IL25434A - Well completion apparatus - Google Patents

Description

C O H E N Z E D E K & S P I S B A C H R E G O . PA T E N T A TT O R N E YS ' 24, LEVONTIN STR., P. O. 8. 1169 T E L - A V I V P A T E N T S & D E S I G N S O R D I N A N C E 15198/66 SPECIFICATION IMPK0VEI4EHTS IH WELL COMPLB'TIOK ΑΡΓΑΚΑΤ113 SOLIS MYBOfi ZANDMIR, a cxtizen of Canada, of 111 Glen Avenue, Branff, alberta, Canada, DO HEREBY DECLARE the nature of this invention and in what manner the same is to be performed to be particularly described and ascertained in and by the following statement: This invention generally relates to well completion ( apparatus of the kind wherein duct-forming elements are secured to a bore hole casing or liner and may be caused to project laterally from the casing to make contact with a producing zone of the formation.

Considered from one aspect, the invention is particularly directed to closures for such duct-forming elements of the kind wherein an acid-soluble metal screw plug is threaded into an end of a tube, sleeve, conduit or the like duct or passage forming device (hereinafter collectively being referred to as "tube") of the duct-forming element for temporarily closing the tube and wherein, upon introduction of acid into the tube, the screw plug is at least partially dissolved or disintegrated in order to become dislodged from, and thus to clear, the respective tube end.

Considered from another aspect, the invention is concerned with valve-controlled low-restricting constructions for use in connection with such duct-forming elements for temporarily blocking the flow of fluid in one direction through a tube, while permitting limited flow of fluid into the tube in the opposite direc-tion, the flow restricting means being made of acid-soluble metal to . cause disintegration of the flow-restricting means by acid.

The invention is also concerned with screen or filtering means extending across the flow passage of the duct-forming tube for filtering out solid material, such as sand particles which may contaminate the entering oil or gas.

Until recently, bore hole casings or liners have been set In bore holes by a cementing process in which a cement slurry is forced down through the casing and then upwardly around the outside of the casing to fill the annular space between the exterior casing surface and the surrounding wall of the formation. After solidification of the cement, communication between the casing and the produc- by means of bullets or shaped charges which also penetrated the hardened cement to form passageways or ducts therethrough. This procedure is unsatisfactory as the bullets or charges tend to crack the cement around the passageways, thereby causing vertical communication, to wit, u land down movement around the casing from one perforation to another, This, in turn, prevents later selective treatment through each perforation to the formation at the end of each duct or perforation, since injected treating material could travel up or down through cracked cement without permitting selective control at the injected places; i. e. the stratum of the formation at the end of each duct.

More recently, an improved method and device for establishing communication between the casing and the producing zone has been suggested. According to this suggestion, a plurality of duct-forming devices are welded or otherwise secured to the outside of the casing in alignment with holes machined into the casing wall. These duct-forming devices comprise telescoping tubes or sleeves which are in a retracted position during the positioning of the casing in the bore hole. When contact with a producing zone is to be made, these telescoping tubes are caused to project substantially horizontally toward the formation wall to make contact with the pay zone and to establish a permanent link between the pay zone and the casing. The cement slurry is introduced into the space between the casing and the formation wall either before or after the lateral telescoping of the tubes so that the cement sets around the tubes and the casing. The telescoping tubes of the duct-forming devices, as previously proposed, are made of steel or the like acid resistant metal, and the outer tube ends which ultimately contact the producing formation are blocked by acid-soluble metal plugs which are lodged within the tube in a sealing manner so as temporarily to prevent passage of material through the tube. When communication between the pay zone and the the casing and into the laterally extending telescoping tubes to cause dissolution of the plugs. Extensive experiments and tests have' established that, irrespective of the strength and the nature of the acid introduced into the tubes, the plugs do not readily and rapidly dissolve unless proper circulation is ultimately provided for the acid. This is so because acid which attacks a surface of a solid acid-soluble material dissolves first the outermost layer or stratum of the material, whereafter the acid is prevented from effectively exerting its dissloving activity, due to the dissolution or reaction product or products which have a tendency to form a protective barrier or cushion between the surface to be dissolved and the acid. For this reason, fresh or unconsumed acid is prevented from contacting the subjacent stratum of acid-soluble material. This phenomenon is particularly pronounced in respect to acid attacking relatively small areas. Thus, for example, if one surface of a magnesium plate or disc is wetted with acetic acid, the acid almost instantaneously dissolves a thin surface layer of the wetted surface, whereafter, how-ever, the acid is rendered substantially inactive due to the formation of magnesium acetate which tends to lodge itself as a barrier between the surface to be attacked and the unconsumed acid, thereby preventing further effective attack of the unconsumed acid on the undissolved material. For this reason, it has been found that an excessive time is required to dissolve the metal plug in the tube referred to so as to cause dislodgement thereof from the tube.

Accordingly, it is one object of this invention to provide for a closure construction wherein the end of the acid-resistant metal tube of the duct-forming element which, upon projection, is intended to make contact with the producing formation is temporarily blocked by an acid-soluble metal plug of a construction that over-comes the prior art drawbacks referred to and that permits effective dissolution of the plug by the acid and ensures sufficient ultimate Another object of the invention is to provide an acid-soluble screw plug of the indicated kind having an external thread which meshes with a complementary interior thread of the tube and which is provided with means for effectively sealing the plug against the interior tube wall without impeding the action of dissolving acid.

Once the acid has eaten away a sufficient portion of the plug to dislodge it from the tube end, the outside pressure acting on the outer end face of the plug tends to hurl the plug towards and into the interior of the tube if the outside pressure is greater than the pressure prevailing within the tube.

Accordingly, it is still a further object of the invention to provide a closure construction of the kind referred to whick has means for retarding the inward movement of the plug until the major portion of the plug has been consumed.

In the previously suggested well completion apparatus with which this invention is concerned, the duct-forming devices are welded or otherwise secured to the outside of the bore hole casing in alignment with holes machined into the casing wall. When contact with the producing zone is to be made, the telescoping tubes are projected from their retracted position to extend laterally from the exterior of the casing toward the formation wall. This is accomplishe by pressurizing the casing. Since the rear end of the tube of each duct-forming device, to wit, the end which is in alignment with the respective hole in the casing wall, communicated with the interior of the casing while the front end of the tube, to wit, the end which is intended to contact the producing formation, is closed by the screw plug, pressure builds up within the interior of the tube. This pressure must be sufficient to overcome the retaining force of retaining means or the like to propel the telescoping tubes in a direction away from the casing and toward the producing formation. In practice, it has been experienced that due to malfunctioning or other misha s as for exam le fault assembl of the duct-formin devices, some of the tubes may sometimes be prematurely propelled toward the producing formation. This, for example, may happen during the lowering of the casing into the bore hole. If a tube has thus been prematurely projected away from the casing, the front portion of the tube which contains the terminal screw plug may be torn off by frictional contact with the formation wall with the result that free communication is established between the interior of the casing and the space surrounding the casing. This, of course, is highly undesired since it prevents effective build-up of pressure within the casing required to propel the tubes towards the formation at the desired time and may cause reentry of liquid cement from the outside into the interior of the casing.

Accordingly, it is a further object of this invention to provide a construction wherein the rear end of each duct-forming device is fitted with a flow-restricting safety means which permits greatly restricted flow of fluid from the interior of the casing toward the terminal screw plug, but which prevents flow of fluid through the tube into the interior of the casing.

A still further object of the invention is to provide a safety device of the indicated kind which, after positioning of the casing with its duct-forming devices in the bore hole and after projection of the tubes toward the producing formation, can at least partially be disintegrated or dissolved by acid so as to permit substantially unrestricted flow through the tubes in both directions.

A still further object of the invention is to provide a safety device of the indicated kind which is in the form of a screw cap and which is constructed so that after the flow-restricting means have been dissolved by acid, a seat surface is exposed on the cap at the location of the associated casing hole to permit blocking of the communication between e interior of the casing and the tube of the duct-forming device by means of a ball-shaped sealing means, liquid contained within the casing and thus has a tendency to be urged against said seat when liquid flows from the interior of the casing through the hole.

It is also an object of this invention to arrange filter or screening means across the flow passage of the ifeube to remove solid material accompanying the entering oil or gas.

Generally, it is an object of this invention to Improve on the art of wefcl completion apparatus having duct-forming elements as presently practiced.

Briefl , and in accordance with the first indicated aspect of this invention, there is provided wfell completion apparatus of the kind wherein a bore hole casing is adapted to be positioned in a bore hole and a duct-forming device of acid-resistant metal is secured to the casing in alignment with a hole machined in the casing wall, said duct-forming device being capable of being laterally extended from the casing for making contact with a producing formation, characterized in that the duct-forming^ device includes a terminal sleeve which is blocked and closed by an acid-soluble metal plug which upon introduction of acid into the sleeve is at least partially dissolved to become dislodged from its associated sleeve, and that a safety cap is secu&d to that end of the duct-forming device which is closest to the casing, said safety cap being substantially in alignment with the wall of the casing and located substantially within said machined casing hole and having a valve-controlled narrow passage which permits flow of fluid from the interior of the casing toward said plug but prevents fluid flow through the sleeve and into the interior of the casing, said safety cap at least partially being made of an acid-soluble metal.

According to an important preferred feature, the acid-soluble metal plug is constructed in the form of a generally cylindrical externally threaded body. The body is formed with an interior bore or cavity which extends inwardly from the rear end of the plug toward the front end, but which terminates short of the front end to leave a front portion of substantial metal layer thickness. The peripheral wall of the body which defines said bore or cavity has an annular zone of substantially reduced radial thickness which forms a diaphragm-like strip. When the plug is to be dissolved, acid is introduced into the rear end of the plug. The. acid enters the bore or cavity of the plug and rapidity dissolves the metal in the region of the annular zone of reduced radial metal thickness, to wit, the diaphragm strip.

The acid then exits outwardly through the opening in the diaphragm zone thus formed and flows along the external threads of the plug to cause rapid dissolution and disintegration of the plug.

According to a further feature of the invention, no chemical sealant is used for sealing the plug against the wall of the tube, but the sealing is advantageously accomplished by an O-ring which is positioned in a ggSB ve located behind the threads and adjacent the rear end of the plug. As is known, O-rings are extremely efficient sealing means and in fact the sealing action of an 0—ring is the greater the greater the pressure. Therefore, the provision - 7b of the O-ring adjacent the rear end of the plug effectively prevents entry of matter into the tube from the outside. The O-ring moreover blocks escape of material from the tube interior toward the outside. The diaphragm strip which is thus first dissolved and eaten through by the acid should be located ahead of the O-ring, to wit , between the O-ring and the front end of the plug so that the flow of the acid is not obstructed.

The annular diaphragm zone of substantially reduced radial thickness is preferably formed by cutting or working a relatively narrow groove into the interior body wall which defines the bore referred to. This groove should have a depth so that the remaining wall portion is extremely thin but, yet, of a strength sufficient to withstand the pressures acting on the plug. Since the diaphragm strip portion is protected from erosion and other forces which may prematurely cause its destruction, the diaphragm may be extremely thin.

In practice, it has been established that at bore hole depth of 15,000 feet for which duct-forming devices of the indicated kind are presently designed, excellent results are ob- tained if the thickness of the diaphragm strip is about between 0.030 to 0.040 inch.

After the acid has eaten through the diaphragm strip and has consumed a portion of the external threads, the plug becomes dislodged from its threaded engagement with the tube. In accordance with a further feature of the invention, the tube is provided with retarding or retaining means which are located behind the rear end of the plug and which advantageously may comprise a flange or" shoulder projecting from the interior wall of the tube in an inward direction so as to provide a seat for the plug against which the plug rests and which prevents inward movement of the plug. Thus, any tendency to urge the plug inwardly is effectively counter- acted. Only after substantially the entire plug has been consumed by the acid, will plug fragments be able to clear the shoulder to enter the interior of the tube.

Turning now to the second aspect of this invention, the flow-restricting means advantageously takes the form of a safety cap which is screwed or otherwise secured to the rear end of the duct-forming device at a location substantially flush with the interior wall of the casing and coinciding with its associated hole. A narrow passage is formed through the cap, con-veniently in the center thereof, with a check valve arranged on the cap to permit flow of fluid from the interior of the casing into the tube of the duct-forming device while preventing flow of fluid from the duct-forming device through the passage into the interior of the casing. The check valve is preferably of the ball check valve type.

While it is feasible to make the entire cap of acid-soluble metal, such as zinc or magnesium, according to a preferred embodiment the cap proper is made of steel in the same manner as the duct-forming device proper, the cap however having a central, circular insert of acid-soluble metal, preferably zinc. The valve controlled passage is located in the acid-3oluble insert and after the telescoping tubes have been projected into their operative position by pressurizing the casing, whereby fluid flow through the narrow passage in the insert causes projection of the tube, acid is inserted into the casing to dissolve and integrate the insert. The fluid which is used for pressurizing the casing may contain weak acid. The weak acid requires, however, a relatively long time to dissolve the insert with its valve, so that sufficient time is available properly to eject the telescoping tubes. The dissolution of the insert by the acid is, of course, facilitated by the provision of the passage through the insert, since this enlarges the contact surface available to the acid for attack. After the insert, including the valve controlled passage, has been destroyed by the acid, substantially unrestricted communication between the interior of the casing and the duct-forming device is thus established, since the remainder of the cap then defines a relatively large passageway.

According to a preferred embodiment of the invention, the acid-soluble insert of the cap forms an inwardly beveled or conical surface which bears against a complementarlly shaped surface of the acid resistant portion of the safety cap. After the acid-soluble insert has been dissolved by the acid, there thus remains the acid-resistant cap portion which defines a passageway having an interior diameter corresponding to the diameter of the acid-soluble insert and forming a conical peripheral seat surface. If this enlarged passage or passageway, during the operation of the well, is to be closed for any reason whatsoever, a ball sealer can be floated down and suspended within liquid in the casing to lodge itself against the conical surface in a sealing manner. The diameter of the acid-soluble insert and thus of the passageway formed upon dissolution should, however, be smaller than the dia- meter of the telescoping tubes to prevent undesired retraction or entry of the tubes into the interior of the casing should they in any manner become dislodged from their retaining means.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific object attained by its use, reference should be had to the accompanying drawings in which there is illustrated and described a preferred embodiment of the invention.

In the drawings : Pig. 1 is a fragmentary side elevation of a bore hole casing having a duct-forming device secured to its exterior surface, the duct-forming device including a terminal tube or sleeve which is closed by an acid-soluble metal screw plug in accordance with this invention. In order not to crowd the drawing, those elements and mechanisms of the duct-forming device which do not form part of this invention have been omitted; Pig. 2 is an end view of the front end of the inventive screw plug; Fig. 3 is a section taken along line 3-3 of Fig. 2; Fig. illustrates, partly in section and partly in side elevation, the screw plug as screwed into a sleeve or tube such as shown in Fig. 1, the tube being fitted with a filtering plate behind the plug; Fig. 5 is a sectional view along line 5-5 of Fig. 1 on enlarged scale; Fig. 6 is a sectional view along line 6-6 of Pig. 5; Pig. 7 is an end view of the safety cap of Fig. 5 seen in the direction of arrow B; Fig. 8 is a transverse section through the duct-forming tube on line 8-8 of Fig. H ; Fig. 9 is an enlarged elevation of the screen removed from the tube; Fig. 10 is a further enlarged section through the screen of Fig. 9, showing a screen composed of a metal core coated with a synthetic resin; and Fig. 11 is a view similar to Fig. 10, showing a screen made from a homogeneous body of synthetic resin.

Referring now to the drawings, and in particular to Figs. 1 and 5» a duct-forming device, generally indicated by refer casing 10. For this purpose, the bore hole casing 10, which has a machined hole or opening 99 as seen in Fig. 5> is provided with a nipple or mounting boss 98 which is welded to the exterior casing surface as indicated by reference numeral 97· The duct-forming device 100 has a hollow, cylindrical rear mounting portion 96 whose external thread 95 meshes with the internal thread 9^ of the nipple 98. Rear mounting portion 6 of the duct-forming element 100 terminates in a front collar or flange portion 93 which fits into an annular space 92 defined by the shoulder 91 formed by the nipple 98. A sealing means, such- as an 0-ring 66, may be inserted between the collar 93 and the shoulder surface 91 of the nipple 98. in order properly to seal the duct-forming element against the nipple 98.

For this purpose, the collar 93 is provided with an annular groove 89 as seen in Fig. 5. The general construction of the duct-forming device has not been illustrated but may correspond to that disclosed in U.S. patent application Serial No. 128,609, now Patent No. 3,245,472 The duct-forming device 100 projects laterally from the casing 10 and includes an outer or terminal inwardly threaded tube or sleeve 13 into which is threaded a screw plug generally indicated by reference numeral 50. The screw plug 50 is illustrated as not being fully screwed into the tube 13.

The construction of the screw plug is illustrated in detail in Figs. 2 and 3. It will be noted that the screw plug 50 has a body portion 1H which is externally threaded as indicated by reference numeral 15 > the external threads extending over about one half of the length of the plug.

An external peripheral groove l6 is cut into the plug adjacent its rear end 17 and an O-ring 18 of customary construction is lodged within the groove.

The interior of the body portion 1 is hollowed out to form an interior cavity or bore 19 which extends from the rear end 19 should not extend too far towards the front since the thickness of the front end 20 must be sufficient so as to be able to withstand the pressures which act on the free surface of the front end 20 from the outside. The thickness of the front end 20 of the plug 50 should also be relatively substantial since the front surface of the plug, during the lowering of the casing to near the bottom of the well bore, will consistently rub against the formation wall so that it must be able to withstand substantial impact, abrasion and friction forces. In accordance with the invention, an internal groove 21 is formed in the body portion 14 which groove 21 communicates with the bore or cavity 19 and forms a body wall portion 22 of substantially reduced radial diameter. Wall portion 22 of the plug is thus weakened and constitutes in fact a diaphragm-like strip. The diaphragm 22 is subject to rapid attack and destruction by acid.

Prom a practical point of view, experiments have demonstrated that for screw plugs of the indicated kind to be used in duct-forming devices at well depth of about 15,000 feet, the thickness of the zone 22 or diaphragm should be between about 0.030 and 0.040".

Pig. 4 illustrates the screw plug of Figs. 2 and 3 as screwed into a conduit or tube such as the tube 13 of Pig. 1.

The tube 13 is provided with an interior thread 25 which meshes with the exterior thread 15 of the plug. Due to the provision of the O-ring 18 lodged within the groove 16 of the plug, effective sealing between the plug 50 and the tube 13 takes place, thereby preventing entry of matter from the outside into the interior of the tube and at the same time preventing penetration of matter from the interior of the tube towards the outside.

It will be noted that tube 13 forms an annular shoulder portion 26 which provides a seat for the rear end 17 of the plug.

While the tubes should be of acid-resistant material such as steel or steel alloys, the plug must be made from an acid- A screen or filter member 120 in the form of a disc ox-plate is positioned across the flow passage 101 of the tube 13 near its forward end behind the plug, the screen member having essentially the same diameter as the flow passage 101. In order securely to position the screen member within the tube 13, the tube forms an interior flange or shoulder portion 102 forward of the screen to prevent forward movement of the screen member 120. A groove 104 is cut into the tube 13 closely adjacent the other side of the screeft' When the screen member 120 has been positioned within the tube, a split or snap ring 121 is inserted into the groove 104, whereby movement of the screen member 120 is effectively prevented. Of course, any other suitable means to secure the screen may be employed. The construction of the screen member will be described in detail further below.

The plug is usually screwed into the tube by means of a screw driving tool such as a screwdriver and for this purpose the fronC end face 20 of the plug is originally provided with a slot.

After the screw plug has been threaded into the tube, the slot is removed by grinding or the like machining of the end surface.

Referring now to Figs. 5 through 7, it will be noted that the hollow threaded rear mounting portion 96, which is screwed into the nipple 98, has an exteriorly threaded end portion 85. End portion '85 extends into the hole 99 formed in the casing wall 10. In accordance with the second aspect of the invention, a safety cap, generally indicated by reference numeral 80, has an internal thread 79 on a flange portion 49 which meshes with the external thread 78 of the end portion 85. The safety cap 80 may thus be screwed onto the end portion 85 and removed therefrom at will. Pigs. 5 and 6 show the cap in the operative position in which it is screwed onto the end portion 85. Cap 80 consists of steel or the like acid-resistant material, but has a central insert generally indicated such as zinc, magnesium or aluminum. The preferred metal, however, is zinc since it has the most desirable characteristics in respect to the resistance to the various pH values which may prevail in the well completion apparatus before the insert is to be dissolved by acid.

A passage 7 traverses the insert 75 and is provided with a ball check valve as seen in Figs. 5 and 6 . The ball check valve comprises a ball 73 which is lodged in a valve chamber 72 which in essence is an enlarged portion of the passage 7^ · The seat for the ball is provided by a conical surface 71 while the ball is retained within the chamber 72 by means of a star-like plate 70 as best seen in Pig. 6 . The plate 70 , in turn, is held in place by a bent-over flange portion 58 of the insert 75 · Of course, different means for retaining the ball within the chamber could be provided.

The acid-resistant body portion 69 of the cap 80 forms a conical or beveled surface 68 against which bears the compiementaril shaped conical or beveled surface 67 of the acid-soluble insert 75 . The acid-soluble insert 75 is held in position within the acid-resistant body portion 69 by means of an outwardly projecting flange 63 which projects beyond the shoulder 62 of the acid-resistant cap portion 69 · As previously mentioned, the star-shaped plate is held in position by a bent-over flange or retaining portion 58 . In practice, the acid-resistant portion 69 of the cap is first manufactured with a passageway of a diameter slightly smaller than the diameter of the acid-soluble insert 75 , whereafter the acid-soluble insert is pressed into the passage. By hammer action or the like, the flange 63 is then formed to retain the acid-soluble insert securely within the cap structure.

Cap 80 acts as a valve-controlled flow-restricting means since, due to the provision of the ball valve, fluid which narrow passage 71* and through the ball check valve Into the interior of the duct-forming device 100. By contrast, due to the provision of the ball 73 and its conical seat 71, any pressure exerted onto the ball from within the duct-forming device urges the ball against the seat 71, thereby preventing entry of fluid into the interior of the casing.

Referring now to Figs. 8 and 9, the screen disc 120 is provided with one or more openings of suitable con iguration and size to pass oil and gas but to retain on the outside of the screen particles of sand and the like solid matter. The axially extending side walls of the elongated openings 122 in the disc may be parallel to each other, or they may be inwardly divergent, or they may be both, as shown in Pig. 10.

In order to render the screen chemically inert or Inactive with respect to any chemical compounds which may be present in the fluids in the well, the screen ia preferably designed to have all exposed surfaces provided by a substance which is characterized by lack of chemical activity with respect to well fluids and also preferably one which has a low tendency to adhere to any solid hydrocarbons that may be present. One such construction of screen 120 for this purpose is illustrated in Fig. 10 in which the screen comprises a metallic body 12 which is coated with a non-metallic coating 125, preferably a coating of a suitable synthetic resin on all surfaces which are exposed to well fluids. It may be desired not to coat or cover the peripheral surface of the screen where it engages the side walls of the flow passage of the tube 13, but the front and back surfaces and the sides of the slots are preferably coated since they are exposed to well fluids and the corrosive action thereof.

A particularly advantageous plastic or synthetic resin for this purpose is tetrafluoroethylene, commonly sold under the o any other particles, particularly sand grains and also hydrocarbon solids that may be carried to the screen. All of the fluorocarbon resins are also insoluble in acids and consequently are chemically inert with respect to well fluids. Other synthetic resins may be entirely satisfactory for this purpose, such as polycarbonates, polyphenylene oxide and the various plastics such as nylon and the like.

Alternatively, the screen disc may be made from a solid or homogeneous body of synthetic resin, as shown at 126 in Fig. 11. The configuration of the screen is the same as before except that it is not a composite member as in Pig. 10.

It is also within the scope of the present invention to apply the same concept to other types of well screens. For example, the slotted type of screen can be made of metal and coated with a suitable synthetic plastic, as shown in Fig. 10. Other types of screens or orifice members which are smaller in diameter than the flow passage and capable of being supported in metal members can be made from a homogeneous body of synthetic plastic.

The operation of the device is as follows: In respect to the safety cap 80; After the casing 10 has been positioned within the bore hole and a cement slurry or the like has been pumped through the lowe open end of the casing to envelop the casing and to fill the space between the exterior of the casing and the wall of the formation, the pressure within the casing is increased to a value so as to overcome the tube retaining means and to propel the telescoping tubes of the duct-forming devices through the cement slurry and toward the wall of the formation to make contact therewith. The fluid which is used for this purpose enters the passage 74 and, since the check valve permits flow in the direction toward the screw plug 50, the retaining force of the retaining means which has prevented the pro However, in the event that the portion of the duct-forming device 100 extending beyond the collar 93, including the screw plug 50, should have prematurely been ejected and been torn or broken off due to faulty assembly or the like, entry of any material into the interior of the tube is prevented by the ball check valve since the ball, upon being subjected to pressure emanating from within the duct-forming device or from the outside, is urged against its seat 71 to block communication between the duct-forming device and the interior of the casing.

Further, even if the front portions of one or several duct-forming devices are broken off, pressure can still be built up within the casing to a sufficient value to eject the remaining devices. This is so because leakage through the narrow passages in the Inserts of the broken off elements can be easily compensated for by increasing the pumping speed. By contrast, in the prior art constructions without safety cap, the breaking off of a single duct-forming element resulted in a relatively large passageway from the casing to the exterior which seriously interfered with the operation .

Once the casing has been installed and the duct-forming tubes have been properly propelled into contact with the wall of the formation, acid is introduced into the casing to eat away and dissolve the acid-soluble insert 75 > whereby a relatively large passageway is formed in the body portion 69 corresponding to the size of the insert 75. If> at a later stage during operation of the well, communication between the interior of the casing and the duct-forming device is again to be blocked, a ball sealer can be floated down the casing interior, whereby the ball sealer will be pressed against the conical surface 67 of the acid-resistant portion 69 of the cap 80 to again block the communication.

If desired, the ball sealer may have a diameter smaller Insert 75 . If this is the case, the ball sealer will flow into the passageway. By providing a suitable seat (not shown) within the duct-forming device, the ball sealer is then urged against this seat to block the communication without projecting into the casing proper as long as the pressure is maintained within the casing.

It is also possible to provide an oil-resistant de-formable ball sealer which is slightly larger than the passaged-formed by the dissolution of the insert 75 but smaller than the passageway of the tube 13. By pressurizing the interior of the casing, the ball sealer is then pressed under deformation through the passage and into the passageway of the duct, where it assumes its original shape to block the communication. The effect can be still further increased by providing a conical seat surface in the inner side of the body portion 60 adjacent the insert 75 · If the pressure within the casing is released and the ball sealer is subjected instead to pressure from fluid flowing from the formation into the tube, the ball sealer is thus urged against the interior seat, thereby permanently blocking the passage. Such arrangement is particularly suitable if the wall is be blocked at a parti- e cular level while other levels are to remain open. The derformable ball sealer may be of any oil-resistant rubber or the like composition If the blocked passageway is to be opened at a later stage, a suitable solvent may be introduced into the casing to dissolve the deformed ball sealer.

The provision of the safety cap 80 has also additional advantages in the operation of the well completion apparatus.

After the telescoping tubes have been propelled toward the wall of the formation and the pressure is released within the casing, the presence of the acid-resistant portion 69 of the cap 80 effectively prevents entry into the interior of the casing of duct-forming telescoping tubes which have become dislodged or been broken off from their moorin s. This is so because as seen in the drawin s the tubes have a larger diameter than the diameter of the passageway which is formed after the acid-soluble insert has been eaten away. Generally, handling and operation of the well completion device is greatly facilitated by the provision of the safety cap 80 since it permits effective control of the device in a superior manner.

In respect to the acid-soluble plug: After the tube 13 with the plug 50 screwed thereinto has been moved from its retracted position within the casing 10 to the extended or projected position shown in Pig. 1, and the insert has been disintegrated by the acid, the acid enters the tube 13· If the plug 50 is made of magnesium or zinc, hydrochloric or acetic acid will normally be used or other organic or mineral acids may be employed. The acid thus enters the bore or cavity 19 of the plug and attacks the wall defining the cavity. Due to the provision of the groove 21 defined by the thin diaphragm wall portion 22, the diaphragm 22 is rapidly eaten through by the acid. The formation of the groove and its particular shape facilitate the acid attack on that region due to local accumulation of acid which speeds up the dissolution of the diaphragm zone. The acid, after having caused disintegration of the wall portion 22, flows within and around the valleys of the threads of the plug 50, as indicated by the arrow A. Since no chemical sealant is introduced between the meshing thread surfaces 15 and 25, the flow of the acid is unobstructed and rapid disintegration of the external surface of the plug 50 is thus caused. As soon as the threads 15 have been consumed to such an extent as to become dislodged from their mating engagement with the threads 25 of the tube 13, the external pressure acting on the front end 20 of the plug may urge the plug 50 towards the interior of the tube if this pressure exceeds the pressure within the tube. Due to the provision of the shoulder 26, the O-rlng 18 prevents the acid from reaching the rear end of the plug so that the front portion of the plug is consumed before the acid eats around the O-ring. Therefore, no large fragments of the plug are hurled towards the interior of the tube 13 > but only small pieces are flushed inwardly which may be formed by the disintegration of the plug.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims (9)

P.A.25434 File 15198 1.1.69 WHAT IS CLAIMED IS:

1. Well completion apparatus of the kind wherein a bore hole casing is adapted to be positioned in a bore hole and a duct-forming device of acid-resistant metal is secured to the casing in alignment with a hole machined in the casing wall, said duct-forming device being capable of being laterally extended from the casing for making contact with a producing formation, characterized in that the duct-forming device includes a terminal sleeve which is blocked and closed by an acid-soluble metal plug which upon introduction of acid into the sleeve is at least partially dissolved to become dislodged from its associated sleeve, and that a safety cap is secured to that end of the duct-forming device which is closest to the casing, said safety cap being substantially in alignment with the wall of the casing and located substantially within said machined casing hole and having a valve-controlled narrow passage which permits flo of fluid from the interior of the casing toward said plug but prevents fluid flow through the sleeve and into the interior of the casing, said safety cap at least partially being made of an acid-soluble metal, said acid-soluble metal plug being in the form of a generally cylindrical, externally threaded body having a front end and a rear end and being formed with an axial bore extending frontwardly from its rear end but terminating short of its front end to define an open rear end and a closed front end, the peripheral wall defining said bore having an P.A.25434 Pile 15198 1.1.69 annular zone of substantially reduced radial thickness between said rear and front enda; whereby, upon introduction of acid into said casing and said bore, the acid will rapidly eat away said annular zone for penetration of the acid externally of the plug to eat away the threads of a id plug. - 22a - 1 2.¾. Well completion apparatus as claimed in claim 3·, wherein said plug is threadedly engaged with an interior thread in said sleeve whereby, upon introduction of acid into said casing and said bore, the acid will rgpidly eat away said annular zone for penetration of the acid externally of the plug to eat away the threads of said plug interengaged with the threads of the associated sleeve; and wherein sealing means are inserted between said plug and the associated sleeve adjacent the rear end of said plug and forming an acid-resistant seal between the rear end of said plug and the associated sleeve.

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3· . Well completion apparatus as claimed in claim 3·, wherein said sealing means comprises an O-ring lodged in an external peripheral groove formed in said plug body adjacent its rear end. 4.5.. Well completion apparatus as claimed in any one of the preceding claims, further comprising retaining means secured to the interior wall of said sleeve behind said plug to prevent movement of said plug into said sleeve.

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5.6·. Well completion apparatus as claimed in claim §, wherein said retaining means is in the form of an inwardly projecting annular shoulder. 6.7·. Well completion apparatus as claimed in any one of claims 1 - Is, wherein said acid-soluble portion of the safety cap is made from zinc. Well completion apparatus as claimed in any one of

6 claims 1 - wherein the flow through said narrow passage is controlled by a ball check valve.

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8· . Well completion apparatus as claimed in claim i, wherein the ball of said ball check valve is retained by a cage ' provided on the cap at a location facing said plug, said valve forming a beveled seat surface adjacent said passage against which the ball is urged in sealing manner upon occurrence of fluid pressure in a direction toward said casing.

9. -i-θ. Well completion apparatus as claimed in any one of the preceding claims, wherein said cap has a body portion of acid-resistant metal and a central portion of acid-soluble metal, said central portion containing said valve^eontrolled passage. 9 10li-T Well completion apparatus as claimed in claim 1-Θ-; wherein said central portion is made of zinc. 11·¾¾. Well completion apparatus as claimed in claims 9 10 It-G- and 1-1·, wherein said acid-resistant body portion has an interiorly threaded flange portion for meshing with an exteriorly threaded end portion of said duct-forming device, whereby said cap can be screwed onto said threaded end portion. 12 ά-3-·· Well completion apparatus as claimed in claims 9 11 i-θ - 4-2, wherein said acid-soluble central portion has an inwardly beveled peripheral surface portion which engages a complementarily shaped surface portion of the acid-resistant body portion, whereby, upon dissolution of the acid-soluble center portion, a substantially conical seat surface is formed on the body portion for receiving a ball sealer located within said casing. 13.1 -. Well completion apparatus as claimed in claims 9 11 ] ½ wherein an interior seat is provided in the duct-forming device for receiving a ball sealer of smaller size than said central portion after said central portion has been dissolved by acid. 14.fc . Well completion apparatus as claimed in claims 11 1-0- - W-, wherein said passage is adapted to be blocked by a deform- able ball sealer after the central portion has been dissolved by acid . 15.-t&. Well completion apparatus as claimed in any one of the preceding claims, wherein the flow through said narrow passage is controlled by a ball check valve, the ball of said valve being retained by a cage located on the central portion of the cap at a location facing the plug, said cage including a flange portion on said central portion for retaining the ball. 16.1-7-. Well completion apparatus as claimed in any one 9 15 of claims 10- - 16-, wherein the diameter of said central portion is smaller than the diameter of said sleeve. 17Jr&.. Well completion apparatus as claimed in any one of the preceding claims, wherein a screen member is positioned across the flow passage of said sleeve. 13 Well completion apparatus as claimed in claim 17 1-8, wherein the screen member has an exposed surface of a material which is characterized by chemical inertness with respect to well fluids and low adhesion to solid hydrocarbons. 19"2&, Well completion apparatus as claimed in claims 17 18 ¾8 or if, wherein the screen is either made from metal coated with a plastic inert to well fluids and having low adhesion to solid hydrocarbons ; s;u.ch as, for example, a fluorocarbon, or is entirely made from such plastic. 202ϊ. Well completion apparatus as claimed in any one 17 19 of claims 1-& - 2©, wherein the screen has a plurality of slots whldh are either parallel, divergent or both. 21.¾*. Well completion apparatus constructed, arranged and adapted to operate substantially as herein described with reference to the accompanying drawings. &ATSD THIS 10th day of March, 19©6. QQW£* ZSZVk &. SrISflACH P. O.BOX ilb9f ϊ-iL-A VIV A t orneys fox Appl icants - 26 -