US 2696169 A
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Description (OCR text may contain errors)
Dec. 7, 1954 J. B. LASSI TER, JR
SHAPED CHARGE WELL-PIPE PERFORATOR Filed April 10, 1948 INVENTOR. Joszph B. Lassifaqlin BQL QQAL United States Patent Office 2,696,169 Patented Dec. 7, 1954 SHAPED CHARGE WELL-PIPE PERFoRAToR Joseph B. Lassiter, Inn, New London, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware Application April 10, 1948, Serial No. 20,331
1 Claim. (Cl. 10220) This invention relates to improvements in well perforators employing shaped charges.
An object of this invention is to provide an improved form of well casing and formation perforator using a shaped charge type of penetrator.
A broad object of this invention is to provide an oilwell casing perforator constructed to obtain uniform tubing or casing perforations thereby to achieve uniform pressure drop into the well bore and hence maximum producing elficiency.
An important object of this invention is to provide an oilwell gun perforator employing shaped charges resiliently mounted in the gun body to insure a constant and uniform stand-off for all charges in order to obtain uniform penetrating forces and thereby produce more or less uniform perforations in the well tubing or casing, surrounding cement casing, if any, and the formation.
Another object of this invention is to provide an improved form of tool for this purpose in which the penetrating charges are resiliently mounted on the tool body to provide a centering action for the tool body and to permit the perforator units to'move with respect to the tool body as they engage irregularities on the interior of the well casing.
Another object of the invention is to provide a construction of this type which permits of using a tool body of smaller diameter, thus facilitating its passage through the well casing.
Another object of the invention is to provide in a device of this kind a tool body of frangible material or a soft material as well as the usual more solid rigid materials such as steel.
Another object of the invention is to provide in tools of the more durable form a structure in which the shaped charge units may be easily inserted and replaced by new units as they are used.
Other and more detailed objects of the invention will be apparent from the following description of the embodiments thereof illustrated in the attached drawings.
This invention resides substantially in the combination, construction, arrangement and all as will be hereinafter described.
In the accompanying drawings Figure l is a vertical, central, cross-sectional view through a section of a cased well bore showing the perforator tool of this invention partly in elevation, partly broken away and partly in cross-section;
Figure 2 is a longitudinal, central, cross-sectional view through one of the perforator units and the supporting structure therefor; and
Figure 3 is a longitudinal, central, cross-sectional view through a modified form of perforator unit showing the exploder unit as a detachable and replaceable element.
The uses and advantages of shaped charge penetrators are well known. By focusing the explosive force at the point of penetration of the well bore casing a clean hole is made and the formation in back of the hole is opened up to cause the well to flow. This invention is concerned with structures by means of which such penetrators may be used with greater facility.
Referring to the drawings, a well bore with its casing is illustrated in vertical section. The body of the tool is preferably of circular cross-section and as shown is of considerably less diameter than the internal bore of the casing 10. It will readily be appreciated that a still greater difference in respective diameters may be effected when desired, thus insuring against the tool sticking in relative location of parts,
the casing permitting its easy passage through the casing.
The body of the tool 15 may be made of the usual materials and when desirable can be made of a frangible material such as a molded plastic or of glass so that it will disintegrate upon explosion of the charges. There will result from the disintegration of the tool body small fragments which can be easily pumped out of the hole. When it is made of the more solid and durable materials as previously explained, it can be made of considerably less diameter than the bore of the casing, so that it will easily pass therethrough. It can also be made of some soft material such as lead or other highly malleable material which will resist the force of the explosive shock when the penetrators are fired but which, if stuck in the well bore, can be pulled out as it will easily groove or tear.
The usual weights 13 are attached to the top of the tool body by means of a threaded connection, for example as illustrated at 14. The tool is secured to a hoist cable Ill by means of a suitable detachable fixture 12. The cable 11 can be prepared with the circuit wire or wires in it by means of which the charges are detonated. The weights have a central passage as shown through which the circuit wire or wires pass, and if desired a suitable electrical coupling fixture can be included or enclosed in the threaded stem 14. The body 15 can be molded with a central passage as shown in which the circuit wire or wires 40 can be inserted or placed when the body is formed.
A suitable number of penetrators 16 are provided, the details of construction of which are shown in Figure 2. The tool body 15 is provided with a series of radial recesses 18 at suitable longitudinal and circumferential points on the tool body. Slidably mounted therein are the sockets or receptacles 20 which are held in place by means of the threaded rings 19. A spring 21 is interposed between the base of the recess 18 and the base of the socket 20 so as to normally urge it radially outwardly.
As illustrated, the shaped charge comprises a suitably shaped metal housing 24 having an internally threaded thickened ring 25 for threaded attachment to the socket 20. The ring 25 forms a shoulder which stops against the ring 19. The shaped charge is diagrammatically illus trated at 26 and is provided with a thin suitably shaped covering 27, all in accordance with the art of explosives. A detonator of Well known construction is shown at 23 mounted in the end of the charge and arranged to engage an electrical contact when the entire penetrator unit 22 is threadedly mounted in or on the socket 20. A flexible circuit wire or connection 41 extends from the detonator 23 and is connected to the circuit wire 46. It will be understood that a one or two wire system may be used, depending upon whether or not a grounded circuit is employed.
The space of recess 18 in back of the socket 20 is connected to the atmosphere by one or more passages 17.
It will be seen that in the use of this device as the tool is lowered into the well casing it is held in substantially centered position by means of the projecting noses of the perforator units 22 which of course are designed so as to serve the function of resilient guides as they move along the casing wall. If any particular unit encounters an obstruction it is forced back into the recess 18 until the obstruction is passed and then is again urged outwardly by the spring 21. Thus, the noses of the units 22 ride along the walls of the casing following the irregularities thereof and maintaining an overall centered position for the tool. As previously mentioned, the shoulders formed by the rings 25 cooperate with the rings 19 to limit the outward radial movement of the units 22.
When the tool is positioned opposite the formation to be perforated the charges may be detonated from the surface by completing the electrical circuit represented by the wire or wires 40 and 41. As is well understood in the art, all of the perforators may be discharged at once, they may be discharged individually or in predetermined groups assuming, of course, that the proper circuit connections are provided in a well known manner.
The explosion of the charges causes the perforation of the well casing 10 and the earth formation in line therewith including, of course, any cement casing or other intervening wall.
When the charges explode the impact reaction causes thesockets20to be driven into the recesses 18 against the action of the springs 21. The passages 17 permit air pressure equalization so that this action can take place.
The pressure equalizing passages 17 also prevent the heavy head of drilling mud into which the perforator may be immersed from forcing the charge and its holderlil inwardly against the resistance of springs 21 and the compression of the air in the spring recesses 18. If these passages were not provided the drilling mud head might cause the charges to recede, thereby changing the standoff distance and thus defeating one of the objects of this invention of establishing uniform stand-off for the charges.
In the case of a frangible tool body when it is shattered it will break into fragments which can easily be pumped out of the well. After destruction of the tool body the weights 13 can be withdrawn by means. of the. cable 11.
If the sockets are made of sufficiently durable matcrial they are available for reuse in the case where the tool body is also of durable material. To insert new perforator units 22 the rings 19 are removed and new units attached to the sockets by means of the threads provided for that purpose. The rings 19 are replaced and the tool is ready for further use.
In the construction shown, in Figure 3, the gun perforator body is diagrammatically illustrated at 15 having a radial bore or passage in which is slidably mounted a socket 20,015 suitable construction. The socket 20A is held in the recess by means of a removable externally threaded ring 31 and is spring loaded as indicated at, 21 so that it is. normally held against ring 31. The socket 20A is provided with a recess which is threaded at 28 and provided with a contact 30 to which the circuit Wire or wires 29 are connected. The exploder unit comprises a suitably shaped casing 32 of any suitable material such as thin metal which is provided at one end with an externally threaded extension 33 for engagement with the threads 28 of the recess inthe socket. The housing 32 is provided with a re-entrant recess in which the detonator charge 23 may be mounted in a position to engage the contact 30 when in assembled relation so that it may be electrically detonated. Within the metal shell 32 is a thin-wall member 27 made of some suitable material such as metal of either a soft or hard variety and forming a liner defining the shape of the forward face of the explosive charge 26. The liner 27 together with the nose portion 32 of the shell 32 forms a cavity or space 34.the overall longitudinal length of which defines the focal length of the charge, that is the distance between the concave side of the charge 26 and the nose 32' of the shell 32. This is sometimes known in the art as the standoff distance and by reason of such construction of this form of the device the, uniform stand-off distance is secured, thereby achieving uniform penetration of the charge. The exact shape of the liner 27 does not specifically form a part of this invention as it is intended that it may assume various shapes suitable to the proper determination of the focal length of. the charge and its maximum penetrating efficiency.
From this construction it will be readily seen that the exploder unit comprising the shell 32 and its charge can readily be replaced somewhat in the manner of replacing an electric light bulb by unscrewing the remaining fragments of the shell after use and replacing it with a new exploder unit.
Experience with shaped charges substantiates the assertion that satisfactory penetration depth through casing, cement and formation is obtained with relatively small quantities of explosive charges suitable for the purpose. The disintegration of shaped charges of this type results in the formation of a high velocity jet having high penetration forces which are especially effective for casing penetration purposes as there is produced a clean unobstructed passage through the casing, surrounding cement and formation, without seriously splitting or bulging the casing. In addition by the use of the structure herein disclosed there is produced a substantially uniform penetration resulting in a uniform pressure drop in the penetrated formation. A uniform or constant stand-off distance not only insures uniform penetration but also uniform diameter of the hole made. it is also to be understood that by varying this stand-off" distance the hole diameter and depth of the penetration hole may be changed at will.
The feature of constant and-uniform stand-off for all charges is secured in both forms of the invention herein disclosed irrespective of any irregularities in the tubing or casing.
As will be clear from the spirit of the whole disclosure the tool herein disclosed is also of utility in open hole completions especially in limestone areas. In open holes where there is no casing to be penetrated charges up to four or five pounds of explosive may be used for deep penetrations. When the tool is provided with a flexible tool body it will be seen on consideration that the size of the charge is limited only by the diameter of the hole. Thus deep penetrations in open hole completions are facilitated by means of the subject matter of this invention.
Those skilled in the art will readily appreciate that the cavity in the charge may be either a void or it may be filled with some suitable material for the purpose that upon detonation intermingles with the high velocity stream of gas produced to increase the penetrating'force.
It will be understood by those skilled in the art that other forms of sockets can be provided and other means of detachably securing the perforator units thereto may be employed. I do not, therefore, desire to be strictly limited to the detailsof the construction illustrated herein, but rather by theiclaim granted me.
What is; claimed is A gun perforator'for an oilwell casing, comprising a gun bodyhaving a plurality of longitudinally and circumferentially spaced and radially extending recesses, a perforator unit slidably mounted in each of said recesses, and means for resilientlyurging said units outwardly of said body, each unit including a shaped charge having a focal point for said charge and a nose piece of such length as tobrir g the focal point of the charge-into coincidence with the end of the nose piece and with the inner wall of said casing and at least one passageway in said body extending from said recess to the exterior of said body to vent the recess.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,210,125 Raymond et al. Aug. 6, 1940 2,362,738 Yarbrough Nov. M, 1944 2,399,2ll Davis et al. Apr. 30, 194-6 FOREIGN PATENTS Number Country Date 28,030 Great Britain Dec. 13, 1911 OTHER REFERENCES Journal of Applied Physics, vol. 19, N0. 6, pp. 563582, June 1948.
Popular Science, February 1945, pp. 66, 67, Article, Propelled Hollow Charges.
Explosives Engineer, pp. -163, July-Aug. 1945, TheShaped Charge.