Drilling short boreholes

[57] ABSTRACT

Short boreholes, e.g., shallow wells for piles and horizontal holes for pipelines, are drilled by directing a series of explosion waves at the closed end of the borehole. This compacts material at the walls thereby extending the hole.

Claims, 10 Drawing Figures

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INVENTORS.

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DRILLING SHORT BOREHOLES

This invention relates to drilling short boreholes, where these are downwardly directed (not necessarily vertically) they will be called “Shallow Wells.”

Shallow wells, i.e., wells up to 50 meters deep, are required for various purposes such as shot holes for geophysical prospecting, water wells and piles. (Piles may be regarded as shallow wells which have been filled with suitable materials, e.g., concrete or prestressed concrete after drilling. A metal lining may be inserted into the well as it is drilled). Short boreholes in directions other than vertical, e.g., horizontal, are required for pipelines. It is an object of this invention to facilitate the drilling of short boreholes at locations where the earth’s surface has a compactible nature.

According to the invention a short borehole, e.g., a shallow well, is drilled into the earth’s surface at a location where the surface has a compactible nature by:

a. Separately and continuously introducing oxygen and fuel into a combustion chamber so as to form an explosive mixture,

b. Intermittently igniting the explosive mixture so as to generate a series of explosion waves in the combustion chamber, and

c. Directing the explosion waves at the closed end of a partially drilled borehole so as to remove material from said end and compact it around the sides, whereby the length of the borehole is increased at each explosion.

The oxygen may be introduced as the pure gas or as a gaseous mixture, e.g., air.

The fuel is preferably introduced into the combustion chamber in the vapor phase and this may be achieved by using a fuel which is a gas at ambient temperature, e.g., hydrogen, carbon monoxide and hydrocarbons which contain one to four carbon atoms per molecule. Substances such as gasoline which can be vaporized and supplied to the combustion chamber in the gaseous phase may also be used as gaseous fuels. It is also possible to use liquid fuels which are sprayed into the combustion chamber so as to form an explosive mist of fuel droplets in oxygen (air).

The invention includes a method of drilling lined short boreholes which comprises generating a series of explosion waves as described above at the free end of a lining pipe, directing the explosion waves at the closed end of the borehole through the lining pipe and applying a force to the lining pipe to cause it to advance into the borehole as the series of explosion waves increases the length of the bore hole. In the case of a shallow well the force is conveniently gravitational, i.e., the lining is allowed to sink under its own weight. Extra weights may be attached to the lining pipe if its own weight is insufficient to cause it to sink.

While the method described in the last preceding paragraph is being carried out the spent gas, i.e., the gas after it has compacted material at the bottom of the borehole, escapes via an annulus formed between the lining member and the sides of the borehole. This helps to reduce friction between the lining and the earth thereby facilitating the advance of the lining member.

The invention includes a method of drilling unlined boreholes in which a combustion chamber operated as described above enters the borehole and a force is applied (preferably gravitational for a shallow well) to cause the combustion chamber to advance into the borehole as the series of explosion waves increases the length of the borehole. The combustion chamber may be fitted with spines which engage with the sides of the bore hole to resist the recoil.

The heat generated in carrying out the method according to the invention modifies certain earth formations, e.g., clays, so that they become less able to flow and this helps to prevent the sides of the borehole collapsing.

The method described above may be carried out by generating the series of explosion waves in a burner which comprises:

i. A oxygen/fuel chamber which has grossly rough walls, and ii. An oxygen-fuel inlet system which has a low resistance to gaseous flow and which is arranged to mix the oxygen and fuel at one end'of the combustion chamber, whereby, during the use of the burner, a series of explosion waves is produced by repeated ignition of an explosive mixture formed in the combustion chamber.

The invention includes an apparatus for drilling lined short boreholes, e.g., shallow wells, which comprises a burner as defined above which is adapted to be fitted to the end of a length of lining pipe. The invention also includes an apparatus for drilling unlined short boreholes, e.g., shallow wells, which comprises a burner as described in the last preceding paragraph which is provided with spines to prevent its being removed from a borehole by the recoil generated by the explosion waves.

Such a burner is conveniently connected to a thrust block adapted to apply a force to advance the burner into the borehole, the thrust block being provided with spines to take the reaction of the forces which advances the burner into the borehole. The spines allow the thrust block to follow the burner as it enters the hole, i.e., the burner and the thrust block advance alternatively.

In most cases piles carry loads, i.e., loads which tend to push the pile further into the earth. However there are cases, known as “tensioned piles,” in which the pile is subjected to a load which tends to pull the pile out of the earth. Shallow wells for tensioned piles may be produced by a method according to the invention which comprises drilling a well to the required depth as described above, supporting the lining tube (if any) so that it can no longer enter the well and generating a series of large explosion waves using a high-gas flow rate and low-ignition rate so as to produce an enlarged cavity at the bottom of the borehole. When the shallow well has been filled with the material of the pile the cavity assists the pile in carrying the tension.

The invention will now be described by way of example with reference to the drawings in which:

FIG. 1 is a vertical cross section through a lined shallow well in a clay soil during the course of drilling in accordance with the invention,

FIG. 2 is a vertical cross section through the well shown in FIG. 1 at the end of drilling and excavation,

FIG. 3 is a vertical cross section through an unlined shallow well during the course of drilling in accordance with the invention,

FIG. 4 is a vertical cross section through the inlet system of the burners shown in FIGS. 1-3,

FIG. 5 is a horizontal cross section on the line 5—5 of FIG. 4,

FIG. 6 shows a modification for drilling in directions other than downwards,

FIG. 7 is a cross section on the line 7—7 of FIG. 6. FIGS. 8α, b and c are diagrammatic views showing an operating sequence of a preferred embodiment of the modification depicted in FIGS. 6 and 7.

FIG. 1 shows a clay soil 10 in which a shallow well 11 is situated. The FIG. 1 shows the condition just after the start of drilling and as the well 11 becomes deeper the lining tube 12 sinks into the borehole.

A burner 13, which has a pulsating mode of operation, comprises:

i. A combustion chamber which has grossly rough walls, and

An oxygen/fuel inlet system which has a low resistance to gaseous flow and which is arranged to mix the oxygen and fuel at one end of the combustion chamber, whereby during the use of the burner, a series of explosion waves is produced by repeated ignition of an explosive mixture formed in the combustion chamber.

The burner 13 receives a continuous supply of fuel and air by the inlet tubes 14 and 15 respectively and the two gas streams are mixed in the inlet system 16 to produce an explosive mixture which enters the combustion chamber of the burner 13. From time to time the mixture is ignited by means of the spark plug 17 which is supplied with electric power by electric cable 18, to produce a series of explosion waves which travel down the lining tube 12 to the bottom of the borehole 11.

3,635,293

As each pressure pulse reaches the bottom it finds that its exit is restricted since the lining tube 12 rests on the bottom of the hole. Therefore each pressure pulse compresses the clay at the side of the hole 11 and it creates a small annulus 19 through which it can escape. The repeated passage of pressure pulses maintains the annulus 19 open to the top of the hole and this facilitates the entry of the lining tube 12 into the hole under its own weight; this may be assisted by the addition of a weight 20 at the top of the lining tube 12.

To start drilling the lining tube 12 is supported in a vertical position by means of a suitable crane (with directional guides) and its open end is allowed to rest on the surface of the ground at the desired location. The lifting forces are reduced until almost the whole weight of the tube is taken by the ground and air is passed in by the inlet tube 15 at a pressure just sufficient to ensure escape at the bottom of the lining tube 12. At this stage sparking is commenced at the desired frequency and the fuel gas admitted to form an explosive mixture with the air, which mixture is ignited from time to time by the spark plug at the sparking frequency to produce a series of explosion waves which travel down the lining tube 12 to the bottom of the borehole 11. This initiates the boring of the well as described above.

In one test a cylindrical steel lining tube 6 meters long 10 centimeters internal diameter and 11 centimeters external diameter was sunk in gravel subsoil to give a hole 12 centimeters in diameter and 6 meters deep; at this stage its end was below the water table. A burner which comprised a rough cylindrical tube 1 meter long and 10 centimeters in diameter was flange mounted on the top of the lining tube and a continuous supply of air and hydrogen was admitted by an inlet system which mixed the two gases to produce an explosive mixture in the rough tube. The mixture was sparked at a frequency of 2 sparks per second and the gas flow rate was such that each detonation produced 100 K joules of energy in each pulse. These pulses caused the tube to sink into the ground at the rate of 1 centimeter per pulse with a weight of 100 kilograms supported by the lining tube 12. When the borehole was inspected after drilling it was found that the earth surrounding the lining tube was well compacted and that no earth had entered the lining tube.

FIG. 2 shows a shallow well, the same as the one shown in FIG. 1, which has been completed with a cavity 21 formed at the base. To form this cavity the lining tube 12 was supported so that it could sink no further and very large explosion waves were fired down the tube by maintaining a high-gas rate input with a low-spark rate.

With a gas input rate of 30 liters/sec. (hydrogen/air) and a sparking rate of 1 per second it was found possible to produce a cavity about 50 centimeters diameter.

FIG. 3 shows a modification of FIG. 1 for producing unlined tubes. In this modification there is no lining tube 12 and the burner 13 together with the weight 20 mounted on the top of the burner both enter the borehole 11. Air, fuel and electric power (to operate the spark plug 17) are supplied by flexible fuel, air and electric power supply cables 14, 15 and 18, respectively.

The burner shown in FIGS. 1-3 comprises a fuel-air inlet system which is shown in greater detail in FIGS. 4 and 5.

The inlet system shown in FIGS. 4 and 5 comprises fuel and air inlet tubes 14 and 5 respectively, which enter the head of the burner parallel to its longitudinal axis. Each tube turns through a right angle so that radial tubes 22 and 23 enter the annulus 24 tangentially (as can be seen in FIG. 5). The center annulus is formed of a casing 25 into which the sparking plug 17 (having annular electrodes) is fitted.

FIGS. 6 and 7 show an arrangement in use to drill a horizontal borehole 11. The arrangement comprises a burner 13 disposed in the borehole 11 connected to a fuel supply line 14, an air supply line 15 and an electric cable 18 (as described above).

The burner is connected to a thrust shaft 30 which slidably engages with a thrust block 32; the shaft 30 has spines 31 and the thrust block 32 has spines 33 which engage with the sides of the borehole to prevent withdrawal. (The spines can be controlled by a linkage, not shown in any drawing, to steer the device or for release when withdrawal is required.) As can be seen from FIG. 7 there are three sets of spines set 120° apart on the thrust shaft 30 (and a similar arrangement on the thrust block 32). The various service cables pass between the spines.

When operated, the thrust block 32 applies a force, for example, a pneumatic or hydraulic force, to the slidable thrust shaft 30 to advance the shaft and the burner 13 along the bore hole 11 and during this time the spines 33 are in engagement with the sides of the borehole 11 to prevent withdrawal or retreat of the thrust block while the spines 31 of the thrust shaft do not resist the advance of the burner. Upon completion of the advance of the burner, the direction of the force applied to the thrust shaft by the thrust block is reversed to advance the thrust block and, during this time, under the action of the thrusting force, the spines 31 of the thrust shaft are in engagement with the sides of the borehole to prevent withdrawal of the burner 13 while the spines 33 of the thrust block do not resist the advance of the thrust block towards the burner. Thus, the whole combination advances into the borehole and, by suitable adjustment of the spines, it can be steered.

In a preferred embodiment diagrammatically depicted in FIGS, a, b and c; the spines form a pneumatically or hydraulically actuated desmodromic system. In this system a set of pneumatically or hydraulically extendable front spines 31' are connected to a set of pneumatically or hydraulically extendable rear spines 33' by means of a pneumatic or hydraulic ram comprising the thrust shaft 30' and the thrust block 32'. The advance of the apparatus into the hole takes place in two phases; in the “preparatory phase” the apparatus is prepared to advance the burner, in the “advance phase” the burner moves forward.

During the “preparatory phase” and as is depicted in FIG. 8α, the front spines 31' are extended and engaged, the rear spines 33' are retracted and disengaged and the ram is then retracted, i.e., the rear or thrust block portion 32' of the apparatus moves forward from the position shown in FIG. 8α to that shown in FIG. Sb. During the “advance phase,” the rear spines 33' are extended and engaged, the front spines 31' are retracted and disengaged and the thrust shaft 30' extended, i.e., the burner 13 moves forward from the position shown in FIG. 8b to that shown in FIG. 8c so that the cycle may then be repeated. Suitably, the desmodromic system depicted in FIGS. 8α, b and c comprises a pair of ganged three-way valves 40 and 41 which may be remotely actuated, flexible fluid transfer lines 42 to which actuating fluid under pressure is supplied via supply line 43 and a sump 44 for fluid circulating in the system.

Since the burner can drill a hole larger than its own diameter it is possible to drill a hole, insert a lining (e.g., as the hole is formed) and then withdraw the burner through the lining.