US2586706A

US2586706A - Seismic surveying

Info

Publication number: US2586706A
Application number: US70402A
Authority: US
Inventors: Jr Josephus Overton Parr
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-01-12
Filing date: 1949-01-12
Publication date: 1952-02-19
Anticipated expiration: 1969-02-19

Description

Feb. 19, 1952 J. O. PARR, JR

SEISMIC SURVEYING Filed Jan. 12, 1949 (Jam, 6% 8mm? a/Jm ATTORNEYS Patented Feb. 19, 1952 SEISMIC SURVEYING Josephus Overton Parr, J12, Sa'n- Antonio,-' Tex,- assignorto Olives. Petty, San Antonio, Tex.

Application J anuary 12, 1949, Serial No. 70,402

(Cl. 18I".5)

9 Claims;

This invention relates an improved method of. propa ating seismic waves ..in..underwater. formations and-to, apparatussuitable. for. use in .the

practice of. the method More.,particularly.,. itJS. an object, oithe invention-to. provide .an improved method. and apparatus .for detonating a charge.

of explosive in water .in.. geophysical prospecting.

of underwater .stratabymeans of whicha num:. ber of difiicultiescommonly. encountered in pres.- ent practice. .canbe minimized or av.oided,-and which will. permit the detonation of.,explosi.ves at depths. greater, than those. nowcommonly. regarded .as the-optimum, with resultant. increase in the efliciency of the explosive.

It. is; well known thatgthe. damage,.to..marinelife. resultingirom. .the firing. of explosives under watermis .caused principally. by transmission.

throughthe water, of.,high velocity energy waves of supersonic. frequency, whereas useful seismic wave, energy,-,withinpthe sound, range,.,is..not in: H

jurious to most living organisms". I have his? covered-that the magnitude of. supersonic. energy released by an explosion beneath water mayi be-i greatly reduced if the explosive chargeis oetonated in a gaseous-medium by which the charge, is isolated from direct contactwith thewatendor instance eby the provision of- -a gaseous ,pocket inn-which the ,charge' is suspended andswithin Pre-. i sumably the-explosiveshock is cushioned by 1 the.

which the:- initial expansion'can occur;

gaseous medium and-the initial impact correspondingly reduced. Whatever the cause; it can.

be. shown that. a charge .so exploded dissipatesmuch-less energy in the form of waves havinga' velocity of the order of 5,000 feet' or more per:

second, and" causes -no substantial damageto-v marine life.

I ;have alsofound. that :when. a charge is detonated under, water-;;and in a surrounding gaseous pocket, the bubble ,efiectnoted by-Lay et;al.,in U. S. Patent 2,351,524, granted'June .13, 19.44,--.is1 practically eliminated. even though the.- charge: is exploded at such ,a depth that; blow-- out? of the. Wateriabove the explosioncannot'ocr; Consequently I am' enabled by the practice cur. of the present invention to improve theeificiency of the explosive in generating seismic :wavesrin theunderlying strata without giving'rise, toisec ondary P waves of undesirable magnitude.

In the preferred method of practicing the invention, the gaseous pocket may be provided by suspending the explosive charge within an enclosure, for instance a balloon or a bell, which is positioned at the desired depth in the water in any conventional manner beforefiring." Al-y ternatively, a .gaseous pocket mayv be created around the explosive by first detonating a relatively small gas releasing charge, whereby the gaseous "pocket isformed in -situ immediately before the firing of the charge which propagates the seismic waves:

Further objectsandjeatures' of the inventionwill'flbe apparent from the following description taken in. connection. with" the accompanying drawings, in whichf.

Figure 1 illustrates :one form of equipment satisfactory for the practice of the invention, in which the. gaseous medium is confined within an enclosure;

Figure 2*? illustrates: an alternative method wherein the surrounding gas pocket is formed by the detonation of. a gas-producing charge prior to thefiring of. the main explosive; and

Figure Srepresents. a modification of Figure 1 in which ,thehcharge .is'. suspended in the air trapped within .a bell havinganopen bottom.

In order. to facilitate. an understanding of the invention, reference is, .I'nade herein. to specific methods and. apnaratflsbu't it will ,be understood thatno limitation of the. scope of, the invention is thereby. intended, variousiurthen methods and alterations, such as .wouldoccur .to those skilled in the art, being ,contempla'ted herein.

Referring fir'sttoi Figure .1, it. .will'jbe observed that-thev charge ofiexplosive I0 is suspended in an enclosure. constituted .by 13- balloonl I, the. supporting, line. ;.I 2 .ttherefor being secured to the upper 'sideottheballoonat l3.' Aweight 18 may be secured totheiballoon for.instance by snood lflorzthelikeuto carry. thelballoondown, a line E5 of'selected'length:servingrto position the balloon at the desireddepthwhen theweight l8 rests on the. bottom. The. balloon maybe filled with air or any: othersuitable gaseous medium,v the. latter term 'beingiemployedherein to include air. Suitable; electrical connections,.such .as the usual shot line...20,.may extend throughlinel 2 to a detonating cap or the like associated with .the explosive charge I, 0, .Itwillbe applfciated thatthe. balloon andichargetmay be.suspended from the. surface of the,-watertin;thgconventionalrmanner .by a

the high ,velocity .-waves..commonly dissipated.

thmugnwnee-ty the-.firingiof an.explosive thereinsane: suppressed .sutficiently to.e1imina.te damage tofishrandothenliving,organismsanddisturbing effects-iofesecondai'fy, -P..waves. ar e minimized, so that thetformula prescribe'd in" the patent. to Lay et algfabove mentioned need not be observed.

In Figure 2 is shown a modification whereby the gaseous pocket is createdxiimmediately' prior to; the detonationof'the main charge: This may be achieved by positio'ning the charge-l0 within a sleeve'or. container22, which may be formed or wood or {water-resistant; fibrous material. A gas releasing charge; for'instance a detonating fuse 23 offthe type known as fprimacord, is wrapped around the sleeve 22; the-latter serving to space the. illsefronithe main'charge. I 0. l One end of the fuse extend's'into' the main charge [0 at to detlength, and the cap 25 is detonated by a shotline 29 or other electrical connections.

It will be appreciated that on detonation, the

fuse 23 first evolves a gas which forms a gaseous explosive is positioned-above the level of water rising in the bell as the latter is lowered. The bell is carried on a line 35 depending from a float 37, the length of line 36 being such that the, de-

sired depth is reached. Detonation is effected by I a shot line 20, which may be carried down .to the charge i0 throughline 36. In order ..to ensure that the bell will remain in the proper. position when lowered, a weight 38 may be secured byv lines 39 to the open mouth thereof. 7

The bell 35 may be fairly heavy, for instance being formed of metal, and may have .a substantially parabolic shape, so that when the char e is positioned substantially at the parabolic focus, the energy released by the explosion will be refiected downwardly .in parallel or converging waves, whereby the force of :the explosion is concentrated and the efliciency of the explosive cor-U respondingly increased. The effect may be heightened by the use of a baflle plate 40, which may be circular in plan, suspended within the bell on support rods 4|, and positioned. beneath.

the charge to reflect against the inner surface of the bell the energy of the explosive. By means of this structure I am enabled to propagate seismic waves of adequate magnitude Withi a charge of substantially less size.

It will be perceived from the .foregoing that the basic concept of the invention is the generation of an explosion within a pocket ofgas and beneath the surface of the water; Various types of equipment, capable of achieving this end, may be substituted for that illustrated herein.

Having thus described the invention, what is claimed as new and desired to besecured by Letters Patent is: v 1. In apparatus for propagating seismic waves in underwater formations, the'combination with the explosive charge, of a casing containing a gaseous medium through whichthe major p9 tion of the energy released on detonation of the charge is transmitted directly to the water, means suspending said charge in said casing and in (l0 charge, said casing having a volume. many'times that of the explosive charge, and sufiicient to said medium, and means; for detonating said materially reduce the "transmission through the water of wave energy having velocities in excess of 5,000 feet per second, thereby minimizing damage to marine life.

2. In apparatus for propagating seismic gaseous medium, means suspending said charge in said casing and in said medium, and means for detonating said charge, said casing compris-.

ing a bell having an open bottom whereby. the I energy released by the explosion is reflected downwardly, said casing having a volume many waves. in underwater formations, the combination with the explosive charge, of a casing containing a,

times that of the explosive charge, and sufiicient to materially reduce the transmission through the water of wave energy having velocities in excess of 5,000 feet per second, thereby minimizing damage to marine life.

3. In apparatus for propagating seismic waves I V in underwater formations, the combination with the explosive charge, of a casing containing a gaseous medium, means suspending said charge in said casing and in said medium, and means for detonating said charge, said casing comprising a bell having an open bottom whereby the energy released by the explosion is reflected downwardly, and baffle means within said bell and below said explosive charge to impede downward dissipation of unreflected energy.

4. In apparatus for propagating seismic waves in underwater formations, the combination with the explosive charge, of a gas releasing charge disposed in proximity to said explosive charge for forming when ignited a gaseous pocket around the latter, and means effecting in quick succession ignition of said gas releasing charge and detonation of said explosive charge.

5. In apparatus for propagating seismic waves in underwater formations, the combination with the explosive charge, of a gas releasing charge disposed in proximity to said explosive charge for forming when ignited a gaseous pocket around the latter, said gas releasing charge comprising .a ,detonating fuse of substantial length extending about said explosive charge and having one end thereof in firing relation with the latter, and means effecting detonation of the other end of said fuse, whereby a gaseous pocket is formed, by the burning of said fuse, around said explosive charge immediately prior to detonation thereof.

6. A method of propagating eismic waves in underwater formations which includes the step of detonating an explosive charge at a point beneath the surface of the water and substantially above the bottom, and within a gaseous pocket having a volume many times that of the explosive charge, and sufficient to materially reduce the transmission through the water of wave energy having velocities in excess of 5,000 feet per second, thereby minimizing damage to marine life, the major portion of the energy released by detonation of the charge being transmitted through the gas in the pocket directly to the water.

7. The method recited in claim 6 in which the gas constituting the gaseous pocket is confined in a gas containing envelope.

8. The method recited in claim 6 in which the gas constituting the gaseous pocket is formed by the step of firing, immediately prior to the detonation of the explosive charge, a gas evolving charge in proximity to the main charge.

9. The method recited in claim 6, which includes the further step of reflecting downwardly and in a confined path the major part of the energy released by detonation of the charge.

JOSEPHUS OVERTON FARR, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number