US 2776817 A
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Description (OCR text may contain errors)
Jan. 81957 J. N. GREGORY ET AL 2,776,817
DRILLING APPARATUS Filed July 21, 1952 2 Shee'ts-Shee"u 2 United States Patent O DRILLING APPARATUS James N. Gregory, Midland, Tex., and Charles A. Yeatman, San Marino, Calif., assignors to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application July 21, 1952, Serial No. 300,056
2 Claims. (Cl. Z55-28) This invention relates to well drilling equipment and pertains more particularly to a new type of drilling apparatus and a new method of well drilling employing this apparatus wherein the pressure of the drill bit on the bottom of the well during drilling operations is controlled by varying the pressure of drilling uid circulating through the drilling apparatus.
In conventional rotary well drilling operations, weight is generally applied to the drill bit at the lower end of a drill string by allowing a portion of the total weight of the drill string to rest on the bit forcing it against the formation at the bottom of the well borehole. The weight on the bit is controlled by measuring the load on the hook or hoisting equipment at the surface. Control of the weight on the bit is necessary in order to control the speed and the direction of penetration, to avoid damaging the drill string o1 drill bit, etC.
It is often dicult for the weight on a drill bit to be accurately controlled by measurement of the hook load at the surface because of lthe frictional resistance developed at various points within a borehole between the wall of the borehole and -the drill string. This is especially true when a well is drilled directionally, thus increasing the area of contact between the bore-hole wall and the drill string.
It is therefore a primary object of the present invention to provide a method and apparatus for insuring the application of adequate bit pressure on the bottom of a well in a manner such that its net value is unaffected by frictional forces which may exist between the borehole wall and the drill string above the bit.
It is also an object of this invention to provide apparatus for applying weight to a drill bit which is independent of the weight of any part of a drill string employed in rotary well drilling operations.
While the use of conventional apparatus to determine the bit load is often very inaccurate in directionalvdrilling operations starting from a vertical position, it can be readily understood that the same equipment is especially unreliable in horizontal drilling operations or in directional drilling operations wherein the drill string is at an angle of about sixty degrees or more to the Vertical.
In substantially horizontal drilling operations, the major portion of the weight of the drill string rests on the lowermost side of the borehole wall with the frictional resistance therebetween being so great that there is, at present, no suitable method or apparatus for determining with accuracy the actual pressure of the bit at any given moment against the formation. Thus, it is diicult to move a drill string in a substantially horizontal borehole while drilling, and at the same time maintain a constant bit pressure.
It is therefore a further object of this invention to provide an apparatus to be used in horizontal drilling operations which is capable of accurately feeding a drill bit against a formation at a constant pressure irrespective of the length or weight of the drill string bearing on the wall of the borehole.
In conventional coring operations, relatively short cores are taken since the raising of a drill string during coring operations to add another section of pipe to the string generally causes the core to break. Another object of the present invention is to provide a method and apparatus for obtaining long cores of a formation by adding additional sections of pipe to the upper end of a drill string without raising the lower end of the string with the core bit off the bottom of the borehole.
Another object of this invention is to provide a novel type of drill bit adapted to be secured to the lower end of a drill string for drilling a well borehole with the drill string remaining fixed against longitudinal or axial movement and free of compressional forces due -to the weight of the string.
These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:
Figures 1 and 6 are longitudinal Views, partly in cross section, of the present drilling apparatus.
Figure 2 is a cross-sectional view taken along line 2-2 of Figure l.
Figure 3 is a cross-sectional view taken along line 3--3 of Figure l.
Figure 4 is a diagrammatic View, partly in cross section, of the present drilling apparatus illustrated as being employed in horizontal drilling.
Figure 5 is a diagrammatic view of the present drilling apparatus suspended in a well borehole at the bottom of a drill string.
Referring to Figure 1 of the drawing, the present drilling apparatus comprises a tubular housing 11 having screw threads 12 formed at its upper end for connection to the lower end of a drill string 13 or to a special sub or short section of drill pipe 14 which is, in turn, threadedly secured yto the lower end of the drill string 13.
Mounted for sliding axial movement within the housing 11 is an elongated inner tubular member 15 which may be of a length equal to that of the housing 11 or slightly shorter or longer, as desired. The lower end of the inner tubular member is threaded, as at 16, for connection directly to a drill bit 17 or to a short intervening sub18 which is in turn connected to the bit 17.
The housing 11 and inner tubular member 15 are provided with suitable means for preventing rotation relative to each other while permitting axial or telescoping movement. Thus, as shown in Figures l, 2 and 3, the inner sliding member 15 is formed so as to have a hexagonal cross section with a central bore 21 for the circulation of drilling fluid therethrough. The inner wall of the outer housing at the lower end thereof is formed with a hexagonal bore section 22 (Figure 3) which mates with Vthe hexagonal member 15 causing it and the attached bit 17 to rotate when the drill string 13 and housing 11 are rotated. The hexagonal bore section 22 at the lower end of the housing 11 may be integrally formed therein as illustrated in Figures l and 3 or alternatively, a bushing having a hexagonal bore may be secured within the lower end of the housing. While the mating parts 15 and 22 are shown as hexagonal in cross section, they may also be square or of any other noncylindrical cross section which prevents relative rotation of the two parts. Likewise, the housing 11 and inner member 15 may be provided with splines and grooves to prevent their relative rotation.
While the housing 11 and the sliding inner member 15 may be machined or formed to t closely with each other, sealing means are preferably provided whereby the member 15 and housing 11 are in fluidtight engagement with each other at all times. For example, a pump piston 23 having sealing rubbers 24 and 25 may be secured to the upper end of the sliding inner member 15 by holding nuts 26. Preferably, an outwardly extending shoulder 27 is formed or secured to the inner member 15 near the upper end thereof to limit the downward travel of said member 15 and to protect the sealing piston 23 from damage.
The length of the present drilling apparatus is preferably sufliciently great for the telescoping members 11 and 15 to move a distance equal to the length of a section of drill pipe used to make up the drill string 13, i. e., about 30 feet. Thus, when the drilling apparatus is in its telescoped position as illustrated in Figure l, the shoulder 27 is about 30 feet above the shoulder 28 formed by the top of the hexagonal bore section 22 of the housing 11. However, the telescoping action of the present drilling apparatus is not limited to 30 feet but may be longer or shorter, as desired. Any type of drill bit 18 may be used, said bit having one or more fluid ports 30 for discharging drilling tluid from the drilling apparatus into the borehole.
As diagrammatically shown in Figure 5, the present drilling apparatus 10 is secured to the bottom of a drill string 13 which is suspended in a well borehole 31. A conventional drill rig 20 is mounted above the borehole which comprises a crown block 32, traveling block 33, hook and swivel unit 34 and fall lines 35 anchored at 36 and having a conventional weight indicator 37 mounted thereon. A rotary table 40 and its prime mover 41 are mounted on the operating platform of the rig 32 together with a conventional hoist 42. A mud pump 43 is provided for circulating drilling fluid through a flexible hose 44 into the top of the drill string 13.
In drilling operations the drill string 13 is made up as illustrated in Figure with the drilling apparatus 10 positioned at the bottom thereof. The top of the drill string 13 may be suspended by hook 34, fall lines 35 and hoist 42 in a conventional manner but remains at a fixed level by clamping it in the rotary table 49 for rotation therewith.
As the drilling progresses, drilling mud is pumped from a mud pit 45 through pump 43, hose 44, hook and swivel unit 34 and drill string 13, into the drilling apparatus 10, and out the ports 30 (Figure l) in the drill bit 18. The fluid is then circulated up the borehole 31 and back into the settling pit 45. The pressure differential between the space within the drilling apparatus and the space outside the apparatus may have, by properly selecting the number, size and shape of ports 30 and applying a suitable pressure at the top, a value of, say, from 500 to 1000 p. s. i. Thus, the total hydraulic pressure applied to the bit 18 causing it to penetrate into the formation is equal to the product of the differential pressure and area of the piston formed by the sliding inner member to which the bit 18 is attached. If the piston has a diameter of 5 inches and the differential pressure is 750 lbs. p. s. i., the total pressure acting against the bit would be about 14,700 lbs. This bit pressure can be readily varied by varying the pump pressure, as indicated on a gauge 39.
In drilling installations where the discharge pump pressure cannot be employed as an accurate indication of the bit pressure, any other suitable pressure or rate of flow indicating means may be installed. For example, a flow restricting device such as a nozzle or orice 46 may be installed in the pump discharge line at the well head together with a gauge 47 for measuring the pressure drop across the oriiice and the rate of ow through the pipe. If the orice 46 in the line 44 at the well head is equal in size and flow characteristics to the orifices or discharge ports 30 in the bit 18, the pressure drop across both orifices 30 and 46 may be considered equal. Preferably, however, the orifice 46 has only a small drop across it to minimize energy losses while the gauge 47 may be calibrated with respect to orifices 30 and 46 to indicate the rate of flow through the drill string 13. Hence by adjusting the pump discharge to obtain the desired pressure differential or rate of flow across orifice 46 at the surface, an accurate indication of the bit pressure is obtained. A reasonably accurate rate of flow from a mud pump of the reciprocating-type may be ascertained by counting the pump strokes over a selected time interval. Knowing the mud volume passing through the bit, the pressure drop across the bit may be calculated.
As illustrated in Figure 5, drilling of the well borehole 31 progresses by the action of the rotary table 40 at the surface rotating drill string 13, drilling apparatus housing 11 and inner sliding member 15 which is keyed to the housing 11. The drill string 13 and housing 11 remain stationary against vertical movement while the inner sliding member 15 and bit 18 are forced downwardly out of the housing 11 and against the formation at the bottom of the borehole by the pressure of the circulating drilling fluid.
When the sliding inner member 15 of the drilling apparatus 1t? has been forced out of the housing 11 as far `as it will go, the top of the drill string 13 is wedged in the rotary table 40 (Figure 5) and the hook and swivel 34 is disconnected from the drill string and secured to another section of pipe (not shown) the lower end of which is then coupled to the top of the drill string. The lengthened drill string is then lowered by the hoist 42 until member 15 of the drilling apparatus is substantially telescoped in the housing 11. Circulation of the drilling mud is then resumed.
An indication as to when another section of pipe should be added to the top of the drill string 13 may be observed in any one of many ways. For example, if the drill string 13 is suspended from the hoist system comprising hook 34, fall lines 35, blocks 32 and 33 and hoist drum 42, the weight indicator 37 in the dead end of the line shows a substantial increase in weight when the inner member 15 is in its extended position at which time the bit pressure drops as the bit 18 is rotating substantially free on the bottom of the borehole 31. Additionally, free running of the bit 18 on the bottom of the borehole can be indicated by a decreased torque reading at the rotary table 40 whether the drill string 18 is suspended from the hook 34 of the hoist system or iixedly suspended from the rotary table.
Alternatively, the housing 11 may be provided with one or more fluid ports Si through the wall thereof having a total area preferably substantially greater than the total area of the ports 30 in the bit 1S. The ports 48 are positioned so as to be uncovered by the piston 23 at the top of the sliding inner member 15 when the latter is at its most extended position. The opening of these large ports 48 greatly reduces the pressure differential between the space within the drill string and the space outside thereof and is indicated by a sudden change in the reading of the pump pressure gauge 39.
This last-mentioned method of determining the extended position of the drilling apparatus 10 is especially useful when the present device is used in horizontal drilling operations, as illustrated in Figure 4, wherein it is impossible to employ a weight indicator 37 as shown in Figure 5 and a torque reading of the rotary table 40 (Figure 4) would be severely alected by the frictional resistance between the drill string and the borehole wall.
As shown in Figure 4, a rotary table 40 is vertically mounted on the bed of a at car 50 or other vehicle which may be propelled by suitable prime mover means (not shown) along tracks 51 to drive a drill string 13 substantially horizontally into a formation adjacent a body of water or other area on which it is not possible or practical to position a conventional drill rig. The present drilling apparatus 10 is found to be especially adaptedfor this type of drilling as, at present, there is no other means for controlling the bit pressure for a substantially horizontal drill string. However, by coupling the surface end of the drill string 13 of Figure 4 to the pump system for circulating drilling mud through the drill string 13 and drilling apparatus 10 as shown in Figure 5, an apparatus is provided for accurately controlling the bit pressure.
In the event that lightweight tubing or casing is used to make up the drill string 13, one or more heavy drill collars 52 and 53 (Figure 5) may be placed in the drill string 13 directly above or below the drilling apparatus so that the drill string need never be subjected to compression. When employing drill collars 52 and 53 in the drill string below the drilling apparatus 10, 'the effective Weight on the bit consists of the force due to the pressure drop across the bit plus the weight of the drill collars.
While the present drilling apparatus has been described as comprising a housing 11 (Figure 1) secured to the lower end of the drill string 13 and having an inner member 15 slidably mounted therein, it is realized that the position of these two elements 11 and 15 could be readily reversed with the inner member 15 being affixed to the lower end of the drill string while the cylindrical housing is slidingly mounted therearound with the drill bit 13 secured to the lower end of the housing 11 for axial movement therewith, as diagrammatically shown in Figure 6.
The relative sizes of the housing 11, inner tubular member 15 and drill string 13 may vary depending upon the type of drilling operations in which the present apparatus is employed. Preferably, when the present drilling apparatus is being used in horizontal drilling, the inside diameter of the drill string 13 is approximately as large as the inside diameter of the housing 11 to avoid a thrust on the drill string immediately above the drilling apparatus which tends to buckle the string 13. In vertical drilling operations when the inside diameter of the drill string 13 is less than that of the housing 15 this thrust may be rovercome by coupling drill collars above the present drilling apparatus.
We claim as our invention:
l. A rotary well drilling system comprising a tubular drill string adapted to be rotated in a borehole, `a weight control member comprising a cylinder member and ia tubular plunger member mounted for limited reciprocation in said cylinder member, means arranged in engage- -ment with each other on the inner periphery of the cylinder and the outer periphery of the plunger member to prevent relative rotation of said members, one of said members being connected to the lower end of the drill string and the other member being connected to a drill bit, normally-closed port means through the wall of said cylinder member, said port means being located at a level to permit fluid flow from said drill string through said port means when the tubular plunger member is substantially fully extended from said cylinder member and means for hydraulically controlling the weight of the bit on the bottom, vsaid means cornprisingpurnp means forcirculating drillingv il undenpressure through the "drill string Y and i thevvell nborehole, conduit, meanis'fwcdonhectinggsgfidwpurnp means to the upper end of lthe drill .d
table for rotating said drill string, suspension means fix-N edly maintaining said drill string at a xed height While said string is being rotated, a fluid pressure operated drilling apparatus secured to the lower end of the drill string and rotatable therewith, a drill bit having orifice means therein aixed to the lower end of said drilling apparatus, means for hydraulieallycontrollingtheweighh of the bit omthe-bottoi'ffhewell borehole, said means conp'siipinpwmeans for circulating a pressure fluid through the drill string and well borehole, conduit means connecting said pump means `to the upper end of the drill string, rate-of-flow indicating means positioned in said conduit means, said drilling apparatus comprising telescoping members having an axial bore therethrough, alignment means carried on the contacting surfaces of said telescoping members preventing rotation relative -to each other, stop means carried by said members limiting the axial extension of said telescoping members and preventing their separation and normally-closed port means through the wall of the outer telescoping member, said port means being located at a level to permit fluid flow therethrough from said drill string when the telescoping members are substantially fully extended.
References Cited in the tile of this patent UNITED STATES PATENTS 1,752,092 Kapeluchnikoff Mar. 25, 1930 1,839,767 Lopez Jan. 5, 1932 1,900,932 Hollestelle Mar. 14, 1933 2,624,549 Wallace Jan. 6, 1953 2,684,835 Moore July 27, 1954