CA1154429A

CA1154429A - Method and apparatus for forming lateral passageways

Info

Publication number: CA1154429A
Application number: CA000371274A
Authority: CA
Inventors: Newton B. Dismukes
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-02-27
Filing date: 1981-02-19
Publication date: 1983-09-27

Abstract

A B S T R A C T
The present invention broadly provides a system for drilling a bore hole laterally in a horizontal plane. Essen-tially, this is accomplished by making the drilling tool and the conduit for applying power and drilling fluid thereto sub-stantially unaffected by the force of gravity. This result is obtained by so constructing the drilling tool and the conduit that they will be substantially neutrally buoyant in the drill-ing fluid used.

Description

BACKGROUND OF THE INVENTION

Field of the Invention _ The present invention relates to the recovery of hydrocarbons and such other underground values as may be recovered through inaccessible bores. More particularly, it provides new and improved apparatus and method for forming a horizontal or lateral passageway, which may have great length.
Such passageway is useful in the recovery of petroleum, more particularly viscous oils and tars, in o~taining bitumans and other semi-solids, in degassing coal seams and in the recovery of any substance which may be disintegxated by the mechanical or hydraulic means disclosed herein and be slurrified.

Description of the Prior Art The value of the presently uneconomically recover-able reserves of heavy oils and tars is inestimableJ The many schemes and inventions disclosed during the past fifty years in an attempt to form lateral boxes attest to the dire need for su~h technology.
The techniques hexetofore proposed for forming hori-zontal or lateral bores suffer major and critical deficiencies.
Some presuppose some idealized or homogeneous conditions ssldom found in nature~ Other require a special comb~nation of strata deposition. Many idea~ require pulling the boring means from , ~
the horizontal into the vertical well with no provision made ~ 1 -- . 1,, for preventing key-seating. It i5 well known in oil well drilling that a change in hole angle exceeding 8 to 10 degrees per one hundred feet of dog-leg severity will cause stuck pipe.
Recently, a subsidiary of Imperial Oil, Esso Re-sources Canada Ltd. in seeking to recover heavy oil from the vast deposits at Cold La~e, Alberta, Canada drilled what it claimed to be "the first horizontal well to be drilled in North America and probably in the western world" using conventional drilling equipment in a special manner described in Oilweek, November 12, 1979, pages 68 to 70. A milled tooth bit rotated by a Dynadrill was used to make hole. Bent subs provided the angle build up. The collars were not positioned just above the bit but rather were located in the "more vertical portion of the hole to provide weight on bit". Special "Hevi-wate pipe was used between collars and bit a~sembly because ordinary drill pipe cannot be used in compression". Oil base mud was used to minimize the tendency of the drill pipe to drag and to reduce the tendency of the curved pipe to stick against the side of the hole. The author of the paper was justifiably proud of the achievement and of the possibilities opened up for improving recovery from the vast heavy oil deposits in North America.
The technology employed, however, was time consuming and costly. Also, there would appear to be limitations as to how far one could proceed in a horizontal direction after it had been attained by pushing a heavy drilling assembly with heavy drill pipe.
Similarly and more recently in an article entitled "Soviets Claim Horizontal Drilling Success", Oil and Gas Jour^
nal, Decem~er 17, 1979, page 23, the horizontal drilling of the ,,, !
terminal portion of oil wells b~ the Russians is disclosed.
While details are lacking, here again apparentLy conventional e~uipment was used ~ut special techniques and procedures D

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employed. The article reports that "the wells (were) spudded a~ a sharp angle" (apparently using slant dri]ling ri~s) "and completed using turbo drills for horizontal c~lillinc3". All that is revealed is that when "the well r~ach~s the proj~cted depth . . . the drill moves horizontally" . . . and "operation of the drill horizontally becom~ more d1fficu]t." Here, as in the case of Esso Resources, presumably steel drill pipe was used throughout the drilling operation and with all the attendant difficulty of keeping weight on bit as the horizontal portion of the hole was extended.
In an invention relating to solution mining Charles ~.
Jacoby, U. S. Patent No. 3,873,156, describes a system for co-alesing the nether ends of spaced apart bores. He attaches floats to a hydraulic jettingltool and to the flexible conduit conducting the jetting fluid thereto and employs two immiscible liquids of different density to locate the system at an interface.
U. S. Patent No. 2,822, 158, to W. C. Brinton, also relates to fluid mining using both solvent action and mechanical forces. Brinton's tool is advanced by the weight of a flexible, partially flattened steel pipe and does not rotate. Change from vertiGal to horizontal course is obtained when the tool caroms off a rounded steel post and slides along a hard stratum. A
lateral passage is formed by solvent action and through the punching ability of the tool as it is advanced by the weight of the shaft.
C. W. Brandon received U. S. Patent No. 2,796,129 on June 18, 1957 on tunnelling between vertical wells. He included wave pulsations to aid oil reGovery. His invention is not re-lated to any particular way for ef~ecting formation of the tunnels but he deems hydraulic methods efficacious.
In U. S. Patent No. 3,844,362, K. E. Elbert et al dis-~lose a rotary boring dev;ce stated to be suitable for cleaning ~ 4'~

conduits or for boring holes. Although not specifically stated the boring tool is obviously metallic and carrie~ a cutting he~d of a suitable material such as diamonds imbedded in a matrix. A
flexible hose delivers fluid to the device and by discharge of the fluid through appropriately positioned nozzles rotation of the cutting head and a tool advancing force are generated.
U. S. Patent No. 142,992 issued September 23, 1873 to C. G. Cross described a drill which rotates by jetting a fluid from a first set of holes into a second set spaced about 90 degrees from the first set. This device is not useful for boring a lateral passageway when using a flexible hollow shaft because the reaction of the tool transmitted to the! shaft would cause it to twist and kink to stop flow of drilling fluid therethrough.
J. N. Pew III reeeived U. S. Patent No. 3,070,361 for a fluid mining process in which a tough, flexible, nonmetallic hose provided with a plurality of cleats will flap about due to the forces induced by escape of high pressure water and air to dislodge coal and float same to the sur~ace. Pew's device is not applicable to forming lateral bores.
The prior art also includes U. S. Patent No. 3,964,792 to W. R. Archibald for an explosive shock mining system; U. S.

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Patent No, 2,515,421 to Robertson disclosing a drilling tool which includes a means inside a vertical bore for positively feeding a drill head and a flexible shaft into rotary cutting position against an earth stratum; U. S. Patent No. 1,628,070 to Sladden for a selfpropelled hose nozzle; U. S. Patent No.

2,710,~80 to Pletcher for a pipe cleaning apparatus which is selfpropelled; U. S. Patent No. 4,010,801 to Terry for in situ gassification of coal with lateral passage forming means not disclosed, and U. S. Patent No. 4rl09~715 to J. S. Adamson for an articulat~ed s~stem for drilling lateral well bores.

~ 3 Thus the present invention provides a method for drill-ing a well bore in a generally horizontal directon from a location in a formation in the earth accessible only via a connecting well bore extending from said location to the earth's surface, comprising utilizing drilling means comprising a flexible shaft conduit adapted to transmit drilling fluid, and having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and conduit to permit relative rotation therebet-ween and means connected to said boring tool and said conduit for generating upon the passage of energy therethrough conducted by said conduit a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to each have substantially the same specific gravity within : the range of ~rom 0.9 to 2.7, and introducing said energy and said drilling fluid through said shaft conduit to cause said tool to rotate and advance, said drilling fluid having a specific gravity substantially the same as the specific gravity of the drilling means, and rendering said drilling means substantially neutrally buoyant in the fluid fil.ing the well bore being drilled.
In another embodiment the invention provides a method for drilling a well bore in a generally horizontal direction from a location in a formation accessible only via a connecting well bore extending from said location to the earth's surface comprising utilizing a set of drilling apparatus comprising a flexible shaft conduit adapted to carry drilling fluid, and having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool 1~J~
and conduit to permit relative rotation therebetween and means connected to said boring tool and in fluid communication with said conduit for generating upon the passage of fluid there-through a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to each having substantially the same average specific gravity within the range of 0.9 to 2.7, and introducing said drilling fluid through said shaft conduit to cause said tool to rotate and advance, said drilling fluid having a specific gravity substantially the same as the specific gravity of the drilling apparatus, and rendering ~aid drilling apparatus substan-tially neutrally buoyant in the fluid filling the well bore being drilled.
And in still another embodiment there is provided for drilling a well bore in a generally horizontal direc-tion from a location in a formation accessible only via a connecting well bore extending from said location to earth's surface comprising utilizing drilling means comprising a flexible shaft conduit, adapted to carry drilling fluid, a rotary boring tool, and a bearing means interconnect-ing said boring tool and said conduit, said boring tool having fluid discharge ports so positioned that the passage of fluid therethrough will generate a force tending to advance said boring tool and a force tending to cause said tool to ; rotate, said shaft condui~, boring tool and bearing being so constructed as to each have substantially the same average specific gravity within the range of from 0.9 to 2.7, and ~ introducing drilling fluid through said shaft conduit to ~ 30 cause said tool to rotate and advance, said drilling fluid~
having a specific gravity substantially the same as the specific gravity of the drilling means, and rendering said , . ~ . . .

~ 9 drilling apparatus substantially neutrally buoyant in the fluid filling the well bore being drilled.

In a different aspect the present invention provides a method of drilling a deviated well bore with a generally horizontal extension in a subsurface strata containing a desired substance utilizing in the drilling of said horizontal extension : drilling apparatus comprising a flexible shaft conduit, a rotary boring tool and a bearing means interconnecting said boring tool and said conduit, said boring tool having fluid discharge ports so positioned that the passage of fluid there-through will generate a force tending to cause said tool torotate and a force tending to cause said tool to advance, said shaft conduit and boring tool being so constructed as to each have substantially the same average density with the range of from 0.9 to 2.7 grams per milliliter, comprising the steps of:
(a) drilling a well bore extending from the earth's surface to the vicinity of the subsurface strata utilizing a drilling bit, steel drill pipe for conducting drilling fluid thereto and weighted with drill collars, said well bore being deviated so that the lower end thereof is inclined at an anglP between about 60 degrees and about 75 degrees from the vertical;
(b) terminating said drilling and circulating through said drill pipe and drilling bit drilling fluid having a density :.; less than the density of the drilling apparatus comprising the :~ rotary boring tool and the flexible shaft conduit until said well bore is filled with drilling fluid of said density;
(c) withdrawing said steel drill pipe, drill collars and drilling bit from said well bore;
(d) introducing into said well bore said rotary boring tool and flexible shaft conduit and allowing them to sink through the drilling fluid until the upper end of the shaft conduit approaches submergence;
(e) connecting steel drill pipe to the upper end of the shaft conduit;
(f) continuing to connect drill pipe and lower the rotary boring tool and shaft conduit until the boring tool reaches the bottom end of the well bore;
(g) resuming circulation of drilling fluid by introducing fluid having a density somewhat greater than the density of the rotary tool and shaft conduit to rotate said tool and to cause it to advance in a forward and upward direction; and (h)- when the direction of advance of said boring tool is generally horizontal reducing the density of the drilling fluid : being circulated to a value such that the boring tool and shaft conduit are neutrally buoyant therein while continuing said circulation and drilling.
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In another embodiment the present invention provides, in a lateral passageway boring means for forming a branch bore from an inaccessible location in a first well bore wherein a drilling fluid is circulated through said boring means for removal of cutting formed by said boring means from said branch bore, the combination comprising:
(a) a flexible shaft conduit for conducting drilling fluid from said first well bore to a rotary boring tool affixed to the end of said shaft;
(b) means mounted in said boring tool for generating from the passage of drilling fluid therethrough a force tending to advance said boring tool and a force causing said boring tool to rotate;

(c) bearing means interconnecting said boring tool and said shaft conduit for permitting relative rota~ion therebetween;
and ~ 8 -.

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(d) means insertable through said shaft conduit adapted to cooperate with means carried by said borin~ tool for revers-ing the direction of rotation of said boring tool.
In a further embodiment the present inventio~ provides a rotary boring tool comprising:
ta) a generally cylindrical body portion formed from mater-ials having an average density less than 2.7 grams per milli-liter;
(b) a cutting element portion fixed to the forward end of the body portion comprising a cutting material embedded in a matrix, said cutting element portion having a density greater than the body portion;
(c) a passageway in said body portion for the entry of drilling fluid and a plurality of passageways in said body portion for the discharge of drilling fluid, at least one of said discharge passageways being so positioned that the discharge of fluid therefrom will be toward the forward end of said body portion and at least one of said discharge passageways being so positioned that the discharge of fluid therefrom will be direct-ed away from the forward end of said body portion, said dis-charge passageways being so proportioned that more drilling fluid will be discharged away from than towards the forward end so that the net effect of the discharge of fluid from such passageways will be to generate a force tending to move said tool toward the forward end, and ~; (d) said tool being so proportioned that the relative volume of the body portion to the volume of the cutting element portion is such that the tool may be made neutrally buoyant in a drill-ing fluid having a density intermediate the densities of the -utting element portion and the body portion.
In another aspect the present invention provides a method for drilling a well bore in a generally horizontal _ g _ 11~J~

direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface utilizing a set of drilling apparatus comprising a flexible shaft conduit having affixed to the nether end there-of a rotary boring tool with bearing means interconnecting said boring tool and conduit to permit relative rotation therebetween and means connected to said boring tool and in fluid communica-tion with said conduit for generating upon the passage of fluid therethrough a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to each have substantially the same average density, com-prising the steps of:

a. determining the densityof drilling fluid within the range of from 0.9 to 2.16 grams per milli-liter desirable for use in drilling said horizontal well bore to remove cuttings and to balance formation pressure;
b. selecting from available sets of drilling apparatus having densities within the range of from 0.9 to 2.7 grams per milliliter, the set having a density closest to the density of the drilling fluid to be used so that the drillinq apparatus will be sub-stantially neutrally buoyant therein;
c. introducing the selected set of drilling apparatus through said connecting well to said loca-tion;
d. connecting to the end of the shaft conduit remote from said boring tool means for introducing drilling fluid;

e. making up drilling fluid having the deter-mined desired density; and f. introducing said drilling fluid through said shaft conduit to cause said boring tool to r~tate and drill said generally horizontal well bore.

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~ 4'1~9 In still another aspect the invention provid~s a system for drilling a generally horizontal well bore comprising:

a. a nonrotating flexible shaft conduit having a rotary boring tool affixed to the nether end thereof for conducting drilling fluid to said boring tool, said boring tool and said shaft conduit being so constructed as to have substantially the same average density within the range of from 0.9 to 2.7 grams per milliliter whereby said boring tool and conduit may be made`neutrally buoyant when immersed in drilling fluid;
b. bearing means for interconnecting said boring tool and the end of said conduit for permitting relative rota-tion therebween; and c. means connected to said boring tool and in fluid - communication with said conduit actuated by the flow of fluid therethrough for generating a force tending to cause said boring tool to rotate and a force tending to cause said boring tool to advance.
In still a further aspect the invention provides a system for drilling a well bore in a generally horizontal direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface for the introduction of drilling fluid for circulation through said drilling system and for the removal of earth cuttings produced by the operation of said drilling system comprising:
a. a flexible shaft conduit for conducting drilling fluid from said connecting well to a rotary boring tool positioned at the nether end of said shaft conduit;
b. means connected to said boring tool and in fluid communication with said shaft conduit for generating from the passage of drilling fluid therethrough a force tending to cause said boring tool to rotate and the sole force of : forward thrust tending to cause said rotary boring tool to bear against the formation being drilled and to advance; and c. means interconnecting said boring tool and said shaft conduit for permitting relative rotation therebetween; said flexible shaft conduit, said boring means and said force generating means being constructed from such materials and in such a manner as to have an average density such that by the selection and use of an appropriate drilling fluid they will be neutrally ~:~ buoyant therein.
In certain aspects the present invention comprises : apparatus and a process for forming generally horizontal or lateral passageways either as an extension of a highly inclined well bore conventionally deviated or via a lateral branch from ' a vertical, inaccessihle well of no~mal diameter. B2sically, the apparatus comprises a rotary bori~g tool and a hollow shaft for conducting drilling fluid thereto to perform inter alia the functions of cooling the drilling bit and, in return flow around the shaft, carrying the cuttings back to the earth surface.
Among the factors important or essential to successful lateral boring, neutral buoyancy of the boring system which enters the lateral bore is of the highest order. If the mater-ials comprising the boring system were precisely neutrally buoyant, it would be weightless. However, precise neutral buoy-ancy is not economical to obtain or to maintain and is not necessary for the successful operation and use of the present invention. Substantially neutral buoyancy is all that is required. As used herein, a device is substantially neutrally buoyant when it is submerged in a fluid if its weight is between 80 and 125 percent of the weight of the fluid displaced.
The basic objective of the passageways drilled in accord-ance with my invention is to penetrate and expose an extended length of a formation having a desired substance, such as heavy 2Q oil. The various earth formations exist as generally horizontal strata. A generally horizontal well bore will therefore expose such strata for the production of values therefrom throughout its entire length. Frequently, however, such formations may be inclined as much as 20 degrees from the horizontal. In such cases, especially where the formation of interest is relatively shallow, it may be desirable to incline the lateral passageway slightly to conform to t~e dip of the formation being drilled and such inclined passageways are encompassed with-in the scope of my invention.
Neither steel drill pipe, which is the conduit convention-~lly used to conduct drilling fluid and power to a drilling bit - , - ~ ~ . .

and has a density of from about 7.5 to 7.8 grams/ml, (i.e. a relative density or specific gravity of 7.5 to 7.8) nor con-ventional drilling bits can be made neutrally buoyant in any liquid feasible for use as a drilling fluid.
The body portion of a neutrally buoyant rotary tool may be cast from a mix of epoxy resin and microballoons to a density as low as 0.80 grams per milliliter. Passages are drilled in the body for entry of drilling fluid and its expulsion through rearwardly facing jet nozzles and forwardly la facing water courses. The more dense cutting elements, such as metallic carbides or diamonds, embedded in a suitable matrix are fixed to the body. The relative volumes of the body and the cutting elements are so proportioned that the average density of the boring tool will be within the desired range for neutral buoyancy in drilling fluid.
The entry bore is threaded for joining to a rotating union bearing device with the ~oint sealed by epoxy. A suitable flexible shaft may be made from any of several low density elastomers such as ultra high molecular weight polyethylene having a density of 0.94 grams per milliliter or a polyurethane elastomer which may range in density from 1.05 to 1.12 grams per milliliter. Such materials may be reinforced with glass, steel, long filament carbon or other fibers for added strength and increased density.
Since in any horizontal drilling system the shaft con-duit and the rotary drilling tool are positioned in the same drilling fluid~ their densities should be substantially identical. In practical operations the conduit-drilling tool sets should be made up in a plurality of densities matched to

3~ densities normally employed for drilling fluids used under various drilling conditions encountered. Typical mud weights and the corresponding densities are as follows:

Mud Weight Density lbs/qal (U.S.) grams/ml 7.5 0.90 9.0 1.08 10.0 l.2q 11.0 1.32 12~0 1.44 13.0 1.56 14.0 1.68 16.0 1.92 18.0 2.16 A high density drilling fluid assists in removal of cuttings from a horizontal bore,. ~owever, if the head of fluid on the exposed formation is too great, lost returns will result.
This would limit fluid density unless artificial lift were employed to lower the fluid level in the vertical well and this is contemplated herein. The driller would determine the mud weight he wished to employ to balance formation pressure, remove cuttings, etc., and then use the conduit-drilling tool set having the closest density. Typically, conduit-drilling tool sets would be available having densities in the range of from 0.9 to 2.7 grams per milliliter. Periodic measurements would be made of the position of the bit. If it tended to rise from the horizontal, the weight of the drilling mud ~ould be reduced.
Conversely, if the bit was tàiling off in a downward direction, weighting agent would be added to the mud. The direction o~
rotation of the bit and the nature and dip of the formations being dr~lled will also influence the direction of advance.
Clockwise rotation will cause the bit to trend to the right, counter clockwise, the reverse.
So long as the system in the lateral bore is substan-tially neutrally buoyant, by making measurements of bit position and by ma~ing appropriate changes in the direction of rotation and the mud weight, a generally horizontal bore~ofsubstantial length may be drilled.

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Because the shaft conduit must make a 90 degree bend in traversing the well bore from the earth's surface and be-cause it must conform to all undulations in the horizontal bore, flexibility of the shaft i~ also important for the suc-cessful operation of my invention.
Boring of latera~ holes is sub~ect to the same con-trolling factors as vertical drilling, namely weight on the bit or thrust, speed of rotation and drilling fluid circulation rate. However, the amount of useful mechanical power which can be transmitted to the nether end of a flexible conduit is quite limited. This fact restricts both weight on bit and rotary torque. Pushing force on a flexible shaft, even inside the relatively small diameter lateral bore, cannot deliver a useful thrust to the rotary bit. He~ce, the feed means is located near the nether extreme of the boring tool and pulls the shaft forward as the hole is bored. Drag on the exterior surface of the shaft is kept to a minimum by having a smooth exterior and by the neutral buoyancy of the shaft. The hydraulic radius of the annulus between the outside of the shaft and the bore wall is designed to provide the lowest possible drag on the shaft by returning drilling fluid consistent with delivery of suf-ficient power to the rotary bit. Boring progress is related directly to thrust per inch of bit diameter. Thus, the lateral bore is no larger than is necessary to permit acceptable return flow velocity. The diameter of the forward facing ~7ater course in the rotary bit is the minimum necessary to provide cooling and lubrication to avoid excessive backward, reactive force.
To add feed or advancing force, impediments to flow may be placed at intervals along the inside of the conduit to convert fluid friction and impact into advancing force~

Where it i9 desired to drill a lateral well bore at a selected point in a vertical well, the shaft conduit must make a 90 degree bend with a relatively short radius. The physical requirements for a shaft conduit having such flexibility are rather strict and somewhat contradictory. High bursting pres-sure, and hence high tensile strength, is needed to transmit pressured drilling fluid to advance and rotate the bit. How-ever, the shaft must be highly flexible and this requires xelatively low tensile modulus material which usually has low te~sile strength. Investigation of a number of materials re-veals that a ratio of tensile modulu~ to tensile strength of less than 40 is required for a satisfactory flexible shaft.
Also, the tensile modulus of the shaft should be less than 100,000, and preferably less ~han 40,000, pounds per square inch.
Commercially available hoses quite often are not made from a single material but are composites of several. Bending of the shaft is related to lengthwise tensile modulus of such a com-posite hose. A simple test was devised to measure this length-wise modulus. A selected convenient length of hose, say 30 feet, is pressurized and the change in length observed. Hoop stress is calculated from the formula S = P(D -e)~2e (Stress equals pres-sure times outside diameter minus wall thickness divided by twice the wall thickness.), reference, Modern Plastics Encyclo-pedia, Volume 54, No. lOA, McGraw-Hill Publisher. Longitudinal stress is one-half hoop stress. This stress divided by frac-tional change in length gives the lengthwise tensile modulus.
For example, a 30-foot length of hose was shortened 3.58 inches when pressured to 82 pounds per~square inch, a fractional change of 0.010 in length. Hoop stress was calculated to be 287 psi and hence, longitudinal stress was 143.5 psi. The effective ~ tensile modulus of this hose, measured lengthwise, is 14,350 ; psi. Tensile strength, calculated from the manufacturer's ~ - 17 -, rated burst pressure was 1575 p~i. The ratio of tensile modulus to tensile strength is 9.1.
To assist the shaft,to make the turn from vertical to horizontal a shaft bending means may be employed. In one form a powered device urges the nether extreme of the boring tool means into initial horizontal contact with the earth stratum by means of a plurality of rollers in frictional contact therewith.
The bending means obviously contributes advancing force to the bit at that time and when the length of lateral hole is short.
Too great a force could stall the bit. Hence, a fluid coupling is installed between the prime mover and the rotating rollers.
The shaft bending means preferably is reversible to prevent key-seating of the shaft as it is withdrawn from the lateral bore.
Another form of shaft-bendinglmeans is disclosed and claimed in my U.S. Patent No. 4,303,134 issued December 1, 1981, dealing with an earth boring guide.
By the use of jet nozzles for generating forward thrust, substantially no torque forces are transmitted to the shaft thus permitting the use of a highly flexible shaft capable of making a 90 bend with a short radius.
The advancing force is obtained by aiming the jet: discharge toward the rear of the tool, i.e., away from the cutting face.
Rotating force or tor~ue is derived by placing the jet nozzles near the periphery of the tool. In axial cross-section the jet nozzle is on a chord of the cylindrical tool and :Located as near to the outside surface as structural limitations wil;L
permit.

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In one embodiment of the invention two sets of rear-wardly facing jet nozzles may be inserted in the tool in a manner such that the first set causes rotation of the bit in one direction and the second set rotation in the opposite direction.
To reverse the rotation the first set of nozzles may be plugged and the second set opened by inserting a device into the shaft at the surface and pumping it into the tool.
The present invention has various applications in the winning of desired substances from subsurface strata. Heat to melt tar and bitumen may be transmitted by means of hot fluids pumped into the lateral bore. Coal may be degassed by reducing ~; pressure in the branch well. Minerals may be comminuted and slurrified to be brought to the surface. The lateral passage-way may be designed to cross ~nduced or natural fractures to increase fluid productivity. A lateral bore will reduce coning of undesired fluids by reduction of flowing pressure differen-tial. Efficiency of water-flooding is increased because linear flow between wells is a more effective process than radial flow.
Other useful applications will become apparent to those skilled ~o in the art.
Accordingly, one object of this invention is to pro-vide a new means and method for penetrating the earth. Another object is to provide novel apparatus and process for forming lateral passageways from a vertical well. It is still another object to for~ such passageways to a length not heretofore attainable.

: BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a ~eneral view in cross section, partly schematic, showing the invention and related equipment.
Figure 2 is a cross sectîonal view of a tool and shaft.
- Figure 3 is a cross sectional view of $he rotary bit taken on the line 3-3 of Figure 2.

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Pigure 4 i9 a cro~s sectional view of the rotary bit taken on the line 4-4 of Figure 2.
Figure 5 is a cross sectional view of a modified shaft.
Figure 6 is a cross sectional view of another modifi-cation useful in ~orming underground cavities.
Figure 7, partly in cross section and partly schema~iç, shows a shaft bending means used to direct a boring means from a vertical bore into position for forming a lateral passageway.
Figure 8 is a cross sectional view of Figure 7 ta~en at the line ~-8.
Figure 9 is a cross sectional view of another modifi-cation showing the use of the invention for forming a horizontal extension of a conventionally deviated well.

DESCRIPTION OF PREF~RRED EMBODIMENTS
_ Figure 1 shows a preferred embodiment of the present invention. Well 1 is drilled through upper earth horizons 2 into earth strata 3 containing desired substance 4. A casing 5 is sealed into strata 3 by cement sheath 6. First tubing string 7 is run into casing 5 and fixed thereto by casing head 8. A low density, flexible shaft conduit 9 having rotary drilling tool 10 affixed to its nether end is run into tubing 7 until tool 10 reaches tube bending means 11. Because casing 5 and tubing 7 contain a drilling fluid 12 in which shaft g and tool 10 are neutrally buoyant, pump 13 is used to force drilling fluid 12 through rearwardly facing ~ets 14 in order to advance drilling tool 1~ through conduit 7. Pumping rate is reduced as tool 1 approaches shaft bending means 11, otherwise it might be damaged by the rotating bit 27, Figure 2. However, after tool 10 has pas~ed through bending means 11 and has assumed a hori-zontal position, full pumping rate is initiated to form branchbore 15 in strata 3. Cuttings 16 and returning drilling fluid 12 pass upwardly through annulus 17 between tubings 7 and 9.

~ eturn fluid flow may be assisted and fluid pressure head on strata 3 reduced by artificial lift of drilling fluid from a below ground level inside casing 5 to the surface. For gas-lift, compressor 18 sends pressured ga~ 19 through pipe 20 and valve 21 into casing annulus 22 where gas entry into tubing 7 is controlled by gas lift valves 23. Drilling fluid 12 re-turns 10w through pipe 24 and valve 25 into tank 26 which may be closed to operate as a gas-liquid separator. Drilling fluid 12 and cuttings 16 may be separated by a shale shaker, not shown, and the fluid recirculated. In the event that desired substance 4, drilling fluid 12 and cuttings 16 are intimately mixed, various means for separation are available such as heat-ing, solvent extraction and centrifuging, but means of surface recovery does not form a part~of the present invention.
Rotary tool 10 is shown in detail in Figure 2. In the preferred embodiment, the tool 10 comprises drag bit 27 having a hardened cutting surface 28 affixed to body 27 by fastenings 29. For use in a drilling fluid having a density of 1.2 grams per milliliter bit 27 may be cast from a mix com-pound of cycloaliphatic epoxy 61 paxts, microballoons 31 partsand glass fibers 5 parts by volume with steel trim 2.5 parts and tungsten carbide 0.5 parts added after drilling suitable fiuid passageway~. Body 27 is covered with two layers of Vectra*cloth 30, a polypropylene fabric sold by National Plas-tics Products Company, applied with epoxy resin, to improve abrasion resistance.
Central fluid passage 31 is formed, bores 32 and 33 drilled to connect thereto and water courses 34 also penetrate to the central passage 31. Bores 32 and 33 face toward the 30 rear so that expulsion of drilling fluid at high velocity im-parts an advancing force to tool 10.

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~ '3 Bores 32 ~nd 33 not only f~ce rearwardly as shown in Figure 2, but also are axially inclined in opposite directions as shown in Figures 3 and 4 so that the discharge of fluid therefrom creates a tangential force tending to rotate bit 27.
The diameter of bores 32 and 33 i8 10 millimeters while water courses 34 have a diameter of 2.4 millimeters. Bores 34 direct a jet 1uid 12 toward cutting edge 28 for cooling and to remove cuttings. Tubes 35 having hardened jet nozzles 36 in their exterior end are cemented, or otherwise fixed, into bores 32 and 33. Smaller diameter tubes 37 are cemented into water courses 34. The end 38 of tubes 37 which extends into passage-way 31 is shaped and sharpened to penetrate a seal as described later. The end of bit 21 away from cutting edge 28 is fitted with threads 39 to engage mat~ng threads 40 of rotating union 41 which has been attached to shaft 9 by means of adhesive 43.
Indentations 42 are for a spanner wrench, no~ shown, for tighten-ing the threaded connection 39-40.
Bore holes 32 initially are closed by means of annular ring 44 having 0-ring seals 45. When it is desired to reverse the direction of rotation of tool 10, an actuating device 46 is pumped through t~bing 9 to contact annular ring 44 and move it outwardly to open bores 32 and simultaneously close bores 33.
Device 46 is closed at its advan~ing end by sealing disk 47 which, being made from soft material, is easily penetrated by the sharp end 38 of tube 37. Cups 48 and centralizing guide 49 assure movement of device 46 through conduit 9 and into tool 10.
After device 46 is seated in tool 10 passages 34 receive fluid 12 as before and fluid ejection through bores 32 causes thP tool 10 to rotate in the opposite direction.
Shaft conduit 9 may be formed from a glass reinforced polyethylene plastic to have a density of 1.20 ~rams per milli-liter, a tensile modulus of 25,000 pounds per squàre inch and a - . .
~ - ~2 -I 1 L ~

tensile strength, determined in burst, of ~,600 pounds per square inch. Conduit 9 conveniently is wound on reel 50 and connected to fluid pump 13 by means of tube 51 and valve 52.
Rotary tool 10 may 'have its advance stopped, or be retracted, by manipulation of reel 50. Branch bore 15 may be enlarged by the hydraulic action of drilling fluid ejected through jet nozzles 36, particularly if the tool 10 is not permitted to advance by reel 50.
In another embodiment of this invention, shown in Figure 5, only enough flexible shaft conduit 9 is used to reach the nether end of branch bore 15 from well 1. The conduit which always remains inside tubing 7 may be a steel tubing 53 to permit use of h~gher circulating pressures safely. Steel tubing 53 is handled in the normal way and eliminates the use of reel 50. Tubing 53 is joined to coupling 54 by mating threads 55 and shaft 9 is fixed to the lower end of coupling 54 by adhesive cement joint 56 reinforced by self-tapping screws 57.
Figure 6 shows an embodiment of the invention adapted for use in forming a large und~rground cavity from a vertical, inaccessible well. Producing well 1 penetrates formation 3 to recover desired substance 4. A modified tube bending means 58 is run on the lower end of casing 5. Power extracted from pressured drilling fluid 12 advances tool 1~ while fastenings 61 across annulus 62 assure simultaneous advance of flexible conduits 59 and 60 and of bearing 41. Returning drilling fluid 12 laden with cuttings 16 and desired substance 4 flows through annulus 62 into well 1 and exits through outlet 63 into casing 5 whence it enters ports 64 of centrifugal pump 65 driven by elec-; tric motor 66 and is lifted to the surface thereby. Control of `~ 30 rate of pumping by pump 65 determines the working fluid level - 67 in casing 5 and hence fluid pressure head on formation 3.

A powered tube bending means i~ shown in Figures i and 8. G~sing 5 and cement sheath 6 have window 142 there-through to expose formation 3., Auxilliary tubing 7 having elbow outlet 143 with power system 144 spaced immediately below are lowered into well 1 until outIet 143 is opposite window 142.
Outlet 143 may be oriented by means well known in petroleum drilling. The power system 144 includes an electric motor 145 driving a fluid couplinq 146 which delivers a constant torque to speed reducing gear 147 carrying sheaves 148 which drive 10 cogged belt 149 in the direction shown by arrows in Figure 7 to cause rollers 150 to turn in a clockwise direction while cogged belt 151 causes other rollers to rotate counterclock-wise. The four powered rollers 150 and the four unpowered rollers 1~2 cooperate to caus~ conduit 9 to move aownwardly and outwardly to put tool 10 into contact with formation 3.
Rollers 150 and 152 are mounted on bearing 153 and shaft 154 while cogged belts conveniently may pass through slots cut into tubing 7. Electrical conductor 155 transmits power from the surface to motor 145. Rollers 156 provide additional guidance to conduit 9.
Figure 9 illustrates my invention in its application to the lateral extension of a deviated well bore. Deviated wells and the techniques for drilling such wells are well known.
Primarily the deviated well is used in situations where it is impractical, i~possible or uneconomic to position a drilling rig over the spQt where it is desired to bottom a well. Advan-~ageously, the Dyna-Drill, available from the DYNA-DRILL Company, Irvine, California, a division of Smith International, Inc. is used. The Dyna-Drill ana equivalent mud turbine powered rotary bit systems used for drilling deviated holes employ conventional steel drill pipe and forward thrust for the rotary drilling bit is obtained by applying the weight of drill collars to the bit.

*Trademark ¢ - 24 -As shown in Figure 9 it i9 not necessary to deviate the well a full 90 degrees before using my invention to form a generally horizontal extension thereof. Well 100 is qpudded and surface casing 102 set and cemented as shown at 104. De-viated drilling is then initiated and when the well reaches the formation 106 above the strata 107 wherein a horizontal bore is desired, intermediate casing 108 is run in and cemented as shown at 110. Deviated drilling with the Dyna-Drill is then continued into strata 107 to point 112 where the hole approaches the horizontal and forward progress is restricted by the dif-ficulty in maintaining weight on the bit. Rather than attempt to deviate the hole a full 90 degrees, when the hole has been deviated between 60 degrees and 75 degrees, the use of the system of the present invention become more advantageous than continuing the use of drill collars to apply the advancing force on the bit.
After the Dyna-Drill is removed from the hole, the drilling tool 10 of the present invention is attached to the flexible shaft 9 which in turn is connected to conventional drill pipe 53 as shown in Figure 4 and run into the hole to bottom. Before running the drilling tool into the hole, it is desirable to condition the drilling fluid to a density somewhat less than the density of the drilling tool and flexible shaft.
This ensures that they will sink through the fluid to the bottom as they are lowered by the introduction of the drill pipe into the hole. Drilling fluid is then weighted to a den-sity slightly greater than the average densities of the flexible shaft and drilling tool. The drilling tool will thus tend to ~ float in the drilling fluid and advance forwardly and upwardly.
; When the direction of advance is substantially horizontal, the weight of the drilling fluid may be reduced and thereafter ~he bit will advance in a substantially horizontal direction.

- 25 ~

11',44,'~

Slnce many modifications and possible embodi-ments and uses may be made of the apparatus of this invention without departing from the scope thereof, it is to be under-stood that all matter herein set forth or shown i9 to be interpreted as illustrative not as limiting.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for drilling a well bore in a generally horizon-tal direction from a location in a formation in the earth accessible only via a connecting well bore extending from said location to the earth's surface, comprising utilizing drilling means comprising a flexible shaft conduit adapted to transmit drilling fluid, and having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and conduit to permit relative rotation therebet-ween,and means connected to said boring tool and said conduit for generating upon the passage of energy therethrough conducted by said conduit a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to have an average specific gravity within the range of from 0.9 to 2.7, and introducing said energy and said drilling fluid through said shaft conduit to cause said tool to rotate and advance, said drilling fluid having a specific gravity substantially the same as the specific gravity of the drilling means, and rendering said drilling means substantially neutrally buoyant in the fluid filling the well bore being drilled.

2. A method for drilling a well bore in a generally horizon-tal direction from a location in a formation accessible only via a connecting well bore extending from said location to the earth's surface comprising utilizing a set of drilling apparatus comprising a flexible shaft conduit adapted to carry drilling fluid, and having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and conduit to permit relative rotation therebetween and means connected to said boring tool and in fluid communication with said conduit for generating upon the passage of fluid there-through a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to have an average specific gravity within the range of 0.9 to 2.7, and introducing said drilling fluid through said shaft conduit to cause said tool to rotate and advance, said drilling fluid having a specific gravity substantially the same as the specific gravity of the drilling apparatus, and rendering said drilling apparatus substan-tially neutrally buoyant in the fluid filling the well bore being drilled.

3. A method for drilling a well bore in a generally horizontal direction from a location in a formation accessible only via a connecting well bore extending from said location to earth's surface comprising utilizing drilling means comprising a flexible shaft conduit, adapted to carry drilling fluid, a rotary boring tool, and a bearing means interconnect-ing said boring tool and said conduit, said boring tool having fluid discharge ports so positioned that the passage of fluid therethrough will generate a force tending to advance said boring tool and a force tending to cause said tool to rotate, said shaft conduit, boring tool and bearing being so constructed as to have an average specific gravity within the range of from 0.9 to 2.7, and introducing drilling fluid through said shaft conduit to cause said tool to rotate and advance, said drilling fluid, having a specific gravity substantially the same as the specific gravity of the drilling means, and rendering said drilling means substantially neutrally buoyant in the fluid filling the well bore being drilled .

4. A method for drilling a well bore in a generally horizon-tal direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface, comprising:
utilizing a set of drilling apparatus comprising a flexible shaft conduit adapted to transmit drilling fluid, a rotary boring tool and bearing means interconnecting said boring tool and conduit each so constructed as to have substantially the same specific gravity,said boring tool having fluid discharge ports so positioned that the passage of fluid therethrough will generate a force tending to advance said boring tool and a force tending to cause said tool to rotate;
selecting for use a drilling fluid having a density within the range of from 0.9 to 2.16 grams per milliliter, desirable for use in drilling said horizontal well bore to re-move earth cuttings and to balance formation pressure;
selecting from available drilling parts having densities within the range of from 0.9 to 2.7 grams per milliliter, a set having a density closest to the density of the drilling fluid to be used so that the drilling apparatus will be sub-stantially neutrally buoyant therein; and introducing said drilling fluid through said shaft conduit to cause said boring tool to rotate and drill said generally horizontal well bore.

5. A method for drilling a well bore in a generally horizontal direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface utilizing a set of drilling apparatus comprising a flexible shaft conduit having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said bor-ing tool and shaft conduit to permit relative rotation there-between and means connected to said boring tool and in fluid communication with said shaft conduit for generating upon the passage of fluid therethrough a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to each have substantially the same average density, comprising the steps of:
a. determining the density of drilling fluid within the range of from 0.9 to 2.16 grams per milli-liter desirable for use in drilling said horizontal well bore to remove cuttings and to balance formation pressure;
b. selecting from available sets of drilling apparatus having densities within the range of from 0.9 to 2.7 grams per milliliter, the set having a density closest to the density of the drilling fluid to be used so that the drilling apparatus will be substantially neutrally buoyant therein;
c. introducing the selected set of drilling apparatus through said connecting well to said location;
d. connecting to the end of the shaft conduit remote from said boring tool means for introducing drilling fluid;
e. making up drilling fluid having the deter-mined desired density; and f. introducing said drilling fluid through said shaft conduit to cause said boring tool to rotate and drill said generally horizontal well bore.

6. A method for drilling a well bore in a generally horizontal direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface utilizing a set of drilling apparatus comprising a flexible shaft conduit having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and shaft conduit to permit relative rotation therebetween and means connected to said boring tool and said shaft conduit for generating upon the passage therethrough of energy conducted by said shaft conduit a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to each have substantially the same average density, comprising the steps of:

a. determining the density of drilling fluid within the range of from 0.9 to 2.16 grams per milliliter desir-able for use in drilling said horizontal well bore to re-move cuttings and to balance formation pressure;
b. selecting from available sets of drilling apparatus having densities within the range of from 0.9 to 2.7 grams per milliliter, a set having a density closest to the density of the drilling fluid to be used so that the drilling apparatus will be substantially neutrally buoyant therein;
c. introducing the selected set of drilling appar-atus through said connecting well to said location;
d. connecting to the end of the shaft conduit remote from said boring tool means for introducing energy and drilling fluid;
e. making up drilling fluid having the determined desired density; and f. introducing energy and said drilling fluid through said shaft conduit to cause said boring tool to rotate and to drill said generally horizontal well bore.

7. A method of drilling a deviated well bore with a generally horizontal extension in a subsurface strata contain-ing a desired substance utilizing in the drilling of said hori-zontal extension drilling apparatus comprising a flexible shaft conduit, a rotary boring tool and a bearing means interconnecting said boring tool and said conduit, said boring tool having fluid discharge ports so positioned that the passage of fluid there-through will generate a force tending to cause said tool to rotate and a force tending to cause said tool to advance, said shaft conduit and boring tool being so constructed as to have an average density within the range of from 0.9 to 2.7 grams per milliliter, comprising the steps of:
a. drilling a well bore extending from the earth's surface to the vicinity of the subsurface strata utilizing a drilling bit, steel drill pipe for conducting drilling fluid thereto and weighted with drill collars, said well bore being deviated so that the lower end thereof is inclined at an angle between about 60 degrees and about 75 degrees from the vertical;
b. terminating said drilling and circulating through said drill pipe and drilling bit drilling fluid having a density less than the density of the drilling apparatus comprising the rotary boring tool and the flexible shaft conduit until said well bore is filled with drilling fluid of said density;
c. withdrawing said steel drill pipe, drill collars and drilling bit from said well bore;
d. introducing into said well bore said rotary boring tool and flexible shaft conduit and allowing them to sink through the drilling fluid until the upper end of the shaft conduit approaches submergence;

e. connecting steel drill pipe to the upper end of the shaft conduit;
f. continuing to connect drill pipe and lower the rotary boring tool and shaft conduit until the boring tool reaches the bottom end of the well bore;
g. resuming circulation of drilling fluid by introducing fluid having a density somewhat greater than the density of the rotary tool and shaft conduit to rotate said tool and to cause it to advance in a forward and upward direction; and h. when the direction of advance of said boring tool is generally horizontal reducing the density of the drilling fluid being circulated to a value such that the boring tool and shaft conduit are neutrally buoyant therein while continuing said circulation and drilling.

8. The method of drilling a deviated well bore with a generally horizontal extension in a subsurface strata containing a desired substance,utilizing in the drilling of said horizontal extension a set of drilling apparatus comprising a flexible shaft conduit having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and said shaft conduit to permit relative rotation therebetween and means connected to said boring tool and in fluid communication with said shaft conduit for generating upon the passage of fluid therethrough a force tending to advance said boring tool and a force tending to cause said boring tool to rotate, said boring tool, shaft conduit and force generat-ing means being so constructed as to have an average density within the range of from 0.9 to 2.7 grams per milliliter, comprising the steps of:

a. drilling a well bore extending from the earth's surface to the vicinity of the subsurface strata utilizing a drilling bit, steel drill pipe for conducting drilling fluid thereto and weighted with drill collars, said well bore being deviated so that the lower end thereof is inclined at an angle between about 60 degrees and about 75 degrees from the vertical;
b. terminating said drilling and circulating through said drill pipe and drilling bit drilling fluid having a density less than the density of the drilling apparatus comprising the rotary boring tool and the shaft conduit until said well bore is filled with drilling fluid of said density;
c. withdrawing said steel drill pipe, drill collars and drilling bit from said well bore;
d. introducing into said well bore said rotary boring tool and shaft conduit and allowing them to sink through the drilling fluid until the upper end of the shaft conduit approaches submergence;
e. connecting steel drill pipe to the upper end of the shaft conduit;
f. continuing to connect drill pipe and lower the rotary boring tool and shaft conduit until the boring tool reaches the bottom end of the well bore;
g. resuming circulation of drilling fluid by introducing fluid having a density somewhat greater than the density of the rotary tool and shaft conduit to rotate said tool and to cause it to advance in a forward and upward direction; and h. when the direction of advance of said boring tool is generally horizontal reducing the density of the drilling fluid being circulated to a value such that the boring tool and shaft conduit are neutrally buoyant therein while continuing said circulation and drilling.

9. The method of drilling a deviated well bore with a generally horizontal extension in a subsurface strata containing a desired substance utilizing in the drilling of said horizontal ex-tension a set of drilling apparatus comprising a flexible shaft conduit having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and said conduit to permit relative rotation therebetween and means con-nected to said boring tool and said conduit for generating upon the passage therethrough of energy conducted by said conduit a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to have an average density within the range of from 0.9 to 2.7 grams per milliliter comprising the steps of:
a. drilling a well bore extending from the earth's surface to the vicinity of the subsurface strata utilizing a drilling bit, steel drill pipe for conducting drilling fluid thereto and weighted with drill collars, said well bore being deviated so that the lower end thereof is inclined at an angle between about 60 degrees and about 75 degrees from the vertical;

b. terminating said drilling and circulating through said drill pipe and drilling bit drilling fluid having a density less than the density of the drilling apparatus comprising the rotary boring tool and the flexible shaft conduit until said well bore is filled with drilling fluid of said density;
c. withdrawing said steel drill pipe, drill collars and drilling bit from said well bore;
d. introducing into said well bore said rotary boring tool and shaft conduit and allowing them to sink through the drilling fluid until the upper end of the shaft conduit approaches submergence;
e. connecting steel drill pipe to the upper end of the shaft conduit;
f. continuing to connect drill pipe and lower the rotary boring tool and shaft conduit until the boring tool reaches the bottom end of the well bore;
g. making up drilling fluid having a density somewhat greater than the density of the rotary tool, the force generating means and the flexible shaft;
h. introducing energy and the drilling fluid made up in step (g) through said conduit to said force generating means and rotary tool to cause said rotary tool to advance in a forward and upward direction; and i. when the direction of advance of said boring tool has become generally horizontal reducing the density of the drilling fluid being circulated to a value such that the boring tool, force generating means and shaft conduit are neutrally buoyant therein while continuing said circulation and drilling.

36 A rotary boring tool comprising:
a. a generally cylindrical body portion formed from materials having an average density less than 2.7 grams per milliliter;
b. a cutting element portion fixed to the forward end of the body portion comprising a cutting material embedded in a matrix, said cutting element portion having a density greater than the body portion;
c. a passageway in said body portion for the entry of drilling fluid and a plurality of passageways in said body portion for the discharge of drilling fluid, at least one of said discharge passageways being so positioned that the discharge of fluid therefrom will be toward the forward end of said body portion and at least one of said discharge passageways being so posi-tioned that the discharge of fluid therefrom will be directed away from the forward end of said body portion, said discharge passageways being so proportioned that more drilling fluid will be discharged away from than towards the forward end so that the net effect of the discharge of fluid from such passageways will be to generate a force tending to move said tool toward the forward end, and d. said tool being so proportioned that the relative volume of the body portion to the volume of the cutting element portion is such that the tool may be made neutrally buoyant in a drilling fluid having a density intermediate the densities of the cutting element portion and the body portion.

11. A self-advancing rotary boning tool comprising:
a. a generally cylindrical body portion formed from materials having an average density less than 2.7 grams per milliliter;
b. a cutting element portion fixed to the forward end of the body portion comprising a cutting material embedded in a matrix, said cutting element portion having a density greater than the body portion;
c. at least one passageway extending through said body portion and the forward end thereof for the trans-mission of and discharge of drilling fluid across the cutting element portion;
d. means connected to said body portion adapted to conduct drilling fluid and actuated by the passage there-through and discharge therefrom of drilling fluid to generate forces causing said boring tool to rotate and to tend to advance; and e. said boring tool being so proportioned that the relative volumes of the body portion, the rotating and advancing force generating means and the cutting element portion are such that the tool may be made neutrally buoynant in a drilling fluid having a density inter-mediate the densities of the cutting element portion and the body portion.

12. A system for drilling a generally horizontal well bore comprising:
a. a nonrotating flexible shaft conduit having a rotary boring tool affixed to the nether end thereof for conducting drilling fluid to said boring tool, said boring tool and said shaft conduit being so constructed as to have an average density within the range of from 0.9 to 2.7 grams per milliliter whereby said boring tool and conduit may be made neutrally buoyant when immersed in drilling fluid;
b. bearing means for interconnecting said boring tool and the end of said conduit for permitting relative rotation therebetween; and c. means connected to said boring tool and in fluid communication with said conduit actuated by the flow of fluid therethrough for generating a force tending to cause said boring tool to rotate and a force tending to cause said boring tool to advance.

13. A system for drilling a well bore in a generally horizontal direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface for the introduction of drilling fluid for cir-culation through said drilling system and for the removal of earth cuttings produced by the operation of said drilling system comprising:
a. a flexible shaft conduit for conducting drilling fluid from said connecting well to a rotary bor-ing tool positioned at the nether end of said shaft conduit;
b. means connected to said boring tool and in fluid communication with said shaft conduit for generat-ing from the passage of drilling fluid therethrough a force tending to cause said boring tool to rotate and the sole force of forward thrust tending to cause said rotary boring tool to bear against the formation being drilled and to advance; and c. means interconnecting said boring tool and said shaft conduit for permitting relative rotation there-between; said shaft conduit, said boring means and said force generating means being constructed from such materials and in such a manner as to have an average density such that by the selection and use of an appropriate drilling fluid they will be neutrally buoyant therein.

14. In a lateral passageway boring means for forming a branch bore from an inaccessible location in a first well bore wherein a drilling fluid is circulated through said boring means for removal of cuttings formed by said boring means from said branch bore, the combination comprising:
a. a flexible shaft conduit for conducting drilling fluid from said first well bore to a rotary boring tool affixed to the end of said shaft;
b. means mounted in said boring tool for generating from the passage of drilling fluid therethrough a force tending to advance said boring tool and a force causing said boring tool to rotate;
and c. bearing means interconnecting said boring tool and said shaft conduit for permitting relative rotation therebetween;
said shaft conduit and said boring means being constructed from materials and in such a manner as to have an average density such that they are neutrally buoyant in the drilling-fluid.

15. The lateral passageway boring means of claim 14 wherein the minimum bending radius of the shaft conduit is less than the diameter of the first well bore.

16. The system for drilling of claim 14 in which the tensile modulus of said shaft conduit in a lengthwise direction does not exceed 40,000 pounds per square inch.

17. The system for drilling of claim 14 in which the ratio of lengthwise tensile modulus to tensile strength of said shaft conduit does not exceed a numerical value of forty.

18. A method for drilling a well bore in a generally horizontal direction from a location in the earth accessible only via a connecting well bore extending from said location to the earth's surface utilizing a set of drilling apparatus comprising a flexible shaft conduit having affixed to the nether end thereof a rotary boring tool with bearing means interconnecting said boring tool and conduit to permit relative rotation therebetween and means connected to said boring tool and said conduit for generating upon the passage of energy therethrough conducted by said conduit a force tending to advance said boring tool and a force tending to cause said tool to rotate, said boring tool, shaft conduit and force generating means being so constructed as to have an average density substantially within the range of from 0.9 to 2.7 grams per milliliter comprising the steps of:

a. introducing said rotary tool and connected shaft conduit through said connecting well to said location;
b. connecting to the other end of said shaft conduit means for introducing energy and drilling fluid thereinto;
c. making up drilling fluid to a density substan-tially the same as the density of the drilling apparatus;
and d. introducing said energy and said drilling fluid through said shaft conduit to cause said tool to rotate and advance and to render said drilling apparatus sub-stantially neutrally buoyant in the fluid filling the well bore being drilled.

19. A system for drilling a generally horizontal well bore comprising:

a. rotary boring tool comprising:
i. a generally cylindrical body portion formed from materials having average density less than 2.7 grams per milliliter;
ii. a cutting element portion fixed to the forward end of the body portion comprising a cutting material embedded in a matrix, said cutting element portion having a density greater than the body portion;

iii. said body portion and said cutting element portion being so proportioned that the boring tool may be made neutrally buoyant in a drilling fluid having a density intermediate the densities of the cutting element portion and the body portion;

b. a flexible shaft conduit having a density such that it will be neutrally buoyant in a drilling fluid in which the boring tool is neutrally buoyant;
c. bearing means for interconnecting said boring tool and the end of said conduit for permitting relative rotation therebetween; and d. means connected to said boring tool and in fluid communication with said conduit actuated by the flow of fluid therethrough for generating a force tending to cause said boring tool to rotate and a force tending to cause said boring tool to advance.

20. A system for drilling a well bore in an earth formation in a generally horizontal direction comprising:
a. a rotary boring tool comprising:
i. a generally cylindrical body portion formed from materials having average density less than 2.7 grams per milliliter;
ii. a cutting element portion fixed to the forward end of the body portion comprising a cutting material embedded in a matrix, said cutting element portion having a density greater than the body portion;
iii. said body portion and said cutting element portion being so proportioned that the boring tool may be made neutrally buoyant in a drilling fluid having a density intermediate the densities of the cutting element portion and the body portion;
b. a flexible shaft conduit for conducting drilling fluid and energy to said boring tool and having a density such that it will be neutrally buoyant in a drilling fluid in which the boring tool is neutrally buoyant;

c. bearing means interconnecting said boring tool and the end of said conduit for permitting relative rotation therebetween and providing a passageway for drilling fluid from said conduit to said boring tool; and d. means connected to said boring tool and said conduit actuated by energy delivered by the conduit for generating a force tending to cause said boring tool to rotate and a force tending to cause said boring tool to advance.

21, A system for drilling a well bore in an earth formation in a generally horizontal direction comprising:
a. a rotary boring tool;
b. a flexible shaft conduit for conducting drilling fluid and energy;
c. bearing means interconnecting said boring tool and the end of said conduit for permitting relative rotation therebetween and providing a passageway for drilling fluid from said conduit to said boring tool;
d. means connected to said boring tool and said conduit actuated by energy delivered by the conduit for generating a force tending to cause said boring tool to rotate and a force tending to cause said boring tool to advance, and e. said boring tool, said shaft conduit and said force generating means being so constructed as to have an average density within the range of from 0.9 to 2.7 grams per milliliter whereby said system may be made substantially neutrally buoyant in a drilling fluid having a density within the range of from 0.9 to 2.16 grams per milliliter."