014 to about 0.0035 inches, more preferably a square mesh weave ranging from about 20 x 20 x 0.014 to about 40 x 40 x 0.009 (the first two numbers referring to the number of wires per inch in each direction, the last number referring to the diameter of the wire making up the screen, in inches) . Other fine mesh screens also may be used, for example screens having up to 200 x 1,400 wires per inch. Various grades or of supported media, having different efficiency removal ratings, can be used in the present invention. The grade of media to be utilized is a function of the particular well application formation permeability and the sand grain size to be used in the gravel packing. Sand grains used in gravel packing in well formations typically range in size from about 20 to about 1000 micrometers. It is known that sand grains of a particular size are effectively removed by media with efficiency removal ratings of about 1/7 to about 1/3 the grain size. For example, in a well formation with average grain size of 100 micrometers, a media rated at 15 to 30 micrometers would be expected to efficiently prevent sand intrusion. A number of methods for measuring efficiency removal are known. Especially useful is the F2 test originally developed at Oklahoma State University in the 1970's. Typically, porous media employed in the present invention will have F2 ratings at beta=lOO ranging from about 2 micrometers to about 200 micrometers, preferably from about 30 to about 100 micrometers, when measured using the modified F2 test as described in U.S. Patent 4,562,039. Typically, supported porous media of this invention will have voids volume in the range of from about 25 to 65%, more preferably 35 to 50%.

The sand screen structures of the present invention exhibit uniform flow distribution. As used herein, uniform flow distribution refers to the utilization of substantially all of the circumferential flow area of the porous media when placed in contact with a perforated pipe. Preferably, at least 95% of the circumferential flow area is utilized. Flow distribution uniformity is enhanced by the use of multiple layers of media, with drainage and/or support layers.

Multiple layers of the supported porous media may be successively spirally or helically wrapped around the perforated production pipe. At least two media layers, although more, e.g., three, four, six, eight, ten, twenty, thirty, forty, or even more media layers, may be used to form the porous structure. In the sand screen assembly shown in Figure 2

(wherein the same numerical designations are used to refer to the same structures depicted in Figure 1) , three layers 10, 11, and 12 of a sintered supported porous metal membrane are helically wrapped around the perforated production pipe 1 of Figure l. Perforations 7 in the production pipe 1, allow flow of production fluid into the work string. A single layer of rectangular wire 8 is helically wrapped directly onto the production pipe l. Drainage material, comprising a woven wire mesh 9, is shown in Figure 2 wrapped over the rectangular wire wrap 8. The three layers of sintered supported porous metal membrane 10, 11, 12, as shown in Figure 2, are helically wrapped over the drainage layer 9. Each layer of supported membrane 10, 11, 12 is tacked to the layer below along the seam by resistance welds 14, 15, 16. In Figure 2 there is also depicted an outer protective layer 13 comprised of a heavy woven wire mesh. The layers of porous media in accordance with the subject invention are preferably all of the same type of material, but need not necessarily be so. The use of multiple layers reduces the susceptibility of the structure to point loading, erosion and shear. Preferred is a structure with two to about nine layers, more preferred is from three to five layers, most preferred is three layers.

The layers of porous media are preferably helically wrapped such that the edges of the media sheets are abutting. While the porous media can be helically wrapped such that the edges of the media sheets are overlapping, this is less desirable. In the embodiment of Figure 2 there are three layers of seven inch wide media 10, 11 and 12 approximately 76 to 85 inches long, helically wrapped at an initial wrap angle of approximately 45°, with no overlap. The wrap angle changes slightly with each successive layer due to the increased outer diameter. The initial outer diameter of the perforated production pipe 1, rectangular wire wrap 8, and woven wire mesh drainage layer 9, over which the porous media is wrapped, is approximately 3 inches.

In those instances where an overlap is used, the effective number of layers of media will be increased by overlapping the media sheets. The amount of overlap used may vary from 0% (abutting) to as much as about 95%.

A diffusion layer, while not essential, may be disposed between two or more of the layers of porous media to enhance uniform flow distribution. The diffusion layer may be formed from any suitable, porous material which has a lower edgewise flow resistance than the layer of porous media, thus allowing a more uniform distribution of flow between the layers of porous media. The diffusion layer may comprise a supported porous metal membrane which is coarser than the layer of porous media. More preferably, the diffusion layer comprises a woven wire mesh which may be as fine as 80 X 80 X .004 or .005 or finer. While the diffusion layer need not be helically wrapped, it is preferably helically wrapped if the media sheets have been helically wrapped. When the diffusion layer is secured to a media sheet prior to wrapping, the diffusion layer will, of course, be wound together with the media sheet in the same configuration.

If an overlap is employed, care must be taken to ensure that wrinkling of the media and/or diffusion layers does not result due to the variable outer diameter of the helically overlapped layers. Any wrinkling of the layers may contribute to fluid flow pathways which bypass the media. However, such wrinkling can generally be avoided by using a sufficiently flexible media to accommodate the small outer diameter changes as successive layers are wrapped.

The media layers, whether helically wrapped to form abutting or overlapping edges, or spirally wrapped, may be bonded or sealed together by any suitable means.

While the exterior of the sand screen structure may be the outermost supported porous media layer, the use of a protective material which wraps around or encases the sand screen structure is preferred for ease of handling and to provide the sand screen structure additional support and damage resistance, especially during handling on the rig floor and during placement into the wellbore. Such an exterior protective material or outerwrap may be of any suitable construction and material appropriate for the severe conditions encountered, e.g. , rough handling, elevated temperature, corrosive fluids, and the like. The exterior material may, for example, be a heavy woven metal mesh or a perforated cage. Materials such as stainless steel or similar alloy are preferred. Typically, the exterior protective material will be a woven stainless steel mesh screen with a square mesh weave of from about l x 1 x 0.125 to about 40 x 40 x 0.009. Especially preferred is a heavy woven metal mesh such as a 10 x 10 x 0.047 square mesh weave comprising 300 series austenitic stainless steel. The sand screen assembly shown in Figure 2 includes a protective outer wrap 13 comprising AISI 300 series austenitic stainless steel 10 x 10 x 0.047 square mesh weave.

The exterior protective material may be applied in any suitable manner. Preferably, the protective material, such as a woven metal mesh, is wrapped in the same manner as the media layers. The exterior protective wrap is preferably secured to the media layers in such a manner as to compress them in order to provide additional protection to the porous media layers. In the embodiment shown in Figure 2, the protective outer wrap 13 is helically wrapped.

Other protective materials may also be used, .e.g., a perforated metal cage designed to fit over the porous media layers.

The sand screen structure of the present invention may also comprise additional layers for support, drainage, or the like. A drainage layer is preferred. Such additional layers may be positioned in any suitable location, e.g., interposed between media layers and/or diffusion layers or positioned between the perforated production pipe and the innermost supported porous media layer. Preferred is to place a drainage layer between the production pipe and the innermost media layer. Especially preferred is a layer of flat or square wire helically wrapped around the production pipe (known as a rectangular wire wrap) , with a layer of drainage material over the rectangular wire wrap. Rectangular wire wrap offers support and drainage for the layers above. Typically, rectangular wire wrap used in the present invention will be stainless steel wire with dimensions of about 0.125 x 0.0625 inches, helically wrapped and spaced 0.25 inches center to center.

Suitable materials for drainage layers are woven metal meshes or perforated metal sheets. Preferred are woven metal meshes comprising stainless steel or similar alloys. Typically, the drainage material will be a woven stainless steel mesh screen with a square mesh weave of from about 30 X 30 X 0.0065 to about 60 X 60 X .009. Especially preferred is a heavy woven metal mesh such as a 40 x 40 x 0.009 square mesh weave comprising AISI 300 series austenitic stainless steel. Drainage layers may also be applied in any suitable manner, e.g. by helically or spirally wrapping such layers in the same manner as the porous media layers. For example, in the embodiment shown in Figure 2, a layer of rectangular wire wrap 8 is laid over the perforated production pipe 1, and a drainage layer of 40 x 40 x 0.009 square mesh weave 9 comprising AISI 300 series austenitic stainless steel is helically wrapped over the rectangular wire wrap 8.

The various layers which may be wrapped around the perforated production pipe to form the sand screen assembly of the subject invention, e.g., the media layers, diffusion layers, exterior protective layer, and drainage layers, may be all wrapped in the same direction or they may be wrapped in opposite directions. However, the media layers are preferably all wrapped in the same direction, and, to the extent, other layers are helically wrapped, the other layers are also preferably wrapped in the same direction as the media layers. The media can be secured in place by various techniques, e.g., by welding or brazing techniques. Examples of suitable welding and brazing techniques include tungsten inert gas, laser, electron beam, electrical resistance, nicrobraze, and silver braze. Preferably, the multiple layers are continuously resistance welded, along the seam, to the layer beneath. In the embodiment shown in Figure 2, resistance welds 14, 15, and 16 run along the seam between layers 10, 11, and 12 of the media. Various techniques may be employed to seal the ends of the media to the perforated production pipe. For example, end caps may be slipped over the perforated production pipe, positioned at the ends of the supported porous media, and welded to the media and the pipe. Alternatively, the ends of the media may be welded together directly to the ends of the perforated production pipe. The sand screen assembly shown in Figure 1 includes end caps 6 welded at either end of the perforated production pipe 1. Modular sand screens will typically include end caps welded to the ends of the media. The modular unit may then be slipped over a perforated production pipe and welded at the end caps to the pipe. Modular sand screens may also include an innermost layer comprising a cylindrical cage positioned on the inner circumference of the drainage layer, or when utilized, on the inner circumference of the rectangular wire wrap layer. The cage, which is designed to slip over the perforated production pipe, provides dimensional stability to the drainage and media layers. The cage may be of any suitable construction and material appropriate for the severe conditions encountered, as mentioned above. The cage may, for example, be a perforated cage. Materials such as stainless steel or similar alloy are preferred. Especially preferred is an AISI 300 series austenitic stainless steel perforated cage between 26 and 8 gauge (0.018 to 0.165 inches) thickness with an open area of greater than 40%.

A sand screen structure according to the present invention is not limited to use with a gravel pack. Figure 3 illustrates an embodiment of a sand screen assembly according to the present invention installed on the lower end of a production pipe 17 within a well bore so that all fluid entering the production pipe 17 must first flow through the sand screen assembly. The unillustrated upper end of the production pipe 17 extends to the well head. The structure of this embodiment is similar to that of the embodiment of Figures 1 and 2. It includes a rigid perforated core 1, such as a perforated steel cylinder or a perforated length of production pipe, and a plurality of layers wrapped around the core 1. The layers include a downstream drainage layer corresponding to the drainage layer 9 of Figure 2 and helically or spirally wrapped around the core 1. One or more layers, and preferably at least two layers, of a sintered porous medium corresponding to layers 10 - 12 of Figure 2 are wrapped around the downstream drainage layer. An upstream drainage layer, which can be the same material as the downstream drainage layer, is helically or spirally wrapped around the outside of the layers of the sintered porous medium. A protective member 22 is then disposed around the outside of the upstream drainage layer to protect the drainage layers and the sintered porous medium. The protective member 22 in Figure 3 is a perforated, rigid outer cage of a corrosion- resistant material such as carbon steel, but it may instead be a woven metal mesh corresponding to the protective layer 13 of Figure 2. End caps 6 are εealingly connected to the axial ends of the core 1 and the wrapped layers, such as by welding or by a potting compound. The assembly may also include any of the other layers described above with respect to the preceding embodiments, such as a diffusion layer between layers of the sintered porous medium, or the rectangular wire wrap 8 of Figure 2. The characteristics of the various layers can be the same as those of a sand screen structure according to the present invention for use within a gravel pack.

The assembly includes a connecting portion at the downstream (upper) end of the core 1 by means of which the assembly can be connected to the lower end of the production pipe 17. In this embodiment, the connecting portion comprises external threads 6a which are formed on the outer surface of the upper end cap 6 and which engage with internal threads on the lower end of the production pipe 17. Alternatively, the connecting portion may comprise a standard coupling having internal threads for engagement with the external threads 6a formed on the upper end cap 6 and unillustrated external threads formed on the bottom end of the production pipe 17. The end caps 6 of the illustrated assembly are secured to the ends of the core 1, but in an assembly of the type described previously in which the end caps are slipped over the core 1, the connecting portion could be in the form of threads formed on the end of the core 1 for engagement with the production pipe 17. Preferably, the connecting portion enables the sand screen assembly to be detached from the production pipe 17, but if the life of the sand screen assembly is expected to be comparable to the life of the production pipe 17, then the assembly can be permanently connected to the production pipe 17, such as by welding.

The outer diameter of the sand screen assembly shown in Figure 3 is preferably selected to be smaller than the inner diameter of the well bore in which the production pipe 17 is installed and of the casing 2, if present, surrounding the production pipe 17.

In this embodiment, instead of being spirally or helically wrapped around the core 1, each of the layers of the sintered porous medium is wrapped around the core l a single time to form a longitudinal seam, and the two ends of each layer are sealed to one another by welding. Figure 4 is a transverse cross-sectional view of the longitudinal seam of one of the layers of the sintered porous medium. This view shows a first layer 10 of the porous support medium and a second layer 11 of the sintered porous medium surrounding the first layer 10. The ends of the second layer 11 are somewhat overlapped, and the resulting seam is sealed by resistance welding. The longitudinal seam of the first layer 10 is staggered in the circumferential direction of the assembly with respect to the seam of the second layer 11 and so is not visible in Figure 4. In order to prevent the two layers 10 and 11 from being joined to one another at the time of the welding, a chill strip 24 is disposed between the layers 10 and 11 along the seam. The chill strip 24 is preferably a material having high thermal conductivity and/or a high melting point. Some examples of a suitable chill strip 24 are a thin strip of copper sheet, woven copper mesh, ceramic paper such as ceramic felt, or a refractory metal. The seams of the other layers of the sintered porous medium are sealed in a similar manner. The embodiments of Figures l and 2 may also employ a longitudinal seam like that shown in Figure 4.

The sand screen structure of the present invention can also be used to protect a down-hole pump from damage due to particulate matter present in a well. A down-hole pump is one which is lowered into a well through production pipe and is used to pump fluids to the well head. Figure 5 illustrates an embodiment of the present invention in which a sand screen assembly similar to the embodiment of Figure 3 is installed on the inlet 19 of a conventional down-hole pump 18. The assembly can be connected to the pump 18 in any suitable manner. Preferably, the assembly includes a connecting portion which enables the assembly to be readily detached from the pump 18. The inlet 19 of a down- hole pump 18 is frequently equipped with internal threads by means of which equipment can be connected to the pump 18, so the illustrated assembly includes a connecting portion comprising external threads 6a which are formed on the upper end cap 6 and which engage with the internal threads of the inlet 19. The outer diameter of the sand screen assembly is preferably selected such that there is clearance between the outer periphery of the assembly and the inner periphery of the production pipe 17 so that the pump 18 can be easily raised and lowered within the production pipe 17. The characteristics of the various layers of the sand screen assembly can be the same as for an assembly according to the present invention employed within a gravel pack. The lower end cap 6 may be tapered or have beveled edges to help guide the assembly as it is lowered together with the pump 18 into the production pipe.

The sand screen assembly need not be connected directly to the pump inlet 19. For example, a section of pipe could be disposed between the pump inlet 19 and the upper end of the assembly. Thus, the assembly can be installed at any location along a flow path of fluid leading to the pump inlet 19. Installing a sand screen assembly on a down- hole pump is advantageous because the sand screen assembly can be readily accessed for replacement or repair simply by raising the pump 18 up the production pipe 17 to the well head. In contrast, in order to replace a sand screen assembly attached to the lower end of production pipe 17, as in the embodiment of Figure 3, the entire pipe string must be withdrawn from the well.

In the preceding embodiments, the layers of the sintered porous medium are wrapped around a perforated core 1. It is also possible for the sintered porous medium to be formed into a multi- layer pleated composite so as to increase the filtering area of the medium. For example, two or more flat sheets of the porous medium can be sandwiched between an upstream and a downstream drainage layer, such as a woven metal mesh like drainage layer 9. The sandwiched layers can then be pleated to obtain a pleated composite, which is formed into a tubular shape and then mounted on a perforated cylindrical core. To protect the pleats from radial forces, they can be surrounded by a rigid cage, or they can be wrapped inside a porous wrap member, such as the protective woven wire mesh 13 of Figure 2. The pleated composite may contain other layers employed in the embodiment of Figure 2, such as a diffusion layer between adjoining layers of the porous medium.

The pleats of the pleated composite can be conventional radially-extending pleats, or as shown in Figure 6, they can be so-called "laid-over pleats" in which the opposing surfaces of adjoining legs of the pleats are in intimate contact over substantially the entire height of the pleats. The sand screen structure of Figure 6 comprises a pleated composite 20 disposed between a perforated core 1 and a perforated, rigid external cage 22 of a corrosion-resistant material such as carbon steel. The composite 20 has a plurality of pleats 21, and each pleat 21 has two adjoining legs 21a connected to each other. The opposing inner surfaces of the two legs 21a of each pleat 21 are in intimate contact with one another over substantially the entire height h of the pleats 21. In addition, the opposing external surfaces of the legs 21a of adjacent pleats 21 are in intimate contact over substantially the entire height h of the adjacent pleats 21. In the laid-over state, the height h of each pleat 21 is greater than the distance between the inner and outer peripheries of the pleated composite 20 ([D-d]/2 in Figure 6). In this state, the pleats 21 may extend, for example, in an arcuate or angled fashion or in a straight, non-radial direction, but there is substantially no empty space between adjacent pleats 21, and virtually all of the volume between the inner and outer peripheries of the pleated composite 20 is occupied by the pleats 21 and can be effectively used for filtration. The pleats 21 can be formed into a laid-over state by methods well known to those skilled in the art.

In some instances, the perforations 7 in the perforated core l may be fairly large compared to the width of each pleat 21. To prevent the pleats from protruding into the perforations 7, a simple coarse wire mesh 23 of stainless steel, for example, may be wrapped around the core 1 to provide support for the radial inner ends of the pleats 21, and the pleated composite 20 can be slipped over the core l and the mesh 23.

While the invention has been described in some detail, it should be understood that the invention is susceptible to various modifications and alternative forms, and is not restricted to the specific embodiments set forth in the Figures. It should also be understood that these specific embodiments are not intended to limit the invention but, on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS :

1. A sand screen assembly for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid, comprising, in combination: a perforated production pipe, coaxially disposed about and secured to the perforated production pipe a cylindrical, porous inner drainage layer, a cylindrical, porous, outer protective layer, and disposed between the inner and outer layers multiple layers of a supported porous medium.

2. The assembly of Claim 1 wherein the supported porous medium is a sintered supported porous metal membrane.

3. The assembly of Claim 2 wherein the outer protective layer is a woven wire mesh and the inner drainage layer is a woven wire mesh.

4. The assembly of Claim 3 wherein the supported porous medium comprises at least three layers helically wrapped with abutting edges.

5. The assembly of Claim 2 wherein the supported porous medium comprises at least three layers spirally wrapped.

6. The assembly of Claim 2 further comprising a perforated cage coaxially disposed within the cylindrical porous inner drainage layer.

7. The assembly of Claim 2 wherein the supported porous membrane is sintered stainless steel, the support for the membrane is a woven wire mesh screen with a mesh weave content in the range of 20 x 20 x 0.014 to about 40 x 40 x 0.009, and the membrane is capable of bending about a radius five times its thickness while maintaining its integrity.

8. A sand screen assembly for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid, comprising, in combination: a perforated production pipe; coaxially disposed about and secured to the perforated production pipe a rectangular wire helically wrapped about the production pipe; a cylindrical, porous drainage layer wrapped over the rectangular wire; a cylindrical, porous, outer protective layer; and, disposed between the drainage and outer protective layers, multiple layers of a supported porous medium, capable of bending about a radius three times its thickness, and having a removal efficiency in the range of from about 2 to about 200 micrometers.

9. A sand screen assembly for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid, comprising, in combination: a threaded perforated production pipe; coaxially disposed about and secured to the perforated production pipe a rectangular wire helically wrapped about the production pipe; a cylindrical, porous drainage layer wrapped over the rectangular wire; a cylindrical, porous, outer protective layer; and, disposed between the drainage and outer protective layers, multiple layers of a supported porous medium, capable of bending about a radius three times its thickness, and having a removal efficiency in the range of from about 2 to about 200 micrometers.

10. A sand screen module for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid, comprising, in combination: a cylindrical, porous inner drainage layer, a cylindrical, porous, outer protective layer, and disposed between the inner and outer layers multiple layers of a supported porous medium.

11. The module of Claim 10 wherein the supported porous medium is a sintered supported porous metal membrane.

12. The module of Claim 11 wherein the outer protective layer is a woven wire mesh and the inner drainage layer is a woven wire mesh.

13. The module of Claim 12 wherein the supported porous medium comprises at least three layers helically wrapped with abutting edges.

14. The module of Claim 11 wherein the supported porous medium comprises at least three layers spirally wrapped.

15. The module of Claim 11 further comprising a perforated cage coaxially disposed within the cylindrical porous inner drainage layer.

16. The module of Claim 11 wherein the supported porous membrane is sintered stainless steel, the support for the membrane is a woven wire mesh screen with a mesh weave content in the range of 20 x 20 x 0.014 to about 40 x 40 x 0.009, and the membrane is capable of bending about a radius five times its thickness while maintaining its integrity.

17. The module of Claim 16 wherein the layers of membrane are sealed with end caps.

18. A sand screen assembly for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid, comprising, in combination: a perforated production pipe and multiple layers of a supported porous membrane coaxially disposed about and secured to the perforated production pipe.

19. A sand screen module for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid, comprising, in combination: a cylindrical perforated cage; a rectangular wire helically wrapped about the perforated cage; a cylindrical, porous drainage layer of woven wire mesh wrapped over the rectangular wire; a cylindrical, porous, outer protective layer of woven wire mesh; and, disposed between the drainage and outer protective layers, multiple layers of a supported porous medium, capable of bending about a radius three times its thickness, and having a removal efficiency range of from 2 to about 200 micrometers.

20. A sand screen module for use in a subterranean well to limit the intrusion of particulate matter into the well production fluid. comprising, in combination: a cylindrical perforated cage; coaxially disposed about and secured to the perforated cage, a cylindrical, porous inner drainage layer of woven wire mesh, a cylindrical, porous, outer protective layer of woven wire mesh, and, disposed between the drainage and outer protective layers, multiple layers of a supported porous medium, capable of bending about a radius three times its thickness, and having a removal efficiency in the range of from about 2 to about 200 micrometers.

21. A sand screen assembly for use in a subterranean well comprising: a perforated core having a downstream end; at least one layer of a sintered porous medium disposed around the core; and a connecting portion at the downstream end of the core for connecting the core to a production pipe within a well bore.

22. An assembly according to claim 21 including an end cap connected to the downstream end of the core, wherein the connecting portion comprises threads formed on the end cap for connection to a production pipe.

23. An assembly according to claim 21 wherein the sintered porous medium is wrapped around the core in a plurality of turns.

24. An assembly according to claim 21 wherein the sintered porous medium is pleated into a plurality of pleats.

25. An assembly according to claim 24 wherein the pleats are in a laid-over state.

26. A sand screen assembly for use in a subterranean well comprising:

5 a perforated core having a downstream end; at least one layer of a sintered porous medium disposed around the core; and a connecting portion at the downstream end of the core for connecting the core to a down-hole pump 10 within a well bore.

27. A pump arrangement for pumping fluid from a subterranean well comprising: a pump disposed within a well and having an inlet; and 15 a sand screen assembly disposed along a fluid path to the pump inlet and comprising a perforated core and at least one layer of a sintered porous medium disposed around the core.

28. An arrangement for removing particulate 20 matter from fluid within a subterranean well: a production pipe disposed within a well bore and having an upstream end; and a sand screen assembly connected to the upstream end of the production pipe and comprising a 25 perforated core and at least one layer of a sintered porous medium disposed around the core.

29. A method of removing particulate matter from a fluid within a subterranean well comprising: passing a fluid through a sintered porous 30 membrane disposed within a well bore; and pumping the fluid from the well bore using a

- 29 - down-hole pump disposed within the well bore.

30. A method of removing particulate matter from a fluid within a subterranean well comprising: passing a fluid through a sintered porous membrane disposed within a well bore; and passing the fluid through production pipe disposed in the well bore to outside the well bore.