US3014424A

US3014424A - Shaped explosive charge

Info

Publication number: US3014424A
Application number: US725404A
Authority: US
Inventors: Delacour Jacques
Original assignee: Societe de Prospection Electrique Schlumberger SA
Current assignee: Services Petroliers Schlumberger SA
Priority date: 1957-04-01
Filing date: 1958-03-31
Publication date: 1961-12-26
Anticipated expiration: 1978-12-26
Also published as: CH345828A; GB883664A; DE1068645B; FR1170520A; BE565361A

Description

Dec. 26, 1961 J. DELACOUR 3,014,424

SHAPED EXPLOSIVE CHARGE Filed March 31, 1958 WA @QQQ FIG. 3.

INVEN TOR. JACQUES DELACOUR s A TTORNEYS 3,014,424 SHAPED EXPLOSIVE CHARGE Jacques Delacour, Paris, France, assignor to Societe de Prospection Electrique, Procedes Schlumberger, Paris,

France, a corporation of France Filed Mar. 31, 1958, Ser. No. 725,404 Claims priority, application France Apr. 1, 1957 2 Claims. (Cl. 102-22) The present invention has for its object improvements in shaped charges of the type used for the perforation of walls and chiefly in those which are used for perforating the casing extending along the inner wall of a borehole together with the concrete, if any, filling the back of the casing and the geological strata extending beyond said concrete. r

his a well known fact that shaped charges used for such perforations normally include on their front surface a generally metallic lining, the purpose of which is to produce a perforating jet. Under the action of the explosion, the detonating wave propagated inside the explosive charge has for its effect to break up the lining and to make it collapse in the direction of the axis of said charge by imparting to a section of said lining a speed which is directed along said axis and which may be substantially higher than the speed of the detonation wave. The actual substance forming the lining assumes a very high speed and forms the perforating jet. Consequently, the conditions governing the formation of said jet have a bearing on its perforating effect.

It has been found experimentally and known for some time that the perforating performances of a shaped charge of a conventional conical type reach their maximum when the charge is fired at .a distance from the target which may be termed the optimum range of operation. In the perforating arrangements including shaped charges as used hitherto in bore-holes and in those cases where the bore-holes are not provided with a tubing for production conditions, there is no substantial difficulty in obtaining at the moment of the explosion of the charge said range of optimum operation. As a matter of fact, in such cases, the shaped charges are carried by a support the diameter of which is smaller than that of the bore-hole only by a small amount and said charges are housed inside said support at a predetermined distance from the outer wall of said support. Consequently, taking into account the difference in diameter between the support of the perforating means and the bore-hole, the shaped charges are actually positioned at said optimum range of operation with reference to the casing. Such an arrangement is illustrated diagrammatically in the accompanying FIG. 1 where 1 designates a bore-hole filled with a boring fluid 2 and provided with a casing 3. The numeral 4 designates the support for the perforating apparatus carrying the different shaped charges 5, 5. With the perforating apparatus being properly centered, if required, through special centering means, it will be readily apparent that it is possible to initially insert the shaped charges 5, 5' in their support, in a manner such that the optimum range of operation may be substantially obtained for all the charges.

In contradistinction, it is a different situation when it is desired to perforate a casing in a bore-hole equipped with a tubing through which the hollow charges are to pass.

The accompanying FIG. 2 illustrates this latter case. A bore-hole 1 is filled with a boring liquid 2 and is provided with a casing 3 which it is desired to perforate at predetermined points. The bore-hole encloses the tubing 6, the diameter of which is, as well known in the art,

much smaller than that of the casing 3. In this arrangement it is necessary to introduce the perforating shaped United States Patent 0 charges through said tubing, so that they may be set underneath the lower level of said tubing. The shaped charges 5, 5, 5" are suspended underneath the tubing after the manner of a string of beads and, because of the slope of the casing with respect to the vertical, the string of heads is urged against said casing. As a result, the operative ranges of the different charges may obviously be extremely different, said ranges being practically Zero for certain charges, such as 5 for instance, while they are comparatively large for others, such as 5". With conventional charges, the optimum range of operation is therefore not reached, generally speaking, and the efficiency of the charges is consequently entirely unforeseeable.

The present invention has for its object to remove the drawback arising from this condition and to produce shaped charges the efiiciency of which is as independent as possible of the range, so that the efficiency of said charges may remain substantially the same, whatever the operative range may be within the limits of use corresponding to practical conditions. Said invention relies on the fact that the actual speed of each of the elements of the jet depends on several factor, provided all other conditions remain unaltered. Among these factors is the angular slope of the section of the lining which is to form said element, with respect to the axis of the charge and/ or the surface of the casing defining the outer surface of the explosive charge. Another factor is the distance between said element and said axis. It is consequently possible to make the angle considered vary as a function of the distance from the axis of the corresponding element of-the lining. In other words, it is possible by acting on the actual shape of the lining or of the easing of the charge to act on the shape and on the properties of the jet. In the present case, it is desired to obtain a jet extending as much as possible along its axis to obtain a'large perforation for small operative ran es while remaining coherent for the maximum operative range. It is therefore necessary to produce comparatively large speeds for the elements of the jet, while retaining a limited gradient of speeds.

To this end and in conformity with the present invention, instead of resorting to a conical lining, a lining constituted by a flaring surface is used. Preferably, it is a surface of revolution the generating line of which is constituted by a curve having two concave sections. The concavity of the line is directed outwardly with reference to the axis of revolution in the vicinity of the apex of the lining and towards the axis for the points nearer the base of the lining, the slope of the generating line with reference to the axis of the charge and/or with reference to the outer casing of the charge and the curvature of said generating line at each point being suitably selected to this end.

This arrangement increases as a matter of fact the drawing out of the jet in the vicinity of the apex of the lining and in its central section, while it reduce; this drawing out in the vicinity of the base of the said lining. The

jet is thereby sufficiently drawn out for the shorter operative ranges and remains homogeneous for comparatively large operative ranges.

The accompanying drawings illustrate the invention by way of example and by no means in a limiting sense. In said drawings:

FIGS. 1 and 2 are diagrammatic explanatory showings of the position of the shaped charges in a bore-hole, as described hereinabove.

FIG. 3 shows one preferred embodiment of the improved shaped charge to be used for the purpose referred to.

In FIG. 3, 7 designates the outer casing of the shaped charge, said casing being provided at its rear end with a 3 port 8 adapted, as well known per se, to contain ignition means which are not illustrated. Reference numeral 9 designates the explosive charge and 10 the metal lining for said charge, said lining assuming, according to the invention, the shape of a surface of revolution designed in the manner described. Designating by D, the diameter of the complete charge, the radius of curvature r of the generating line in the vicinity of the apex should be preferably comprised between 0.2 and 0.5 D while the angle a defining the slope of said generating'line at the point at which it meets the inner end of the lining 10 should range preferably between 10 and 30. As to the radius of curvature r; of the generating line near the outer end or base of the lining, it should be preferably of the same magnitude as the radius in the first described section of the charge while the angle }9 of the generating line with the outer wall of the casing of the charge ranges preferably between 10 and 40. In the case illustrated, the charge casing is cylindrical but this is obviously not essential and the casing may assume a frusto conical shape the apical angle of which is more or less marked. The surface of such a frustocone may furthermore converge towards the front or towards the rear of the shaped charge as desired.

In all cases, the extreme conditions referred to hereinabove and related to the angle B should be retained preferably, the value of fl being of course different, if desired, from that which is selected in the case of a cylindrical casing for the charge.

Experience agrees with theory and shows that with such shaped charges, an elongated jet is obtained the efficiency of which varies but little with the range. Consequently, all the charges of the string of charges illustrated in FIG. 2 have an efficiency approximating optimum efficiency.

Obviously, many modifications may be brought to the shaped charges described within the scope of the accompanying claims.

What I claim:

1. A shaped charge for producing a perforating jet of substantially constant characteristics over its intended operative range, comprising an explosive charge having a rearmost portion, lateral side portions and a front surface having a hollow depression positioned therein uniformly about a longitudinal axis of said charge, an outer casing having an inner surface enclosing the charge laterally and rearwardly, and a rigid lining extending over said front surface including said hollow depression and being comprised of a substantially flat transverse inner portion seated about said axis at the bottom of said depression and a generally outwardly flaring shape surrounding said axis of the charge and defined by a surface of revolution around the axis of the charge extending from said fiat inner portion to said inner surface of said casing, the generating line of said surface being substantially continuously curved with a double curvature consisting of two concave sections, the concavity, of a first one of said sections adjacent said flat inner portion of the lining being directed outwardly with reference to the axis of the charge and the concavity of the second of said sections extending towards said inner surface of the casing being directed toward said axis of the charge, the radii of curvature for both said concave sections being between 0.2 and 0.5 times the total diameter of the charge as determined by the diametrical spacing of the intersection of the lining with the inner surface of the charge casing, the angle defining the slope relative to said axis of the generating line where it intersects said flat inner portion of the lining being in a range from 10 to and the angle formed by the generating line and said inner surface of the charge casing being in a range from 10 to 2. A shaped charge according to claim 1 wherein said radii of curvature are substantially equal.

Aberdeen Proving Ground Photograph A61,525. (Taken May 2, 1950.)

University of Utah Bulletin, vol. 37, No. 5, published July 1946. (Pages 18 and 23 relied on.)

Aberdeen Proving Ground Photograph A615,528. T-aken May 2, 1960. Copy in Div. 10.