Guidance System For A Horizontal Drilling Apparatus

Abstract

A drilling apparatus for forming a horizontal borehole substantially parallel to a first drilled horizontal borehole which has a signal generating apparatus inserted into the first borehole. A horizontal drill is inserted into the subterranean strata adjacent the first drilled borehole and operated until it is in the formation. A signal receiver contained in the horizontal drill apparatus will then receive a signal generated by the signal generating apparatus. The signal generating apparatus will always be maintained a fixed distance behind or in front of the horizontal drilling apparatus. The signal receiver in the horizontal drill will also include an antenna sensitive to direction which can orient itself with the signal generating apparatus. Knowing the angle between the horizontal drill and the signal generating apparatus, along with the distance along the first borehole between the horizontal drill and the signal generating apparatus, will provide sufficient data to calculate the distance between the first horizontal borehole and the drilling apparatus.

Description

BRIEF DESCRIPTION OF THE PRIOR ART

The closest prior art relating the concept disclosed herein is the U.S. Pat. Nos. to Barrett, 3,578,807 and 3,521,796, both of which relate to a tunnel digging apparatus. A U.S. Pat. No. to James C. Coyne, 3,589,454, discloses a system for controlling an underground mole in accordance with a pair of antennae which are positioned on the surface of the earth. The patents to Barrett disclose a method for digging a tunnel utilizing a radioactive stripe which is placed along the edge of the tunnel which has been dug. A radioactive sensor is mounted on the tunnel digging machine and picks up the radiation released by the radioactive stripe. The digging machine maintains its distance from the first formed hole by maintaining a constant radiation being detected. The patent to Barrett also discloses the concept of tuned radio frequency lengths, for example, metal rods or painted stripes being placed along the tunnel wall. A signal generated by the digging machine is tuned to the rods or stripes which provide a reflected signal which is picked up by the tunnel digging machine. The patent to Coyne discloses a concept of mounting an antenna on the surface of the earth and controlling a mole or horizontal drill in accordance with a rotating magnetic field generated by the pair of antennae.

BRIEF DISCUSSION OF THE INVENTION

This invention relates to a method for drilling a second elongated, horizontal borehole which is substantially parallel to a first drilled horizontal borehole by inserting a horizontal drill into the ground along an axis parallel to the first drilled hole and spaced from the first hole. A signal generating means is then positioned in the first hole a known distance with respect to the horizontal drill. As the horizontal drill is operated, the signal generating means is maintained a fixed distance in the first bored hole with respect to the distance the horizontal drill has penetrated. A receiving antenna contained in the horizontal drill determines the angle between the horizontal drill and the signal generating means. Knowing the angle and knowing the distance that each device is in its respective borehole, the distance can be easily calculated by the use of trigonometry.

A more nearly parallel hole can be drilled by adding a second loop antenna detector and determining a second angle. A comparison of the first and second angles will determine the exact orientation of the drill with respect to the originally drilled hole.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a top sectional view taken through two horizontally bored holes, illustrating the signal generating means and the horizontal drill;

FIG. 2 is a perspective view of the boreholes illustrating the method for controlling the penetration of the signal generating means with respect to the horizontal drilling apparatus; and,

FIG. 3 is a perspective view of a signal generating means.

DETAILED DESCRIPTION OF THE INVENTION

Referring to all of the figures, but in particular to FIG. 1, a formation 10 has a bored horizontally drilled hole 11 and a horizontal borehole 12 which is in the process of being drilled by a horizontal drilling apparatus generally referred to by the number 13. A signal generating means 14 has an antenna 15 used for radiating a radio frequency signal. A control cable 16 is attached to the signal generating means 14. The horizontal drill 13 generally comprises a rotary drill 8, a deflection unit 9, a drilling motor 17, which is mechanically coupled to a shaft 18, to drill 8, an instrument package 19, which contains a loop antenna 20. A power mechanism 21 is coupled to the horizontal drill and comprises a plurality of pressure feet 22. A second portion of the power-driving mechanism 23 likewise has a plurality of pressure feet 24. Portion 23 is connected to portion 19 by a shaft 25.

A second housing 26 may be attached to the second portion 23. Cable 16A is attached to housing 26. A second loop antenna 24 is mounted in housing 26.

Referring to FIG. 2, the signal generating means 14 has its antenna 15 mounted on the front of the housing. Along the side of the housing is positioned a plurality of drive wheels 30. Drive wheels 30 are operably coupled to a motor (not shown) which in turn is coupled to a power source 31 which may, for example, be a battery. Power source 31 is coupled through wires 32 and 33 to a pressure switch 34, which is mechanically maintained in a closed position by a spring 35. Cable 16 is connected to switch 34 in a manner to open switch 34 if signal generating means 14 progresses past the length of cable 16. Power source 31, however, maintains power at all times to the signal generating system coupled to antenna 15.

The cable control system is illustrated in FIG. 3 and essentially comprises a reel 40 coupled to a flexible cable 41 to a drive motor 42 and a reel 43 coupled to a flexible drive cable 44 to motor 42. A slip clutch 45 couples flexible cable 41 to reel 40. A cable metering system comprises a roll 50 coupled through a flexible cable 51 to a second roll 52. A pressure roll 53 maintains a tight pressure against cable 16A and roll 52. Likewise, a second pressure roll 54 maintains a firm pressure against cable 16 and roll 50.

OPERATION

The operation is best illustrated by referring to all of the figures but in particular to FIG. 1. As horizontal drill 13 forces its way into formation 10, cable 16A will be pulled by the horizontal drill. As the cable is pulled, roll 52 will turn. Any rotation of roll 52 will be transmitted through flexible cable 51 to roll 50, which will likewise rotate causing a slacking in tension of cable 11. As cable 11 slacks in tension, switch 34 will close, applying power through power source 31 to the drive motor and wheel 30. Signal source 14 will then move following the movement of horizontal drill 13. In the above operation then, the distance d.sub.2 will always be known. As the signal is being transmitted from antenna 15, loop antenna 20 contained in the horizontal drill instrument package 19 will continue to seek the angular direction .phi..sub.1 between the horizontal drill and the signal generating antenna 15. When .phi..sub.1 is determined and d.sub.2 is determined, the distance d.sub.1, which represents the distance of the horizontal drill from the signal source, can then be determined. Since the tangent of .phi..sub.1 is equal to d.sub.1 /d.sub. 2, such information can be easily calculated and corrections as necessary applied to the horizontal drill to cause it to drill so as to maintain a constant distance between borehole 11 and borehole 12. Such a control system is completely described in application 419,157, filed Nov. 26, 1973, titled Control System for a Drilling Apparatus, by Henry A. Bourne, Jr., and Rondon L. Schroeder, and assigned to the assignee of this invention. The control system basically comprises a deflection unit 16 which can be positioned around the axis of drill 13 to 360.degree.. As the drill requires deflection, the roll control rotates the deflection unit 9 in a desired direction; the deflection unit then is pressed against the borehole wall, causing pressure on the drill in the direction desired. The cable 16A is coupled to the drive propulsion unit portion 21. Since portion 23 of propulsion unit 21 is coupled through shaft 25 directly to instrument package 19, the cable will move whenever the instrument package moves, thus always maintaining a known distance between the terminus of cable 16A and cable 16.

The drilling apparatus can be made to drill substantially parallel with the previously bored hole 11 by comparing the null angle .phi..sub.2 of the second loop antenna with the null angle .phi..sub.1 of the first antenna. Both antennae can be fixed in position so that .phi..sub.1 and .phi..sub.2 provide a parallel hole with a predetermined distance d.sub.1. The drill operator will then maintain the drill so that the null conditions are maintained.

It is obvious, of course, that other systems can be used to couple the roller 52 to roller 50 so that the same amount of cable is played out into both holes. For example, an electrical servo controlled system can measure the cable being played out in 16A and transfer electrically the information to roll 50. Roll 50 can then be operated to a simple circle system so that it will play out the same mount of cable 16. It is further obvious, of course, that the signal generating means 14 can be either advanced in the hole further than antenna 20 or behind antenna 20, and the system will function equally well.

It is obvious that changes can be made in the apparatus herein disclosed and still be within the spirit of the invention as described in the specification in the appended claims.

Claims

What we claim is:

1. A method for drilling a second elongated horizontal borehole substantially parallel to a first drilled horizontal borehole comprising:

a. inserting a horizontal drill into the ground along an axis parallel to a drilled hole and spaced from said first hole;

b. positioning a signal generating means in said first hole a known distance with respect to said horizontal drill;

c. maintaining said known distance along the axis of said first hole as said second hole is drilled;

d. receiving said generated signal on said drill;

e. calculating the distance of said signal generated from said receiver; and

f. controlling said horizontal drill in accordance with said calculation to maintain a predetermined distance between said drill and said signal generating means.

2. A method as described in claim 1 wherein said signal generating means is positioned in said first hole equal to the distance said receiving means is positioned in said hole being drilled.

3. A method as described in claim 1 wherein said signal generating means is maintained a known distance with respect to said receiving means in said borehole being drilled.

4. Apparatus for drilling a second elongated horizontal borehole substantially parallel to a first drilled horizontal borehole comprising:

a. means for inserting a signal means in said first borehole;

b. horizontal drilling means;

c. means for propelling said horizontal drill means into the ground along an axis parallel to said first drilled borehole to form a second elongated horizontal borehole;

d. signal means in said horizontal drill means;

e. means for generating a signal in one signal means and receiving said generated signal in said remaining signal means; and

f. means for maintaining said first signal means a predetermined distance in said drilled borehole with respect to the position of said second signal means in said second borehole.

5. An apparatus as described in claim 4 wherein said signal is generated by said first-mentioned signal means and wherein said signal is received by said second-mentioned signal means.

6. An apparatus as described in claim 4 wherein said second-mentioned signal means comprises:

a. a directional antenna;

b. means coupled to said directional antenna for determining the direction of said horizontal drill axis from said first-mentioned signal means; and

c. means for maintaining said first signal means a predetermined distance from said second signal means, whereby the angle between said first and second signal means can be determined and whereby the linear distance between said first and second receiving means can be determined so that the distance between said borehole containing said first signal means and the borehole being drilled containing said second signal means can be calculated.

7. An apparatus as described in claim 4 wherein said second-mentioned signal means comprises:

a. first and second directional antenna means mounted on said drilling apparatus and spaced apart a predetermined distance; and,

b. means coupled to each of said first and second directional antenna to determine its orientation with respect to said signal means in said first hole.

8. An apparatus as described in claim 4 wherein said means for maintaining said first signal means a predetermined distance in said drilled borehole with respect to the position of said second signal means in said second borehole comprises:

a. a first reel having a first line stored thereon;

b. a second reel having a second line stored thereon;

c. means for connecting said first line to said first-mentioned signal means and means for connecting said second line to said second-mentioned signal means; and,

d. means for metering the lengths of said first and second lines played out by said respective first and second reels.

9. An apparatus as described in claim 8 wherein said first-mentioned signal means comprises a housing; means for propelling said housing along said borehole; and, means for attaching said first line to said housing.

10. An apparatus as described in claim 7 wherein said means for attaching said first line to said housing comprises a pressure sensitive switch, and means for coupling said pressure sensitive switch to said propelling means, whereby when said propelling means moves said housing against the tension on said first line, said pressure sensitive switch means will turn off the propulsion means.