US2716018A - Apparatus for bore hole drilling - Google Patents

Description

Aug. 23, s w U S APPARATUS FOR BORE HOLE DRILLING Filed Oct. 17, 1951 3 Sheets-Sheet l huip S. "(Elli am 53 five rztor 5257 0, 0, Gbtorrzezs Aug. 23, 1955 P. s. WILLIAMS 2,716,018

APPARATUS FOR BORE HOLE DRILLING Filed Oct. 17, 1951 TI er '2 5 Sheets-Sheet 2 Omu & mumms poventor U. Clttoxneg Aug. 23, 1955 P. s. WILLIAMS 2,716,013

APPARATUS FOR BORE HOLE DRILLING Filed Oct, 17, 1951 3 Sheets-Sheet 3 Fla- 2:

Pum 6. wiumms z deq Cor United States Patent l APPARATUS FOR BORE HOLE DRILLING Philip S. Williams, Tulsa, Okla., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 17, 1951, Serial No. 251,743

6 Claims. (Cl. 25524) This invention concerns a novel and improved techthe use of two drilling fluids maintained as separate and distinct bodies of fluid in the borehole.

The present invention is generally directed to the provision of a new drilling method economically preferable to presently known drilling procedures. The drilling procedure of this invention overcomes a great many disadvantages of presently used drilling techniques and at the same time provides many advantages in drilling heretofore unobtainable.

The following disclosure is presented to fully disclose the nature of this invention, to characterize the invention, and to bring out certain features of the invention, with. particular reference to the prime feature of the invention not shared by former drilling techniques, that is, the use of two drilling fluids in the manner herein disclosed.

In drilling a borehole by the rotary drilling method it is necessary to employ a so-called drilling fluid or drilling mud to supply a number of functions. This drilling mud is maintained in the borehole during drilling operations to raise drill cuttings to the surface, to lubricate and clean the drill bit, to lubricate the hole. to provide hydrostatic pressure to overcome uncontrolled release of high pressure fluids present in formations encountered during drilling, to seal the borehole wall against loss of drilling mud, to condition the borehole wall to minimize caving, and to provide other functions. These desirable'functions of a drilling fluid, may logically be classified in two principal groups:

1. The drilling fluid should maintain the borehole in the best possible conditionsealing porous formations, overcoming fluid production from the well, etc., and

2. The drilling fluid should cool, clean, and lubricate the drill bit and carry cuttings from the hole.

It has been found by experience and can be demonstrated by analysis that, in fact, the compositions required to provide each of these classes of functions are quite different in nature; that is, a given com-position cannot best fulfill each of these groups of requirements. Thus, for example, the ideal fluid for aiding the operation of the drill bit is a low viscosity fluid containing substantially no solids, such as plain water. Such a fluid wouid not be of a suitable character for maintaining the condition of the borehole; for example, it would not be adapted to sealing the wall of the borehole. Consequently, it has been the general practice to select a drilling fluid by striking the best practical compromise between the properties of the fluid in conjunction with the indicated criteria. Alternatively, it has been suggested that different fluids be used in the borehole during different phases of the drilling operation or even that two partially independent circulation systems be employed in the borehole. It is the principal feature of this invention, that the objective of supplying the best available drilling 2,716,018 Patented Aug. 23, 1955 fluid to a borehole be attained by employing two separate and distinct bodies of drilling fluid in the borehole, so that each of the two bodies of drilling fluid may have different compositions and optimum characteristics.

The general manner in which this is achieved is to closely follow the drill bit into the hole with a string of casing which need not be rotated and which is spaced from the wall of the borehole to provide an annular space between this casing and the borehole. Packing arrangements are provided at the bottom of the casing adjacent to but above the drill bit, and preferably at the top of the casing adjacent the surface of the earth, so that this annular space is effectively sealed to permit the mainteance of a body of a high viscosity fluid between the casing and the wall of the borehole. This fluid is selected to provide the best practical sealing properties and to provide the other properties required to maintain the borehole in good condition without regard to the properties of the fluid as regards lubrication of the drill bit, etc. This fluid will hereinafter be referred to as a sealing fluid. A second drilling fluid of a different nature may then be employed within the casing, selected solely in connection with its properties as regards drill bit lubrication, removal or" cuttings, pumping characteristics, etc. This second body of drilling fluid, which will be called a cutting fluid, by virtue of its maintenance within the casing extending throughout the borehole, is substantially free of contact with the borehole. To permit the circulation of this fluid, if desired, an inner tubular member is referably positioned within the aforementioned casing. This inner tubular member may be employed as a drill string to rotate the drill at the bottom of the borehole. The cutting fluid referred to, as differentiated from the sealing fluid referred to, may then be circulated downwardly through the inner tubular member to the drill bit and thence back to the surface of the earth through the annular space between the tubular member and the casing.

It is a particular feature of this invention that the generally described technique for maintaining two separate distinct bodies of fluid having different properties in the borehole, may be carried out in employing a wide variety of drilling techniques. Thus, the technique de scribed may be employed with any desired type of rotary drilling, and if desired, may even be employed with wire line percussion type drilling procedures, i. e. cable tool drilling. Consequently, in order to fully disclose the nature and scope of this invention the appended drawings diagrammatically illustrate different embodiments of the invention employing different drilling techniques with the general two-fluid system of this invention. Thus, in the drawings:

Figure 1 illustrates in elevation, the basic two-fluid technique as adapted to the use of rotary drilling employing a drill string; and

Figure 2 illustrates a suitable packer, expansible drill bit and thrust bearing for use in any desired embodiment of the two-fluid system; and

Figure 3 illustrates the two-fluid technique of this invention as applied to a drilling method employing a bottom hole hydraulic motor as the drive for the drill bit.

It may be emphasized that in each of these, and other possible embodiments of the invention, the apparatus is characterized by an outer casing extending from the surface of the earth to a point adjacent and above the drill. This casing is spaced from the borehole wall; that is, has a diameter smaller than the cutting diameter of the drill bit which in all cases necessitates the use of an expansible drill bit. The lower end of this casing is provided with a packer of a character to effectively seal the annular space between the casing and the borehole at its lower termination while permitting the packer and casing to I be placed on the drill bit. In addition to these elements,

means mu'stbe provided to drive the drill bit; the easing referred to cannot be employed as a drill string. Thus "a drill string may be provided Within the casing to' drive the drill, a bottom hole hydraulic or electric motor may be used, or other means independent of the casing may 7 be used to operate the drill.

In the case in which a bottom hole electric motor or hydraulic turbine is employed, the motor or turbine may be anchored to the casing referred to, in order to provide power to the drill bit. Suitable mating elements or latching devicesmay be used to lock the motor or turbine in the casing in this manner. The inner string of tubing is then required only to provide circulation of cutting fluid to'the drill bit, and may be dispensed with entirely. Alternatively the electric motor or hydraulic turbine may be fixed to a string of tubing extending through the casing to provide support, and to permit circulation of cutting fluid to the drill bit. 7

As a result of the general arrangement described, it is possible to maintain a body of sealing fluid outside. the casing in contact with the borehole but free of contact with the .drill bit, while maintaining a cutting fluid within the casing having access to the drill bit and the lower extremity of the borehole. These two fluids, the sealing fluid and the cutting fluid, are thus maintained as separate and distinct bodies of fluid, each particularly selected to provide the proper functions in their compartmented application. The cutting fluid will generally be a low viscosity, low solids content liquid, and in many instances may comprise plain water. Preferably the cutting fluid is characterized by a solids content less than about.5% and a viscosity less than about 5 centipoises. Higher limits of solids content and viscosity are generally not desired but may be employed at some sacrifice in drilling rate, pumpability characteristics, etc. The sealing fluid on the other hand is generally a high viscosity, high solids content liquid. The-solids content is preferably greater than about 10% although not ordinarily above about 25%. The density of the sealing fluid is adjusted to give proper column weight for the formation pressures expected; This fluid should be so formulated that it'will not damage or swell thevarious formations, will exhibit low loss to porous formations and will provide proper lubrication for the drill pipe.. What is known as a gum type mud may be employed, for example, containing solids such as clay, weighting materials, starch and gum modifiers and the like. Generally the sealing fluid will be particularly characterized by high gel strength. Flakes, strands, or other particles of-solid or plastic materials commonly employed to control lost circulation, such as cellophane flakes, oat hulls, fibrous materials and the like may be added bothto control'loss to the formations and to improve the seal at'the bottom of the packer. Since the sealing fluid does not circulate in the ordinary sense, gel strength rather than viscosity. is a controlling factor. However, the viscosity of the sealing fluid is generally in the range of about 10 to 200 centipoises. As stated, the sealing fluid is particularly characterized by-a high gel strength; As measured in aStormer viscosimeter after a ten minute period of quiescence, the gel strength should fall in the range of about 10 to 100 grams.

Referring now to Figure l, attention will first be drawn 'to the down-the hole portion of the drilling apparatus illustrated. A conventional large diameter surface casingl is extended for some distance into the earth at the initiation of the drilling operation. A drill bit 19 rotated by a drill string 13 operated in the conventional rotary drilling manner is employed to drill the borehole beneath 7 the level of the surface casing 1. A continuous string of easing 3 is provided in the borehole having a smaller diameter than the surface casing 1 and a greater internal diameter than the drill string 13; At the same time the external diameter of easing 3 is somewhat less than the maximum cutting diameter of the drill .bit 19. As a consequence, the casing 3 can pass freely down the borehole behind the drill bit as it progresses into the earth and the casing 3 will be spaced from the wall of the borehole.

The drill bit 19 in the embodiment illustrated in Figure 1 is of the expanding type consisting of a body member 20 sufficiently small to pass through the casing ployed to force the reamers outwardly in response to the pressure drop of drilling fluid passing through the bit. Again, as will be brought out, it is a particular concept of this invention that at least a portion of the weight of the casing 3 should be placed on the drill bit 19. Consequently, the bit may be designed so that the weight of the casing on the drill bit will cause the desired extension .of the reamers 21..

A collar assembly 22 is provided above the drill bit and is positioned within the lower termination of the casing 3 to permit the rotation of drill string 13 within this collar. As a part of the collar, or as a separate element spaced between the collar and the drill bit, thrust bearings 23 are provided. Latching dogs 24 associated with the collar assembly 22 or with the thrust bearings 23 are employed to extend beyond the internal diameter of casing 3 so that the weight of the casing may be placed on the drill bit through .the thrust bearing. Again, the extension of the latching dogs 24 may be controlled by hydraulic means or by other suitable methods. A packer element 7 is maintained at the lower termination of the casing 3 adapted to seal the annular space between the casing and the borehole;

Referring now to the up-the-hole portion of the apparatus, a rotary table 14 is employed to rotate the drill pipe 13 and the drill bit 19. The rotary table is supported so as tobe movable vertically, upwardly or downwardly, as required in adding succesive sections of pipe to the drill string in following the drill bit into the earth.. As illustrated, a mechanical arrangement employing a rack and pinion lift 15 may be employed to support the rotarytable or alternatively for example, a

This, cutting fluid will pass downwardly through drill 1 string 13 through and around drill bit 19 and thence.

back to the surface of the earth through water courses in the collar assembly 22 and through the annular space between drill string 13 and the casing 3. The cutting fluid returned to the surface of the earth in this manner may be withdrawnthrough conduit 27 associated with the draw-ofl arrangement 5 at-the top of casing3; Prior to or after introduction of this cutting fluid to vessel 18, the fluid may be treated to separate drill cuttings or to recondition it for recycling to the well as desired.

A second lifting arrangement 4, which is again illustrated as a rack and pinion lift assembly, is associated with the casing 3 and is adapted to permit the raising and lowering of casing 3 as required in introducing the casing into the borehole following the downward travel A flexible conduit 16 is of the drill bit. A separate mud circulation system is maintained for introduction of sealing fluid to the annular space between casing 3 and the walls of the borehole 11. Thus a fluid 8, particularly selected for sealing and wall conditioning properties is maintained by vessel 9 and is introduced into the annular space referred to by means of pump 10 and conduit 28. If de-- sired, a pressure control device 12 may be positioned in conduit 28 to maintain the pressure of sealing fluid in the annular space at a desired value.

A packing arrangement 2 is provided at the surface of the earth to seal the upper termination of the annular space between casing 3 and borehole 11, in which the sealing fluid is maintained. The packer assembly 2 is designed to seal the upper termination of this annular space while permitting the sliding of casing 3 through this packer. At least in some applications of this invention, the upper packing arrangement 2 is not required. As will be emphasized, a principal feature of employing this upper packer is to permit application of pressure to the sealing fluid. When this is not required, the packer may optionally be dispensed with. Similarly a packer 7 is positioned at the lower termination of casing 3 adapted to seal the lower portion of the annular space in which the sealing fluid is maintained Thus the packer 7 is of a character to permit sliding along the borehole 11 while preventing any substantial leakage of sealing fluid past the packer to the drill bit. A number of packing arrangements may be employed for this purpose. For example, an elastic packer resembling an inverted umbrella, urged continuously outwardly against the walls of borehole 11 by spring elements may be employed. Such a packer operates in the fashion of a check-valve permitting movement of the packer downwardly in the borehole, but preventing flow of sealing fluid downwardly past the packer and preventing flow of cutting fluid upwardly past the packer. The packer is effective in this latter function, in part since the hydrostatic head of the sealing fluid 8 maintained in the annular space is generally greater than the hydrostatic head of the cutting fluid 6 maintained within casing 3.

In the operation of the apparatus of Figure 1, as the drill bit 19 proceeds into the earth, the casing 3 is caused to follow this progression. Actually, it is particularly contemplated that a substantial portion of the weight of the casing 3 be placed on the drill bit 19 to aid in the drilling action. Successive sections of drill pipe are added to drill string 13 as required and successive sections of casing 3 are similarly added as required. This necessitates provision for moving rotary table 14 to one side somewhat out of the line of drill string 13. It is preferable that equal length sections of drill pipe and easing be employed so that additions of pipe may be simultaneously conducted. By virtue of the fact that any desired portion of the weight of casing 3 may be placed on the drill bit during drilling, drill string 13 may be fabricated of lighter weight tubing than that ordinarily required. This also simplifies the lifting arrangement 15 required since the lifting capacity of this equipment can thereby be reduced. When necessary to remove drill bit 19, the latching dogs 24 and the extendable reamers 21 are retracted and drill string 13 is pulled back to the surface of the earth. It will be noted that casing 3 is not removed at any time during the drilling procedure and no equipment is required for this purpose.

It is preferable to supply suitable bearings between drill string 13 and casing 3 at intervals to eliminate metal to metal wear. The bearings may be a part of the tubing joints, for example, and are provided with water courses for the passage of drilling fluid therethrough. Again it is desirable to employ spacing elements about casing 3 to maintain the central position of the casing within the borehole 11. It is suitable, for example, to employ rubber plug-like elements to be fixed to the casing containing slots or perforations through which the sealing fluid may pass.

In order to clearly disclose the operation of the apparatus described generally in Figure 1, reference is made to Figure 2 of the drawings which shows in enlarged sectional detail the lower portion of the drilling apparatus. Figure 2 particularly illustrates a suitable form of sliding packer, a suitable form of expansible drill bit, and a thrust bearing arrangement to permit the weight of the outer casing to be placed on the drill bit. In Figure 2, as in Figure 1, numeral 3 designates the outer casing, while numeral 13 designates the drill string.

The packer shown in Figure 2 comprises an invertedumbrella-like packing element 25, fabricated of elastic material such as rubber, fabric, or preferably, rubber impregnated fabric. This element is fixed to the outer casing 3 by means of spring elements 26 which are suitably fixed to the casing 3 at a plurality of points about the casing. Some six to ten or more spring elements may be circumferentially distributed about the casing. The elastic packer may be vulcanized to the spring supporting elements 26, or, as shown in the drawing, the spring supports may be mounted directly in the packer. By virtue of this construction, the spring supports 26 continuously urge the elastic packing element 25 against the Wall of the borehole. Even though the borehole does not conform to a circular shape, the independently acting spring elements 26 cause the packer to conform to the particular cross section of the borehole so as to effectively maintain the packing element against the sides of the borehole. Again, by virtue of the arrangement illustrated, the packer will readily slide downwardly in the borehole as the casing 3 progresses downwardly; the packer will oppose no obstruction to the downward movement of the casing. The manner in which the packer eifectively seals the body of sealing fluid from the body of drilling fluid adjacent the drill and below the packer can also be readily appreciated. The sealing fluid above the packer will normally have a considerably higher density than the cutting fluid below the packer. As a result, the hydrostatic head of the fluid above the packer will be substantially greater than the hydrostatic head of the fluid below the packer. This pressure differential permits the sealing fluid to forcibly maintain the packer against the wall of the borehole without opportunity for the cutting fluid to rise upwardly past the packer.

The expansible drill bit illustrated is of the nature disclosed and claimed in U. S. Patent No. 2,338,670, issued to Sewell on January 4, 1944. The complete operation of this expansible drill bit will not be described herein, but reference will be made to the general nature of the drill. The drill string 13 is fixed to an enlarged coupling 31 which supports a bifurcated body 32 having extensions 33 on which the cutters 35 are pivotally positioned. A tubular sleeve 38 is positioned on coupling 31 having two downward extensions 39, the lower portions of which are joined together by a wedge-shaped member 40. Cone shaped rock cutters 41 may be positioned on the lower terminations of the two extensions 3?. In this arrangement, when the drill string is lowered to the bottom of a borehole, the rock cutters 41 are forced upwardly by the bottom of the borehole so as to cause the wedge-shaped element 40 to force the expansible cutters 35 apart and place them in operative cut-' ting position. This is accompanied by movement of sleeve 38 upwardly along the coupling 31 to the position shown in Figure 2 of the drawing. The drill bit is then in a position so that it may be turned by the drill string in order to cut a borehole having a diameter defined by the extended cutters, greater in size than the drill string 13 and the casing 3. As disclosed in the aforementioned patent at least one longitudinal passage is provided within the drill bit structure to conduct drilling fluid from the interior of the drill string 13 to the bore hole in the vicinity of the cutters. When desired remove the drill from the borehole, lifting drill string permits collar 38 to slide downwardly on :coupling 31 so as to permit the collapse of. the extended offer many advantages.

, as follows:

of the "cutters; to such a diameter that the entire drill bit may be pulled upwardly through casing 3 to the surface of the earth. This or other desired forms of expansible bits may be employed in the practice of this invention.

In order to placethe weight of the outer casing 3 ,on a drill bit'of the character described, a tubular thrust collar 23 is employed Collar 23 is constructed so as .to encircle drill string 13 permitting sufiicient clearance for the drill string 13 to rotate within the collar. Thrust bearings 34 may be positioned at suitable points along collar 23 so as to prevent relative longitudinal movement of collar 23,and drill string 13 while permitting rotation of drill string 13 within the collar. The lower portion of the collar is machined as a separate tubular member 29 having guide extensions 30 fitting within a recessed portion of collar 23. This arrangement permits the lower section 29 to move upwardly or downwardly within the upper section of the tubular collar; Latching dogs 36 may be fixed in pivotal relation to the lower section 29 of the tubular collar. Diagonal slots 37 in these latching dogs are arranged to enclose pins 43 fixed to the upper portion 'of the tubular collar. As a result, while the drill bit assembly is lowered to the bottom of a borehole, collar 38 of the expansible'bit will be in a downward position free of contact with the termination .of the lower section 29 of the tubular collar. The weight of section 29 will cause the collar to drop away from the upper portion of the tubular collar to the extent permitted by the pins 43, acting in slots 37; This will cause latches 36 to be maintained in a retracted position. However, when the expansible drill bit contacts the bottom of the borehole, collar 38 will be forced to the position shown in Figure 2, forcing the. tubular collar element 29 upwardly with the result that the latching dogs 36 will be forced out wardly to an extended position as shown in Figure 2. Thereafter by lowering the outer casing 3 so as to contact latching dogs 36, any desired portion of the weight of. easing 3 may be placed on the drill bit acting through latching dogs 36, collar 23 and thrust bearings 34. If desired, additional thrust bearings 44 may be positioned between the lower termination of collar 29 and collar 38 of the expansible bit, so the rotation of collar 38 will not be impeded by friction with the thrust collar.

The apparatus of Figure '1 and Figure 2, and the general drilling technique embodied in the present invention,

Certain of these advantages are As pointed out, by the provision of two separate bodies of drilling mud, the sealing fluid can be chosen with out regard to its drilling characteristics and may be 7 betteradapted for sealing the well and maintaining the condition of the borehole than conventional drilling muds. Again, the cutting fluid actually circulated to and through the drill bit may be chosen solely in regard to its properties in improving the drilling rate without necessity for fluids produced in formations encountered by simple.

drill stern testing procedures. The invention makes it practical to maintain the pressure in the cutting fluid .zone at a lower value than formation pressures.

On encountering a producing zone during drilling, therefore, fluid produced by this zone will be released into the return stream of cutting fluid. The possibility of inadvertently passing 'a producing zone during drilling may virtually be eliminated therefore. Again,fby maintaining the pressure in the cutting fluid zone lower than formation pressures, cutting fluid will not .be forced into producing formations to impair production. A conventional blowout preventerrmay be employed to control excessive production during drilling without loss of the advantages referred to. These and other advantages of the drilling arrangement described uniquely qualify the method of thisto upper formations, which ordinarily exists in reverse circulation conducted in an uncased hole. If desired, pressure drilling may be employed by placing weighting materials in the drilling fluid, or by positioning a blowout preventer at the top of the drill string. The apparatus described makes it attractive to employ a planetary. gear train at the'bottom of the tubing since he casing provides an effective anchor for such a gear train. It is thus possible to step'up the speed of the drill at the bottom of the well and thereby to reduce the rotational speed required at the surface of the earth.

. As exemplary 'of other possible variations of the in- I vention, reference will be made to Figure 1. Drill string 13 maybe fabricated of large diameter tubing somewhat smaller in outside diameter than the inner diameter of easing 3. The annular space formed therebetween is adjusted to the minimum space required for satisfactory circulation of cutting fluid. The use of the larger diameter drill string 13 makes possible the employment of a Wire line retractable drill bit having the extensible reamers or cutting edges formerly referred to. Thus, the drill bit assembly comprises a body element adapted to closely fit within the drill 13, in slidable relationship therewith. Extensible latching dogs extending from the body serve to meet in projections of the termination of the drill string 13. Consequently, the weight of drill string 13 on the latching dogs will serve to permit rotation of the drill bit on rotation of the drill string. However,

use of the large diameter tubing as the drill string makes it possible to retrieve the entire drill bit assembly by means of a wire line, after retraction of the latching dogs, without necessity for removing the drill string 13 from the borehole. Another notable variation of the invention is illustrated in Fig. 3 which will be briefly described.

Referring now to Figure 3, anembodiment of the invention is illustrated employing the use of a bottom hole hydraulic motor as a drive source for the drill bit. Thus the drill stem 13 terminates at the bottom of the borehole in a hydraulic motor 45 arranged to drive the expansible bit 46 .of the general character formerly identfied. In all other respects the apparatus of Figure 3 is similar to the apparatus of Figure 1 with the notable exception that V the rotary table formerly employed to rotate the drill string is no longer required. Thus, both the drill string 13 and the casing 3 are maintained in the borehole without rotation. Pumping of the drilling fluid from reservoir 18 through drill srting 13 to the hydraulic motor 45 serves to drive drill bit 46 to drill the desired hole. Again latching dogs 47 may be provided on, or adjacent the hydraulic motor assembly to support any desired portion of the weight of csaing 3. 'Since the drill string 13 is not required to provide the necessary'drilling weight on the drill bit 46 and since the drill string is not rotated, the weight of the drill string and the size of the tubing required may be minimized. Again, any possible wear due to the rotation of the drill string in the c'asing' is thereby eliminated. In other respects the apparatus and drilling procedure of Figure 3 embodies the advantages brought out in connection with Figure 1.

As described therefore, the drilling procedure of this invention entails the use of two separate and distinct bodies of fluid in a borehole. One body of fluid is maintained in an annular space between a casing and the Walls of the borehole terminating at the top and bottom of the casing in packers to permit maintenance of a static head of sealing fluid. The second body of fluid maintained in the well is passed through a central tubular member and through the annular space between this tubular member and the casing referred to. As brought out, a great many different types of drilling techniques may be adapted to this general system. Thus, the drill bit may be rotated by the inner tubular member, the drill may be driven by a hydraulic motor, retractable drills may be employed eliminating the necessity of removing either the tubing or the casing from the well during drilling 'or other practices may be adopted.

What is claimed is:

1. An apparatus for drilling a bore hole in the earth comprising, in combination, a casing, means supporting said casing in a bore hole, a tubular member of less diameter than said casing, means supporting said tubular member within said casing in a manner defining therewith a first annular space, a drill bit supported by said tubular member at the lower end thereof and extending beyond the lower termination of said casing, said bit having extensible cutting members adapted for drilling a bore hole substantially greater in diameter than the diameter of said casing whereby said casing will define with the bore hole a second annular space, a packing member supported on the exterior of said casing adjacent the lower termination thereof whereby to seal said second annular space from the borehole below said lower termination, said first annular space and the bore of said tubular member constituting, respectively, first and second circulating paths for fluid, each circulating path extending independently through the entire length of the bore hole from the surface to the vicinity of the bit below said packing member, a first fluid reservoir, a conduit system connecting said first fluid reservoir with said tubular member and said first annular space whereby a first fluid may be circulated from said first reservoir through the entire length of the bore 10 hole through one of said fluid circulating paths and returned to said first reservoir through the remaining path, a second fluid reservoir and a second conduit system connecting said second reservoir to said second annular space whereby a second fluid may be supplied to said second annular space, said first conduit system and said first reservoir being isolated from said second conduit system and said second reservoir whereby two separate and distinct isolated bodies of fluid may be supplied to said bore hole, said first fluid serving to lubricate the drill bit and to remove cuttings from the bore hole and said second fluid differing from said first fluid and serving to control formation pressures and to maintain the walls of the bore hole.

2. Apparatus as defined by claim 1 including a thrust bearing on the lower end of said tubular member and means for transferring a downward force from said casing on said thrust bearing.

3. Apparatus as defined by claim 1 including driving means positioned at the surface of the earth and adapted to rotate said tubular member, said drill bit being fixed to said tubular member whereby to be rotated by said tubular member.

4. Apparatus as defined by claim 1 including a hydraulic motor fixed to the lower termination of said tubular member and coupled to said drill bit.

5. An apparatus as defined by claim 1 wherein said packing member is circumferentially fixed to the casing member and has a peripheral skirt portion urged against the bore hole wall in sliding arrangement therewith.

6. An apparatus as defined by claim 1 including a drive motor supported by the apparatus adjacent the lower termination of the casing and adapted to rotate the drill bit assembly.

References Cited in the file of this patent UNITED STATES PATENTS 1,585,969 Ferguson May 25, 1926 1,777,961 Capeliuschnicotf Oct. 7, 1930 1,944,838 Hill Jan. 23, 1934 2,338,670 Sewell Jan. 4, 1944 2,353,372 Stone July 11, 1944 2,561,075 Sidwell July 17, 1951 2,567,451 Smith Sept. 11, 1951

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