Well screening method and device therefor

April 25, 1961

Μ. K. MILLER ETAL 2,981,333

WELL SCREENING METHOD AND DEVICE THEREFOR

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Filed Oct. 8, 1957

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April 25, 1961

Μ. K. MILLER ETAL

2,981,333

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WELL SCREENING METHOD AND DEVICE THEREFOR

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2,981,333

Patented Apr. 25, 1961 perforations formed in such pipe, into the pipe and up the tubing of the oil well.

Another object is the provision of procedure and apparatus for screening oil or other liquid passing from ⁵ a producing formation adjacent a well bore into the well, employing an expansible screening element through which the oil or liquid passes before entering the well bore or casing, said screening element being expandible into tight engagement with the wall of the well bore ¹⁰ and being formed, of a material having resilient characteristics, i.e., being able to expand, in a plurality of directions so that holes or apertures formed in the element are substantially filled by expansion therein of the resilient screening material, and said screening material ¹⁵ having a porosity such that the liquid flows readily therethrough yet having sufficient toughness and resistance to abrasion by sand particles, and sufficient compressibility to butress and reinforce the adjacent wall of the well bore against which the element is expanded, to aid in preventing collapse of the formation forming said wall.

The instant invention comprises as a feature thereof the use of a screening element which is mounted around a tube or pipe, which may be the well casing, the screening element being a resilient, expansible, foraminous, porous material which has multidirectional characteristics, e.g., such element is expansible in a longitudinal as well as in a lateral direction, so that the screening element will expand laterally when a force holding it under compression is released, and when holes are formed therein in the direction of such expansion, as by gun perforating, such holes will be substantially filled by expansion of the resilient screening material in a 35 direction at right, angles to such lateral expansion to substantially fill said holes, and thus retaining the fluid screening properties of said element following formation of such holes.

, The screening element of this invention can be an ₄₀ elastomeric, material such as sponge rubber or any similar, synthetic or natural polymeric or resinous material which has substantial resiliency and is foraminous or porous and allows passage of fluids through such pores. Of particular importance these screening elements have _4g the property of expanding in a plurality of directions on removal of a compressive force exerted against the element.. The following types of materials can be employed. m forming the resilient screening element of the invention: Sponge rubber which can be formed from 50 foamed natural or synthetic rubber including butadienestyrene, butadiene-acrylonitrile, mixed natural rubber and butadiene-styrene, or the chlorinated synthetic rubbers such as neoprene; plastic foams such as polyurethane. ether foam and polyurethane. ester foam; and 55 polyvinyl chloride foam. 'These materials have good compactibility, resilience, and resistance to heat and chemicals such as acids,. and are substantially inert to oil. The synthetic sponge rubbers, such as those formed from butadiene-acrylonitrile and butadiene-styrene - are ₆₀ preferable to the natural rubber sponges.

The above types of porous resilient materials employed as screening elements herein differ from the fiber glass mats or batts of the aforementioned. Miller-Kumler application, in that said glass fiber batts or. mats substan65 tially only expand outwardly on release of a compressive force, that is, on removal of the constricting element, whereas the screening elements of the instant application not only expand laterally outwardly,. but also in a plane perpendicular to such outward lateral 70 expansion, e.g., longitudinally of the well bore, to fill the holes or apertures formed in the screening element as described more fully below.

2,981,333

WELL SCREENING METHOD AND DEVICE THEREFOR

Montgomery K. Miller, Pasadena, Calif. (2404 W. 7th St, Los Angeles, Calif.), and William L. Kumler, 1104 Pacific Mutual Bldg., Los Angeles 14, Calif.

Filed Oct §, 1957, Ser. No. 689,002

Claims. (Cl. 166—12)

This application is a continuation-in-part of U.S. application Serial No. 637,687, filed February 1, 1957.

This invention relates to the introduction of well fluids such as oil and water from a formation into a well, while preventing accumulation of particles of earth and sand in the well. The invention is particularly concerned with procedure for screening earth and sand particles against introduction into a well with the well fluid, and for maintaining and supporting the wall of the bore adjacent the producing zone, and apparatus for these purposes.

It is known to mount filter elements on perforated liners which are inserted in oil wells. Frequently, however, a condition of running sands or cave-ins is encountered in a well, which causes the liners to stick, and also causes the introduction of sand and other particles particularly into the annulus between the liner and the wall of the bore, and also into the oil well string.

In application Serial No. 637,687, filed February 1, 1957 by Montgomery K. Miller and William L. Kumler, there is described the use of an expansible screening element which surrounds a perforated liner and has an outside diameter which permits the introduction of the liner through the casing and into the open portion of the hole, and when the liner is in position said element can be permitted to expand to fill the entire annulus. For this purpose it is noted in the above application that any suitable resilient material which can be compressed and expanded can be utilized as the screening element. A specific form of screening element according to said application, can be, for example, a circular tube or mat of glass fiber, mineral wool, metal filament such as metal wool, or other similar fibrous or foraminous material, including elastomers, which can be compacted around the outside of the liner and held against its outer periphery to permit the introduction of the wrapped liner into the casing, the liner being perforated at the place where the mat is positioned. A constricting element is positioned about the screening element or screen to hold it in compression. When the liner is placed in position in the well, the constricting element is released, so that the mat can expand due to its resiliency, into compressive contact with the wall of the bore. Preferably glass fiber mats or batts are employed in the aforementioned application, the filaments of such glass fiber mats or batts being preferably coated with a resin to decrease the brittleness of the glass fibers.

The mam object of this invention is to provide an improved screening element around a pipe which maj be either the casing itself or a liner, so that said element fills the annulus between the wall of the well and the casing or liner to prevent the introduction or the accumulation in said annulus of earth and sand which would block off the pipe and cause the difficulties previously defined, but which would be porous to permit the movement of oil through the screen and through

2,081,333

The screening element, shaped in the form of a ring or tube, is preferably mounted about the pipe or well casing prior to its introduction into the well. The element is placed under radial compression by positioning a constricting element about the screening element. As constricting elements which may be employed for compressing the resilient screening element, we can, for example, wrap the resilient porous member, e.g., spong rubber, forming said screen with an outside coating or sheath sufficiently strong to compact it, which sheath I can then be removed by solution with a solvent or acid introduced into the annulus of the well to disintegrate said sheath and release the screening element.

According to one embodiment, the casing with the screening element wrapped thereon is passed through the well bore to the production zone. The casing, at a location above the formation adjacent the sceening element and above the screening element, is then cemented in the usual manner to form a cement plug in the annulus between the casing and the well bore. The placement of the cement plug acts as a water shut-off preventing drainage of water from above into the annulus adjacent the screening element.

The casing adjacent the screening element, and said element can then be gun perforated for the purpose essentially of providing fluid communication from the screening element to the interior of the casing. Thereafter, the constricting element can be released by flowing a dissolving solution through the perforations in the casing and through the screening element into the annulus between said element and the well bore, and into contact with the constricting element. The resiliency of the screening element permits it to expand partially into tight engagement with the face of the wall of the well bore. The screening element then takes a position against the wall.. In this expanded position, the tubular, screening element substantially completely fills the annulus between the wall of the well and the casing on which the screen is mounted. The resiliency of the screening element maintains it in contact with said wall, and the differential pressure between the fluid passing into said element and the opposite force due to resiliency of the screen, is controlled so that it is insufficient to compress and force the screen element away from the well wall.

Simultaneously with outer lateral expansion of the screening element into contact with the well bore, the resilient, porous elastomeric material forming said element expands in a number of directions at right angles to said lateral direction of expansion, e.g., in a direction axially of the well bore, to substantially or practically fill the holes formed in the screening element by gun perforating, so that no bypassing of the fluid takes place through such perforations in the screening element, and the oil or fluid passing from the formation must proceed through the pores in the screening element before passing into the perforations in the casing and into the interior thereof.

Thus, the resilient screening element in its operative position substantially completely closes off the annulus between the casing and well wall so that sand and earth particles adjacent the wall cannot fall into the annulus, and hence the outer surface of the resilient tubular element functions to reinforce the wall of the bore and screen off such particles while permitting the fluid to pass through to the casing. Any minor portion of said sand particles which may be carried through the screening element are usually deposited within the resilient screen and are not carried into the casing. The resilient screening element functions essentially to block par- 70 tides of sand at the wall of the bore at the outer contact surface of the screening element. The sponge rubber or equivalent material· employed as screening element is resistant to abrasion by sand or other formation particles. The clogging of particles of sand or 75 force the screen element away similar material in the pores of the screening element is advantageous because under these conditions such sand particles do not pass into and through the perforated holes in the metal casing and hence do not cause such holes to be undesirably eroded and enlarged due to this abrasive action. Such clogging further does not reduce the flow of fluid passing from the formation through the screening element, but merely causes the fluid to pass through the pores of the screening element around the clogged particles.

Where the constricting means for the screening element is a sheath or is in the form of bands, of a metal such as zinc, magnesium, or aluminum, a mineral acid such as hydrochloric acid can be used to disintegrate the constricting member, a conventional inhibitor being added to the acid to prevent corrosion of the steel well equipment. Inhibited acids of this type which can be used are those conventionally employed in acidizing wells. Where the constricting means is a plastic sheath or bands made of plastic, e.g., a cellulosic or a vinyl resin, an organic solvent which will readily dissolve the plastic is employed. For example, in the case of cellulose acetate-butyrate, the solvent may be a ketone such as acetons, and in the case of polystyrene the solvent may be an aromatic or chlorinated hydrocarbon. The plastic employed should be inert to oil and preferably also inert to acids.

We may also employ as the constricting means a sheath or bands composed of a material which will disintegrate by heat to release said means. Thus, we may employ certain alloys which will melt or disintegrate by contact with hot water or hot oil, preferably bismuth alloys. In this case, the temperature required for melting the particular alloy employed should be higher than the temperature of that portion of the well through which the liner passes and in which it is positioned, so that the constricting member will not melt or disintegrate before it is positioned at the desired location in the well.

In the above cases, the screening element employed should be constructed of a material which is inert to the means employed for releasing the constricting means. Thus, where an acid is employed for this purpose, the screening element should be inert thereto, and when an organic solvent is utilized for disintegrating said constricting means, the screen should be composed of a material inert thereto. Further, the screening element should not only be inert to oil, but also should be resistant to the temperatures encountered in the well.

Instead of gun perforating the casing and the adjacent screening element prior to removing the constricting member, we can first remove the constricting member to cause the screening element to expand into contact with the well bore wall, and then proceed to gun perforate, i In the latter instance the dissolving chemical solution or liquid can be spotted or placed in the well bore at the predetermined location of the screening element, prior to introducing the casing into the well bore, so . that when the screening element is in position adjacent the produc) ing formation, the constricting element will be disintegrated to permit expansion of the element, following which the gun perforating procedure may take place. Alternatively, the casing and screening element can first be positioned with said element adjacent the producing formation, and such dissolving solution then introduced in any suitable or known manner into the annulus between the screening element and the well bore to cause expansion of said element, followed by gun perforating.

If desired, an impermeable expandible robber ring or packer can be positioned around the casing above the porous screening element and below the cement plug.

According to another embodiment a surface string can be cemented in the well first and the casing containing the screening element thereafter inserted through said surface string’in the well bore, with the screening element

2,981,333 positioned below the cemented lower end of the surface string.

The invention will be more clearly understood by reference^to the description below of various embodiments thereof taken in connection with the accompanying drawings wherein:

Fig. 1 is an elevational sectional view of one form of the invention device, located in position in a well bore;

Fig. 2 is a horizontal section taken on line 2—2 of Fig. 1;

Fig. 3 is a view similar to Fig. 1, showing the screening element in expanded position against the wall of the bore;

Fig. 4 is a horizontal section taken on line 4—4 of Fig. 3;

Fig. 5 is a partial sectional elevation of a modification of the invention;

Fig. 6 is an elevational view of another modification of the invention; and

Fig. 7 is a detail of a modification of the structure of Fig. 1.

Referring to Figs. 1 to 4, a casing 10 is provided having connected to its lower end by means of a collar 11 a tubular member 12, said tubular member being closed off at its lower end as indicated at 14. Said tubular member 12 may be integrally connected to the casing 10 or it may be a separate element connected to the casing in any suitable manner, such as by a conventional tool joint. In any event, the tubular member 12 forms a part of the casing and is intended to be included in the term “casing” employed in the claims. A cementing shoe 13 is threadably connected to the lower portion of the collar 11 by means of external threads 15 on the collar.

A pair of spaced supporting rings 16 are mounted about the outer periphery of the tubular member 12 of the casing, adjacent the upper and lower ends of said tubular member 12. On member 12 and between rings 16 is supported a tubular or ring-shaped screening element 18 composed of sponge rubber, e.g., a butadienestyrene sponge, or other equivalent resilient foraminous or porous material noted above, said screening element 18 covering the major portion of the tubular member 12. Preferably the screening element 18 is connected to the outer periphery of pipe 12 by a suitable cement applied between their surfaces and which may cover only narrow peripheral portions near the top and bottom of the inner surface of the screening element and adjacent surface areas of the pipe 12, as indicated at 20. However, if desired, a greater surface portion between elements 12 and 18 may contain such cement. The cement should be one that will withstand temperatures up to about 250° F. or more, is insoluble in water and crude oil, and which will be inert to the acid or solvent used to disintegrate the constricting element, e.g. sheath 22, which is removed by chemical means as described below. Such cement can be employed, together with the supporting rings 16, or the cement can be used alone without such rings, or the rings 16 alone can be used to support the screening element 18 on the pipe 12. Cements which can be used for this purpose are well known in the prior art and may include, for example, cements of the phenol-formaldehyde or urea formaldehyde type, and the like. The sponge rubber element 18 is compressed by a cylindrical metal sheath 22, e.g., of zinc, magnesium, aluminum and the like, which fits tightly about the sponge rubber element 18. It will be seen in Fig. 1 that the outside diameter of the constricting metal sheath 22 and the outside diameter of casing 10 are each less than the internal diameter of the well bore 24, and also the shoe 10 has an outside diameter, slightly less than the internal diameter of the well bore, permitting passage of this unit through and into the well bore.

In employing the unit 25 including the casing 10, pipe 12 and the screening element 18 thereon, suchunit is in-: troduccd into the well bore 24 and is positioned therein with the screening element 18 adjacent the producing formation 26. This formation may be located either adjacent to the bottom of the well bore or it may be at any position along the well bore above the bottom thereof. . When the casing with the screening element 18 thereon is properly positioned in the well bore, a cement plug 28 is formed between the casing 10 and the wall of the bore, at a location just above the pipe 12 and the screening element 18 thereon. Such cementing is accomplished in conventional manner by passing cement through holes 30 in the lower end of casing 10 just above the shoe 13, into the annulus between the casing 10 and the well bore, the cement plug being supported by the shoe 13. It will be seen that the cement plug 28 produces a water shutoff substantially preventing drainage of water from the annulus above the plug into the annulus below between the screening element 18 and the well bore.

When the casing 10 has been cemented in place as described above, the pipe 12 and the screening element 18 thereon can be gun perforated by conventional gun perforating procedure well known in the art, forming the perforations 32 in the pipe 12, as shown in Fig. 3. Following the gun perforating procedure an acid solution such as inhibited hydrochloric acid, usually employed in acidizing wells, is then circulated through the bore 34 of the casing 10 and the bore 35 of pipe 12, through the holes 32 of the pipe 12 and the holes 36 shown in dotted lines and formed in the screening element 18 bv the gun perforation procedure, and into the annulus 38 between the constricting element 22 and the wall of the well bore. On contact of the acid solution with the metal sheath 22, such metal sheath disintegrates. Removal of sheath 22 results in partial expansion of the sponge rubber screening element 18 into contact with the wall 24 of the well bore, as seen in Figs. 3 and 4, and filling the annulus 38.

It will be particularly noted in Figs. 3 and 4, that during expansion of the sponge rubber element 18 radially outward into contact with the wall of the well bore, ⁴⁰ the sponge rubber also expans in a plurality of directions so that the sponge rubber material adjacent the holes 36 formed therein by gun perforation, expands radially inwardly into such holes substantially to the center thereof, as indicated by arrows 40. and essentially filling such holes. Thus, it is noted that while the screen element 18 expands radially outward from the pipe 12 to the wall 24 of the well bore, it also expands in a direction at a 90° angle to such outward expansion, e.g., in a direction axially along the casing 10 or well 50 bore. However, it should be recognized that such expansion of the resilient or sponge rubber element into holes 36 may not completely fill these holes, and small irregular passages 42 at the center of these holes may be formed when the rubber defining the walls of holes 55 36 is forced inwardly toward the center of the holes as shown in Figs. 3 and 4.

A screen such as the sponge rubber element 18 having an initial thickness of about 2 under full compression. may expand say 1 or one-half the original thick60 ness when it makes contact with the bore wall 24. The element 18 in the position shown in Figs. 3 and 4 has sufficient remaining resiliency or outward force so that it is hot pushed away from the wall by the pressure of the fluid passing from the producing zone 26 into the 65 screen 18.: The maintenance of the screening element 18 in substantially snug contact with the wall of the bore during the operation of the well not only prevents introduction of sand and earth particles into the annulus between the wall of the well and pipe 12, but also serves 70 to buttress and reinforce the wall of the bore against running sands and cave-ins of the earth and sand forming the walls of the bore.

If large particles of sand become clogged say in the^: passages 42 of the screening element as indicated at 44, this will not prevent flow of oil through the porous ele10

2.9ί 7 meht 18, but rather will simply cause the oil in the vicinity of such particles 44 to flow into and through the pores of the sponge rubber around such particles 44 and through the element 18 and into the bore 35 of pipe 12, via the holes 32. Also, the lodging of large sand par- 5 tides such as 44 in the pores of the screening element will prevent such abrasive particles from passing through such element and into the holes 32 of the pipe 12 and thus preventing abrasion of the metal around such holes 32 and undesirable enlargement of such holes. 10

The screening element 18 is maintained in the expanded position shown in Fig. 3 throughout the period of production of the well, or until after an extended period, the screening element may become unduly clogged and require replacement. 15

Instead of gun perforating prior to removal of the constricting element 22, as described above, we can spot the fluid such as hydrochloric acid employed for removal of the constricting element 22, in the portion of the well adjacent the producing zone 26 prior to introduc- 20 tion of the casing and screening element 18. We can then introduce the unit including the casing and the screening element 18 to its proper position adjacent the producing zone 26, and proceed to cement the casing in place as described above. When the constricting ele- 25 ment 22 contacts the dissolving liquid in the annulus 38 adjacent the well bore 24, the constricting element will disintegrate, permitting the screening element or sponge rubber member 18 to expand into contact with the well bore as described above. At this point, with the screen- ³⁰ing element 18 filling the annulus as shown in Fig. 3, we can then gun perforate to form the holes 32 in the pipe 12 and the holes 36 in element 18, the holes 36 being almost instantaneously filled by expansion of the resilient member 18 into said holes to form the con- ³⁵stricted passages 42 in the sponge rubber element 18, as described above. It will be understood that whether gun perforation is accomplished first, followed by removal of the constricting member 22, or whether the constricting element 22 is removed first followed by gun ⁴³perforation, the sponge rubber will expand in the same manner both outwardly toward the well bore and in other directions essentially at right angles to such outward expansion, to substantially fill the holes 36 formed in the screening element 18 as indicated in Figs. 3 and 4. 45

Instead of spotting the dissolving liquid for removal of the constricting element in the well bore prior to insertion therein of the unit including casing 10 and the screening element 18, we can instead first insert such unit in proper position in the bore with element 18 adia- 50 cent the producing formation, and thereafter pass the dissolving liquid down the annulus between the casing and well, bore past the shoe 13 to the annulus 38 in which is located element 18 and constricting element 22, to cause expansion of element 18 to the wall of the bore, followed bv cementing in plug 28 and gun perforating pipe 12 and element 18 as described above.

In Fig. 5 an expansible impermeable ring in the form of a conventional packer 50 is positioned on pipe 12 of the unit 25, above the permeable sponge rubber screening element 18, the packer 50 being mounted between supporting rings 52. When the unit 25 is induced into the well bore 24. When the unit .25 is introduced into the well bore 24, the packer 50 is in contracted position and has an outside diameter less than the diameter of the bore 24, to permit passage of the unit through the bore to its proper position with the element 18 adjacent the producing formation 26 at the bottom of the bore. At this time the packer, which is of conventional well known design, such as the disc wall packers marketed by the Larkin Company, Inc. of Butler, Pennsylvania, expands into contact with the wall of the well bore, as seen in Fig. 5; The procedures of cementing plug 28, gun perforating and removal of constricting element 22 can then be accomplished in any Of the desired .,333 s sequences described above. The packer serves to isolate the well zone below containing the screening element 18 from the well zone above, prevents the falling of cement particles from the cement plug 28 into the annulus adjacent screening element 18, and aids in maintaining pressures in the zone of the well bore below said packer.

It will be noted that in the modification of Fig. 5 employing the packer 50 together with the cement plug, there is provided a space 54 between the screening element 18 and packer 50. This space 54 permits testing of the well for water shut-off by usual methods, that is, by gun perforating holes through the casing or pipe 12 at 56 between the packer 50 and the. screening element 18, to determine whether there is any water drainage into the well bore from the formation 58 adjacent the space 54, thus indicating whether or not there is sufficient water shut-off accomplished by the members 28 and 50.

In Fig. 6 is shown still another modification wherein a surface string 60 is first set and cemented in position at 62 in the usual manner. A unit 66 including casing 68 and the elements 18 and 22 positioned at the lower end of the casing, as shown in Fig. 1, is introduced into bore 64 to the proper location therein. Removal of the constricting element is then accomplished by means of a dissolving solution followed by gun perforating of casing 68 adjacent member 18, and the member 18, or by gun perforating first followed by removal of element 22, causing the screening element 18 to expand into snug engagement with the wall of the well bore as shown in Fig. 6, and forming the constricted passages 42 in element 18, through multidirectional expansion of the resilient, e.g. sponge rubber, porous material of screening element 18. The provision of the surface string 60 cemented in position above the screening element 18 serves substantially the same purpose as the cement plug 28 of Fig. 1 and 3, namely, to form a water shut-off and protect against water drainage into the annulus between screening element 18 and the wall of the well bore. The well can be closed off at the top (not shown) to maintain pressures in the annulus 69.

Instead of employing a metal sheath such as 22, we can use a plurality of spaced metal bands such as indicated at 70 in Fig. 7 as constricting elements to hold the screening element 18 under compression. Also, we can use a plastic bag or sheath, or we can employ plastic bands or cords to compress the screen element, said plastic material being, for example, polystyrene. In these instances the plastic sheath or bands can be dissolved or disintegrated by means of a suitable solvent such as an aromatic hydrocarbon. We can also use a sheath 22 or bands 70 composed of bismuth or bismuth alloys, and disintegrate such sheath or bands by the application of heat. Suitable alloys are, for example, the following:

Table

<td rowspan="2"> Alloy. an</td><td colspan="4"> Composition in parts by weight</td><td rowspan="2"> Melting point, ⁰ F.</td>

<td> Tin .</td><td> Lead</td><td> Bismuth</td><td> Cadmium</td>

<td> c c 1 I 1 1 &gt; I I I I 1 I I III &gt;1 ill i i t i t 11 1 1 1 1 1 1 t 11 1 1 i</td><td> 4- 25 2 24.6 24.8</td><td> 8 25 2 28.1 22.1</td><td> 15 50 5 50. 53.1</td><td> 4</td><td> 140-160 203 221 230 250</td>

Where the well temperature is relatively low, we may use a lower melting bismuth alloy such as alloy A or B in constructing the above sheath or bands, and introduce hot water into the annulus between the wrapped liner and 70 well bore, for melting the alloy to remove said sheath or bands and cause the screen 18, to expand to the wall of the bore. When the well temperature is higher, we may use the higher melting alloys C, D or, E, and melt the alloy by circulating hot oil in said annulus to disintegrate the sheath or bands. It will thus be understood

2,0 that not only can we employ any suitable expansible scree screening element according to the invention, but we can employ any suitable form of restraining means to maintain said element in compressed condition for passage through the well bore or casing therein to the desired location in the well, and we can also utilize acids, solvents, or heat to disintegrate or remove said restraining means.

Also, instead of employing a chemical solution for disintegrating the constricting member, e.g. 22, holding the resilient screening element 18 in compression, we can employ as the constricting element a tape helically wound around the screening element, the tape being of a nature such that on gun perforation of the casing or pipe 12 and the screening element 18, as described above, such gun perforation through the tape will cause it to tear and disintegrate physically, permitting the screening element to expand to the well bore, while at the same time expanding to fill the holes, e.g., 36 shown in Fig. 3, due to multidirectional expansion of the material forming the screening element, as described above.

. From the foregoing, it is seen that the invention provides a facile method and novel apparatus, which permit removal of oil, water or other fluids from the production zone of a well, and passage of such fluids into the well bore of casing usually employed, without causing particles of sand and earth to be introduced into the annulus between the bore and the pipe or casing, and thus interfering with the flow of fluids into the well. Our method and device have additional advantages, for example, the expansible screening element when partially expanded and compressed against the earth forming the wall of the bore, helps to support the wall against collapse while at the same time being insufficiently compressed against said wall so that the well fluids can pass into and through the screening element and into the casing. Further, our de- 35 vice reduces the amount of earth particles introduced into the casing itself, and thus aids in preventing erosion and enlargement of the perforations formed in the casing according to the invention.

While we have described particular embodiments of our 40 invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.