US2974589A - Jet perforators - Google Patents

Description

March 14, 1961 P. J. BRYAN 2,974,589

JET PERFORATORS Filed June 3, 1957 2 Sheets-Sheet 1 Big. 1 Fig.2

zaZ Yg 4 6 o o/K INVENTOR PAUL JOHN BRYAN March 14, 1961 P. J. BRYAN JET PERFORATORS 2 Sheets-Sheet 2 Filed June 3. 1957 IN VEN TOR PAUL JOHN BRYAN ATTORNEY Patented lll'iar. l4, 1961 2,974,589 JET PERFORATORS Paul John Bryan, Philadelphia, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed June 3, 1957, Ser. No. 663,285 2 Claims. (Cl. 102-40) The present invention relates to a novel unit and assembly for perforating oil well casings.

After an oil well has been drilled, the well walls must be cased to prevent the entrance of undesired fluids and solid material into the Well. The casing consists of a metal pipe cemented in position; In order to prepare'the well for oil production, the casing and the cement layer must be perforated at the portion surrounded by the oilbearing strata. This step is known as well completion. For many years, bullet perforators were used to punch the holes through the casing and cement; these perforators consist essentially of a barrel containing a charge of a propellant explosive and a solid projectile. More recently, much of the well completion has been performed by using shaped charge perforators in place of the bullet perforators. The shaped charge perforators consist essentially of a charge of a high-velocity detonating explosive having a metal-lined concavity, usually conical. Upon detonation of the charge, the liner is expelled in the form of a high-velocity jet having excellent penetrating power.

Until recently, the completion of the well by perforating the casing preceded the installation of the smalldiameter tubing through which the oil flow from the producing zone of the Well to the surface is controlled. In this type of completion, the perforators are mounted in tubular, sealed, pressure-resistant carriers in such position that the axis of the perforator is perpendicular to the surface of the well casing. The carrier is lowered to the desired depth in the well and the charges initiated. To prevent the well from flowing before the valves can be installed and set, the perforating is done while the heavy drilling muds are still in the well. The muds provide a hydrostatic pressure great enough to prevent the oil from the perforations. After the charges have been fired and the carrier removed from the well, the tubing is installed and the valves are set on the tubing. The heavy drilling muds are displaced by lighter fluids and the production of the well begun.

This system of well completion is advantageous in that no debris from the perforating operation remains in the well. On the other hand, the carriers are ditficult to handle because of their size, weight, and inflexibility; they are very expensive and can be used only several times before major repair or discard is required, and failure of the fluid seal of the carriers may cause extensive damage to the well in addition to the carrier because of the pressures generated by the confined explosive charge. In addition, the heavy drilling muds, due to their great hydrostatic pressure, flow into the perforations in the casing and may clog the perforations.

A variation of the foregoing procedures involves the use of individually sealed perforating units mounted in an expendible frame, usually a steel strip, instead of the sealed carrier. This modification reduces the handling and cost disadvantages of the sealed carrier but in turn has the disadvantage that metal debris is left in the well, which debris seriously hinders well operation.

A more recent procedure for well completion, the socalled through-tubing method, involves the perforation of the casing after the tubing and valves have been set in place. In this procedure, the heavy drilling muds are removed before the perforating charges are introduced. Because of the small diameter of the tubing, perforating units designed to be lowered in a position perpendicular to the casing walls must be very short. Loss of penetrating strength due to the small size is inevitable. In addition, before the casing is of considerably larger diam eter than the tubing, the bullet or jet will have to pass through considerable fluid before it reaches the casing, thus decreasing even more the depth of penetration through the casing.

The foregoing objection has been overcome by an alternative through-tubing method in which perforating units are used which are so designed that they can be lowered through the tubing in such position that their longitudinal axis, i.e., the direction in which the jet is projected, is" parallel to'the axis of the tubing." When the units have passed through the tubing and are in the large-diameter casing, the units are swung to a perpendicular position.

This latter well-completion procedure is advantageous in that the perforating equipment is relatively light and easy to handle, no expensive carrier is required for the perforating units, the heavy drilling muds are not present to clog the perforations, and additional perforation servicing can be done without pulling the tubing. On the other hand, the present tilting perforators require a relatively intricate mechanism to provide the support and pivot action needed; such mechanism is subject to jamming or failure to operate in which case the bullet or jet is not directed properly toward the casing. Moreover, considerable debris is produced in the well and an auxiliary initiating device, for example a length of Primacord extending the entire length of the assembly, must be used to provide the initiating stimulus for each unit. Use of this auxiliary device often causes mechanical and handling difficulties.

Accordingly, an object of the present invention is to provide a perforating unit and assembly which can be used Without a carrier or other complicated holding device and Without an auxiliary initiation means. A further object is to provide a perforating unit and assembly which produces only a minimum amount of debris in a well. A still further object is to provide a perforating unit and assembly for through-tubing well completion, which unit and assembly can be swung into firing position without the use of intricate mechanisms. Other objects Will become apparent as this invention is more fully described.

I have found that the foregoing objects can be achieved when I provided individual sealed shaped-charge perforating units so constructed that they can be. joined one to the other, either directly or through an explosive-filled connecting link, to form a chain of perforators, the joining elements on the said units being so located that the jet produced by the detonation of the first charge in the sequence will provide the initiation stimulus for the second charge, whose jet will in turn provide the initiation stimulus for the third charge, and so on for the entire chain. The joining elements will further be so constructed that the individual units can be joined in axial alignment to permit lowering through a tubing, and, subsequent to such lowering, can be rearranged without separation to perforate the walls of the casing.

In order to more fully illustrate my invention, reference is now made to the accompanying drawings. In the drawings, Figure 1 illustrates schematically a chain of perforating tuiits within a tubing of an oil Well; Figure 2 illustrates schematically the same chain of perforating units in perforating position within the casing of an oil well; Figure 3 is a detailed view of a portion of a chain in which the units are assembled in accordance with one embodiment of this invention; and Figure 4 is a detailed view of a portion of a chain in which the units are assembled in accordance with an alternative embodiment of the present invention.

Referring now particularly to Figures 1 and 2, 1 is the natural wall of the well formed by the drill, 2 is a metal casing within the well, 3 is a filling cement beween casing 2 and Well wall 1, 4 is a tubing within casing 2, and5 is a spacing element'used to center tube 4 within casing 2. All of the foregoing represent typical well construction features.

6 represents a perforating unit constructed in accordance with the present invention, 7 is an initiating device attached to the uppermost unit 6, 8 is a lowering line attached to the top unit 5, and 9 is a positioning means attached to the bottom unit 6., 7

Referring now to Figure 3, 10 is a-case body, 11 is a case cover, 12 is charge of a high-density detonating explosive, 13 is a metal liner in concavity 14 of charge 12, and 15 is a booster charge. The foregoing perforator components are conventional inthe art. 16 and 17 are pivot elements externally positioned on case cover 11 and body 10, respectively.

In Figure 4, the parts are as in Figure 3, with the exception that the perforating units 6 are connected indirectly by a tubular link 18 containing a column of detonating explosive 19, one end of the link being attached to pivot member 16 of one unit and the other end to pivot member 17 of the adjacent unit.

The functioning of an assembly in accordance with this invention is as follows. After the units have been properly positioned with respect to casing 2, initiator 7 is actuated, for example, by application of a firing current. The booster charge 15 of the uppermost unit is initiated by the actuation of initiator 7 and in turn initiates the main charge 3.2 of this unit. Detonation of charge 12 produces a high-velocity jet of molten metal issuing in axial alignment with the cone 13', this jet passes through pivot element 16 completely disintegrating all material in its path, and then perforates the easing 2, cement layer 3, and continuing on into the strata surrounding the well wall 1 until the energy of the detonation has been expended. The passage of this jet through the pivot element 16 initiates the booster charge 15 of the next perforating unit in the chain. This sequence is continued along the chain of perfo rators, In 7 the embodiment shown in Figure 4, the sequence is as described, except that the jet after passage through the pivot element 16 passes through the end of the connecting link 18 and initiates the explosive in column 19 which in turn initiates the booster charge 15 of the next perforating unit in the chain.

The following examples serve to illustrate specific embodiments of the perforating units and assemblies of the present invention. However, they will be understood to be illustrative only and not as limiting the invention in any way.

7 EXAMPLE 1 Four perforating units were made up and assembled as shown in Figure 3. In the 'units, the main charge comprised 18 grams of waxed RDX and was 1.31 inches in diameter, and the booster charge comprised 2.7 grams of RDX pressed (200 pounds pressure) into a bronze shell in 8 increments. The booster and main charges were assembled in aluminum cases, and a copper conical liner having a 60, As-inch-radius apex and 0.025-inchplates as the targets. The assembly disintegratedupon thickwalls was inserted in the concavity of the main testing, and the performance of the assembly is summarized in the following table.

Table 1 Entry Hole Diam. tin.)

Depth of P enetration (111.)

EXAMPLE 2 Four perforating units were made up and assembled as shown in Figure 4. The units were prepared as described in Example 1 with the exception that the booster charge comprised 0.5 gram of RDX pressed at 200 pounds pressure and the cases used were about 3 inches in length. The units were assembled by means of connecting links attached to the pivot elements of the units. Each link was prepared by pressing at 200 pounds approximately 3 grams of RDX, in 10 increments, into a pair of slidably engageable metal shells, each shell having one end closed and provided with means for engaging the pivot element. The assembly was tested as afore-described and, upon detonation of the explosive charges, disintegrated. The results obtained were as follows:

Table II Unit No. Entry Hole Depth oiPen- Diam. (in) etration (in) O. 44 3. 0D 0. 42 3. 1O 0. 44 2 7G 0. 42 3. 42

The perforating units and assemblies of the present invention are easily prepared and assembled, and give excellent results, not only from the point of view of extent of perforation but also with respect to the limited amount of debris produced. The case portions 10 and 11 and connecting link 18 are so constructed that they resistthe extremely high pressures encountered in well bores. When these. components of the assembly are made of a nonductile material, such as for example, plastic, glass, or aluminum, the detonation'of the enclosed explosive charges will pulverize most, if not all, of this material, so that no objectionable debris will be produced. Thus, a preferred embodiment of this invention is the'use'o-f a nonductile material. for the case and the connecting link. However, the use of more ductile materials, e.g. steel, for these components of the assembly is also within the scope of the present invention.

'The design of the case and cover of .the perforating unit essentially is that used conventionally for shaped charge perforators. The cover is sealed into place in the case, for example by force-fitting or by an O-ring, to give a liquid-impervious unit. The external pivot members 16 "and 17 on the cover and case, respectively, advantageously oif (distance between the concavity end of unit and well casing) and spacing between units. Therefore; these dimensions will vary, depending upon the s'izeof well tubing and casing and the distance desired between perforations. In general, well tubing of about 2 inches in inner diameter and casing of about 5 inches in inner diameter are used in the preparation of oil wells. Therefore, the unit for use in such Wells be designed to have a diameter of slightly less than 2 inches, e.g. about 1% inches, and a length such that the effective diameter of the assembly when in firing position will be slightly less than 5 inches, e.g. about 4% inches. The length of the connecting links, when used, also will influence the spacing between units and thus between perforations, and hence, this factor will be considered in selection of the length of the connecting links.

The perforating unit is so designed that when in firing position its axis forms with the longitudinal axis of the well casing an angle of to 90, a 30 angle giving minimum'practical depth of penetration and a 90 angle giving maximum depth of penetration. Although, as previously discussed, the perforating units and assemblies of the present invention preferably are used in well casing of a diameter slightly greater than the effective diameter of the assembly in firing position, the flexibility of these assemblies is such that they also can be used in well casing of diameter slightly less than the diameter of the well casing for which they were designed.

The main and booster charges of explosive and the charge liner are those conventionally used in shaped charge perforators. The main and booster charges may comprise the same high-density detonating explosive, such as the exemplified RDX, or the main charge may comprise one of such explosives, e.g. pressed PETN, while the booster charge comprises another explosive, e.g. RDX. Other suitable explosives comprise trinitrotoluene, pentolite, tetryl, and the like. The explosives may be pressed into the case or else they may be molded or cast into the desired shape and then positioned in the case. Although the specific high-density detonating explosive used in the units of the present invention is not critical, RDX, because of the ease of handling and because of the excellent results obtained by its use, is preferred. In general, the main charge is about 18-25 grams in weight but may be more or less depending upon the kind of performance desired. The aforementioned high explosives, especially RDX, also are suitable for use as the continuous train of explosive in the connecting links. The continuous train of explosive extends substantially the entire length of the connecting link.

The metal charge-liner conforms to the concavity in the main explosive charge and conventionally is made of a thin metal, for example, copper, steel, aluminum, and so forth. The angle of the apex of the liner generally is between 30 and 90, depending upon the dimensions of the main charge and the depth of penetration desired.

The critical feature of the present invention is the connection of the perforator units to each other either directly or indirectly by means of connecting links containing a detonating explosive. Thereby, the need for a carrier and for auxiliary initiating means, e.g. Primacord, to initiate each unit is eliminated, and the units can be lowered through the small-diameter well tubing with their axis parallel to the axis of the tubing and when the assembly is at the desired position, the units can be aligned into firing position, i.e. with their axes directed towards the wall of the well casing, without resort to intricate mechanisms. Although the exact method for aligning the units is not critical and does not form a part of the present invention, the method illustrated in Figure 2 is simple and can be readily used to effect the desired alignment. In this method, two lengths of cord or cable are attached to the assembly, one length being attached to the uppermost unit and constituting the lowering line 8 and the other as a yoke to the lowest unit, forming the positioning device 9. When the lowest unit reaches the desired position in the well casing, the yoke attached to this unit, one end of the yoke to the front and the other the assembly,

to the back, is held taut, while the lowering line is allowed to slacken until the units fold in upon themselves and thus maintain themselves in firing position.

As has been illustrated, the initiator, which may be one of the type of electric blasting caps specially designed to resist the high temperatures and pressures encountered in well bores, preferably is attached to the uppermost unit of the assembly, in order to minimize the length of elecric conducting Wires and facilitate handling and lowering of the assembly. However, the initiator may also be attached to the lowest unit of the assembly, in which case the arrangement of the units illustrated in the accompanying drawings is reversed.

Both embodiments of the assembly, i.e., the direct connection of the units or indirect connection by means of the connecting links, give satisfactory results. The selection of the embodiment used in a given instance depends upon the depth of penetration desired. The directly connected units give penetrations not so deep as those given by the indirectly connected units, because the jets from the former units enter the well casing at an angle whereas the jets from the latter units enter the casing perpendicularly. In many instances, very deep penetrations are not required, and, thus, the directly connected units are selected for use. The use of these units is especially advantageous in perforating oil-bearing strata in which greater oil flow results from perforations of large area rather than from deep penetrations. In cases in which deep perforations are required, the assembly which contains the connecting links is used.

The invention has been described in detail in the foregoing. However, it will be apparent to those skilled in the art that many variations, for example the attachment of propagation detonators to selected perforating units in are possible without departure from the scope of the invention. Therefore, I intend to be limited only by the following claims.

I claim:

1. An assembly for perforating oil wells comprising a plurality of perforating units and a tubular connector joining said units, each of said units comprising a charge of a high-density detonating explosive having a conical concavity at one end lined with a conforming metal liner, a pressure-resistant case body completely surrounding said charge, a pressure-resistant case cover sealed to said case body at the concavity-containing end of said charge in such a manner as to provide an unobstructed chamber at said concavity-containing end and as to form a liquidimpervious container, an external pivot element on said case cover in axial alignment with said conical concavity, and an external pivot element on said case body in axial alignment with said conical concavity, said tubular connector being provided with an external pivot element at each end and containing a continuous train of a highvelocity detonating explosive extending substantially the entire length of said connector between said pivot ele ments on said connector, one end of said connector being pivotly secured to the external pivot element on the case cover of one of said units and the other end of said connector being pivotly secured to the external pivot element on the case body of another of said units.

2. An assembly according to claim 1, wherein the highvelocity detonating explosive contained in the tubular connector is RDX.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CETTFTCATTN 0F CGECTTQN Patent No., 2 974 589 March l l 1961 Paul John Bryan It is hereby certifiedthat error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1. line 43 after them first occurrence,

insert flow of column 2 line 3 for "before" read because column 5 line 5 after 'wells" insert will Signed and sealed this 8th day of August 1961,

Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OF CORECTTON Patent No a 2 97 1 589 March 141 1961 Paul John Bryan A It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1, line 13 after "the" first occurrence insert we flow of column 2 line 3 for "before" read me because column 5 line 5 after "Wellsf" insert will Signed and sealed this 8th day of August 1961.,

(SEAL) Attes t:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

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