US3894402A

US3894402A - Apparatus and method for emplacing a conduit along an underground arcuate path

Info

Publication number: US3894402A
Application number: US489979A
Authority: US
Inventors: Martin D Cherrington
Original assignee: Martin D Cherrington
Current assignee: SPIE GROUP Inc
Priority date: 1974-07-19
Filing date: 1974-07-19
Publication date: 1975-07-15
Anticipated expiration: 1992-07-15
Also published as: YU183175A; DE2531582C2; DE2531582A1; CA1047481A; FR2279009A1; FR2279009B1; GB1501919A; NL7508627A; NL174293C; JPS6059398B2; JPS5136711A; CH604060A5; ES439516A1; BR7504618A; BE831519A; EG11759A; AU8282875A

Abstract

A method for emplacing a production casing such as a pipeline or other conduit beneath a surface obstacle such as a water course is disclosed. A drill is provided which has a trailing drill string. A pilot hole is drilled along an inverted arcuate path beneath a surface obstacle from one side to the other side of the obstacle so that the drill string occupies the pilot hole. A reamer is provided which has a relatively smaller leading end and a larger trailing end. The leading end of the reamer is attached to one of the ends of the drill string, and an end of the production casing is attached to the trailing end of the reamer. The production casing is thrust into the pilot hole at one side of the surface obstacle to project the reamer with the production casing following into the pilot hole. As the production casing is thrust into the pilot hole at one side of the obstacle, the drill string exits the pilot hole at the opposite side of the obstacle. The reamer is operated by rotating the production casing or other method simultaneously with thrusting the production casing into the pilot hole to scarify and dislodge the earth circumscribing the pilot hole. The pilot hole is enlarged to a diameter slightly greater than the production casing to provide an annulus between the production casing and the reamed hole. Drilling mud is injected through the drill string to exit at the reamer where it entrains the dislodged earth. The drilling mud containing the dislodged earth is allowed to flow into the annulus surrounding the production casing.

Description

United States Patent 1 Cherrington 1 1 APPARATUS AND METHOD FOR EMPLACING A CONDUIT ALONG AN UNDERGROUND ARCUATE PATH [76] Inventor: Martin D. Cherrington, P.O. Box

4994, Sacramento, Calif. 95825 22 Filed: July 19, 1974 [21] Appl. No.: 489,979

2.349.033 5/1944 Elliott 175/53 X 2.633.334 3/1953 Lavender... 175/171 2.839.271 6/1958 Kandle 175/53 3.589.135 6/1971 Ede 61/72.] 3.635.036 1/1972 Hooper 6l/72.7 3.730.283 5/1973 Kostylev et a1. 175/53 3.805.899 4/1974 Hicks et al 175/62 X Primary ExaminerDennis L. Taylor Alrorney, Agent, or Firm-Townsend and Townsend {57] ABSTRACT A method for emplacing a production casing such as a 1 1 July 15, 1975 pipeline or other conduit beneath a surface obstacle such as a water course is disclosed. A drill is provided which has a trailing drill string. A pilot hole is drilled along an inverted arcuate path beneath a surface obstacle from one side to the other side of the obstacle so that the drill string occupies the pilot hole. A reamer is provided which has a relatively smaller lead ing end and a larger trailing end. The leading end of the reamer is attached to one of the ends of the drill string, and an end of the production casing is attached to the trailing end of the reamer. The production casing is thrust into the pilot hole at one side of the surface obstacle to project the reamer with the produc tion casing following into the pilot hole. As the production casing is thrust into the pilot hole at one side of the obstacle. the drill string exits the pilot hole at the opposite side of the obstacle. The reamer is operated by rotating the production casing or other method simultaneously with thrusting the production casing into the pilot hole to scarify and dislodge the earth circumscribing the pilot hole. The pilot hole is enlarged to a diameter slightly greater than the production casing to provide an annulus between the production casing and the reamed hole. Drilling mud is injected through the drill string to exit at the reamer where it entrains the dislodged earth. The drilling mud containing the dislodged earth is allowed to flow into the annulus surrounding the production casing.

15 Claims, 5 Drawing Figures APPARATUS AND METHOD FOR EMPLACING A CONDUIT ALONG AN UNDERGROUND ARCUATE PATH BACKGROUND OF THE INVENTION The present invention relates to a method for emplacing a production casing such as a pipeline or other conduit beneath a surface obstacle such as a water course.

The traditional method for laying pipelines, telephone cables and other underground conduits is to dig an open trench, lay the conduit in the trench and then close the trench. This method is quite efficient in general, but problems arise when an obstacle such as a water course or a heavily traveled road is encountered, and the conduit must traverse the obstacle.

When a road is encountered, the road must either be closed, the traffic diverted, or parts of the road closed and the conduit laid in sections, all of which are inconvenient and interfere substantially with the use of the road. When a conduit must span a water course, other problems arise. First, the trench must be dug to a depth considerably below the level at which the conduit is to be laid since the current will partially fill the trench before the conduit can be inserted. This is a significant problem because such trenches have a generally triangular cross section, and the volume of dirt which must be removed increases with the square of the depth of the trench. Such trenching also stirs the alluvium at the bottom of the water course interfering with the natural flora.

Even after a trench has been dug in a water course, difficulties arise in placing the conduit therein. One method of placing the conduit is to float it across the span of the water course and then remove its buoyancy to sink the pipe into the trench. The difficulty with this method is that the water course must be closed to traffic, floating objects are trapped by the floating conduit, the current of the river bends the conduit, and when the conduit is sunk, it quite often misses the trench. A second method is to attach a sled or skid to the leading end of the conduit, and drag this leading end through the trench to lay the conduit. With this method, the conduit must be coated with a substance to give it negative buoyancy, and this coating is quite expensive since the entire length of the conduit must be so coated.

In my previously filed patent application entitled, APPARATUS AND PROCESS FOR DRILLING UN DERGROUND ARCUATE PATHS," Ser. No. 421,548, now pending, a method for drilling along an inverted underground arcuate path under a surface obstacle is disclosed. However, such methods are used primarily for drilling a relatively small pilot hole which must be significantly enlarged in order that a production casing such as a pipeline, telephone cable and other underground conduits can be placed therein.

One of the methods which has been tried experimentally to enlarge an arcuate pilot hole so that a production casing can be placed therein has been to pull a reamer through the pilot hole with the drill string used in drilling the pilot hole, and having a larger drill string trailing the reamer. After the hole has been reamed from end to end, a production casing is attached to the end of the larger drill string, and the larger drill string is dragged through the hole with the production casing following to place the casing therein. However, this method was unsuitable for several reasons. First, pulling the reamer through the arcuate hole results in the drill string knifing through the soil and the reamer does not follow the original reamed hole. Another reason is that pulling the production easing into the hole without providing lubricating drilling mud scars the outside of the casing, which is particularly critical when gas or oil lines are being installed. The results of this method were found to be commercially unfeasible because the integrity of the pipeline installed could not be guaranteed, and also the complexity and difficulty of the method did not warrant its use over other alternative methods.

SUMMARY OF THE INVENTION The present invention relates to a method for emplacing a production casing such as a pipeline or other conduit under a surface obstacle. A drill is provided having a trailing drill string. A pilot hole is drilled along an inverted arcuate path beneath the obstacle from one side to the other so that the trailing drill string occupies the pilot hole. A reamer is provided having a relatively small leading end and a relatively larger trailing end, and the leading end of the reamer is attached to one of the ends of the drill string. The production casing is attached to the trailing end of the reamer. The production casing is thrust into the pilot hole to project the reamer with the production casing following into the hole, and the drill string exits the pilot hole at the other side of the obstacle. The reamer is rotated either by rotating the production casing or other method simultaneously with the thrusting of the production casing to operate the reamer to scarify and dislodge the earth surrounding the pilot hole. The pilot hole is enlarged to a diameter at least equal to the diameter of the production casing so that the production casing is placed along the arcuate path as the pilot hole is being enlarged.

in the preferred embodiment of the present invention, drilling mud is injected into the drill string so that it exits at the reamer. The drilling mud thus entrains the earch scarified and dislodged by the reamer. The pilot hole is reamed to a diameter slightly larger than that of the production casing and the drilling mud with the entrained earth therein flows into this annulus. The drilling mud lubricates the production casing as it is thrust ino the hole so that friction on the production casing is minimized and there is no damage to the outer surface of the casing. Insertion of the production casing can be further facilitated by matching the buoyancy of the casing to the drilling mud and the casing will slip easily into the hole.

When the surface obstacle is relatively wide, it is preferred to remove excess drilling mud containing the entrained earth therein from the hole. A relatively small return pipe is placed internal to the production casing, and is connected to the annulus around the casing. Drilling mud still fills the annulus to lubricate the production casing, but the excess drilling mud exits the hole through the return pipe so that the hole is not enlarged more than necessary and does not blow out, as described below. The diameter of the return pipe can be selected so that the casing has neutral buoyancy and other weights are not required.

In one of the embodiments of the present invention, the reamer is non-rotatably attached to the production casing, and the production casing itself is rotated in order to operate the reamer. This has the secondary advantage that the friction between the production casing and the sides of the hole is reduced because the casing rotates as it enters the hole. However, the production casing is being placed along an arcuate path and the side walls of the casing are flexed upon each revolution of the casing. For larger diameter production casings, this flexing can cause fatigue failure. Hence, an alternate embodiment of the present method is provided wherein the production casing is rotatably attached to the reamer, so that the casing does not rotate, and a drive shaft or other mechanism is employed to operate the reamer.

The novel features which are believed to be characteristic of the invention, both as to organization and method of operation together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the completion of the pilot hole underneath the surface obstacle;

FIG. 2 is a perspective view similar to that of FIG. 1 illustrating the reaming of the pilot hole to selected larger diameter;

FIG. 3 is a fragmentary elevation view of the reaming apparatus of the present invention;

FIG. 4 is a fragmentary elevation view of the reaming apparatus of the present invention partially cut away; and

FIG. 5 is a fragmentary elevation view of an alternate embodiment of the present invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drilling of the pilot hole beneath a surface obstacle such as water course 12 is illustrated by way of reference to FIG. 1. An inclined drill rig I4 is placed in an inclined pit 16 at one side of water course 12. A drill bit 18 having a trailing drill string 20 is directed along the desired arcuate path to exit at the other side of obstacle l2. Drill string 20 comprises a plurality of interconnected drill string segments which are joined to form the drill string. After drill bit 18 emerges at the other side of obstacle 12, drill string 20 occupies the entire pilot hole 10.

In order to enlarge pilot hole 10, the smaller leading end of a frustro-conical reamer is attached to one end of drill string 20 as illustrated in FIG. 2. In the preferred embodiment of the present invention, production casing 32 is non-rotatably attached to the larger trailing end of reamer 30. The production casing is forced into pilot hole 10 by thrusting the casing at its trailing end using drill rig l4, and reamer 30 is operated by rotating the casing. Production casing 30 can be either a steel or cement pipe such as used for oil and water pipelines, protective casings for telephone lines and the like. Production casing 32 consists of a plurality of segments such as 34.

In the embodiment of the present invention illustrated in FIG. 2, a tube 36 is attached to the leading end of drill string 20. Tube 36 is attached to a pump 38 which forces drilling mud through the drill string to exit at the reamer. As sections of drill string 20 emerge from the pilot hole as production casing 32 is thrust therealong, the segments are placed in a pile 40 and tube 36 is reattached to the leading end of the next segment. Hence, drilling mud is continuously injected into pilot string 20 to exit at the reamer. As the segments of drill string 20 are taken off the leading end thereof, segments 34 of production casing 32 are added at the trailing end. The drill rig 14 used for drilling the pilot hole also acts to thrust the production casing 32 into the ground in this embodiment as illustrated by arrow 42, and in the preferred embodiment rotates the production casing as well as operates the reamer.

The manner in which reamer 30 is interposed between drill string 20 and production casing 32 is illustrated in more detail in FIG. 3. The narrower leading end of frustro-conical reamer 30 connects nonrotatably to drill string 20. In the preferred embodiment, the larger trailing end of reamer 30 is nonrotatably connected to production casing 32. Reamer 30 has a plurality of reamer teeth 42 which enlarge pilot hole 10 to a diameter slightly larger than that of production casing 32. This provides a small annulus 44 about the outer diameter of production casing 32. Drilling mud which is injected through drill string 20 and exits at reamer 30 flows around the reamer and entrains the earth 46 scarified and dislodged by reamer teeth 42 as illustrated by arrows 48. The drilling mud containing the dislodged earth flows into the annulus 44 circumscribing the production casing 32 as illustrated by arrows 50. The used drilling mud serves to lubricate production casing 32 so that it slips easily into the enlarged hole.

When the relatively long production casing is to be placed under the ground, the buoyancy of the production casing can be a critical problem. Since the density of production casing 32 with its hollow interior is substantially less than that of the drilling mud in annulus 44 for larger production casings, the production casing will be forced upwardly and will distort the path of the production casing as it is being emplaced. For smaller production casings, the density of the casing with its hollow interior is greater than that of the drilling mud and the weight of the casing distorts the path. One of the features of the present invention is to weight the production casing 32 so that its density including the hollow interior is substantially equal to that of the drilling mud. In this situation, the production casing 32 will have neutral buoyancy with respect to the drilling mud and will slip easily into the hole along the axis of pilot hole 10. Such neutral buoyancy can be achieved by placing foam inside the production casing, coating the casing, placing weights in the casing, and the like.

A preferred embodiment of the present invention wherein excess drilling mud is removed as the production casing 32 is being emplaced is illustrated by way of reference to FIG. 4. In this embodiment, drilling mud is injected through drill string 20 as illustrated by arrow as previously shown. This drilling mud exits at the reamer and flows into the annulus 44 around production casing 32. However, in order to relieve the pressure of the drilling mud in annulus 44, an internal return pipe 62 is provided inside production casing 32. Return pipe 62 has a plurality of extensions 64 which communicate with holes 66 in the walls of casing 32. In this manner, a connection is provided between return pipe 62 and annulus 44 so that excess drilling mud in the annulus can flow out through return pipe 62 as illustrated by arrow 68.

Since volumetric flow of drilling mud into the hole is generally greater than that which can be accommodated by annulus 44, failure to provide a return pipe such as 62 forces the drilling mud to flow backwardly along the production casing 32. In the placing of a relatively long production casing, the pressure on the enlarged hole adjacent the reamer will be relatively large to force the mud along the entire casing. As a result, when drilling under river bottoms and the like, the hole may blow out due to this pressure and water from the river can flow into the hole. Also, the excess drilling mud will flow into the water course and pollute the stream and destroy the natural wildlife. The provision of return pipe 62 will avoid such a blow out when long production casings are emplaced. A further advantage of the return pipe is that the diameter of the pipe can be selected so that the drilling mud will weight production casing 32 so that it has neutral buoyancy with respect to the drilling mud. Hence, a separate weighting mechanism need not be provided to achieve neutral buoyancy.

In the preferred embodiment, pipe 62 is used to return used drilling mud as illustrated by arrows 68. However, as an alternative embodiment, a pipe such as 62 can be used to inject drilling mud so that it exits near reamer 30 rather than inject drilling mud through drill string 20. To this end, pipe 62 would be extended as illustrated in phantom 69 so that the drilling mud would be injected at reamer 30 rather than into annulus 44. After the drilling mud entrains the earth scarified and dislodged by reamer 30, the used drilling mud flows into annulus 44 as in the previous embodiments.

An alternate embodiment to those discussed above which is primarily adapted for use with relatively large production casings is illustrated in FIG. 5. When a production casing such as casing 70 has a diameter of greater than approximately inches, rotating the production casing in the arcuate path can cause excessive fatigue of the casing and it is preferred not to rotate the casing. For such large production casings 70, the casing is rotatably attached to the trailing end of a reamer such as 72. The leading end of reamer 72 is nonrotatably attached to drill string 74, and drilling mud is injected through drill string 74 as illustrated by arrow 76, similar to the method described above. However, reamer 72 is operated by means of a drive shaft 78 which rests along the bottom of casing 70. A pulley 80 or gear arrangement is connected to reamer 72 so that rotation of drive shaft 78 operates the reamer. As an alternative, a drilling motor as known in the art can be placed at the leading end of casing 70 to operate the reamer.

In the embodiment illustrated in FIG. 5, a return pipe, such as return pipe 62 illustrated in FIG. 4, could also be provided. Also, the production casing 70 could be rotated slowly (relative to the rotation of the reamer 72) to make the casing slip more easily into the hole and reduce friction thereon. Fatigue of the casing is dependent upon the speed of rotation of the casing so that at low speed rotation may be acceptable where high speed rotation such as required to operate the reamer is not acceptable.

In many applications such as the installation of telephone lines, several smaller product pipes are installed in the production casing after it is in place. This installation is facilitated by filling the production casing with a fluid such as treated water or oil and sealing the leading ends of the product pipes before inserting them in the production casing. As a result, the product pipes will be at least partially buoyant so that they will float easily into the production casing.

While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of that embodiment will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.

What I claim as new is:

1. A method for emplacing a production casing beneath a surface obstacle such as water course, said method comprising the steps of:

providing a drill having a trailing drill string;

drilling a pilot hole along an inverted arcuate path beneath the surface obstacle from a first side to a second opposite side of the obstacle with said drill so that the drill string occupies the pilot hole with the opposite ends of said drill string being on opposite sides of the obstacle;

providing a reamer having a relatively smaller leading end and a relatively larger trailing end; attaching the relatively smaller leading end of the reamer to one of the ends of the drill string;

attaching an end of the production casing nonrotatably to the relatively larger trailing end of the reamer; forcing the production casing into the pilot hole at one side of the surface obstacle to project the reamer with said production casing following into said pilot hole, the drill string exiting the pilot hole at the other opposite end of the obstacle; and

rotating the production casing simultaneously with said thrusting step to operate the reamer to scarify and dislodge the earth around the pilot hole to enlarge the pilot hole to a diameter at least equal to the production casing so that said production casing is emplaced along the arcuate path as the pilot hole is being enlarged.

2. A method as recited in claim 1 wherein said forcing comprises thrusting the production casing at its trailing end.

3. A method as recited in claim I wherein rotating the production casing to operate the reamer is adapted to enlarge the pilot hole to a diameter slightly larger than the diameter of the production casing to provide a narrow annulus circumscribing said production casing, said method additionally comprising the steps of injecting drilling mud into the end of the drill string opposite from the end of the drill string attached to the leading end of the reamer so that said drilling mud flows through said drill string to exit at the reamer; entraining in said drilling mud the earth scarified and dislodged by the reamer; and allowing the drilling mud containing the scarified earth to flow into the annulus around the production casing to lubricate the casing as it is forced into the pilot hole.

4. A method as recited in claim 1 wherein rotating the production casing to operate the reamer is adapted to enlarge the pilot hole to a diameter slightly larger than the diameter of the production casing, said method additionally comprising the steps of providing an inlet pipe internal to the production casing, said inlet pipe having one end terminating adjacent the reamer; injecting drilling mud into the inlet pipe so that said drilling mud flows through said inlet pipe to exit at the reamer; entraining in said drilling mud the earth scarified by the reamer; and allowing the drilling mud containing the scarified earth to flow into the annulus around the production casing.

5. A method as recited in claim 1 wherein attaching the leading end of the reamer to one of the ends of the drill string comprises attaching the leading end of the reamer to the end of the drill string at said first side of the surface obstacle.

6. A method as recited in claim 1 wherein said attaching the leading end of the reamer to one of the ends of the drill string comprises attaching the leading end of the reamer to the end of the drill string at said second side of the surface obstacle.

7. A method as recited in claim 1 wherein said trailing drill string comprises a plurality of drill string segments, and additionally comprising the step of removing the segments individually from the drill string as said drill string segments exit the pilot hole at the opposite end of the obstacle.

8. A method as recited in claim 1 and additionally comprising the step of providing an inclined drill rig at the first side of the surface obstacle, and wherein said drilling step additionally includes thrusting the drill string into the pilot hole with said drill rig, wherein said production casing forcing step additionally includes thrusting the production casing with said drilling rig, and wherein said production casing rotating step additionally includes rotating the production casing with said inclined drill rig.

9. A method as recited in claim 1 and additionally comprising the steps of filling the emplaced production casing with a liquid, and inserting a plurality of product pipes in the filled production casing, the leading ends of said product pipes being sealed to provide buoyancy to said pipes as said pipes are inserted in the production casing.

10. A method for emplacing a large diameter production casing beneath a surface obstacle such as a water course, said method comprising the steps of:

providing a drill having a trailing drill string;

drilling a pilot hole along an inverted arcuate path beneath the surface obstacle from one side to the other with said drill so that the trailing drill string occupies the pilot hole with the opposite ends of said drill string being on opposite sides of the obstacle;

providing a reamer having a relatively smaller leading end and a relatively larger trailing end;

attaching the leading end of the reamer to one of the ends of the drill string;

attaching an end of the large diameter production casing to the trailing end of the reamer; providing means for rotating the reamer internal to the production casing,

forcing the production easing into the pilot hole to project the reamer with said production casing following into said pilot hole; and

rotating the reamer with said rotating means simultaneously with said forcing step to operate the reamer to scarify and dislodge the earth around the pilot hole to thereby enlarge the pilot hole to a diameter at least equal to the production casing so that the said production casing is emplaced along the arcuate path as the pilot hole is being enlarged.

1 1. A method as recited in claim 10 wherein said providing means for rotating the reamer comprises the step of providing a drive shaft internal to the production casing, said drive shaft having a power output end attached to the reamer, and wherein said rotating the reamer step comprises rotating the reamer by rotating the drive shaft simultaneously with said forcing step to operate the reamer.

12. A method for emplacing a production casing beneath a surface obstacle such as a water course, said method comprising the steps of: providing a drill having a trailing drill string; drilling a pilot hole along an inverted arcuate path beneath the surface obstacle from a first side to a second opposite side of the obstacle with said drill so that the trailing drill string occupies the pilot hole with the ends of said drill string being on opposite sides of the obstacle; providing a reamer having a relatively smallerleading end and a relatively larger trailing end; attaching the leading end of the reamer to one of the ends of the drill string; connecting an end of the production casing to the trailing end of the reamer; providing means for rotating the reamer; thrusting the production casing into the pilot hole to project the reamer with said production casing following into said pilot hole; rotating the reamer with rotating means simultaneously with said thrusting step to operate the reamer to scarify and dislodge the earth around the pilot hole; injecting drilling mud into the end of the drill string opposite from the end of the drill string attached to the leading end of the reamer so that said drilling mud flows through said drill string to exit at the reamer; and allowing the drilling mud containing the scarified earth to flow into the annulus around the production casing so that the production casing slips easily into the enlarged hole.

13. A method as recited in claim 12 and additionally comprising the steps of providing a return pipe internal to the production casing; providing communication between said return pipe and the outer surface of the production casing; and allowing the drilling mud contained in the annulus around the production casing to flow out of the production casing through the return pipe.

14. A method as recited in claim 12 wherein the trailing end of the reamer is nonrotatably attached to the production casing, and wherein providing means for rotating the reamer comprises providing means for rotating the production casing to rotate the reamer.

15. A method as recited in claim 12 wherein said providing means for rotating the reamer comprises providing a drive shaft internal to the production casing, said drive shaft being connected to the reamer so that rotation of the drive shaft rotates the reamer.

Claims

1. A method for emplacing a production casing beneath a surface obstacle such as water course, said method comprising the steps of: providing a drill having a trailing drill string; drilling a pilot hole along an inverted arcuate path beneath the surface obstacle from a first side to a second opposite side of the obstacle with said drill so that the drill string occupies the pilot hole with the opposite ends of said drill string being on opposite sides of the obstacle; providing a reamer having a relatively smaller leading end and a relatively larger trailing end; attaching the relatively smaller leading end of the reamer to one of the ends of the drill string; attaching an end of the production casing non-rotatably to the relatively larger trailing end of the reamer; forcing the production casing into the pilot hole at one side of the surface obstacle to project the reamer with said production casing following into said pilot hole, the drill string exiting the pilot hole at the other opposite end of the obstacle; and rotating the production casing simultaneously with said thrusting step to operate the reamer to scarify and dislodge the earth around the pilot hole to enlarge the pilot hole to a diameter at least equal to the production casing so that said production casing is emplaced along the arcuate path as the pilot hole is being enlarged.

3. A method as recited in claim 1 wherein rotating the production casing to operate the reamer is adapted to enlarge the pilot hole to a diameter slightly larger than the diameter of the production casing to provide a narrow annulus circumscribing said production casing, said method additionally comprising the steps of injecting drilling mud into the end of the drill string opposite from the end of the drill string attached to the leading end of the reamer so that said drilling mud flows through said drill string to exit at the reamer; entraining in said drilling mud the earth scarified and dislodged by the reamer; and allowing the drilling mud containing the scarified earth to flow into the annulus around the production casing to lubricate the casing as it is forced into the pilot hole.

10. A method for emplacing a large diameter production casing beneath a surface obstacle such as a water course, said method comprising the steps of: providing a drill having a trailing drill string; drilling a pilot hole along an inverted arcuate path beneath the surface obstacle from one side to the other with said drill so that the trailing drill string occupies the pilot hole with the opposite ends of said drill string being on opposite sides of the obstacle; providing a reamer having a relatively smaller leading end and a relatively larger trailing end; attaching the leading end of the reamer to one of the ends of the drill string; attaching an end of the large diameter production casing to the trailing end of the reamer; providing means for rotating the reamer internal to the production casing; forcing the production casing into the pilot hole to project the reamer with said production casing following into said pilot hole; and rotating the reamer with said rotating means simultaneously with said forcing step to operate the reamer to scarify and dislodge the earth around the pilot hole to thereby enlarge the pilot hole to a diameter at least equal to the production casing so that the said production casing is emplaced along the arcuate path as the pilot hole is being enlarged.

11. A method as recited in claim 10 wherein said providing means for rotating the reamer comprises the step of providing a drive shaft internal to the production casing, said drive shaft having a power output end attached to the reamer, and wherein said rotating the reamer step comprises rotating the reamer by rotating the drive shaft simultaneously with said forcing step to operate the reamer.