WO2003042717A1

WO2003042717A1 - Seismic wave generator

Info

Publication number: WO2003042717A1
Application number: PCT/AU2002/001536
Authority: WO
Inventors: Roger Clyde Webb
Original assignee: Poly Systems Pty Limited
Priority date: 2001-11-12
Filing date: 2002-11-11
Publication date: 2003-05-22
Also published as: AUPR881201A0

Abstract

A seismic wave generator comprising an enclosed cylinder (1), a piston (4) movable within the cylinder between an inlet manifold (15, shown in Fig. 2) at or near one end (2) of the cylinder and an anvil (10) at or near the other end (3) of the cylinder adapted to engage with the ground. The piston (4) is adapted to be propelled towards and to strike the anvil (10) by a gas propellant that enters the cylinder via the inlet manifold. The propellant is initially stored as a liquid and adapted to be heated by a heating means (12, shown in Fig. 3) which induces a phase change such that the propellant becomes a highly dense gas.

Description

SEISMIC WAVE GENERATOR

TECHNICAL FIELD

The present invention relates to a seismic wave generator, and more particularly to such a device that uses a gas propelled piston that strikes an anvil engaged with the ground to propagate a seismic wave or pulse.

BACKGROUND

It is known in mining and other geological applications, such as oil and mineral exploration, to generate a seismic wave or pulse through earth, and use known detection and recording equipment to detect and record a signal for the purposes of ascertaining the location and extent of ores, minerals, oil and the like located below the earth's surface.

There are number of known methods that are used to propagate a seismic wave or pulse. The first method is by placing an explosive charge within the ground and detonating the charge. The second method is by placing a steel plate or anvil on the ground, and manually hitting the steel plate or anvil with a "sledge-hammer" or like hand held tool. The third method involves taking a weapon such as a "shot-gun" and firing it into the ground. Some of these methods consist of unsafe practices, whilst all three methods suffer from not being able to easily reproduce the magnitude of the seismic wave or pulse being generated.

A fourth method of propagating a seismic wave or pulse is by way of a hydraulically actuated ram system having a ram adapted to strike against the ground with great force. Whilst such a system allows for reproducing the magnitude of the seismic wave being generated, it typically suffers from being bulky and expensive, requiring the ram and its associated hydraulic power pack to be mounted on a truck or trailer. A disadvantage of such a system is its size and weight, which hinders its use in difficult to access locations. In a fifth method, seismic wave or pulse generators utilise compressed gas to drive impact pistons towards target plates. A number of such generators are disclosed in US Patent Nos. 4284165, 4484657, 4770269 and 4819759 as well as GB Patent Application Nos. 2067289 and 2188150. A drawback of these devices is that they are mechanically complicated, heavy and expensive devices. For example, US Patent No. 4,819,759 discloses a seismic pulse generator which has a telescopic firing tube and is designed for mounting on a transport vehicle. A disadvantage of such a seismic pulse generator, like that of the earlier mentioned hydraulic system, is its size and weight, which hinders its use in difficult to access locations.

The present invention seeks to provide a seismic wave generator that overcomes the disadvantages associated with conventional methods of seismic wave generation.

SUMMARY OF THE INVENTION

According to a first aspect the present invention is a seismic wave generator comprising an enclosed cylinder, a piston movable within said cylinder between an inlet manifold at or near one end of said cylinder and an anvil at or near the other end of the cylinder adapted to engage with the ground, said piston adapted to be propelled towards and to strike said anvil by a gas propellant that enters said cylinder via said inlet manifold, characterised in that said propellant is initially stored as a liquid and adapted to be heated by a heating means which induces a phase change such that said propellant becomes a highly dense gas.

Preferably said device comprises at least one chamber for holding said highly dense gas propellant, said chamber being in fluid communication with said inlet manifold via a valve means adapted to release said highly dense gas propellant to propel said piston.

In a first preferred embodiment said gas propellant is initially stored as liquid in a reservoir remote from said cylinder and said chamber and adapted to be introduced into said chamber, and heated therein by said heating means.

Preferably the anvil is slidable relative to said cylinder and a first portion thereof is located within said cylinder and a second portion thereof is located external to said cylinder. Preferably said gas propellant is carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described with reference to the drawings in which:

Fig. 1 is a schematic cross-sectional elevational view of the main body of a seismic wave generator according to a first embodiment of the present invention, in which the piston is shown in a pre-firing configuration.

Fig. 2 is a schematic cross-sectional elevational view of the main body of a seismic wave generator as shown in Fig 1., in which the piston is shown in a fired configuration striking an anvil.

Fig. 3 is an enlarged schematic view of the high-pressure chamber that is in fluid communication with the main body of the seismic wave generator of Fig 1.

Fig. 4 is an enlarged schematic cross-sectional elevational view of the piston of the seismic wave generator shown in Fig 1.

Fig. 5 is an enlarged schematic cross-sectional elevational view of the anvil of the seismic wave generator shown in Fig 1.

MODE OF CARRYING OUT INVENTION Figures 1 to 5 depict a first embodiment of seismic wave (or pulse) generator in accordance with the present invention. As shown in Fig 1 the seismic wave generator has a main body in the form of a cylinder 1 having an upper end cover 2 and a lower end cover 3.

Preferably cylinder 1 is manufactured from stainless steel tube and is about 1 metre in length. It has an internal diameter of about 75mm and a wall thickness of no less than 5mm. Both ends of the cylinder 1 are externally threaded to allow for attachment of upper and lower end covers 2,3. The upper end cover 2, which is also preferably manufactured from stainless steel, encapsulates the upper end of the cylinder 1 and provides added strength. An exhaust port 5 is located in the lower section of the side wall of cylinder 1. A piston 4 is housed within the cylinder 1 and adapted to slidably move therein. Piston 4 is preferably manufactured from high-grade steel incorporating an upper seal 6 and a lower seal 7. The front face of piston 4 is chamfered to prevent burring and jamming inside the cylinder 1. Preferably piston 4 is casehardened to provide it with good impact qualities.

A retaining mechanism 14 in the form of a ball spring assembly is located about 30mm from the upper end of cylinder 1. Retaining mechanism 14 holds the piston 4 in place inside the cylinder 1 , prior to firing. A soft seal 22 is disposed between upper end cover 2 and piston 4 as shown in Fig 1. A threaded entry hole 9 in the centre of upper end cover 2 provides fluid communication with an inlet manifold 15 mounted above upper end cover 2. Handles 13 are also provided on upper end cover 2.

An anvil 10 is located at the lower end of cylinder 1 and extends through an opening in lower end cover 3. Anvil 10 has an impact plate 11 projecting therefrom, located outside cylinder 1.

In use the cylinder 1 , is held with anvil 10 against the ground and the piston 4 is "propelled" or "fired" from the upper end of cylinder 1 by means of a "gas propellant" introduced into cylinder 1. Piston 1 impacts with anvil 10, thereby allowing a transfer of kinetic energy into the ground and propagates a seismic wave.

The gas propellant is carbon dioxide (CO₂) that is initially stored as a liquid in a remote reservoir such as a canister or tank (not shown in the figures). The reservoir of liquid C0₂ is fluidally connected to a high-pressure chamber 8 via a valve arrangement 16. Liquid C0₂ in chamber 8 is heated by a heating element 12 that is powered by an electrical battery power supply (not shown).

When C0₂ is heated to 31.06°C, it changes to a "super critical state" which is a "highly dense" gas at high pressure. In this embodiment the critical state of C0₂ as it changes phase from liquid to a highly dense gas, provides the explosive energy required to propel piston 4 at high velocity towards anvil 10, regardless of the ambient temperature. The following table depicts the temperature/pressure relationship of Liquid/gas C0₂.

Temperature (°C) Pressure (bar)

21 54

31 74 Critical point

100 250

500 1250

1000 2500

The suitability of C0₂ as a preferred propellant can be appreciated by the following:

• 1 gram of liquid C0₂ will liberate to 500cc of gas at 25°C

• 1 gram of C0₂ = 0.759cc at 25°C

• 1 cc of liquid C0₂ will liberate to 660cc at 25°C

The high-pressure chamber 8 is connected to the inlet manifold 15. In use, once liquid CO2 has been heated to induce a phase change to a highly dense gas, a person will hold the cylinder 1 firmly in an upright position by means of handles 13, with anvil 10 engaged with the ground. An electro-magnetic valve 17 which isolates chamber 8 from inlet manifold 15 is activated to open by a trigger or button (not shown), and the gaseous CO2 is fed through inlet manifold 15 into the top of the cylinder 1.

The piston 4 is forced down at high velocity, preferably about 350m/s and strikes the anvil 10. At the point of impact, the rear of the piston 4 uncovers the exhaust port 5 and relieves the pressure in the cylinder 1. Upon impact the movement of the anvil 10 relative to cylinder 1 , transfers kinetic energy into the ground. As the anvil 10 is not solidly connected to the cylinder 1 it is allowed to semi-float within the lower end cover 3 that acts as a retaining guide assembly. A bearing 21 is disposed between cover 3 and anvil 10. Shock-absorbing material 18 in the lower end cover 3 minimises reverberation within the cylinder 1. This provides a singular high sound, physical Shockwave at low frequency. A secondary exhaust port 19 may be incorporated in the anvil 10 to relieve any trapped air between piston 4 and anvil 10 within the cylinder 1.

The anvil 10 may also preferably incorporate a bore through its centre that is plugged by a removable plug 23 to provide a means by which the piston 4 may be accessed and urged to the top of the cylinder after use. Alternatively in another not shown embodiment, the cylinder 1 may incorporate a device for returning the piston to the top of the cylinder, which utilises exhaust gas exiting port 5 as the energy means to reposition piston 4.

A relief valve 16 is incorporated into the inlet manifold 15 at the top of the cylinder 15 to release gas, allowing the piston 4 to be returned to the start position. The retaining mechanism 14 located at the top of the cylinder 1 retains the piston for firing.

The size of the cylinder 1 for this embodiment makes the pulse generator of this invention greater portability than the hydraulic ram and compressed gas systems of the prior art. Furthermore, the explosive energy of the C0₂ as it undergoes a phase change from liquid gas, allows the present invention to operate effectively, in a manner not achievable by the prior art.

It should be understood that whilst C0₂ has been selected as the preferable propellant due to its properties and commercial availability, other liquid/gaseous propellants could be used in alternative embodiments.

Also, in another not shown embodiment it may be possible to utilise a cylinder, anvil and piston arrangement, similar to that of the earlier embodiment, but using a propellant gas stored in a compressed gaseous state.

It should be understood that the present invention is not limited in size to that of the above described preferred embodiment, and in other not shown embodiments may be larger or smaller.

The term "comprising" as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of".

Claims

1 . A seismic wave generator comprising an enclosed cylinder, a piston movable within said cylinder between an inlet manifold at or near one end of said cylinder and an anvil at or near the other end of the cylinder adapted to engage with the ground, said piston adapted to be propelled towards and to strike said anvil by a gas propellant that enters said cylinder via said inlet manifold, characterised in that said propellant is initially stored as a liquid and adapted to be heated by a heating means which induces a phase change such that said propellant becomes a highly dense gas.

2. A seismic wave generator as claimed in claim 1 , further comprising at least one chamber for holding said highly dense gas propellant, said chamber being in fluid communication with said inlet manifold via a valve means adapted to release said highly dense gas propellant to propel said piston.

3. A seismic wave generator as claimed in claim 2, wherein said propellant is initially stored as liquid in a reservoir remote from said cylinder and said chamber, said liquid adapted to be introduced into said chamber, and heated therein by said heating means.

4. A seismic wave generator as claimed in claim 1 , wherein said anvil is slidable relative to said cylinder and a first portion thereof is located within said cylinder and a second portion thereof is located external to said cylinder.

5. A seismic wave generator as defined in any one of the claims 1 to 5, wherein said gas propellant is carbon dioxide.