CA2163754A1

CA2163754A1 - Sand screen structure

Info

Publication number: CA2163754A1
Application number: CA002163754A
Authority: CA
Inventors: Paul Charles Koehler; Stephen Arthur Geibel; Michael B. Whitlock; Reza Hashemi
Original assignee: Individual
Current assignee: Oiltools International BV
Priority date: 1993-05-25
Filing date: 1994-05-17
Publication date: 1994-12-08
Also published as: WO1994028284A1; AU679081B2; NO954746D0; EP0699271A1; EP0699271A4; AU7042194A; NO954746L; CN1124517A

Abstract

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

Description

94128284 21 6 ~ 7 54 PCTrUS94/05720 SAND SCREEN STRUCT~RE

Field of the Invention This invention relates generally to struc*ures for use in h~ocarbon well completion and workover applications, and, in particular, to sand screens for limiting the intrusion of particulate matter into the well y c~ction fluid.

Back~round of the Invention U~co~colidated particulate matter, hereinafter referred to as "formation sand," is often associated with subterr~ne~ d~ocarbon formations. A major problem in ~r~ucing l.y~.ocarbon fluids from ~ ~ol.-olidated formations is the intrusion of formation sand, which is typically very fine, into the ~ c~ion fluid and equipment. The presence of sand in the ~o~uction fluid often leads to the rapid erosion of eYpe~sive well machinery and hardware. Furthermore, the ~hifting of sand in an ormation may result in the coll~rse of perforations ~c~cfully blasted in the formation, thereby ~ c;n~ or even halting ~ ction. In order to ~ the ~hifting of for~ation sand, ~uch formations are typir~lly ~gravel packed." The gravel packing also acts as a filter, pL~ Ling the fine sand from entering the ~LG~ction fluid. Gravel r~ing involves the ~Lv~ction of a part;~vl~ grade of cand into the well bore, often by pumping it down as a dense wo ~n$~ ~16 3 7 ~ ~ PCT~S94/0~720 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 ~L ~ction fluid, ~s well as to prevent the intrusion of fine formation sand ( which often initially r~ C~?S through the gravel pack) into the ~lod~ction 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 ~uL~L~.Lial expense.
The production of hydrocarbon fluids from horizontal wells is highly desirable in that ~ultiple bores may be drilled rA~;Ally from one central ~ertical bore, thereby increasing p~od~ction efficien~y from a particular formation. However, horizontal well completion involves several tec~nical impediments, and as a result, has, heretofore, not been extensively practiced. Placing a ~cd~ction pipe deep into the earth and then attemptiDg to snake the pipe at an angle approaching ninety degrees requires pipe made from a material which co bines merh~n;cal D~Lel~y~h with flexibility ~nd ductility. The problem of placing ~o~uction pipe ~n the well is often exacerbated by the fact that many horizontal wells are of an ~ncQT~olidated nature. Gravel packing and sand screen use are very difficult under such circumst~nces.
With regard to the problem of sand intrusion in ~ ~ ~ 3 7 ~
~0 ~n8~ PCT~S94/05720 unconsolidated formations, several sand screens struc~ules have been designed. Exemplary designs include a wire-wrapped screen assembly (see, for example, ~.S. Patent Number 3,958,634), a wire-wrapped screen and prepacked gravel A~CD~hly (see,for example, U.S. Patent Number 5,050,678) and a sintered metal unitary body assembly (see, for example, ~.S. Patent Number 5,088,554). Wire-wr~pre~ screen assemblies exhibit several undesirable ~nAen~i es: erosion induced by fine sand that initially flows pzst the wire/gravel pack interface; plugging with carbonaceous, siliceo~-c or organic solids; and coll~ps~ 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 ~re A~ ~.o~e-i, making initial placement and retrieval difficult.
Wire-wrapped, and to some degree prepacked, ~and ~creen structures are not particularly damage resistant; they require very careful hAnAling 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 rr~ring which could lead to erosion ~nd failure of the screen. Furthermore, ~G..~.Lional wire-~la~e~ 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 stru~L~es are cost prohibitive for use in all but the most wo ~n8u~ PCT~S94/05720 21637~4 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 ~nitary body thickness. Sintered metal unitary assemblies also have a tendency to plug from fines entrained in the formation fluid. To ~nh~n~ their performance, sintered metal unitary sand screens may need to be el~Lol-Q~i~hed which adds to their cost.
While ~intered metal unitary sand screen assemblies exhibit an effective open area (voids volume), they lack a me~ni~m 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 prepac~ed 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.

Summarv of the Invention In accor~n~e with the present invention a structure is provided that in large measure o~comes the ~ubstantial problems described aboYe.
T~e ~L~ t invention comprices a damage resistant sand screen structure for use in hyd~ocarbon wells which is particularly suited for applications involving ~.~o -olidated and horizontal formations.
In one embodiment the invention comprises multiple layer~ of -~1 Led porous media, co~Yi~lly disposed about a perforated production pipe. In a 094n$~ 2 I fi 3 7 ~ 4 PCT~S94/05720 method of forming such a structure, a sheet or strip of ~u~ed 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 di~ 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 ~u~yo~Led porous membrane which is designed to slip over and be ~e_~le~ 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 ~event particulate matter from entering the pump.
The sand screen structures of the present il.v~.Lion ~hihit ~c~llent damage resistance, have 8 high voids volume, and provide uniform flow distr~bution. The preferred media used in the ~ ~~ent ~-v~-~ion are . ~ ed or reinforeel, and are preferably helically wrapped with abutting cl~ R ~

Rr~ ef Degcri~tion Of The Drawinqs Figure 1 chows a well bore con~i n i ng a W094fi$U~ ~16 3 7 ~ ~ PCT~S94/0572~

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 emho~iment of the present invention installed on the lower end of ~od~ction pipe.
Figure 4 is a transverse cross-sectional view of a seam ~f the assem~ly of Figure 3.
Figure 5 is a partially cross-sectional schematic elevation of another embodiment of the ~.e-cnt invention installed on the inlet of a down-hole pump.
Figure 6 is a transverse cross-sectional view of a portion of an emho~iment of the present invention including a pleated composite.

Detailed DescriDtion Of Embodiments The subject invention is directed to a sand screen structure exhibiting damage resistance to forces encountered in well completion applications and ha~ing particular application in unconsolidated and horizontal well formations. For ~Ul~G~es of the present invention, "damage resistance" refers to a sand screen structure's ability to substantially maintain its "integrity" when collAp-e~ from about 1/3 to about 1/2 its original diameter, i.e., the stru~ule has at least 90S, more preferably ~t least 95%, of its original integrity. As used herein, ~integrity" refers to the ~tated removal efficiency.
The stru~Lule~ of the present invention include sand screen ass~mhlies, wherein a section of perforated y~Gduction pipe is part of the structure, and sand screen modules, wherein the structure is designed to 2 1 6 3 7 5 4 pcTrus94los72o be slipped over and secured to a section of perforated production pipe.
The invention may further comprise multiple layOEs of a porous media co~Y;~lly wrapped around a small dia eter perforated pipe that is i..L~o~uced into the vork string via a continuous coiled tube of the type used in worko~er applications (where a sand screen has been damaged). In this manner the o.._t_aam life of a well can be ex~enA~ by producing through a da~aged ~and ~creen.
Referring now to the drawing~, Figure 1 shows an exemplary sand ~creen assembly in a well formation application, with the ~oduction 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 posi~ion~ inside a well bore casing 2 showing a perforation 3 in the ~ing wall, with the gravel pack 4 in the ~nn~llar ~r~c~ betveen the production pipe 1 and the casing 2. The production pipe 1 may be thre~A~ at its ends or along its entire length. The assembly in Figure 1 also includes ~ alizers S, which prevent the assembly from bumping against the casing wall.
Figure 2, ~ in more detail below, is an DYr~nded cross-sectional view of the sand D~'e~
assembly in Figure 1 showing in ~o-~ section the layers of the sand screen assembly.
The ~ bed ~ s materials utili 7~ in the ~ t ~n~ention produce a damage resi~tant ~and D~L~ tructure when co-Y;~lly ~ro~ed ~bout a perforatd production pipe. This is Du~.ising, in that, un~er typical well completion DbL~-~e-~ the raterial~ useful for the ~ ~t i..~ ion would nor~ally be expected to be ~^c~rtible to point 35 lo~ng~ erosion and shearing. Prefe ~ed for use as ~ 21 6 3 7 5 'I PCT~S94/05720 the ~VL Led porous media, to limit the intrusion of particulate matter into the well production fluids, are ~ -~ Led 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 maint~ini~ its integrity. Preferred m_terials for the ~e~el.L invention are ~ho-?
capable of h~nA; ~ about a radius five times the ~hi~nqsr of the material, or less, while still maintainin~ the integrity of the material.
Particularly preferred are materials which can bend about a radius three times their thickness, or less, while main~i n ;n~ their integrity.
Preferred flexible materials for use in the ~ cnt invention are ~ olLed porous metal sheet materialc. Particularly preferred are D~olLed ~intered ~v vus metal sheet materials such as those ~;rclosed in U.S. Patent No. 4,613,369, which is in~,~G~Led herein by reference, and which are referred to herein as - ~o-Led porous membranes.
These membranes comprise a foraminate metal ~ oLL, e.g., a woven wire mesh, and metal particulate cont~in~ within the oreni~s in the ~ llort, the individual particles of the metal particulate - bonded to each other and to the ~-'1'1-' L by sintering. ~peci~lly preferred are ~ o~Led sintered metal membranes wherein the metal particles are no more than one-fifth the ~ize of the fimalle~t dime~ of the opo~in~ of the foraminate ~ L.
These materi~l~ are available from Pall ~oL~G~Lion under the trademark PMM~.
The metal par~ te and foraminate metal ~ can be of any of a variety of metals, such as nickel, iron, chromium, rol.~ , molybdenum, ` wo ~n*u~ 216 3 7 5 ~ PCT~S94/05720 tungsten, zinc, tin, aluminum, cobalt, iron, and magnesium, as well as combinations of metals and metal alloys including boro~ a i n i n~ alloys.
Nickel/chromium alloys are preferred. Of these the S AISI designated stainless steels which contain nickel, chromium and iron are most preferred.
Examples of suitable woven mesh screens, useful as the foraminate ~ L, include stainless steel mesh s~-e_.~ 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 esh 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 ;~ch~s). 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 pLe_ent 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 qravel packing. Sand grains used in gravel packing in well formations typi~lly range in ~ize from about 20 to about 1000 micrometer~. It is known that sand qrains of a particular size are effectively removed by media with effici~cy removal ratings of about 1/7 to about 1/3 the grain ~ize. For example, in a well formation with average qrain size of 100 m~crometer~, a media rated at 15 to 30 micrometers would be eYpected to efficiently ~L~v~ sand intrusion.

wo ~n$u~ 21 6 3 7 5 ~ PCT~S94/05720 A number of methods for measuring efficiency removal are known. Especially useful is the ~2 test originally developed at Oklahoma State University in the 1970's. lypically, porous media employed in the ~e-^~t invention will ha~e ~2 ratings at beta=100 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.
Tyric~lly, .~ o.Led porous media of this in~ention will ha~e 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 ut;li~tion of substantially all of the circumferential flow re~ of the ~o~ous media when placed in contact with a perforated pipe.
Preferably, at least 95~ of the circumfe-enLial flow area is utilized. Flow distribution uniformity is ~h~n~ by the use of multiple layers of media, with drainage and/or ~ layers.
Multiple layers of the ~ o Led ~o.ous media may be ~ oe~ively spirally or helically wr~rr~
a~o~.~ the perforated production pipe. At least two media layers, al~ho~yh more, e.g., three, four, six, eight, ten, tw~.~r, thirty, forty, or even more media layers, may be used to form the ~o~ous L~ Le.
In the sand screen as~embly shown in Figure 2 (wherein the ~ame numerical ~D~i~n~tions are u~ed to refer to the same stru~uLe~ depicted in Figure 1), ~LLee layers 10, 11, and 12 of a sintered ~ ed ~GL~UD met~l ~embr~ne are h~ lly wrapped around the per~orated production pipe 1 o~ Figure 1.

wo ~$~ 216 3 7 5 4 PCT~S94/05720 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 1. 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 lO, 11, 12, as shown in Figure 2, are helically wr~p~e~ over the drainage layer 9. Each layer of r~ro~ted membrane lO, 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 necess~rily be so.
The use of multiple layers reduces the ~ cer~ihility 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 ~edia are preferably helically wrapped such that the edges of the media 6heets are abutting. While the porous media can be helically wr~pp~ such that the edges of the media sheets ~re overlapping, this is less desirable. In the emhcAi~ent of Figure 2 there are three layers of seven inch wide media 10, 11 and 12 a~Loximately 76 to 85 inches long, helically w~a~ed at an initial wrap angle o~ a~o~imately 45O, with no overlap.
The wrap ~ngle changes slightly with each r~cc~scive layer due to the increased outer diameter. The initial outer diameter of the perforated ~o~uction wo ~n8~ 216 3 7 5 ~ PCT~S94/05720 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 ins~an~e6 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 O% (abutting) to as much as about 95%.
A diffusion layer, while not essential, may be ~i~rQ~^-i between two or more of the layers of porous - media to ~nh_n~o uniform flow distribution. The diffusion layer may be formed from any suitable, ~v~s 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 ~Ol~S media. The diffusion layer may comprise a ~G~ed 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 .OO5 or finer. While the diffusion layer need not be helically wr-rp~, it is preferably helically ~rA~ if the media sheets have been helically wL~ When the diffusion layer is ~c_~e~ to a s 25 media ~ t prior to wrapping, the diffusion l~yer will, of oourse, be wound together with the media sheet in the same configuration.
If an overlap is employed, care must be taken to ensure that wr~n~lin~ of the media and/or 30 diffusion layers does not result due to the variable outer dia~eter of the helically overl~rp^~ layers.
Any wr~n~l~ng of the layers may contribute to fluid flow p~thways which bypass the media. Hcu~ , such wrin~l;ng can generally be avoided by using a 35 suff;~ tly fl~Y~hle media to accommodate the small ~1~3~4 WO94J2~4 PCT~S94/05720 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 ~eans.
While the exterior of the sand screen structure may be the outermost ~u~olLed porous media layer, the use of a protective material which wraps around or ~ncA~?~ the sand screen structure is preferred for ease of h~n~li"g and to provide the sand screen structure additional ~ o-- 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 h~n~ g, 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 ~creen with a square mesh weave of from about 1 x 1 x 0.125 to about 40 x 40 x O.OO9. Especially preferred is a heavy woven metal mesh such as a lO x 10 x 0.047 ~guare mesh weave comprising 300 ~eries ~u~tenitic 6tainless steel. The sand screen a~sembly ~hown in Figure 2 includes a protective outer wrap 13 comprising AISI 300 series austenitic stAin~ teel lO x 10 x 0.047 square mesh weave.
The exterior protective material may be applied in any ~uitable manner. Preferably, the protective material, such as a woven metal mesh, is wrapped in the same manner as the media layers. The exterior -W094/2$~4 216 3 7 ~ 4 PCT~S94/057~

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 emho~iment 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 ~and 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 ~ny 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 ~lod~ction pipe and the innermost media layer. Especially preferred is a layer of flat or sguare 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 in~hPc, helically wrapped and spaced 0.25 inches center to center.
Suitable materials for drainage layers are woven ~etal meshes or perforated metal sheets.
Preferred are woven metal meshes compri~ing stainlesc 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.

2~637~
Wo ~$U~ PCT~S94l05720 Especially preferred is a heavy woven metal mesh such as a 40 x 40 x O.OO9 square mesh weave comprising AISI 300 series austenitic stainless steel. Drainage layers may also be applied in any suitable anner, e.g. by helically or spirally wrapping such layer~ in the same manner as the porous media layers. For example, in the e~h~iment shown in Figure 2, a layer of rectangular wire wrap 8 is laid over the perforated production pipe 1, and a drsinage layer of 40 x 40 x O.OO9 square mesh weave 9 ~u~prising 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 ~-od~ction 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 ~ame direction or they may be wr~ppe~ in opposite ~;~ections. 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 ~e ed in place by various ~echniques, e.g., by w~l~ing or brazing ~echniques.
Examples of suitsble wel~ing snd brazing te~n;~ues include L~.y~en inert gas, laser, ele- ~LV~ beam, electrical resistance, nicrobraze, and sil~er braze.
Prefer~bly, the multiple layers are continuously resigtance w~ , slong the s ~m, to the layer beneath. In the emhqA;ment chown in Figure 2, resiDL~.~e welds 14, lS, and 16 run along the ~eam between layers lO, 11, and 12 of the media.
3S Various ~ec~iques may be employed to seal the wo 21 6 3 7 5 4 PCT/USg4/0~720 ends of the media to the perforated production pipe.
For exa~ple, end caps may be slipped over the perforated production pipe, positioned at the ends of the supported porous media, and welded to the S media and the pipe. Alternatively, the ends of the ~edia ~ay be welded together directly to the ends of the perforated production pipe. The sand screen s~mbly shown in Figure 1 includes end caps 6 welded at either end of the perforated ~,G~ction pipe 1- Mo~ A 6and C~e~ will typically include end caps welded to the ends of the media. The m~llar unit may then be 5lirre~ over a perforated ~r~ction pipe and welded at the end caps to the pipe.
McA~lAr sand screens may also include an inner~ost layer comprising a cylindrical cage posi~jo~ on the inner circumfeLe,.~e of the drainage layer, or when utilized, on the inner circu~ftlel.~c of the rectangular wire wrap layer.
The cage, which is designed to slip over the perforated production pipe, provides dimensional st~hi~ity to the drainage and media layers. The cage may be of any suitable cGn_LL~ction and material ~ro~iate for the ~evere conA;tions e~ .Lered, as ment;on~ above. The cage may, for - example, be a perforated cage. Materials such as st~in~ steel or similar alloy are preferred.
c~ly preferred i8 an AISI 300 fieries au~tenitic st~ steel perforated cage between 26 ~nd 8 gauge (0.018 to 0.165 inches) th;rkness ~- with ~n cpen area of greater than 40~.
A ~and ~creen ~tructure according to the ` preeent invention i~ not limited to use with a 1 pack. Figure 3 illu~L.aLes an emh~iment of a sand DU~eel- a~sembly according to the present ~ . .

~ - 16 -~0 g~n~Q1 21 6 3 7 54 PCT~S94l05~

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 throug~ the sand screen assembly. The unillu~L~ed ~el end of the production pipe 17 extends to the well head. The st~ucture of this emho~iment is similar to that of the embodiment of FiyuLe~ 1 and 2. It includes a rigid perforated core 1, such as a perforated steel cyl;n~r or a perforated length of y ~~ on pipe, and a plurality of layers wrapped a~o~,d the core 1. The layers include a dos..~LL~3m drainage layer CO~L~ r~ g to the drainage layer 9 of Figure 2 and h~li5~11y or spirally wrapped aLo~.
the core 1. One or more layers, and preferably at lS least two layers, of a sintered ~o ~us medium c~r~e~ li~g to layers 10 - 12 of Figure 2 are wr~rr~ ~o~,d the downstream drainage layer. An ~_L~a~a drainage layer, which can be the same materi~l as the d~ aam drainage layer, is h~lic~lly or spirally wrapped around the outside of the layers of the sintered porous medium. A
protective member 22 is then Ai~po^^~ a~.d the out~ide of the ~_~eam drAin~g~ layer to protect the dra~nage layers and the sintered ~LoUs medium.
The protective ~ember 22 in Figure 3 is a perfor~ted, rigid outer cage of a corrosion-resi~ta~t material ~uch as cA~bon steel, but it may in6tead be a w~ metal mesh ~ol,~ .ponA;~ to the protective layer 13 of ~igure 2. End caps 6 are F-al~ngly connected to the axial ends of the core 1 ; ~nd the W1AP~ layers, ~uch as by w 1~:~g or by a potting oompound. The assembly may also include any of the okher layer~ de~cribed above with respect to the ~r~ - l;ng embodiments, ~uch as a diffusion layer between layers of the ~intered ~o~ous medium, or the w~94n$u~ 216 3 7 S 1 PCT~S94/0572~

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 emho~;ment, the co~cting 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 co~necting portion may comprise a st~ rd 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 ~and 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 ass~hly can be permanently co~ cted to the production pipe 17, such as by welding.
~ he outer diameter of the sand screen assembly ~hown 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 wo ~n$~ 2 1 ~ 3 7 5 ~ PCT~S94105720 casing 2, if present, surrounding the production pipe 17.
In this ~mho~iment, instead of being spirally or helically wrapped around the core l, each of the layers of the sintered porous medium is wrapped around the core l a single time to form a longit~ nAl seam, and the two ends of each layer are sealed to one another by welding. Figure 4 is a transverse cross-sectional view of the longitu~
seam of one of the layers of the sintered porous medium. ThiC view shows a first layer lO of the porous ~ o~ medium and a second layer ll of the sintered porous medium surrounding the first layer lO. The ends of the second layer ll are somewhat overlapped, and the resulting seam is sealed by resistance welding. The longitl~inAl seam of the first layer lO is staggered in the circumferential direction of the assembly with ~e~ect to the seam of the ~on~ layer ll and so is not visible in Figure 4. In order to prevent the two layers lO and ll from being joined to one another at the time of the welding, a chill strip 24 is disposed between the layers lO and ll along the seam. The chill strip 24 is preferably a material having high thermal conductivity and/or a high melting point.
Some examples of a suitable chill strip 24 are a thin strip of copper sheet, woven copper mesh, ceramic paper such as ceramic felt, or a refractory metal. The seams of the other layers of the sintered porous medium are sealed in a similar manner. The emho~iments of Figures l and 2 may also employ a longit~i n~ 1 seam like that shown in Figure 4.
The sand screen structure of the present invention can also be used to protect a down-hole W094~$U~ 216 3 7 5 ~1 PCT~S94/05720 pump fro~ 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 S illustrates an emho~inent 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 co~,vel,~ional down-hole pump 18. The assembly can be connected to the pump 18 in any suitable manner.
Preferably, the assembly includes a connecting portion vhich 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 punp 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 ~Gdu~ion 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. $he 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 l9 and the ~y~ end of the ass~mhly. Thus, the asse~bly can be installed at any location along 2 1 6 3 73 5 4 ;

a flow path of fluid leading to the pump inlet 19.
Installing a sand screen assembly on a down-hole pump is advantageous ~ecause the sand screen assembly can be readily a~e~r~ for replacement or S repair 8imply by raising the pump 18 up the ~ ction pipe 17 to the well head. In co..~.ast, in order to replace a sand screen assembly at~r to the lower end of production pipe 17, as in the emh~ment of Figure 3, the entire pipe string must be withdrawn from the well.
In the ~eeli ng 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-lS layer pleated composite so as to increase thefiltering area of the medium. For example, two or more flat sheets of the po-ous medium can be sandwiched between an~ Leam 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 ~b~ r sh~p~ and then mounted on a perforated cylindrical core. $o protect the pleats from radial forces, they can be ~1 G!~J~ by a rigid cage, or they can be wrapped inside a ~o~ G~S
wrap member, such as the protective woven wire mesh 13 of Figure 2. The pleated composite may contain other layers employed in the emkodiment of Figure 2, 8uch aS a diffusion l~yer between adjoining lay OES
of the porous medium.
The pleats of the pleated composite can be ~o.lventional r~;ally-ex~en~ing pleats, or as shown in Figure 6, they can be so-called "laid oveL
pleats~ in which the opposing surfaces of adjoining legs of the pleats are in intimate contact over wo s~n~ ~ PCT~Sg4/0~2 216375~

substantially the entire height of the pleats. ~he sand screen structure of Figure 6 comprises a pleated composite 20 di~ between a perforated core 1 ~nd a perforated, rigid external cage 22 of a ~o~osion ~e_istant material such as carbon steel.
The composite 20 has a plurality of pleats 21, and each pleat 21 has two adjoining legs 21a co~ected to each other. The opposing inner surfaces of the two legs 2la of each pleat 21 are in intimate contact with one another over substantially the entire height h of the pleats 21. In addition, the oprosin~ 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 (tD-d]/2 in Figure 6). In this state, the ple~ts 21 may extend, for example, in an arcuate or angled fashion or in a straight, non-r~; al 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 method~ well known to Lh_-o skilled in the art.
ln ~ome ins~nc~6, the perforations 7 in the perfvL~e~ core 1 may be fairly large compared to the width of each pleat 21. To prevent the pleats from ~L~LL~ding into the perforations 7, a simple coar~e wire mesh 23 of stainless ~teel, for example, may be wrapped around the core 1 to provide ~ rL
for the radial ~nner end~ of the pleats 21, and the pleated composite 20 can be Cl~rpe~ over the core 1 2 ~ 6 3 7 ~ ~ PCT~S94/05720 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 emh~Aiments set forth in the Figures. It should also be understood that these specific embodiments are not int~nAe~ to limit the i,.vel.Lion but, on the eo-.L~ary, the intention is to COVeL 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:
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 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 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 is disposed around the core.

28. An arrangement for removing particulate 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 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 membrane disposed within a well bore; and pumping the fluid from the well bore using a 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.