Drill bit having improved hydraulic action for directing drilling fluid

Abstract: A rotary drill bit (10) has three roller cutters (20A, 20B and 20C) mounted thereon for rotation with a plurality of cutting elements (26) arranged in concentric annular rows (28A, 28B, 28C, 28D) thereon. A high velocity drilling fluid is discharged from the nozzle orifices (40, 42, 52) and the orifices are sized and positioned so that more hydraulic energy is directed against the cutting elements (26) in the gage row (28D) than against the cutting elements (26) in the remaining rows (28A, 28B, 28C). The drilling fluid impinges the cutting elements (26) on the leading side of the roller cutters (20A, 20B, 20C) immediately prior to engagement of the cutting elements (26) with the bore hole bottom (30) and then sequentially strikes the bore hole bottom formation at or closely adjacent the juncture (35) of the horizontal bottom portion (32) with the vertical side portion (34).

Description: This invention relates to rotary drill bits for drilling oil wells and the like, and more particularly to an improved hydraulic action of the drilling fluid against the roller cutters of the drill bit and the formation being drilled. While conventional drill bits have been satisfactory for drilling relatively brittle formations, they do not provide satisfactory rates of penetration when drilling relatively plastically deformable formations. Many commonly encountered formations, such as salts, shales, limestones, sandstones and chalks, become plastically deformable under so-called differential pressure conditions, when the hydrostatic pressure of the column of drilling fluid bearing on the bottom of the well bore exceeds the pressure of the formation surrounding the bore, as often occurs in deep hole drilling. Whereas brittle formations tend to crack or fracture when engaged by the cutting elements of a drill bit, these plastic formations tend to deform and thus remain intact under such loads. In addition, certain of these plastic formations tend to form a relatively thick coating of drilling debris on the roller cutter which can result in so-called "bit-balling" and limited penetration of the formation by the cutting elements. Attempts have been made to increase the rate of penetration in plastic formations by using extended nozzles for improving the cleaning action of the hydraulic system. While this nozzle arrangement may offer some measure of improved cleaning action, this action is still not satisfactory for many types of plastic formations. Moreover, in this arrangement, the nozzles extend down to points closely adjacent to the bottom of the well bore, and thus are subject to damage by irregularities, such as projections or ridges, on the bottom of the well bore, which may form from time to time during drilling operations. One area of the formation, particularly in so-called "sticky" formations, tends to adhere abnormally to the gage row of cutting elements on the roller cutter which is the outermost row that determines the diameter or gage of the bore hole. The cutting elements of the gage row normally engage the bore hole bottom at the juncture of the horizontal bottom portion and the cylindrical side portion. Thus, the cutting elements of the gage row are normally engaging the portion of the formation defined by two separate formation surfaces generally at right angles to each other. As a result it has been found that oftentimes an increased amount of so-called sticky formations tends to adhere to the gage row of cutting elements. The present invention is particularly directed to a rotary drill bit having three roller cutters with a plurality of concentric rows of cutting elements on each cutter, and an improved cleaning action for the gage row of cutting elements and the adjacent bore hole formation generally at the juncture of the horizontal bottom portion and cylindrical side portion of the bore hole. It is noted that the gage row of each roller cutter is the row that most affects the rate of penetration of the rotary drill bit. The gage row normally has more cutting elements therein than the remaining rows. Also, the formation is stronger at the annular corner of the bore hole formed at the juncture of the horizontal bottom surface and the vertically extending cylindrical side surface of the bore hole formation. Thus, the gage row of cutting elements is the critical row in determining the rate of penetration. Additionally, in a rotary drill bit having three roller cutters, a so-called "interlocking" row of cutting elements is provided immediately adjacent the gage row normally on two of the three roller cutters. The interlocking row includes cutting elements which are staggered and fit between the cutting elements of the gage row in radially offset relation. The interlocking row of cutting elements along with the gage row are thus provided for cutting the formation at its strongest area. It is desirable that maximum cleaning action by the pressurised drilling fluid be provided particularly for the cutting elements in the gage row, and the present invention is directed to such a cleaning action in combination with a subsequent scouring action of the drilling fluid against the adjacent formation in the area of the corner of the bore hole. US-A-4516642 discloses, in a roller cone bit, a liquid stream which impinges first on cutters on the leading side of a roller cone and thereafter on the bottom of the well bore. None of the roller cutters incorporates an "interlocking" row of the kind described above. There is no recognition of the importance of ensuring that maximum cleaning action by the pressurised drilling fluid is directed particularly at the cutting elements in the gage row. Furthermore, each stream of drilling fluid impinges on the bottom surface of the well bore, and there is no appreciation of the advantage to be gained by directing the stream of drilling fluid generally against the juncture between the bottom wall and side wall of the bore hole. Similarly, WO-A-8805107 also discloses a roller cone bit, but again reference is only made to the streams of drilling fluid being directed to the working face, i.e. the bottom surface of the hole, or at the side wall of the hole. There is no appreciation of the importance of directing the fluid stream generally against the juncture between the bottom wall and the side wall of the bore hole, neither is there any disclosure of the particular importance of ensuring maximum cleaning action on the cutting elements in the gage row. Also, WO-A-8805107 does not disclose roller cutters having "interlocking" rows of cutting elements adjacent the gage rows. The present invention relates to a rotary drill bit for drilling a well bore, of the kind comprising: a bit body having three cylindrical journals extending therefrom and three roller cutters mounted for relative rotation on said journals, each roller cutter comprising a generally conical roller cutter body and a plurality of cutting elements on the roller cutter body arranged in a plurality of spaced concentric annular rows including an outermost large diameter gage row of cutting elements; and a plurality of nozzle orifices on the bit body for discharge of liquid drilling fluid from the bit in a plurality of high velocity liquid streams, at least one roller cutter including an interlocking row closely adjacent the gage row thereof with the cutting elements in said interlocking row staggered relative to the cutting elements in said gage row and having a cutting path extending into the cutting path of said gage row, said at least one roller cutter having an associated nozzle orifice of a predetermined size positioned on the bit body at a location above the rotational axis of said one cutter at the connection of its associated journal to the bit body and closer to the bore hole side wall than to the centreline of the bit, said associated orifice being formed and positioned to direct a stream of drilling fluid against cutting elements on the leading side of said one cutter. According to the invention a drill bit of this kind is characterised in that said associated orifice for said one roller cutter is formed and positioned to direct at least a part of the liquid stream emerging therefrom first against the cutting elements in the gage row of said one cutter and thereafter generally against the juncture between the bottom portion and side wall of the bore hole, and to direct a greater proportion of said liquid stream against the cutting elements in the gage row than against the cutting elements in any other row of said one cutter, including the interlocking row. In one embodiment said nozzle orifice for said one roller cutter has an increased cross-sectional dimension at its radially outermost area thereby to direct a greater proportion of the liquid stream emerging therefrom against the cutting elements in the gage row of said one cutter. The other said roller cutters may have associated therewith respective nozzle orifices on the bit body formed and positioned to direct streams of drilling fluid against cutting elements on the leading side of said cutters, said nozzle orifices being formed and positioned to direct a greater proportion of the liquid streams emerging therefrom against the cutting elements in the gage rows of said other cutters than against the cutting elements in any other rows of said other cutters. Each of said other roller cutters may have associated therewith a plurality of nozzle orifices with the radially outermost orifice being of increased size to direct a greater proportion of the liquid streams emerging from the orifices against the cutting elements in the gage rows of said other cutters. The following is a more detailed description of embodiments of the invention, reference being made to the accompanying drawings in which: Figure 1 is a perspective of one embodiment of the rotary drill bit of this invention including three cones or roller cutters of a generally conical shape thereon and discharge nozzles along the outer periphery of the bit body; Figure 2 is an axial plan view of the rotary drill bit of Figure 1 showing the three roller cutters with annular rows of cutting elements thereon; Figure 3 is an elevation of a portion of the rotary drill bit of Figures 1 and 2 taken generally along line 3-3 of Figure 2 and showing a stream of drilling fluid directed against the gage row of cutting elements of a roller cutter and the adjacent formation at the bottom of the bore hole; Figure 4 is a schematic view of apportion of the rotary drill bit shown in Figure 3 taken generally along line 4-4 of Figure 3 and illustrating the stream of drilling fluid directed against the gage row and interlocking row at the juncture of the horizontal bottom portion and vertical side portion of the bore hole; Figure 5 is a perspective of a modified rotary drill bit having a more central discharge nozzle for each roller cutter and arranged to direct a greater proportion of the liquid stream against the cutting elements of the gage row of the roller cutters and the adjacent bore hole formation; Figure 6 is a bottom plan of the modified rotary drill bit shown in Figure 5; Figure 7 is a generally schematic view of the stream of drilling fluid taken generally along line 7-7 of Figure 6 and showing the drilling fluid directed against the gage row of cutting elements and the adjacent formation; and Figure 8 is a generally schematic view taken generally along line 8-8 of Figure 7 and showing the stream of drilling fluid against the gage and adjacent row of cutting elements. Referring now to the drawings for a better understanding of this invention, and more particularly to the embodiment shown in Figures 1-4, a rotary drill bit 10 is shown in Figure 1 comprising a central main body or shank 12 with an upwardly extended threaded pin 14. Threaded pin 14 comprises a tapered pin connection adapted for threadedly engaging the female end of a drill string (not shown) and to receive drilling fluid which is connected to a source of drilling fluid at a surface location. Main body or shank 12 is formed from three integral connected lugs to define upper body portion below pin 14 and three downwardly extending legs 16. Each leg 16 has an inwardly and downwardly extending, generally cylindrical bearing journal 18 at its lower end. Roller cutters a, b and c are mounted on journals 18 for rotation and each roller cutter is formed of a generally conical shape. Each roller cutter 20A, 20B and 20C comprises a generally conical body 22 having a recess therein receiving an associated bearing journal 18. A plurality of generally elongate cutting elements 26 have cylindrical bodies mounted in sockets within body 22 and outer tips extending from the outer surface of body 22. Cutting elements or inserts 26 may be made of a suitable powder metallurgy composite material having good abrasion and erosion resistant properties, such as sintered tungsten carbide in a suitable matrix. A hardness from about 85 Rockwell A to about 90 Rockwell A has been found to be satisfactory. The cutting elements 26 are arranged on body 22 in concentric annular rows 28A, 28B, 28C, and 28D. Row 28D is the outermost row and comprises the gage row of cutting elements 26 that determine the final diameter or gage of the formation bore hole which is generally indicated at 30. Row 28C is adjacent to row 28D and comprises an interlocking row on cutter 20A. Cutting elements 26 on row 28C are staggered circumferentially with respect to cutting elements 26 on row 28D and a portion of cutting elements 26 on row 28C projects within the circular cutting path of row 28D. Thus, the cutting paths of the cutting elements 26 on rows 28C and 28D of roller cutter 20A overlap. It is noted that row 28C for cutters 20B and 20C is not an interlocking row as it is spaced substantially inward of row 28D and cutting elements 26 on row 28C do not project within the cutting path of row 28D. In some instances, it may be desirable to provide two cutters or possibly all of the cutters with interlocking rows of cutting elements. The bottom of bore hole 30 includes a horizontal bottom portion and an adjacent cylindrical side wall portion 34 extending vertically generally at right angles to horizontal bottom portion 32. The juncture of horizontal bottom portion 32 and cylindrical side wall portion 34 is shown at 35. The cutting elements 26 on gage row 28D engage the formation in cutting relation generally at the juncture 35 formed by horizontal bottom portion 32 and the vertical side wall portion 34. To provide high velocity drilling fluid for the improved cleaning action, particularly for the gage row 28D and adjacent row 28C of cutting elements 26, a directed nozzle fluid system is provided. The fluid system includes a nozzle generally indicated at 36 positioned between each adjacent pair of legs 16 on the outer circumference of bit body 12. Each nozzle 36 has a drilling fluid passage 38 thereto from the drill string which provides high velocity drilling fluid for discharge. Nozzles 36B and 36C for respective roller cutters 20B and 20C each have a large diameter orifice 40 and a small diameter orifice 42 provided therein for the discharge of high velocity drilling fluid. Large diameter orifice 40 has a stream 44 directed therefrom primarily against the gage row 28D and the adjacent row 28C. Small diameter orifice 42 has a stream 45 directed therefrom primarily against the cutting elements 26 in the remaining rows including row 28B. Thus, as a result of the large diameter orifices 40 directing a stream of drilling fluid radially outwardly of the stream of drilling fluid discharged from small diameter orifices 42, an increased flow of drilling fluid therefrom provides increased hydraulic action for the gage row of cutting elements. Referring to nozzle 36A and particularly to Figure 4, which relates particularly to roller cutter 20A including the interlocking row 28C of cutting elements 36, a nozzle body is shown at 48 having a split ring 50 for mounting body 48. An orifice 52 in nozzle body 48 is elongated in a radial direction and increases progressively in cross-sectional area in a radially outwardly direction thereby to direct a greater proportion of the stream of drilling fluid at the radially outermost area of bit 10 at gage row 28D. In this manner, an increased amount of drilling fluid is delivered progressively in a radial direction thereby to provide the gage row 28D of cutting elements 26 with increased hydraulic cleaning action. As shown particularly in Figures 3 and 4, drilling fluid stream 54 from orifice 52 is shown striking bore hole bottom 30 on the leading side of and ahead of roller cutter 20A. A direction arrow 56 indicates the direction of movement of leg 16 in the bore hole as bit 10 is rotated. A rotation arrow 58 indicates the simultaneous rotation of cutter 20A with the movement of drill bit 10 in the bore hole. Thus, the high pressure drilling fluid stream 54 is directed toward the leading surface of the roller cutter body. Such a placement of stream 54 allows effective cleaning of inserts 26 as the inserts move through stream 54. After fluid stream 54 passes inserts 26, it strikes the bore hole bottom 30 generally at the juncture 35 of horizontal portion 32 and vertical side portion 34 as shown particularly in Figure 4. Then, the drilling fluid along with cuttings that are chipped or gouged from the formation by inserts 26 move in an upward direction outside drill bit 10 through the bore hole in a conventional manner for return to the surface. Streams 44 and 45 of drilling fluid for roller cutters 20B and 20C are directed against the leading sides of roller cutters 20B and 20C in a manner similar to that of stream 54 against roller cutter 20A. Thus, the formation and the cutting elements 26 impinged by stream 54 are subjected to separate or sequential cleaning actions immediately prior to their engagement thereby to provide relatively clean engagement surfaces. Such a separate or sequential cleaning action has been found to result in improved drill bit cutting action and increased rates of drilling penetration, particularly in drilling sticky formations. It is to be understood that various sizes, shapes, and types of nozzles and orifices may be provided and located in various positions on the bit body to deliver a greater proportion of the liquid stream against the cutting elements in the gage row than the cutting elements in the remaining rows, including the interlocking row where such is provided, thereby to provide a more efficient use of the hydraulic energy from the drilling fluid, and improved cleaning of the cutting elements in the gage row. For example, separate nozzles could be provided for orifices 40 and 42 if desired. As pointed out previously, the gage row and interlocking row of cutting elements are provided for cutting the bore hole formation at its strongest area generally at the juncture of the horizontal bottom portion with the vertical side portion. It is desirable that maximum cleaning action by the pressurised drilling fluid be provided particularly for the drilling elements in such gage row, and the present invention is directed to a nozzle fluid system in which a greater proportion of the liquid stream is directed against the cutting elements in the gage row than against the remaining rows. As an example of such orifices for directing fluid streams in such manner, elongated orifices may be provided as illustrated by orifice 52 with the orifice being elongated in a radial direction and increasing in area in a radially outward direction. Therefore, a more efficient utilisation of hydraulic energy is provided by the present invention as an increased supply of drilling liquid is provided at the area of maximum need, i.e. in the area at or closely adjacent the juncture of the horizontal bottom portion with the vertical side wall portion of the bore hole where the formation is the strongest. Referring now to Figures 5-8, a modified drill bit 110 is shown having a bit body 112 with legs 116 extending therefrom. Roller cutters 120A, 120B and 120C are mounted on legs 116 thereon for rotation. Cutting elements 126 are arranged in concentric annular rows on roller cutters 120A, 120B and 120C with each cutter having a gage row 128D of cutting element 126 and an adjacent row 128C. Row 128C of roller cutter 120A provides an interlocking row of cutting elements. Formed at the juncture of each pair of legs 116 is a recessed portion indicated generally at 127 which interrupts the generally smooth outer circumference of bit body 112. Each recessed portion 127 extends in a generally vertical direction along the juncture of each pair of adjacent legs 116 and provides an upward flow passage way for drilling fluid and entrained cuttings from bore hole bottom 130. Since the main upward flow stream of drilling fluid and cuttings will be directed through the generally vertical flow passages formed by recessed portions 127 of bit body 112, it is desirable that the discharge nozzles be positioned so that minimal overlapping interference occurs between the main downward and upward flow streams. A high velocity drilling flow chamber is shown at 129 receiving pressurised drilling fluid from a connected drill string. A nozzle 136 positioned inwardly of the outer circumference of bit body 112 is provided for each roller cutter 120A, 120B and 120C and has a flow passage 135 in fluid communication with chamber 129. Nozzle 136 has a single circular orifice 137 for directing a high velocity stream 154 of drilling fluid against the outer gage row 128D in a manner similar to the embodiment of Figures 1-4. Stream 154 engages the bore hole bottom 130 at the juncture 135 of horizontal bore hole portion 132 and vertical bore hole portion 134 as shown in Figure 7. Thus, the location of nozzle 136 and orifice 137 is such that high velocity drilling fluid is directed against the cutting elements of the gage row to deliver a greater proportion of the fluid stream against the cutting elements in the gage row than against the cutting elements in the remaining rows. The high velocity drilling fluid after cleaning the cutting elements of the gage row 128D then engages the bore hole bottom formation at or closely adjacent the juncture 135 of the horizontal portion 132 with the vertical side portion 134 where the formation is normally the strongest thereby to provide an efficient and economical utilisation of drilling fluid. While only a single nozzle is shown for each roller cutter in the embodiment of Figures 5-8, it is to be understood that large diameter bits, such as, for example, bits around 46-61cm (18-24 inches) in diameter, may have additional nozzles or orifices for each roller cutter. However, in this event, the nozzles and orifices would be positioned and sized so that a greater proportion of the fluid stream would be applied against the gage row of cutting elements than against the remaining rows of cutting elements.

Claims: A rotary drill bit (10) for drilling a well bore, said bit comprising: a bit body having three cylindrical journals (18) extending therefrom and three roller cutters (20A, 20B, 20C) mounted for relative rotation on said journals (18), each roller cutter (20A, 20B, 20C) comprising a generally conical roller cutter body and a plurality of cutting elements (26) on the roller cutter body arranged in a plurality of spaced concentric annular rows (28A, 28B, 28C, 28D) including an outermost large diameter gage row (28D) of cutting elements; and a plurality of nozzle orifices (40, 42, 52) on the bit body for discharge of liquid drilling fluid from the bit in a plurality of high velocity liquid streams (44, 45, 54), at least one roller cutter (20A) including an interlocking row (28C) closely adjacent the gage row (28D) thereof with the cutting elements (26) in said interlocking row (28C) staggered relative to the cutting elements (26) in said gage row (28D) and having a cutting path extending into the cutting path of said gage row, said at least one roller cutter (20A) having an associated nozzle orifice (52) of a predetermined size positioned on the bit body at a location above the rotational axis of said one roller cutter (20A) at the connection of its associated journal (18) to the bit body and closer to the bore hole side wall (34) than to the centreline of the bit, said associated orifice (52) being formed and positioned to direct a stream of drilling fluid (54) against cutting elements (26) on the leading side of said one cutter (20A), characterised in that said associated orifice (52) for said one roller cutter (20A) is formed and positioned to direct at least a part of the liquid stream emerging therefrom first against the cutting elements (26) in the gage row (28D) of said one roller cutter (20A) and thereafter generally against the juncture (35) between the bottom portion (32) and side wall (34) of the bore hole, and to direct a greater proportion of said liquid stream against the cutting elements (26) in the gage row (28D) than against the cutting elements (26) in any other row of said one roller cutter (20A), including the interlocking row (28C). A rotary drill bit (10) according to Claim 1, characterised in that said nozzle orifice (52) for said one roller cutter (20A) has an increased cross-sectional dimension at its radially outermost area thereby to direct a greater proportion of the liquid stream emerging therefrom against the cutting elements in the gage row (28D) of said one cutter. A rotary drill bit (10) according to Claim 1, characterised in that the other said roller cutters (20B, 20C) have associated therewith respective nozzle orifices (40, 42) on the bit body formed and positioned to direct streams of drilling fluid (44, 45) against cutting elements on the leading side of said cutters, and that said nozzle orifices are formed and positioned to direct a greater proportion of the liquid streams emerging therefrom against the cutting elements in the gage rows of said other cutters than against the cutting elements in any other rows of said other cutters. A rotary drill bit according to Claim 3, characterised in that each of said other roller cutters (20B, 20C) has associated therewith a plurality of nozzle orifices (40, 42) with the radially outermost orifice (40) being of increased size to direct a greater proportion of the liquid streams emerging from the orifices against the cutting elements in the gage rows of said other cutters.

Inventors: DEANE JOHN D, IVIE CRAIG R, DEANE, JOHN D., IVIE, CRAIG R.
Applicants: CAMCO INT, CAMCO INTERNATIONAL INC.
Application year: 1990
Main classification: E21B10
IPC codes: E21B10