US2558924A

US2558924A - Seismographic prospecting apparatus for directing explosive energy

Info

Publication number: US2558924A
Application number: US629728A
Authority: US
Inventors: Norman B Blake
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1945-11-20
Filing date: 1945-11-20
Publication date: 1951-07-03
Anticipated expiration: 1968-07-03

Description

B. BLAKE July 3, 1951 N. RAPHIC PR CTING APPARATUS FOR OSIVE SEISMOG OSPE DIRECTI EXPL Fil Nov.

ENERGY 945 M VEA Ta? Mar/72427 5;

71 4. 5 3 mm M M 4 w Patented July 3, 1951 UN TE-D STAT ES SEISMOGRAPHIC PROSRECT ING APPA- RATUS FOR DIRECTING. EXPLOSIVE.

ENERGY Norman-B. Blake, Beaumont 'lex assignor to Sun OilCompa-ny; Philadelphia; Pa; arcorpora My invention" relates to seismographicpros- )ecting, which comprisesdetonating an explosive at or below groundlevel and recording at distant pointsithe propagated waves of'refraction" and reflection'.

Th object ofmy invention is .to confine within practicable limits'th'e propagation of the waves in agenerally downwarddirectionso tliat,1within practicable limits; the detectors will record mainly waves reflectedifrom axsubsurface layer lying. beneath the locus of explosion. This. ob?

ject is in large measure obtained by my invention, in which the total energy of the explosion is so directionally controlled as to increase the energy downward to the reflecting horizon with a corresponding substantial diminution of energy expended in other directions. To the extent that this object is accomplished the amount of energy reflected to the detector will be substantially larger than that received from other or random paths, thereby enabling the reflected layer to be more readily identified by observing the increased amplitude on the record.

It follows, also, that this concentration of explosive energy in a generally downward direction, especially in difiicult areas, will change the frequency spectrum of the energy received by the detectors, which change often produces an improvement in the recorded reflections.

It follows, also, that any concentration of energy in a given direction will more effectively penetrate any hard strata lying in such direction. a

While the attainment of the above objects is not dependent upon the employment of the specific construction shown in the drawing, such construction is well adapted to the practice of the process embodying my invention. The drawing is a vertical section through such a construction.

In a shot hole a, which may have any selected depth, preferably between and 125 feet, is inserted a cylindrical casing b, preferably of high strength steel, the lower part of which has a relatively thick or reinforced wall 0. In the lower part of this casing is inserted an explosive charge at. The length of the thickened portion of the casing wall somewhat exceeds the length of the explosive charge. Provisions are made to oppose resistance to discharge of explosive energy in an upward direction. One way of doing this is to fill the shot hole with liquid 6, convem'ently water, to provide a liquid column overlying the explosive and adapted to absorb the reaction of explosion. It is desirable, but may not be necessary, to provide beneath the ex- 2: plosive charge an open-space the upper part :at least of which is surrounded by thecasing, the thick wall of which is preferably taperedfat its end as shown. To avoid the filling ofithisjspace with water'from the-column e, the space 1 may be occupied'by a thinwalled empty-container affording no effective resistance to the'force of explosion.

The explosive charge is lowered into the'casing by means of cap wires g, which" also lead to the blasting cap (not shown). The 'cap'wires are secured at their upper ends to a cross-bar" h; which may rest on the top of the casing b; The explosive charge is thereby suspended inthe casing and its vertical position therein accurately fixed. Connected with the upper end of the cap wires is a lead 2' (which may be an extension of the cap wires g) to the blasting machine (not shown). The casing may be suspended from a rope is having at its end a ring m closely grasping the upper end of the casing. This rope should be subjected to a strong pull to hold the casing stationary during the moment of exploding the charge.

When the explosive charge is detonated, the casing 1) functions in a manner similar to that of a cannon and, seeking the line of least resistance, the explosive energy is directed largely in a downward direction. While the distribution of the energy of explosion is in all directions, the amount of shot energy in a directly downward direction and in oblique directions having relatively small angles to the vertical is dominant, or, more accurately expressed, greater than that obtainable from a shot of equal size free to distribute its energy equally in directions varying between vertical and lateral.

Since the energy of an unconfined explosive charge is effectively discharged equally in all directions, it will be understood that a casing of practicable maximum weight, unless very short, would have its wall so thin that it would be penetrated by the lateral discharge of explosive energy. By substantially thickening, by reinforcement or otherwise, the part of the casing wall that encloses the explosive, rupture of the casing by the shot energy directed in a horizontal direction and in directions having relatively small angles to the horizontal is prevented. It is practicable to make the entire casing of high strength steel, the thickened lower end being then an integral part of the casing; or the extra thickness of this part of the casing may be secured by reinforcing the casing in any known manner. The thickened casing wall being effective to protect the casing from rupture, the part of the explo- 7 plosive energy in boreholes within the earth comprising a borehole casing, an explosive charge suspended within and above the bottom of the casing and a substantial distance above the bottom of the borehole, the part of the casing enclosing the explosive charge being of substantially greater thickness than the remainder of the casing, a readily disruptable member closing the bottom of the casing, and a liquid column resting on said member and extending to a substantial distance above the explosive charge.

2. Seismographic apparatus for directing explosive energy in boreholes within the earth largely in a general downward direction comprising, in combination: a casing inserted in and above the bottom of the borehole; an explosive charge suspendable in said casing above the bottom of the borehole; 'a liquid tamping column in the casing extending a substantial distance above the explosive charge; and a member substantially non-resistant to the force of explosion and sealing the lower end of said casing against downflow of tamping liquid into the bottom of the borehole.

3. The apparatus defined in claim 2 in which the wall of said casing, for a limited vertical distance opposite the locus of suspension of the explosive charge, is of a thickness substantially greater than that of the main body of the casing wall.

4. The apparatus defined in claim 2 in which the casing has a flared mouth in the lower end thereof and in which the sealing member is a hollow plug and is seated in said mouth.

NORMAN B. BLAKE.

REFERENCES CITED The following references are of record in the file of this patent? UNITED STATES PATENTS Number Name Date 733,492 Little July 14, 1903 1,106,606 Wilhelmi Aug. 11, 1914 1,832,132 Lanier Nov. 17, 1931 2,272,741 Failing Feb. 10, 1942 2,316,596 Kennedy Apr. 13, 1943 2,334,414 Klotz Nov. 16, 1943 2,340,314 Farnham Feb. 1, 1944 2,384,851 Reichert Sept. 18, 1945 2,399,211 Davis Apr. 30, 1946 2,407,442 Parr Sept. 10, 1946 FOREIGN PATENTS Number Country Date 367,858 Great Britain Feb. 26, 1932