US2669928A - Perforating device for wells - Google Patents

Description

1954 w. G. SWEETMAN PERFORATING DEVICE FOR WELLS 2 Sheets-Sheet 1 Filed June 15. 1948 W. 6. SWEETMAN 4 l?) //c A; 127/ IN V EN TOR.

ATTORNEY W. G. SWEETMAN PERFORATING DEVICE FOR WELLS v Feb. 23, 1954 2 Sheets-Sheet 2 Filed June 15, 1948 FIG. 4-A

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FIG. 5

W. G. SWEETMAN IN V EN TOR FIG. 4

ATTORNEY Patented Feb. 23, 1954 q;

UNITED STATES ATENT OFFICE PERFORATIN G DEVICE FOR WELLS William G. Sweetman, Houston, Tex.

Application June 15, 1948, Serial No. 33,062

2 Claims.

This invention relates to a perforating device for use in perforating well casings, especially in oil and gas wells.

Conventional perforating methods employ various forms of heavy metal guns which are arranged to fire projectiles through the easing into the surrounding formations for providing access passageways from the formations into the well casing for production of oil and gas. Due to space limitations and other conditions encountered particularly in deep wells, the effectiveness of such present gun perforating methods is considerably limited and present bullet-type uns are sometimes totally ineffective for penetrating well casings as well as the often thick layer of cement which is generally interposed between the casing and the face of the formations lining the well bore.

More recently, in an efiort to overcome the disadvantages of the conventional gun perforation methods, particularly to provide greater penetrative force, there has been proposed the employment of charges of detonating explosives having hollowed ends facing the casing to be perforated. B-y thus employing the so-called cavity" effect, perforation of the casing and the surrounding cement may be effected with or without the use of a projectile and greater perforating effectiveness may be obtained from such charges than is possible with the more conventional bullet-type gun.

As presently designed, guns using the cavity charges, employ a, heavy metallic body, having the charges inserted therein and provided with detonating connections extending through the body and connected to an electric firing cable by which the tool is suspended and lowered into the Well. Such gun bodies, particularly when they are designed to carry a plurality of perforating charges, as is required in most instances, are ordinarily of very heavy construction in order to be able to withstand the very heavy pressures generated by detonation of the charges without deformation of the body. Such gun bodies are relatively expensive to build and require careful machining to close tolerances for proper reception and sealing of. the charges and firing connections, and their re-use, therefore, becomes essential for economic considerations. Also in the event suchgun bodies should become broken or lost in a. well, the well may become plugged there- -by and because of their heavy metallic construction, they may be very difficult to drill-out or fish-out of the well.

Accordingly, it is a primary object of the present invention to provide a charge carrying body for perforating guns which is of very simple and cheap construction; which may be completely disintegrated and expended in use without plugging the well; and which is highly effective in operation.

An important object is to provide a fully disintegrable gun body carrying cavity charges for perforating a well.

An additional object is the provision of a perforating gun body constructed of such a monolithic frangible material having a plurality of perforating charges embedded therein.

Another object is the provision of a perforating gun body constructed of a monolithic frangible material having perforating charges embedded therein and enclosed in a disintegrable fluidtight casing constructed of non-metallic, flexible material, such as rubber, rubber-like plastics and the like, or of light easily shatterable metal.

A further object is the provision of a perforating gun having a body constructed of Portland cement or the like, in which the perforating charges are embedded during formation of the body.

Other and more specific objects and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings which illustrate useful embodiments in accordance with this invention.

In the drawings:

Fig. 1 is an elevational view of a section of a well device in accordance with one embodiment of this invention;

Figs. 2 and 2a, together, comprise a longitudinal sectional view of the perforating device;

Fig. 3 is a cross-section through line 33 of Fig.

Figs. 4 and 4a constitute a longitudinal sectional view of the perforating device, employing a somewhat modified form of firing train; and

Fig. 5 illustrates still another embodiment in accordance with this invention.

Referring to the drawings, the perforating device or gun in accordance with the illustrative embodiment of this invention comprises an elongated generally cylindrical structure, designated by the letter G, which is adapted to be inserted in a well. Structure G includes an elongated generally cylindrical body It having a head H at one end thereof and an end-piece I2 at the opposite end thereof. Body It is constructed of a cementitious, monolithic, frangible material to be described in greater detail hereinafter.

Head II will normally be constructed of a heavy metal such as steel and is adapted to be recovered for re-use, while end-piece 12 will ordinarily be constructed of a relatively brittle and easily shatterable material, such as cast aluminum, magnesium, or various solid plastics and which is expended in use. Extending longitudinally through body ID are a plurality (two illustrated) of reinforcing rods I3 which are fastened to head I l, as by means of the threaded portions indicated at M, or in any other suitable manner. The opposite ends of rods l3 extend through the opposite end of body 18 and are adapted to be slidably received in sockets l5 provi'dedin 'endpiece 12. A plurality of perforating units, indicated generally by the numerals 15, are 'embedded in the material forming body H], as will be described in greater detail hereinafter. Perforating units l3, which are generally cylindrical in outline, are disposed at right angles to the axis of body and are longitudinallyspa'ced from each other and angularly oriented relative to each other, so as to produce any desired perforation pattern. One or more stripsof flexibledetonating cord IT, commonly known in'the explosive art as Prima-Cord, are threaded through the body and suitably connected to the explosive charges contained in the several units [.3 in 'a manner well understood in the explosive art for providing a detonating train for the :several charges. The ends of the Prima-Cord strips are led into head I I through an axial passageway l8 which communicates with the interior of an internally threaded socket l9 carried by the outer 'end of head I l. A sealing plug [8a is provided at the entrance to passageway It to seal the end .of "the passageway about strips ll. Socket I9 is adapted to receive a threaded pin member '20 .which'is carried by the end of a lowering cable 21 in which is enclosed an electrical conductor lead The latter is threaded through an axial passageway 23 in pin member 20, being suitably insulated therefrom, and connects to an electrical contact 14, which is mounted in the lower end of passageway 23. A tubular bushing 25 is screwed intoithe lower end of passageway 23 and carries on its upper end, insulated therefrom, an electrical contact 28 which is adapted to be put into conductive connection with contact when bushing has been properly screwed or otherwise inserted into passageway 23. Bushing 25 is provided with an axial bore 21 in the lower end of which is inserted an electrical 'detonating fuse 28 of conventional form, which is connected by wires 29 to contact 23 and to the' metallicportions of the pin member 20, which forms "the ground for the firing circuit. When pin member 28, carrying the electrical connectionsand fuse '28, as described, is screwed into socket l9, fuse '28 will extend into passageway 18 into 'detonating relationship to the ends of the Pr-ima-Cord strips. A pellet 30, composed of a'suitable-booster explosive, may be inserted between fuse 2-8 and the ends of the Prima-Cord strips to additionally assure the setting-off of the Prima- Cord strips upon detonation of the fuse. "It'will be'understood that the fusing arranging describ'ed is :more or less conventionalrand is one of many conventional arrangements which may be .employed for setting-oif-substantially simultaneously astringxof explosivecharges. Accordingly, it will be understood that theparticular type of ifusing or firing arrangement employed for setting-off the perforating charges is not, .of itself, -;a critical feature of this invention.

Each of the perforating units 16 consists of a generally cylindrical shell 3| closed at its opposite ends and which will ordinarily be of sectional construction. In the form illustrated, the shells, which may be constructed of a metallic or nonmetallic, easily shatterable material, such as aluminum, magnesium, or various plastics, are formed of two parts adapted to be joined together by means of a telescoping friction-type joint 32 "intermediate the ends of :the unit. iEx'tendin generally diametricallythrough one "end of shell 3| is an opening 33 through which the Prima- Cord strip is threaded. Enclosed within each ashell 3lisra "charge 34 of detonating explosive of any of the well-known highly brisant types, such as *tzini'trdtdluene, pentaerythritoltetranitrate, :trimethyleneatrinitramine, and the like. These explosives are employed in highly compressed forms "and are normally molded to the desired shape, being provided on the end facing the wall of zthe 'well to be .:perforated with =a cavity 35 which may be generally conical, hemispherical or of other suitably hollowed shape, well "known ini'theexplosive art asadapted to concentrate'the 7 force of the detonation of the charge substantially along .the axis of thecavity in the direction facedthereby. Thehollowed'end of the charge is preferably spaced inwardly a suitable distance from the end of the enclosing .shell, depending generally upon theangle of the cavity and the degree 'of'penetration-desire'd, and a thin metallic liner 36 of shape complementary to that-of :the .cavityis installed'against-th'e face of the'cavity. -A pellet .31 of a suitable booster :explosive is inserted in the center .of the :opposite end of the charge'contiguous toith'e Prima-Cord.-strip. opening 38 is provided .in the adjacent end 701 shell 3| for insertion of the pellet :31 and a threaded 'plug 39 ;is adapted to be :screwed .into opening 38 to close the latter and taforce 'th'e Prima-Cord strip into close contact 'with pellet 3:1 and .theend of charge 34. The lengths "of the shells 31 are generally .made substantially equal .to the diameter .of z'boidy l 0 .so that-the zshellcends will be .flush with atheface of the body.

;Body In is constructed of.a .cementitiousmono- 'lithic material which is adapted to The cast for molded about .the perforating charges, so that the latter :and the Prima-Cord" strips will 'be firmly embedded'itherein when the structure has been completed, and become, in effect, an "integral part :of the body. In every case,'-the:maiteri-al'will'be one which, when it hasbeen' 'allowed to harden, will have a crushing strength which will withstand the hydrostatic pressures which may be encountered ina well, and which, at 'the same time, will be highly frangible sozthat, .up'on detonation rof the perforating charges, the date-- natinjg force will thoroughly shatter the body into small pieces which may be easily bailed or washed out of the well, or evenzifdeft-inithe W511, will not form :a plug therein. 1.

Materials which satisfactorily imeet ,thesezree quirementsdnclude various Portland cementmixtures, iplaster iOf Paris, :and the :like. The aper ticular mixes emp1oyed,:the1curing times, .etc. will, of course, be varied'toimeetuparticularEconditions under which :the ,guns :are ato :be srun, the ."mixes andzpreparations conditions necessary tofpro duce a monolithic cnaterial :of the :desired :prcp'erties beingwellknown by those skillediin ithe Jar-t.

The perforating device will normally be constructed: in the following manner: .Head 41' iWlllbB placed in the inverted position. Rods -|3 will be screwed into the-headand will extend upwardly.

If 'flexible wires areused in place of the stiff rods I3, the free ends of the wires will be supported in'any suitable mannerto hold them straight during construction of the gun. Perforating units I6 will then be attached to rods I 3 in any suitable or convenient manner, as by means of wires 5&1 (see Fig. 3). Rods I3 form a supporting frame on which the charges are hung in any desired arrangement to produce the desired perforation pattern. Prima-Cord strips I i are then threaded through openings 33 in the respective groups of shells and plugs 39 are inserted in the ends of the shells and made up tightly. The firing ends of the Prima-Cord strips are passed-through plug I811 and into passageway I3, plug I8a being forced into the end of the passageway to seal it tightly A cylindrical mold (not shown): of any suitable and conventional construction is then placed about the charge-carrying structure to enclose the latter with head I I forming the bottom of the mold. A slurry of the material of which body Ill is to be constructed is then poured into the open top of the mold to fill the latter and bring the top or" the body material to a point just below-the outer ends of rods I3; The-material is then allowed to set and harden to form the solid body-I0 in which the perforating charges I6 will be firmly embedded and completely sealed therein. Rods I3 will provide reinforcement for the body to prevent its cracking in handling prior to detonation of the charges. Head II may be provided witha grooved socket, indicated at M, to provide additionally firm attachmentbetween head II and body Iil.- A metal end ring 52 may be embedded in the upper end of body I0 before it hardens to form a seat for end-piece I2 and to protect the outer edges of body It against cracking or spalling during handling prior to detonation. After body ID has hardened to the desired degree, end-piece I2 will be placed over the protruding ends of rods I3 and pushed firmly against the end of body II]. The mold will then be removed from about the body and the primary gun structure will be complete. 1 Where the gun is to be employed in a well containing Water or other well fluids which will subject the gun to substantial hydrostatic pressure, this invention provides an additional protective feature in the form of sleeve 40 which is adapted to form a fluid-tight casing for body Ill to prevent direct contact of anywell fluid with the body or any of the explosive materials or connections carried thereby. 'Sleeve 40 maybe constructed of any of the natural or synthetic rubbers or of any other flexible plastic material which, under external pressures" will become tightly compressed about the body and thereby improve its sealing action. To additionally assure tight sealing by sleeve 48, head II and endpieoe I2 may be provided with series of grooves or notches M and 42, respectively, in which the ends of sleeve 40 will be tightlyv compressed by means of suitable compression rings 43.

It will be understood that sleeve 40 need not be employed in cases where the perforating device is run in a well in which there is no fluid present. In cases where only relatively small hydrostatic heads are likely to be encountered, sleeve 40 may be merely a seal coat for the body and may be obtained by dipping or spraying body ID with a suitable plastic material, which, when suitably dried, will form a fluid-impermeable coating for the body.

Sleeve 40 may, if desired, be constructed of thin metallic material, such as sheet aluminum, mag- 6. nesium, brass, or iron which will form a fluidtight seal about body ID but which will shatter or tear into relatively small pieces upon detonation of the charges.

The gun, constructed as described, is prepared for firing by inserting booster pellet 30 in passage-'- way I8 between the ends of Prima-Cord strips I I, and then screwing pin member 20, carryin fuse 28 into socket I9. The device is then lowered into the well opposite the point thereof in which perforations are to be made, and electric current, supplied from any conventional and suitable source on the surface, will be transmitted through cable 22 to detonate the charges. Upon detonation, the explosive forces will be directed by the hollowed ends of the charges against the casing and the surrounding well bore to effect the desired perforation thereof. At the same time, the explosive forces will act to completely shatter body II], as well as shell 3! which enclose the several charges, and will effectively disintegrate these parts. Similarly, end-piece I2 will be shattered, the latter being cored out at 44 to reduce its mass and provide a relatively thin section in the center thereof which will give way easily under the shattering force of the explosion of the charges. All of the broken material will then fall to the bottom of the well and because of its rather complete disintegration may be easily washed-out or bailed-out of the well, or easily ground up, if desired, by drilling. After detonation, head II, which will usually be found to be unaffected by the detonation of thecharges', will be withdrawn from the well and'may be re-us ed in the manner previously described in constructfing another gun.

As indicated previously, the perforating charges will be arranged in any pattern desired prior to embedding them within body Iii. It will be understood that any number of such charges may be'employed and may be spaced as closely or as widely as desired. I

It will be understood that various more or less conventional support and reinforcing members, suoh as wires, may be employed instead of the stiff rods E3 in constructing the gun.

" From the foregoing, it will be evident that the perforating device constructed in accordance with this invention may be made very cheaply and, when set off, the body and perforating units will be thoroughly disintegrated without undesirable damage to the well. The device is found to be highly efiicient in operation and by use of the cavity charges particularly will produce deep and effective penetration of well casing, the formations lining the well bore, and the usual cement liners normally placed between the casing and the well bore. v

It will be understood that while the frangible type gun body herein described is primarily designed for carrying cavity type perforating charges, such bodies may also be employed for carrying the more conventional bullet type charges.

Figs. 4 and 4a illustrate another embodiment in accordance with this invention, differing from that previously described only in the specific form of firing train employed to set off the perforating charges.

In this embodiment, an electrical detonating fuse 53, very similar to fuse 28 of the previous embodiment but normally having incorporated therein a pellet (not shown) of a suitable booster explosive, corresponding to pellets 31, is inserted axially into the rear ends of charges 34. All 01'

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