WO1997048989A1

WO1997048989A1 - Tool

Info

Publication number: WO1997048989A1
Application number: PCT/GB1997/001624
Authority: WO
Inventors: Andrew William Stevens
Original assignee: Geco-Prakla International Resources Inc.
Priority date: 1996-06-17
Filing date: 1997-06-17
Publication date: 1997-12-24
Also published as: GB9612632D0; AU3101497A

Abstract

The invention relates to a tool (1) for burying an object (2) comprising an elongate body (3) of substantially uniform cross section throughout its length from a proximal end to a distal end having a cavity (8) with a lateral opening (9) formed therein for receipt of an object (2) to be buried, attachment means (5) at the proximal end of the body (3) for attachment thereof to a thrust means and a ground penetration tip (7) on the distal end of the body (3), the cavity (8) extending from a lip (11) at a distal end of the lateral opening (9) towards the proximal end of the body (3) and having a ramp surface (12) extending from the lip (11) towards the proximal end of the body (3) and inclined with respect to the longitudinal axis of the body (3), whereby, upon forcing the tool (1), with an object (2) to be buried received in the cavity (8), downwardly into the ground by applying downward force to the tool (1) by means of the thrust means, the ground penetration tip (7) penetrates the ground and the tool (1) carries the object (2) to a desired depth and whereby, upon retracting the thrust means (4) upwardly with the tool (1) attached thereto, the object (2) is ejected from the cavity (8) into the ground by interaction with the ramp surface (12) and is thereby buried at a desired depth.

Description

TOOL

The present invention relates to a tool for positioning objects at depth, either below ground level or underneath a sea bed. The tool is particularly useful in seismic surveying as a means for positioning hydrophones.

Seismic surveying involves the use of an explosive charge buried at depth and of one or more hydrophones located some distance away from the charge. When the charge is detonated, the resulting sound waves travel at different speeds through different media. Careful selection of the relative position of a charge and one or more hydrophones can allow the user to calculate, from information provided by the hydrophone, the speed of sound through the particular medium under investigation. The user may be able to draw conclusions from this information, such as the presence or absence of oil deposits in the area.

Planting hydrophones can be a complex engineering problem. In certain types of media, such as clay, hard muds and firm sand, it is possible simply to make a borehole for the hydrophone by known drilling or flushing methods. After withdrawal of the drilling or flushing tool, the hydrophone may then be lowered into the borehole on the end of a length of electrical cable. This cable also provides a means of retrieving from the hydrophone its data following a seismic blast. However, in certain types of media, such as loose sand and soft mud, this technique is not feasible. The borehole simply closes up after the drilling or flushing operation and before the hydrophone can be inserted. To address the problem of borehole closure in soft or loose media, there has been developed a technique in which the hydrophone to be planted is mounted in a disposable tip which is inserted into the medium on the end of a long shaft. When the shaft is withdrawn the disposable tip and hydrophone are disconnected from the shaft and left in the ground at a desired position. The shaft may be inserted into the ground by a simple pushing action or. commonly, by a ramming method whereby the shaft is subjected to short, intermittent bursts of pressure which serve to hammer the shaft into the ground. Usually, the borehole will close up after the tool is withdrawn therefrom. This means that the water table does not become exposed to surface contamination and also that no hole is left as a potential trip/fall hazard.

The tip of the shaft has two principal design considerations. It is pointed on its outer surface to facilitate its motion through the ground. It has a generally cylindrical body which serves as a chamber for housing the hydrophone. The hydrophone itself is a somewhat delicate piece of equipment containing a piezo-electric crystal circuit. It is therefore important to shield the hydrophone to some extent from direct exposure to the ground through which the shaft is moving. The cylindrical body of the tip is seated in the shaft sufficiently securely such that the tip is not dislodged from the shaft during the ramming process. However, the outer surface of the tip extends from its apex across the end of the shaft. In this way, the tip remains connected to the shaft as the downward bore is made but becomes dislodged from the shaft when the shaft is retracted. The conical portion of the tip serves to anchor the tip in the ground at the maximum depth reached by the shaft. The hydrophone, contained within the cylindrical portion of the tip, becomes dislodged also.

The methods of the prior art have attendant disadvantages. Notably, the tip used to protect the hydrophone cannot be recovered from the ground easily. Accordingly, the tip is designed to be disposable. However, seismic surveying often involves the boring of a very large number of holes. For example, it is not uncommon for a team surveying an area for oil deposits to make in the region of from 10,000 to 100,000 or more boreholes in an attempt to characterise the under-surface nature of the area under investigation. Accordingly, the requirement to use disposable shaft tips places a substantial and undesirable economic burden on the surveyor. Furthermore, the use of disposable tips represents an environmental problem, both in terms of the necessity to leave the tips in the ground after use and because of the use of consumable materials in the shaft tips.

A further disadvantage of the prior art is the tendency for the hydrophones to remain lodged inside the tip as both are separated from the main shaft upon withdrawal. The encasement of the hydrophone in this way lowers its sensitivity to the sound waves from the detonated explosive charge. According to the present invention, there is provided a tool for burying an object comprising an elongate body of substantially uniform cross section throughout its length from a proximal end to a distal end and having a cavity with a lateral opening formed therein for receipt of an object to be buried, attachment means at the proximal 5 end of the body for attachment thereof to a thrust means and a ground penetration tip on the distal end of the body, the cavity extending from a lip at a distal end of the lateral opening towards the proximal end of the body and having a ramp surface extending from the lip towards the proximal end of the body and inclined with respect to the longitudinal axis of the body, whereby, upon forcing the tool, with an object to be l o buried received in the cavity, downwardly into the ground by applying downward force to the tool by means of the thrust means, the ground penetration tip penetrates the ground and the tool carries the object to a desired depth and whereby, upon retracting the thrust means upwardly with the tool attached thereto , the object is ejected from the cavity into the ground by interaction with the ramp surface and is thereby buried at a

15 desired depth.

The tool of the invention has a number of significant advantages over the prior art device described above. The distal ground penetration tip of the tool does not need to be detached from the main body of the tool in order to release the object to be buried into the ground. Indeed, in one preferred embodiment of the invention, the ground 0 penetration tip is formed integrally with the body of the tool. Accordingly, the entire tool is recoverable after a single boring operation, thus obviating the need for expensive and environmentally undesirable disposable shaft tips.

Another advantage of the tool of the invention is that it allows the object to be buried to be discharged from the tool without simultaneous discharge of any housing, 5 as was necessary with the prior art method described above. This is a particularly advantageous feature of the invention when the object for burial is a hydrophone, designed to have a high degree of sensitivity to sound waves in the burial ground. Any encasement or partial encasement of the hydrophone, as tended to occur with the methods of the prior art, is likely to reduce the sensitivity of the hydrophone and thus 0 make seismic surveying more difficult and inaccurate In order that the invention may be clearly understood and readily carried into effect, a preferred embodiment thereof will now be described with particular reference to the accompanying drawings, in which:

Figure 1 is a side elevation of the tool of the invention and also of a hydrophone mounted in the tool whilst the tool is being inserted into the ground;

Figure 2 is a second side elevation of the tool and hydrophone of Figure 1 , the tool of Figure 1 being rotated by 90 about its longitudinal axis to obtain the view of Figure ?•

Figure 3 is a third side elevation of the tool and hydrophone of Figures 1 and 2 whilst the tool is being retracted from the ground and the hydrophone is being discharged from the tool;

Figure 4 is an enlarged view of the tool of Figures 1 to 3; Figure 5 is a further enlarged view of the tool of Figures 1 to 4 of the invention, the tool being rotated by 90 around its longitudinal axis with respect to the view shown in Figure 4;

Figure 6 is a cross section on line A-A of Figure 4 and on line B-B of Figure 5; Figure 7 is is a cross section on line C-C of Figure 5; and Figure 8 is a cross section on line D-D of Figure 5.

For the avoidance of doubt, it should be understood that the following description is intended to describe particularly a single preferred embodiment of the invention. It will be obvious to those skilled in the art that many of the features described may be altered or adapted to suit the particular requirements of a given terrain or object to be buried. Thus, the dimensions of the tool and ancillary features thereof which are not explicitly claimed as part of the invention are included merely to assist reproduction of the invention and are not to be taken as limiting its scope in any way. Moreover, for convenience the following description relates to a tool for use in burying a hydrophone. However, it should be clear from the foregoing passages that it is envisaged that other objects may also be buried using the tool of the invention.

Referring to Figure 1 , there is shown a tool 1 for burying an object 2 which, for the purposes of Figure 1 and the following description, is a hydrophone for use in seismic surveying. Tool 1 comprises an elongate body 3 which is of substantially uniform cross section throughout its length. In the exemplified embodiment, body 3 is of substantially circular cross section. However, it is envisaged that other cross sectional shapes may be used. For example, triangular, rectangular, pentangular, hexangular, heptangular or octangular cross section shapes may be used. However, it will normally be preferred to use a tool body 3 of circular cross section, both for ease of manufacture and effectiveness in relation to the boring of holes in the ground. Conveniently body 3 is formed from a length of tube.

Reference numeral 4 indicates a drive head for receipt of a ramming mechanism (not shown) of known construction which is used to force tool 1 into, and retract it from, the ground. In the embodiment shown, elongate body 3 of tool 1 is provided with a shank (indicated by reference numeral 5 in Figures 4, 5 and 6) of smaller diameter than the remainder of body 3. Shank 5 fits inside body 3 and is welded or otherwise secured thereto. The thrust means for driving tool 1 into the ground may be a ramming mechanism, as indicated above. Commonly, such a mechanism comprises a tube or pipe (which is perhaps 75 feet in length), one end of which fits over shank 5 and is secured thereto by means of a bolt passed through hole 6. This tube or pipe may be provided with a racked portion, which racked portion is driven by a gear. Thrust may be applied as short, intermittent bursts of power which cause drive head 4, and hence tool 1 , to vibrate whilst being urged downwardly into the ground. This vibrating or ramming action is often convenient when surveying areas in which the ground is composed largely of loose sand, shale or similar media. The vibrating motion of tool 1 serves to shake material loose from around its ground penetration tip 6, thus clearing a bore for passage of the tool into the ground.

As an alternative to a ramming mechanism, the thrust means may simply utilise a pushing action. This may also be achieved using a gear in combination the a racked member on the pipe or tube. In this case, the tool is inserted into the ground smoothly with little or no vibrating motion. Power is applied to drive head 4 not in short, intermittent bursts, but constantly so as to achieve a prolonged pushing action. This type of thrust mechanism is particularly suitable when the tool 1 is to be inserted in soft mud or a similar medium. Alternatively, the thrust means may comprise a piece of smooth pipe which is pushed down between two rotating wheels, which may be rubber faced to provide extra grip. Ground penetration tip 7 is formed on the distal end of body 3 as a sharp point. In the exemplified embodiment, in which body 3 is of circular cross section, ground penetration tip 7 is conical. Pyramidal shapes are also possible. Ground penetration tip 7 may be formed integrally with body 3. However, it is often convenient to form ground penetration tip 7 as a releasable tip which may, for example, be secured to body 3 by means of a screw threaded portion.

Tip 7 may become damaged after several boring operations. Thus, provision of a releasable tip 7 means that replacement can be made without the need to replace the remainder of body 3. Normally, ground penetration tip 7 will be made of mild steel or a hard-wearing plastics material such as high molecular weight polyethylene although any other suitable hard-wearing material may be used. For example, other metals which may be mentioned are tungsten steel and aluminium. Alternatively, a carbon fibre tip may be used. It is often convenient to manufacture body 3 from the same material as tip 7, particularly if an integral join is preferred. One preferred material for both body 3 and tip 7 is a plastics material. Tool 1 has a cavity 8 formed in body 3. Cavity 8 has a lateral opening 9 for receipt within cavity 8 of hydrophone 2. Hydrophone 2 is of known construction. Hydrophones which are suitable for use with the invention include MP24 available from OYO Geospace, Houston, and P44 available from Mark Products, of Houston. Cavity 8 is narrowed at its proximal end to prevent hydrophone 2 from sliding up inside the proximal end of hollow body 3 while the tool 1 is inserted into the ground. In the embodiment shown, the narrowing of cavity 8 is achieved by a retention ring 10 mounted inside body 3. Retention ring 10 thus provides a surface against which hydrophone 2 abuts while tool 1 is inserted into the ground. Part of ring 10 is cut away, as indicated at 10a, for a purpose to be described hereafter. Cavity 8 extends from a lip 1 1 at the distal end of lateral opening 9 towards the proximal end of body 3. Cavity 8 has a ramp surface 12 extending from lip 1 1 towards the proximal end of body 3 and inclined with respect to the longitudinal axis of the body. Ramp surface 12 may be formed as a solid surface extending from lip 1 1 , as shown in the exemplified embodiment. Alternatively the outer surface of hollow body 3 may simply be cut away so as to form an apex at lip 1 1. In this case, it is necessary to provide one or more bars inside body 3 at an inclination to its axis so as to form a deflection ridge on the inner surface of hollow body 3 to prevent hydrophone 2 from sliding into the distal end thereof when tool 1 is retracted from the ground.

As shown in Figures 1 and 2, tool 1 is inserted into the ground with hydrophone 2 received within cavity 8. A hydrophone cable 13 is attached to hydrophone 2 and is introduced through the cut away 10a in retention ring 10 and so passes through retention ring 10 into the proximal end of hollow body 3 and then along in slot 14 in the wall of body 3 and communicates ultimately with the ground surface (not shown). As tool 1 is driven into the ground, tension on hydrophone cable 13 prevents hydrophone 2 from slipping downwards within cavity 8. Hydrophone 2 therefore remains seated against retention ring 10 when tool 1 is driven down into the ground applying thrust to drive head 4.

Drive head 4 is operated by the action of a driven gear (not shown) upon a racked member (not shown) associated with the tube or pipe of the thrust means. The action may be a continuous pushing action, suitable for inserting tool 1 into soft mud or similar media. Alternatively, the driving action may involve short, intermittent bursts of power which produce a ramming action suitable for driving tool 1 into loose sand or similar media.

The dimensions of a particular tool according to the invention may of course be chosen to suit a variety of parameters, such as the burial depth required and the size of hydrophone to be buried. However, the dimensions of one preferred tool are as follows, with particular reference to Figure 4. However, the hydrophone is omitted from Figure 4 for the sake of clarity of the drawing. Referring to Figure 4, there is shown a tool 1 of circular cross section. The main body 12 of the tool has an external diameter of from about 50 mm to about 100 mm, for example about 75, mm and is formed from a mild steel pipe. Shank 5 of body 3 has an external diameter of from about 25 mm to about 75 mm, for example about 60 mm. The projecting length of shank 5 may be from about 100 mm to about 200 mm, for example about 150 mm. Ground penetration tip 7 is conical, the height of the cone from its apex to the centre of its base being from about 35 mm to about 85 mm, for example about 60 mm.

A distal portion 15 of body 3, which extends from the base of ground penetration tip 7 to a point indicated by reference numeral 16 on Figure 4, may be from about 190 mm to about 290 mm, for example about 240 mm in length. An intermediate portion 17 of body 3 extends from point 16 to a point indicated by reference numeral 18 and may be from about 150 mm to about 250 mm, for example about 200 mm in length. A proximal portion 19 of body 3 extends from point 18 to the distal end of shank 5 and may be from about 250 mm to about 350 mm, for example about 300 mm, in length. The total length of tool 1 may be between about 725 mm and 1 175 mm, for example about 950 mm in length. The length of ramp surface 12 when measured from the apex of lip 1 1 along the longitudinal axis of tool 1 to a point indicated by reference numeral

20 whereat ramp surface 12 meets the internal surface of body 3 may be between about 120 mm and about 220 mm, for example about 170 mm. Retention ring 10 is seated within body 3 at a distance of from about 30 mm to about 80 mm, for example about 55 mm from point 18 towards the proximal end of tool 1. However, it is stressed that all of these foregoing dimensions are provided simply to aid reproduction of the invention and are not intended to limit its scope in any way with regard to the dimensions of a tool according to the invention or of parts thereof.

Figure 7 shows a cross section on line C-C of Figure 5. Ramp surface 12 extends from the apex of lip 1 1 and meets the internal surface of body 3 at all its edges, point 20 indicating the join of ramp surface 12 and body 3 which is most remote from the apex of lip 1 1.

Figure 8 shows a cross section on line D-D of Figure 5. Retention ring 10 is indicated within body 3. Ring 10 is slotted at 10a to allow insertion and release of hydrophone cable 13. When tool 1 is driven into the ground, as indicated in Figures l a and l b, tension on hydrophone cable 13 keeps hydrophone 2 seated within cavity 8 against retention ring 10. When ground penetration tip 7 has reached a point somewhat below the depth at which it is desired to bury hydrophone 2, the drive head may be driven in reverse to withdraw tool 1 from the ground. The additional depth required to be reached by ground penetration tip corresponds approximately to the length of tool 1 from retention ring 10 to the apex of ground penetration tip 7.

As tool 1 is withdrawn from the ground, as indicated in Figure 3, tension on hydrophone cable 13 maintains hydrophone 2 in position and prevents it from slipping downwardly. As ramp surface 12 meets hydrophone 2, the latter is deflected out of cavity 8 through lateral opening 9 and into the ground at the desired depth.

Hydrophone cable 13 slips free from tool 1 and out of slot 14.

Tool 1, once with drawn is then ready to receive another hydrophone and for the process to be repeated at a new site.

Claims

CLAIMS:

1. A tool for burying an object comprising an elongate body of substantially uniform cross section throughout its length from a proximal end to a distal end and having a cavity with a lateral opening formed therein for receipt of an object to be buried, attachment means at the proximal end of the body for attachment thereof to a thrust means and a ground penetration tip on the distal end of the body, the cavity extending from a lip at a distal end of the lateral opening towards the proximal end of the body and having a ramp surface extending from the lip towards the proximal end of the body and inclined with respect to the longitudinal axis of the body, whereby, upon forcing the tool, with an object to be buried received in the cavity, downwardly into the ground by applying downward force to the tool by means of the thrust means the ground penetration tip penetrates the ground and the tool carries the object to a desired depth and whereby, upon retracting the thrust means upwardly with the tool attached thereto, the object is ejected from the cavity into the ground by interaction with the ramp surface and is thereby buried at a desired depth.

2. A tool according to claim 1 , wherein the elongate body is of cylindrical cross section.

3. A tool according to claim 1 or claim 2, wherein the cavity is adapted to receive a hydrophone.

4. A tool according to any one of claims 1 to 3, wherein the ground penetration tip is formed integrally with the body of the tool.

5. A tool according to any one of claims 1 to 4, wherein a retention ring mounted within the body of the tool in the region of the proximal end of the lateral opening provides a surface against which the object can abut during burial.

6. A tool according to claim 5, wherein the retention ring is cut away to permit lateral insertion of a cable or the like attached to the object by means of which the object may be held against the retention ring during insertion of the tool into the ground.

7. A tool according to any one of claims 1 to 8, wherein the elongate body of the tool comprises a longitudinal slot for receipt of a cable attached to the object to be buried, which longitudinal slot communicates with the lateral opening to allow release of the cable from the tool when the tool is withdrawn from the ground.

8. A tool substantially as described herein with reference to the accompanying drawings.