CA1086299A

CA1086299A - Rotary drilling bit

Info

Publication number: CA1086299A
Application number: CA306,633A
Authority: CA
Inventors: Heino Rohde; Rainer Jurgens; Robijn Feenstra
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1977-08-17
Filing date: 1978-06-30
Publication date: 1980-09-23
Also published as: BE869758A; FR2400610B1; DE2835660A1; GB1537000A; DE2835660C2; FR2400610A1; MX146381A

Abstract

A full-hole rotary bit with scraping elements (such as diamonds) and waterways in the face thereof, has the scraping elements arranged along one side of each of the waterways, Ridges are arranged to guide the mud flow through the waterways.

Description

The invention relates to a rotary drilling bit for full hole drilling as may take place in underground formations for forming holes or wells that may be used for recovering valuable materials such as gas, oil and/or water from underground formations.
The invention relates in particular to a drilling bit comprising a bit body provided in the face thereof with a plurality of waterways extending from the central area of the face of the bit body to the j~ gauge side of the bit. Liquid supply passage means are further - arranged in the bit body, said means communicating with the waterways.
Each waterway is enclosed between a blank land and a row of scraping elements. The scraping elements scrape the bottom as well as part of the wall of the hole wherein the bit may be operated for drilling purposes, and are carried by the bit body. Each row of scraping elements forms part of the wall of the adjoining waterway. Each blank land extends from the central area of the face of the bit body to the gauge side thereof.
The scraping elements of drilling bits of the above type scrape the bottom of the hole in which the bit may be operated for drilling said hole, and liquid such as drilling mud is supplied to the water-ways via the liquid supply passage means. In the operative position ;, of the bit, the mud passes through fluid courses that are defined I by the bottom and wall parts of the waterways in the face of the bit ; body, and by those parts of the bottom and the wall of the hole that face the waterways during rotation of the bit around the central ~xi: of the bit b~dy. The mud ~n flowing through the ~aterway~

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1~86299 cools the scraping elements that are arranged in one of the side walls of each waterway, and further continuously cleans the scraping elements from the cuttings and drilling flour collected thereon.
To prevent the bit body from contacting the bottom of the hole if such hole is passing through formation layers that behave plastically under drilling conditions, the scraping elements are arranged with the scraping edges thereof located at some distance from the face of the bit body. A free space is thereby formed between the blank lands and the bottom of the hole being drilled, this free space preventing the bit body from being exposed to ~ contact with the hole bottom when drilling through formation layers ; that behave plastically.
Object of the invention is to improve the drilling efficiency of drilling bits of the above type.
This is reached by arranging a plurality of ridges on the bit body, each ridge bordering a blank land near the gauge side of the , bit. Thereby, on operation of the bit, the mud is forced to flow substantially through the waterways and the leakage of mud through the space between the blank lands and those parts of the hole bottom facing said lands is prevented. It will be appreciated that this will improve the efficiency of the bit for a given mud supply to the bit per unit of time, since it is only the volume of mud passing through the waterways that takes an active part in cooling and cle~ning the scrapin~ elements.

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The invention will be described in more detail with reference to the drawings, which show by way of example an embodiment of the invention.
Figure 1 of the drawings shows a side view of a drilling bit ~` 5 according to the invention;
Figure 2 shows the bottom view of the bit of Figure 1 taken in the direction of the arrow II;
Figure 3 is a section of the bit of Figure 2 showing (on a ', larger scale) details of one of the waterways and the scraping . 10 elements arranged therealong, said section being taken in the direction of arrows III-III; and -Figure 4 is a section of the bit of Figure 2 showing (on a larger scale) details of one of the ridges, said section being taken in the direction of arrows IV-IV.
The rotary drilling bit shown by way of example in the drawings comprises a bit body 1 attached to a shank 2. The shank 2 is provided with a conical screw thread 3.
Waterways 4 for guiding drilling mud along the scraping elements 5 lining one side of each waterway are arranged in the :
, 20 face of the bit body 1. Mud supply passage means consisting of .
three openings 6 are arranged in the central area of the face of the bit body 1, these openings communicating with the waterways 4.
. Supply of mud to the openings takes place via a central conduit (not shown) passing through the bit body and communicating with a ` central passage (also not shown) through the shank 2.
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: The scraping elements 5 are arranged in a plurality of rows, each row bordering one side of a waterway 4.
The central area of the bit body 1 carries aplurality of separate cutting or scraping means in the form of diamonds 7.
The scraping elements 5 are carried by the bit body 1 as can best be seen in Figure 3 of the drawings which shows i.a. a water-way 4 and a scraping element 5 and the relative position thereof with respect to the bottom 8 of a hole being drilled by the bit.
Each scraping element 5 is made of a wear-resistant abrasive material (such as the material knownunder the trade name "STRATAPAX") and bonded to bit body 1 such that it covers part of the side wall of the waterway 4 with which it cooperates. Each scraping element 5 protrudes from the surface of the bit body l and the row of elements 5 is supported at the rear side thereof by a local protuberance 9 of the bit body 1.
Since the scraping edges 10 of the scraping elements 5 are situated at some distance from the face of the bit body 1, a free space is formed between each blank land 11 and the bottom 8 of a '~ hole that is being drilled by the bit. The presence of the free spaces allows the bit to be used for drilling in formation layers behaving plastically under drilling conditions. The bottom of the hole is locally compressed by the scraping elements OD rotation of the bit under such conditione and exp:nds aeain after i ':

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:c ;-. .,: . : : . : : : - . : -the scraping elements have passed. Such expansion takes place in the free spacesbelow the blank lands11, and the face of the bit body is ~, not contacted by the formation parts that form the bottom of the hole being drilled. Such contact would result in damage of the bit body and would take up substantial part of the torque that is supplied to , the bit, thereby reducing the efficiency of the bit to an undesired extent.
The blank lands 11 extend from the central part of the bit body 1 to the gauge side thereof. The gauge side is constituted by the part 12 of the bit body which part has a diameter equal to or somewhat smaller than the diameter of the hole that can be drilled by the bit. The surface of the gauge side has wear-resistant properties to prevent abrasion thereof that would result in a decrease in diameter of said gauge side.
, Wear-resisting elements (not shown) may be embedded in the surface of the gauge side to this end.
Junk slots 13 are provided in the gauge side 12 of the bit to ~ -: . .
' prevent large drilling cuttings from being wedged between the gauge side 12 and the wall of the hole that is being drilled.
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Ridges 14 are arranged on the surface of the bit body 1 such that they border the blank lands 11 thereof, thereby preventing the drilling mud from short-circuiting the waterways 4 by flowing directly from the mud supply openings 6 to the junk slots 13. The ,:~
~, presence of ridges 14 forces the mud to flow along the row of scraping elements 5 bordering each waterway 4 to cool and clean the scraping elements.
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1/~86299 The ridges may be made of wear-resistant material or have wear-resistant elements (not shown) embedded therein to prevent undesired abrasion thereof on contacting the wall or bottom of the hole being drilled.
As shown in the drawings, the ridges 14 border the blank lands 11 at a location near the gauge side 12 of the bit, without, however, obstructing the junk slots 13. In case no junk slots are present, the ridges may be arranged between the gauge side area and the blank lands or even on the gauge side area.
The flow of mud across the blank lands 11 can even be hampered to a greater extent by providing a second ridge on each land 11, this second ridge being situated near the central part of the face of the ; bit body. Such second ridge 15 is indicated in phantom in Figures 1 and 2 on the land 11'.
The invention is not limited to the application of ridges that have a cross-section of semi-circular shape as shown in Figure 4 of the drawing. Other forms of cross-section may be used as well.
The ridges are preferably of circular curvature such that any contact during rotation of the bit with the bottom of the hole being drilled is restricted to the smallest possible area of the bottom.
The mud supply passage means 6 arranged in the central part of the face of the bit may be of a configuration and/or number that differs from the shape and number shown in Figure 2 of the drawings.
; Also, additional supply of mud to the scraping elements may takeplace through openings that are situated outside this central area, ;
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-1~86299 such as through mud supply nozzles (not shown) that are arranged in the waterways 4.
The cross-section of the waterways is chosen such that the flow rate of the mud that is forced to pass therethrough matches the cooling and cleaning requirements of the scraping elements. Further, the invention is not restricted to a bit equipped with six waterways ; as shown in the drawings. Any number of waterways may be used, but for practical purposes this number will mostly be between three and eight.
The waterways may be of spiral configuration if such is considered desirable, or of any other configuration that differs from the one shown in the drawings.
Although the bottom of the waterway shown in Figure 3 is substantially flush with one side of the scraping element 5, it is apparent that this bottom may also be shaped in the way indicated by the broken line 4'. Preferably, the total area of the leading plane 5' of each scraping element 5 should be exposed to the flow of mud passing through the waterway to obtain optimum cooling thereof.
, In the majority of bit designs a single set of ridges bordering the blank lands near the gauge side of the bit (such as the ridges 14) `~ will be found sufficient to guide the bulk of the mud flow through the waterways. As has already been mentioned above, some further ~ improvement may be obtained by a second set of ridges (such as the .~ ridges 15) that border the blank lands near the central area of the ; 25 face of the bit body. Under extreme conditions, however, one or more . ~
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, 1~86299 further sets of ridges may be provided, these sets being arranged on the blank lands somewhere between the first two sets of ridges. If desired, the inner set of ridges may be replaced by a set of ridges that is arranged at somewhat greater distance from the central area of the face of the bit body. Each additional ridge carried by a blank land may be arranged substantially parallel to or concentric to the ridge bordering the blank land near the gauge side of the bit.
The invention may, as has already been observed hereinabove, also been used in a drill bit that is not provided with junk slots in the gauge side area. Also, the waterways that are shown to pass through the gauge side area of the bit shown in the drawings, may be omitted from this area.
The scraping elements 5 of the bit shown in the drawings form a continuous scraping edge along each of the waterways. However, the invention may also be applied in drill bits wherein the scraping elements are mounted along one side of each of the waterways according to any pattern different from a continuous row. Further, the scraping edges of the rows may be situated along a line that is not smoothly curved as shown in the drawings. Bits having the scraping edges of the scraping elements set in a pattern adapted for scraping a stepped profile in the hole bottom may also be equipped with the ridges according to the invention to prevent short-circuiting of mud between the mud supply openings and the gauge side of the bit.
The configuration of the scraping elements may differ from the one shown in the drawings. Triangular, circular or semicircular configurations may be used with good results.
A scraping element 5 may consist of a single material such as ' 9 ., ' .
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a composition of synthetic diamonds sintered with carbide, or be formed of a synthetic diamond supported by a blank of sintered carbide, which blank is bonded to a support element. The protuberance 9 forms such support element that runs parallel to the waterway 4 and carries a plurality of scraping elements. Also, each scraping element may be carried by a separate support element. If desired, the synthetic diamonds may be replaced by other materials, such as natural diamonds of configurations allowing setting of the diamonds in one of the walls of each waterway such that a substantially flat plane of each of the diamonds coincides with the wall of the relevant waterway and the scraping edge protrudes from the bit body.
The ridges are preferably within the surface of revolution that contains the scraping edges of the , scraping elements, which surface substantially coincides with the bottom profile of a hole being drilled by the bit. Hereby, a gap 16 ;~ (see Figure 4) of small width is formed between the bottom 8 of the hole and the ridge 14 of the bit during drilling of the bit. If the width of this gap 16 is insufficient, the top of each ridge 14 will wear off by contact with the formation material exposed in the surface of the hole being drilled, whereby the required width will ,! automatically be obtained.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Drilling bit for full hole drilling, said bit comprising a bit body, said body being provided on the face thereof with a plurality of water-ways extending from the central area of the face of the bit body to the gauge side of the bit, liquid supply passage means arranged in the bit body and communicating with said waterways, each waterway being enclosed between a blank land of the bit body and a row of scraping elements, said scraping elements being carried by the bit body and protruding from the surface thereof, each row of scraping elements forming part of the wall of the adjoining waterway, each blank land extending from the central area of the face of the bit body to the gauge side thereof, and each blank land being bordered near the gauge side of the bit by a ridge arranged on the bit body.

2. Drilling bit according to claim 1, wherein each blank land has a further ridge arranged near the central area of the face of the bit body.

3. Drilling bit according to claim 1, wherein the ridges are of circular curvature in plan view.

4. Drilling bit according to any one of the claims 1-3, wherein the ridges are situated within an envelope of rotationally symmetric configura-tion that contains the scraping edges of the scraping elements.

5. Drilling bit according to any one of the claims 1-3, wherein junk slots are provided in the gauge side area of the bit body, said junk slots being separated from the blank lands by the ridges near the gauge side.

6. Drilling bit according to claim 1 and claim 3 wherein each blank land carries at least one additional ridge arranged parallel or concentric to the ridge bordering the blank land near the gauge side of the bit.