AN IMPROVED BIT DESIGN FOR A ROTATING BIT INCORPORATING SYNTHETIC POLYCRYSTALLINE CUTTERS

Abstract: Hydraulic flow may be rendered substantially uniform throughout the waterways on a rotating bit from the center of the bit to the outer gage. This is accomplished by defining waterways into the bit face below a primary surface of the bit face. A colinear land is then disposed into the waterway, but does not extend above the primary surface of the bit face. A plurality of teath are then disposed on the colinear land and extend above the primary surface of the bit face. The flow of hydraulic fluid is prevented from dispersing as the fluid moves from the center of the bit to the outer gage. Cutting by kerfing is further optimized by arranging triads of cutters on each of the pads disposed in the waterways into a set. Each triad of cutters corresponds to additional triads of cutters in azimuthally subsequent and adjacent pads in the next subsequent waterway, thereby forming the set of associated triads of cutters. Each triad of cutters in the set is radially offset from the corresponding triads in the set. Therefore, while each triad cuts through a kerfing action individually, each triad relates to the preceding triad of cutters to cut into the kerfed lands made by that preceding triad of cutters and thus to cut through a kerfing action as well.

Description: The present invention relates to a rotating bit as set forth in the pre-characterising portion of claim 1. A bit of the kind referred to is known from EP-A-0 117 552 and includes an alternative series of waterways and collectors which are sparilly formed to define lands therebetween with a plurality of teeth positioned so as to be substantially parallel to the adjacent segment of a waterway or collector, respectivly. The teeth being exposed above the primary surface of the bit defined by the uppermost surface of the lands. To evenly distribute hydraulic pressure across the shoulder-to-gage transition of the bit the height of a portion of lands adjacent the gage may be varied in a graduated manner. Additionally the height and distance of the lands is chosen to equalize fluid flow from the center of the bit to the outer gage. EP-A-0 127 077 teaches a plurality of waterways emanating from a central crowsfoot, and collectors on the gage of the bit between junk slots in communications with some of the waterways. The lands between the waterways define the primary surface of the bit and include teeth comprising a structure means for retaining each tooth on its respective land and for exposing said tooth above the primary surface of the bit. US-A-4 176 723 discloses single rows of diamond cutting elements disposed at the trailing edges of spiral waterways leading from the crowsfoot or nozzles to the gage of the bit. The lands on which the rows of diamond cutters are disposed are at the same level as the primary surface of the bit face. What is needed is a design whereby cutting elements, particulary synthetic polycrystalline diamond elements on a rotating drill bit can be employed in a manner to maximize cutting efficiencies, performance and lifetimes. To this end the invention provides a rotating bit as claimed in claim 1. Further embodiments are included in claims 2 - 8. By reason of the disposition of the lands, the cutting teeth are immersed in the hydraulic flow of the waterways as the fluid flows radially outward to the outer gage of the bit. Therefore, instead of the hydraulic flow radially dispersing as it moves toward the gage, thereby altering the fluid dynamics, the fluid is substantially retained within each waterway, thus providing improved tooth cooling and cutting flushing. Hydraulic flow is therefore maintained substantially uniform in the proximity of the cutting elements. Some of the waterways are disposed on the bit so that they terminate in junk slots defined into the outer gage of the bit. In this cas these waterways are slightly shorter than waterways which extend to the extremity of the outer gage and hence have a different fluid flow resistence. In order to compensate for the variation in flow resistance between the various waterways, the invention varies the waterway widths and depths to substantially or at least approximately equalize the effective flow resistance of each of the waterways. Figure 1 is a diagramatic cross-sectional depiction of a triangular pismatic diamond element incorporated into the present invention. Fig. 2 is a simplified plan view of a petroleum bit incorporating the invention illustrated in Figure 1. Figure 3a is a plan view in an enlarged scale of one tooth as used in the embodiment as used in Figures 1 and 2. Figure 3b is a side elevational view of the tooth shown in Figure 3a. Figure 4 is a plot diagram of diamond teeth upon the cutting lands of the bit illustrated in Figure 2. The invention can be better understood by first turning to the diagrammatic sectional view of Figure 1. Figure 1 is a simplified cross-sectional view of a single tooth 10 disposed on a land 12. Land 12 in turn is disposed within a waterway 14 defined within a bit face generally denoted by reference numeral 16. According to the invention, bit face 16 is characterized by a general or primary surface 18 which extends between waterways 14 as better shown in plan view in Figure 2. Within each waterway 14 is at least one land 12 and teeth 10 disposed upon land 12. Land 12 is characterized by having an uppermost surface 20 which lies below primary surface 18 of bit face 16. Teeth 10 are disposed on land 12 and extend upwardly beyond upper surface 20 of land 12 and beyond primary surface 18 of bit face 16. Therefore at least a portion of tooth 10 is exposed above the outermost extending surface, primary surface 18 of bit face 16. Tooth 10 has been diagrammatically shown as having a generally triangular cross section and simply placed upon land 12. However, it must be understood that the tooth structure may include any design now known or later devised. In the illustrated embodiment, as will be shown in greater detail in connection with Figures 3a-b and 4, the tooth structure is substantially more complex than that depicted in Figure 1 and includes various means for retaining the tooth on the bit while also maximizing exposure of the diamond cutting element. However, turn first to the plan view of Figure 2 which shows a petroleum bit, generally denoted by reference numeral 22 in which a plurality of reversed spiral waterways 14 are defined. Within each waterway is at least one land 12 upon which teeth 10 are disposed (not shown). Waterways 14 communicate with a central crowfoot 24 through which drilling fluid is supplied from the interior bore of the drill string. Drilling fluid exits crowfoot 24 and enters the plurality of waterways 14 communicating with crowfoot 24 at the center of bit 22. From the center of bit 22 the drilling fluid proceeds radially outward along the reverse spirals of waterways 14 to outer gage 26. Outer gage 26 furthermore has a plurality of junk slots 28 defined therein. Junk slots 28 similarly communicate with certain ones of the waterways such as waterways 14b, 14c and 14e while waterways 14 d, 14f, 14g and 14h, for example, lie entirely between junk slots 28 and extends to the outermost perimeter of gage 26. In each case, tooth bearing lands 12 are disposed within the center of waterways 14 in the manner diagrammatically depicted in Figure 1, which is a cross-sectional view taken through line 1--1 of Figure 2. Drilling fluid flows on both sides of land 12 and tends to be confined and channeled within the respective waterway during the course of its entire transit. Turning to the plan view of Figure 2, waterways 14 are set forth on the face of the bit in the illustrated embodiment in a threefold symmetry. Consider the waterways as provided in one of the three sectors, the waterways in the remaining two sectors being identical. Crowfoot 24 communicates directly with waterway 14d, 14g and waterways 14a. Waterway 14d is a singular or nonbifurcated waterway which extends from the crowfoot to the extremity of gage 26. Waterways 14a are each bifurcated in that they communicate at one end with crowfoot 24 and later divide into a plurality ]of subwaterways. For example, the first of waterways 14a bifucates into waterways 14e and 14b. The second of waterways 14a bifurcates into waterways 14c and 14f. Waterway 14g communicates directly with crowfoot 24 and extends toward gage 26 but bifurcates into two waterways 14h in its outermost radial portion. The hydraulic characteristics of each of these waterways are approximately equivalent although the sink in which they terminate, the source from which they originate, and the lengths of their runs may each be different. The hydraulic performance is maintained approximately uniform along the waterways and within any given waterway from its innermost to outermost point by the branching as depicted in Figure 2 and furthermore by proportionate dimensioning of the waterway. For example, waterways 14a are approxately 0.25" in width and 0.094" in depth with a generally rectangular cross section. Waterway 14e which branches from the first of waterways 14a and radially extends to the leading edge of junk slot 28 has a width of approximately 0.125" and a depth of 0.047" with a rectangular cross section. Waterway 14b which is the companion branch to waterway 14e, extends to the rear portion of junk slot 28 and is characterized by a width of approximately 0.187" and a depth of 0.104" with a V-bottom cross section. The second waterway 14a branches into waterway 14c which has a width of approximately 0.125" and a depth of 0.031" with a rectangular cross section. Waterway 14f, which also originates with second waterway 14a, is led to the gage 26 near collector 36. Waterway 14c is led to a rear portion of junk slot 28. Waterway 14f has a cross-sectional configuration approximately equivalent to waterways 14g and 14h, namely a width of approximately 0.187" and a depth of 0.160" with a triangular cross section. Waterways 14h which provide the outermost radial portions for waterway 14g have a full cross section approximately equal to that of waterway 14e. Therefore, the cross sections or TFA's of each of the waterways, regardless of the exact details of their termination or sink at gage 26 are provided with a substantially uniform rate of volume or fluid per tooth across the face of the bit. Thus, in this sense, the flow of drilling fluid is approximately equally distributed among all of the waterways on bit 22. Before further considering the overall bit design, turn now to the details of the tooth configuration as used in the illustrated embodiment. Turning to Figure 3a, a tooth, generally denoted by reference numeral 38, is shown in enlarged scale in plan view. Tooth 38, as described in greater detail in the application entitled "Improved Diamond Cutting Element in a Rotary Bit", filed March 7, 1983, Serial No. 473,020 (now issued), assigned to the same assignee as the present invention, is comprised of a diamond cutting element 40 around which an integral collar of matrix material 42 has been formed. A prepad 44 of matrix integrally extends from collar 42 and is contiguous and congruous with the front face of diamond element 40. In alternative embodiments prepad 44 may in fact not be congruous with the front face 46 of diamond element 40 and may contact only a portion of the front face. In the illustrated embodiment diamond element 40 is a prismatic triangular polycrystalline synthetic diamond such as sold by General Electric Co., under the trademark GEOSET. A tapered tail 48 of integrally formed matrix material extends from the rear face 50 of diamond element 40 to the surface 52 of the land 12 as better illustrated in connection with the side elevational view of Figure 3b. As illustrated in Figure 3b only a small portion 54 of diamond element 40 remains embedded below the surface 52 and diamond element 40 is substantially exposed thereabove and supported by the surrounding tooth structure. As described below, surface 52 is the uppermost surface of the pad on which the tooth is disposed and in fact lies below the primary surface of the bit face. Turn now to Figure 4 which illustrates the plot detail of the teeth such as shown in Figures 3a and 3b in the petroleum bit shown in plan view in Figure 2. The design of bit 22 of Figure 2 is divided into three sectors. Each 120° sector is identical to the other and includes three waterways. Waterways 14a-h, for example comprise eight waterways in one sector of bit 22. One such sector is illustrated in the plot diagram of Figure 4 which is a diagrammatic view of one of the pie-shaped sectors which has been figuratively cut from bit 22 and laid out flatly to show the plot detail. The plot detail from the center of the bit extending outwardly and down outer gage 26 is shown. A curved surface has been imaginarily cut from bit 22 and laid out to form a flat illustration as in Figure 4. The proportions and distances between elements as illustrated are approximately true on each land, although the distance between lands is necessarily distorted in order to represent the three-dimensional surface in two dimensions. Turn first to Figure 4. A first row of leading teeth 66-72 and so forth are disposed on land 12 within waterways 14a-c. Each of the teeth of the leading row, such as teeth 66-72, are one per carat in size and are of a design and structure such as shown by tooth 38 of Figures 3a and 3b. Behind the leading row of teeth is a second row of teeth on land 12, such as teeth 74-82, which lie in the half spaces between the teeth of the preceding row. Again the teeth of the second or trailing row, such as teeth 74-84, are similar in design, disposition and structure to tooth 64 of the triad of teeth as shown in Figures 3a and 3b but are three per carat in size and are provided as redundant cutters and nose protectors according to conventional design. Land 12 may also be provided with conventional cutters, such as natural diamond surface-set elements, generally denoted by reference numeral 84, which provide for abrasion resistance and apex protection in the conventional manner. Similar synthetic polycrystalline surface-set GEOSETS 86 are provided for abrasion resistance in outer gage 26 as depicted by the exposed rectangular faces (86) in Figure 4.

Claims: A rotating bit (22) including a bit face (16) defining a primary surface (18), a plurality of teeth (10, 38) on said bit face (16), an outer gage (26), a source of drilling fluid (24) and a plurality of waterways (14) extending from said source of drilling fluid (24) to said outer gage (26), said rotating bit (22) having means for maintaining flow of said drilling fluid in said waterways (14) substantially uniform from said source of fluid (24) to said outer gage (26) and means for exposing said plurality of teeth (10, 38) above said primary surface (18) of said bit face (16), and in said substantially uniform hydraulic flow the improvement characterized in that said bit (22) includes at least one tooth bearing pad (12) disposed in at least one of said waterways (14), the uppermost surface (20) of said pad (12) being below said primary surface (18) of said bit face (16). The rotating bit (22) of Claim 1 wherein said at least one pad (12) is colinear with said at least one waterway (14). The rotating bit (22) of Claim 1 or 2, wherein said at least one pad (12) comprises a plurality of pads (12) corresponding to said plurality of waterways (14). The rotating bit (22) of Claim 1, 2 or 3, wherein said means for exposing said plurality of teeth (10, 38) comprises a tooth structure means (42) for retaining each cutting tooth (10, 38) on its respective pad and for exposing said cutting tooth (10, 38) above said primary surface (18) of said bit face (16). The rotating bit (22) of Claim 1, further comprising means for substantially equalizing hydraulic flow among said plurality of waterways (14). The rotating bit (22) of Claim 5 wherein said means for equalizing hydraulic flow among said waterways (14) comprises a selected corresponding uniform width and variable depth for each waterway (14), said corresponding uniform width and variable depth selected to approximately equalize flow resistance of each of said waterways (14). The rotating bit (22) of Claim 5, wherein at least some of said waterways (4) have an unequal length, each said waterway (14) characterized by a selected corresponding uniform width and variable depth throughout said waterway (14) to render the flow resistance of each waterway substantially equal. The rotating bit (22) of Claim 3 further comprising at least one auxiliary waterway (14h) in communication with a selected one of said waterways (14g).

Inventors: GRAPPENDORF, RICHARD
Applicants: EASTMAN CHRISTENSEN COMPANY
Application year: 1987
Main classification: E21B10
IPC codes: E21B10