US2779278A - Apparatus for perforating well casings - Google Patents

Description

Jan. 29, 1957 R. KLOTZ, JR

APPARATUS FOR PERFORATING WELL CASINGS Filed Feb. 19, 1947 INVENTOR. 5 05612 J cfi BY W United States Patent APPARATUS FOR PERFORATING WELL CASINGS Robert L. Klotz, In, Hazelton, Pa., assignor, by mesne assignments, to Borg-Warner Corporation, Chicago, 111., a corporation of Illinois Application February 19, 1947, Serial No. 729,655

8 Claims. (Cl. 102-20) The present invention relates to apparatus for perforating well casings, particularly in connection with oil or gas wells. Specifically, the present invention relates to apparatus for more efiiciently utilizing explosives in connection with perforating well casings.

There are several cases in the production of oil where well casing perforation is used. Thus, in the drilling of new wells, it is frequently desirable to case the bottom of a well, cement the cased well at the bottom to exclude water from the casing and then perforate the casing and cement to admit oil from the oil bearing formation into the casing. Again, it is frequently desirable to perforate a cased well at two or more points along the length of the borehole to permit oil to flow into the hole from two or more superimposed oil bearing formations.

Also, in the drilling for oil in the past, it was customary to drill through many deposits of oil which were not of the gusher variety so that when the well casings were sunk, such oil bearing deposits were rendered inaccessible so that the deeper lying more heavily yielding pockets of oil could be obtained. In recent years it has been found economically desirable and'commercially feasible to obtain the oil contained in the oil deposits through which prior wells had been drilled. To eliminate the cost of drilling new holes for new wells, it would be desirable toutilize the existing wells and perforate the well casings at the level desired to afford access to the oil at the various levels through which the prior wells had been drilled and the casings sunk.

In connection with perforating oil well casings, it must be remembered that the casing must not be damaged. It must merely be provided with a plurality of perforations through which the oil contained in layers of the earths surface through which the casing extends may enter the casing. Consequently, it is desirable to use explosive charges having a directionalized effect so as to produce a perforation rather than actual desctruction of the casing wall. The well itself may be filled up with concrete or other suitable filling material to the desired level thereby closing the lower portion thereof whereby pumping of the oil obtained through these perforations may be more advantageously accomplished. There has been developed a casing perforating gun which has had fairly widespread use. However, this casing perforating gun generally comprises special equipment not generally used by crews engaged in oil well and easing shooting. Furthermore, this perforating gun has been relatively expensive. It would be desirable to provide new and improved apparatus forcasing perforations which employs the same type of equipment common'ly employed by those engaged in oil .well shooting 2,779,278 Patented Jan. 29, 1957 vide apparatus for perforating well casings in which an explosive charge having laterally extending oppositely directed cavities therein for imparting opposed directionalization to the explosive energy developed upon detonation of the charge is employed.

It is another object of the present invention to provide apparatus for perforating well casings comprising a plurality of spaced charges arranged on a detonating element, each charge having oppositely directed cavities therein in order to provide a plurality of perforations at spaced points in the casing without damaging the casing.

Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present invention reference may be had to the accompanying drawing in which Figure 1 is a sectional view somewhat schematic of the apparatus of the present invention disposed in a well for perforation of the same;

Figure 2 is an enlarged view of a small portion of Figure 1 showing a sectional view through one of the explosive units;

Figure 3 is a sectional view taken on line 33 of Figure 2 assuming that Figure 2 shows a complete device;

Figure 4 is a sectional of Figure 3;

Figure 5 is a view taken on line 55 of Figure 2 to show an end view of one explosive unit assuming that Figure 2 shows a complete device;

Figure 6 is a sectional view taken through an explosive unit illustrating a modification of the explosive unit shown in the prior figures of the drawings; and

Figure 7 is an enlarged sectional view of a portion of view taken on line 4-4 an explosive unit showing still another modification of the present invention.

Referring now to the drawing and more particularly to Figure 1 thereof,'there is illustrated a cross-section taken through the earths crust designated as 10. Extending down into the earth is a well 11 which is bounded by a tubular casing 12, generally in the form of a metal tube. It will be understood that the well 11 and the casing 12 extend down through the earths crust and beyond casing may be filled up with concrete or other suitable material and the oil in the oil bearing strata which enters the well 11 may be removed by suitable means well known to those skilled in the art.

Since such oil bearing strata are often of substantial thickness, it is desired to perforate the casing 12 over a substantial length thereof such as a length of from 5 to 10 feet or the like. In order that this casing 12 may be perforated throughout this length with the desired number of perforations without requiring a large'number of successive perforating operations to be performed, there is provided in accordance with the present invention, a housing 13 which is in the form of a torpedo shell and which is ofsuch a diameter as to be readily inserted in well casings such as 12. 'It has been found that for casings having an internal diameter of 6" or 8", that a torpcdo shell or housing such as 13 having an external diameter of 4.8", is very satisfactory. According to Mechanical Engineers Handbook, Fourth Edition, the wall thicknesses for 6 inch casings varies from 0.280 inch to 0.69 inch and for 8 inch casings from 0.322 inch to 0 89 k i l shot cable 30 which may extend to any suitable detonating means such as 31 disposed above the surface at a safe distance from the well. The shell 13 is filled to the top with the filling material such as the sand 27. Under certain conditions it maybe desirable to provide a lid or closure member for the top of the shell 13. For example, a tar seal formed of melted tar poured into the topof theshellllaa above the sand when cooled, provides a very desirable waterproof closure member. It is obviously necessary to keep thehot melted tarproperly insulated and separate from the cap 28. V

In addition to assisting in. maintaining the explosive units in proper position in the housing, the filling material 27, performs several other important and desirable functions. First, it supports and,.reinforces the housing .13

against inward collapse under the external hydrostatic pressure of the fluid in the well, thus permitting the use of a housing ofless wall thickness than could be used without filling material. It is obvious that a reduction in housing wall thickness reduces the amount of fragmentized material left in the well, and also reduces the amount of energy of the jet which isexpended in perforating the housing. Secondly, the filling material serves to partially absorb and cushion the laterally directed shock wavesdeveloped by detonation of the explosive charges. This not only reduces the likelihood of damaging the well casing but also reduces the possibility that the shock wave from detonation of one charge may impinge on the next succeeding charge before the formation of its jet has been completed, with resultant deformation of the jet.

In order to insert the torpedo 13 into the well 11, suitable means not shown forming no part of the present invention may be employed. A lowering reel of some sort and a depth meter would be employed in the same manner as they are usedin connection with equipment used heretofore.

Although the various parts of the apparatus for perforating well casings described above may have various shapes and sizes, it has been found for example that if a seven foot section of 6" casing is to be perforated with eight holes per vertical foot of length or in other words, a total of 56 holes, the torpedo housing 13 should be approximately eight feet in length and as mentioned above, about 4.8 in diameter. This shell could be loaded with double-ended explosive units such as 15 spaced every 3" or'four-ended explosive units suchas 15 to be described hereinafter spaced every 6". The detonating cord 14 would extend from 6" to 12" both above and below the topmost and bottommost explosive units 15. Preferably the tubular members 16 are in the neighborhood of l" in diameter with a loading hole of about 1". As shown, each charge is approximately 3" in overall length and measures approximately 1 /2."'from the detonating cord 14 to each cavitated end of the charge. The opening 22 at the bottom of each tubular member 16 for the detonating element 14 should'be approximately three tenths of an inch. The capacity for the explosive 20 in the tubular member 16 should be such as to take about .0865 lb., the maximum amount of explosive which will not damage the casing 12 being desirable. If the tubular member 16 had a diameter of eight tenths of an inch instead of an inch, the charge would have an explosive capacity of only about 64 percent of what it would have if the l" tubular casing 16 were employed. a

It will be understood that although the explosive units 15 described above are provided with two oppositely directed cavities 18, explosive units employing one cavity or more than one cavity may be employed. It is preferable to employ two or multiples of two cavities to provide opposed directionalization of the explosive energy upon detonation of the charge. Accordingly, in Figure 6 there is illustrated an explosive unit 15' having four cavities 34 and 35. The pair of cavities 34 are arranged in opposed relationship as are also the pair of cavities 35,

thereby providing laterally extending oppositely directed cavities for imparting opposed directionalization to the explosive energy developed upon detonation of the charge. The four-ended explosive units shown in Figure 6 of the drawings would require somewhat less explosive, due to the common mid-section, than two double-ended explosive units, and to this extent, would be preferred since the amount of explosive required is substantially reduced where a large number of units such as are shown in Figure l of the drawing are employed.

It difiiculty is found in obtaining perforations of sufli cient size and regularity, particularly if the amount of explosive must be reduced to prevent damage to the casing, then the arrangement shown in Figure 7 of the drawings may be'employed. In this case a steel ball 36 of the desired size, preferably about one-half inch in diameter, is gummed as by means of gum 37 in the cone-shaped cavity 18, or if the four-ended explosive unit 15' of Figure 6 is employed, in the cavities 34 and 35. This steel ball 36 aids the portions of the cone such as the walls 19 thereof in producing the perforation in the well casing 12.

In view of the detailed description included above, the operation of the apparatus for perforating well casings described above, will be apparent and no further discussion is deemed necessary. With the present invention there is provided an arrangement for producing simultaneously alarge number of perforations over a predetermined area of the well casing. Furthermore, this apparatus may be employed by any one having the experience and tools common to oil well shooting and easing shooting without recourse to special equipment, as has been the case heretofore. In addition, the arrangement described is considerably less expensive and produces re sults at least as satisfactory, if not more satisfactory than prior art arrangements.

While there have been disclosed particular embodiments of the present invention, it will be apparent. that many changes and modifications thereof may be made. Accordingly, it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Well perforating apparatus comprising, in combination: an imperforate-walled housing adapted to be lowered into a well; a plurality of shaped explosive units, means mounting said units in said housing, each unit including an explosive charge having an outwardly facing cavity in at least one end thereof; means including detonating means interconnecting said units in assembled relation and positioning said units in positions spaced apart axially of said housing with their cavities facing the wall of said housing, said interconnecting and positioning means determining, independently of the said wail of said housing, the axial an angular spacing be tween adjacent units; said housing being of such material and wall thickness as to be perforated, upon detonation of said charges, without materially diminishing the well perforating elfectiveness of said charges; and means for detonating said charges.

2. Apparatus as set forth in claim I wherein each explosive unit comprises a container and a charge of explosive therein having an outwardly facing cavity in at least one end thereof, said container having transversely aligned openings defining a transverse passage through the unit; and wherein said interconnecting and positioning means comprises an elongated element threaded through said transverse passages in each of said units in succession.

3. Apparatus as set forth in claim 1, wherein the un occupied space within said housing is'filled with a pourable filling material comprising discrete particles with interspersed air spaces cooperating with said interconnecting and positioning means to maintain the axial and angular spacing of said units.

4. -Well perforating-apparatus comprising, incornbina- *tion: an imperforatewalled housing adapted to below- -ered into-a' well; a plurality of shaped explosive units, means mounting said units insaid-housing, each unit including-an explosive'charge-having an outwardly facing cavity-in at least one end thereof andea'ch having a transverse passage therethroug'h for =reception of a of said housing, and said housing being ofsuch material and wall-thickness as to be perforated, upon detonation of said charges, without materially diminishing the well perforating eiiectiveness of said charges; and means including said detonating element for detonating said charges substantially simultaneously.

5. Well perforating apparatus comprising, in combination: an imperforate-Walled housing adapted to be lowered into a well; a plurality of charge containers each of a length slightly less than the inner transverse dimension of said housing, means mounting said containers in said housing, each containerhaving a transverse passage therethrou'gh substantially in the median transverse plane thereof, said containers 'being positioned transversely in said housing with said passages in alignment substantially along the axis of saidhousing; an explosive charge in each container between its transverse passage and each end of the container, said charges having cavities therein facing each end of said containers; an elongated detonating element threaded through each of said passages; means coacting solely with said detonating element and said containers, and independently of said housing, for securing said containers in any desired spaced relation along said detonating element; and means including said detonating element for detonating said explosive charges substantially simultaneously.

6. Apparatus as set forth'in-"clain1 5, wherein each container is of generally-cylindrical form and includes means at each end thereof cooperatingwith said "housing to maintain the container with its'axis substantially perpendicular to the aixs ofthe housing.

7. Apparatus asset forth'in claim 5, whereinthe unoccupied space within said housing-is filled with a pourable filling material comprising discrete particles with interespers'ed air spaces cooperating with said detonating element to maintain the axial and angular spacing of said units. I

8. Apparatus as set .fort-hin claim 4, including a pourable filling material filling the 'sp'acesbetween 'and'around said units and cooperating with said 'deto'natin'g element to maintain the axial and angular'spacing of the units.

7 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES The Shaped Charge, an article by Torrey in The Explosives Engineer, July-August 1945.

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