GB1602807A

GB1602807A - Earth boring bit

Info

Publication number: GB1602807A
Application number: GB22806/78A
Authority: GB
Original assignee: Dresser Industries Inc
Current assignee: Dresser Industries Inc
Priority date: 1977-07-01
Filing date: 1978-05-25
Publication date: 1981-11-18
Also published as: MX147222A; NL7805380A; SE7806864L; JPS5414302A; IT1105345B; BR7804216A; FR2396152A1; FI781181A; AU3618578A; IT7850099A0; AU518619B2; NO782265L; DE2828798A1

Description

(54) EARTH BORING BIT (71) We, DRESSER INDUSTRIES, INC.

a corporation organized under the laws of the State of Delaware, United States of America, of the Dresser Building, Elm k Akard Street, Dallas, Texas, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following state ment The present invention relates to earth boring bits in general and more particularly to a method of constructing a rotary rock bit and a system for equalizing pressures in the lubrication system of a rotary rock bit.

Problems have been encountered with prior art systems of supplying lubricant to the bearings of a rock bit because of the relatively long lifetime of modern bits and the wide variation of environmental conditions encountered during the drilling operation. When a rotary rock bit is lowered into a well bore, the environmental pressure surrounding the bit increases at the rate of approximately 1/2 pound per square inch for each foot of depth. This means that at a depth of 10,000 feet the hydrostatic pressure on the outside of the bit is approximately 5,000 p.s.i. or more because of the weight of the drilling fluid in the well above the bit.In order for a lubrication system to function properly at the elevated downhole pressures, some means must be provided to equalize the internal pressure of the lubricant in the lubrication system with the hydrostatic pressure of the drilling fluid in the well bore.

Failure to provide an effective pressure equalizing system in prior art rock bits has resulted in the destruction of one or more elements of the lubrication system. The elements of the lubrication system that have been the most susceptible to destruction in the prior art rock bits are the seal and the flexible diaphragm in the lubricant reservoir.

A wide variety of other environmental conditions also affect the performance of a pressure equalizing system. For example, the temperature will rise as the well bore penetrates deeper into the earth and temperatures in the range of 250"F to 350"F at 10,000 feet depth may be expected with even higher temperatures at greater depths.

As the bit is rotated and the cone cutters engage the formations, a large amount of heat is generated causing the environmental temperature of the bit to rise. The elevated temperature has an adverse effect on the lubricant, the structural elements of the bit including the lubrication system, the pressure equalizing system and the bearings.

Vacillating pressure conditions, including the magnitude of vacillation, must also he considered when providing a pressure equalizing system. Periodic pressure varia- tions are produced during the drilling operation and these pressure variations can damage the structural elements of the lubrication system and the pressure equalizing system. During drilling, joints of pipe must be added to the drill string for progressively deeper penetration. This may mean that 50 or 60 joints of pipe are added to the drill string during the normal life of a sealed bearing rotary rock bit. In order to add a joint of pipe, which is usually 30 feet in length, rotation of the bit must be stopped and the entire string of pipe, including the bit, must be raised high enough to allow the kelly to clear the rotary table (35-50 feet).Since operating costs of an oil well drilling rig are quite high, the time that the bit is off bottom and not drilling must be kept to a minimum. Therefore, the addition of a joint of pipe must be accomplished quickly and the drill string must be raised and lowered as rapidly as possible.

This raising and lowering of the drill string creates pressure variations that affect the lubrication system and the pressure equalizing system.

When the bit is on bottom, the pressure of lubricant is the same as, or nearly the same as, the hydrostatic pressure of fluid in the well bore. However, as the drill string is elevated in the well bore, the bit body acts in much the same manner as a piston in a cylinder. The enlarged diameter of the bit body exerts a force on the column of fluid above it due to the velocity of the bit travelling up the well bore. The velocity of the fluid moving past the large diameter portion of the bit may be fairly high causing a low pressure area in the zone between the cutters and the main bit body where the seal is located. The pressure differential between the presure of fluid in the area of the seal and the pressure of the lubricant inside of the bit may be in the order of 100 p.s.i. or more during periods of high acceleration of the drill string.

In a substantial number of sealed bearing rotary rock bits, seals are used that resist flow in both directions. An example of this type of seal is an O-ring seal. Bits using this type of seal may encounter a substantial pressure build-up within the lubrication system. Some of the potential sources of the pressure build-up are the pressure differential between lubricant inside of the bit and the fluid in the well bore outside of the bit and thermal expansion of the lubricant caused by the elevated temperatures encountered during the drilling operation.

According to one aspect of the present invention there is provided a method of constructing an earth boring bit, comprising the steps of: providing a lubrication system for said bit including a lubricant reservoir cavity in said bit: positioning a flexible diaphragm in said lubricant reservor cavity, said flexible diaphragm being resilient and being such that in its relaxed condition it divides the cavity into a lubricant portion and an expansion portion; filling said lubricant portion of said lubricant reservoir cavity with a lubricant and applying pressure to said lubricant so that said flexible diaphragm is stretched into said expansion portion; and removing the pressure from said lubricant allowing said flexible diaphragm to relax and withdraw from the expansion portion.

According to another aspect of the present invention there is provided an earth boring bit, comprising: a bit body: a lubricant system in said bit body including a reservoir cavity; a flexible resilient diaphragm in said lubricant reservoir cavity, said diaphragm being such that in its relaxed condition it divides the cavity into a lubricant portion and an expansion portion and such that it may be resiliently stretched from its relaxed condition into said expansion portion by filling said lubricant portion with lubricant and applying pressure to said lubricant: and lubricant filling said lubricant portion of said lubricant reservoir cavity.

The invention will be better understood from the following description of preferred embodiments thereof, given by way of example only, reference being had to the acompanying drawings, wherein: FIGURE 1 illustrates a sectional view of one arm of an earth boring bit showing the lubrication system; FIGURE 2 is an enlarged view of the lubricant reservoir shown in Figure 1; FIGURE 3 is a view corresponding to Figure 2 and illustrating the expansion of the flexible diaphragm in the lubricant reservoir; FIGURE 4 illustrates another flexible diaphragm; and FIGURE 5 shows the expansion of the flexible diaphragm in the lubricant reservoir of Figure 4.

Referring now to the drawings, and to Figure 1 in particular, illustrated therein and generally designated by the reference number 10 is a three cone sealed bearing rotary rock bit with one arm of the bit 10 being shown in Figure 1. As illustrated, the bit 10 includes a bit body including an upper threaded portion 11. The threaded portion 11 allows the bit 10 to be connected to the lower end of a rotary drill string (not shown. Depending from the bit body 11 are three substantially identical arms with one of the arms 13 being shown in Figure 1. The lower end of each of the arms is provided with an extended journal portion and the details of this journal portion will be discussed subsequently. Three rotary cone cutters, cutter 22 being shown in Figure 1, are rotatably positioned on the three bearing pins extending from the arms.Each of the cutters includes cutting structure on its outer surface adapted to disintegrate the formations as the bit 10 is rotated and moved downward. The cutting structure 21 is shown in the form of tungsten carbide inserts. However, it is to be understood that other cutting structures such as steel teeth may be used as the cutting structure on the cone cutters.

The cutter 22 is rotatably positioned on the journal portion of the arm 13 and adapted to disintegrate earth formation as the bit is rotated. The cutting structure 21 on the outer surface of cutter 22 contacts and disintegrates the formations in a manner that is well known in the art. The journal portion of arm 13 consists of a bearing pin 18 upon which the cutter 22 is mounted. A plurality of bearing systems are located in the bearing area between the cutter 22 and the bearing pin 18. The bearing systems in the bearing area include an outer friction bearing 26 and a thrust button 25. An O-ring seal 19 is positioned between the cutter 22 and the bearing pin 18. This seal retains lubricant in the bearing area around the bearing systems and prevents any materials in the well bore from entering the bearings. A passageway 17 is provided to allow lubricant to be transmitted to the bearing systems. The pass ageway 17, as shown, also allows the balls that make up the ball bearing system 27 to be inserted into position after the cone cutter 22 is placed on the bearing pin 18.

The series of ball bearings 27 serve to lock the cone cutter 22 on bearing pin 18. After the balls are in place, a plug 16 is inserted into the passageway 17 and welded therein by weld 15. Plug 16 has a reduced diameter throughout the major portion of its length to allow lubricant to be transmatted to the bearing area. Additional passageways 23, 24 and 28 extend from passageway 17 to the bearing area to insure a sufficient supply of lubricant to bearings 20, 27, 26 and 25.

A lubricant reservoir is located in the arm 13 to provide a supply of lubricant to the bearings. A passageway 14 connects the lubricant reservoir with the passageway 17 to allow lubricant to be transmitted from the reservoir directly to the bearings. A flexible diaphragm is positioned in the lubricant reservoir bore and encloses the lower portion of the reservoir. The area within the lubricant reservoir bore, but outside of the diaphragm, is vented to the dome of the bit by a passageway 29 that connects the lower end of the lubricant reservoir bore with the dome of the bit. The upper end of the lubricant reservoir bore is closed by a cap locked in place in the arm 13 by a snap ring. An O-ring seal is positioned around the cap to retain lubricant in the lubricant reservoir.A passageway extends through the cap to allow lubricant to be introduced into the lubricant reservoir. A plug 9 closes the passageway.

The bit 10 includes a central passageway 12 extending along the central axis of the bit 10 to allow drilling fluid to enter from the upper section of the drill string (not shown) immediately above and pass downward through three jet nozzles (not shown) past the cutting structure of the cone cutters.

In use, the bit 10 is connected as the lower member of a rotary drill string (not shown) and lowered into a well bore until the cone cutters engage the bottom of the well bore.

Upon engagement with the bottom of the well bore, the drill string is rotated, rotating bit 10 therewith. Drilling fluid is forced down through the interior passage of the rotary drill string and continues through the central passageway 12 of bit 10 passing through the nozzles past the cutting structure of the cutters to the bottom of the well bore thence, upward in the annulus between the rotary drill string and the wall of the well bore carrying with it the cuttings and debris from the drilling operation.

Referring now to Figure 2, an enlarged view of the lubricant reservoir area of the bit 10 is shown that illustrates the structural elements of the lubricant reservoir in greater detail. The lubricant reservoir bore 30 extends into the arm 13 of the bit 10.

The lower end of the bore 30 is vented to the dome of the bit by the passageway 29.

The lubricant passage 14 extends from the bore 30 to the bearing area. A threaded portion 36 of the lubricant passageway 14 is provided to receive a plug during the welding operation when the ball plug 16 is welded in place by weld 15. The arm 13 is imersed in water to prevent damaging of any of the elements affected by heat. The plug locked in threads 36 prevents the water from entering the bearing area.

A flexible and resilient reservoir diaphragm 32 is positioned in the bore 30.

The diaphragm is locked in place by the reservoir cap 37. A molded "0" ring type seal 35, being primarily an axial seal and secondarily a radial seal, is compressed by the reservoir cap 37 to provide a positive seal between the flexible diaphragm 32 and the bore 30. An O-ring cap seal 38 is positioned between the reservoir cap 37 and the bore 30 above the passage 14 to provide a positive seal for the lubricant reservoir. The reservoir cap 37 is locked in place by snap ring 39. A threaded filler hole 40 is provided to allow the lubricant reservoir to be filled with lubricant. The threaded filler hole 40 is closed by a plug 9.

The lubricant reservoir as shown in Figure 2 has not yet been filled with lubricant. The reservoir area 34 will receive the lubricant which will be pumped into place through threaded filler hole 40. The lubricant will be transmitted to the bearings through the passageway in cap 37 and the lubricant passageway 14. The flexible and resilient diaphragm 32 in its relaxed condition does not completely fill the bore 30.

An expansion space 31 is provided outside the flexible diaphragm 32. As will hereinafter be explained, it has been found that the expansions space should preferably re not less than 5% of the lubrication system's full capacity and the expansion space 31 of the lubrication system shown in Figure 2 is approximately 10% of the lubrication system's full capacity. A bonded metal plate 33 is positioned in the end of the flexible and resilient diaphragm 32.

Referring now to Figure 3, the filling of the lubricant reservoir will be described.

A tube 8 is connected to the threaded filler hole 40. A vacuum is applied to the lubricant reservoir system to evacuate the entire lubrication system. Lubricant is then introduced through the tube 8 into the reservoir area 34, the passages to the bearing and the bearing area. Pressure is applied to the lubricant being introduced through tube 8 causing the flexible and resilient diaphragm 32 to be stretched and expanded so that it fills substantially the entire a9a of the reservoir bore 30. The flexible diaphragm 32 is shown in its initial position in Figure 2 prior to introduction of the lubricant and is shown in its expanded position in Figure 3 when the pressure is being applied to the lubricant.

The pressure is removed from the lubricant.

The resiliency of the diaphragm 32 will cause it to return to its original unfixed condition, forcing some of the lubricant back out through the filler hole 40. This will provide the expansion space 31 as shown in Figure 2 to accommodate any expansion of volume within the lubricant area during the drilling operation.

Tests were conducted to determine the preferred size of the expansion space 31.

As a result of the tests, it was determined that the expansion space 31 should prefer- ably be not less than 5% of the lubrication system's full capacity. Analysis of the tests indicated that the preferred embodiment should have the expansion space 31 to take up approximately 10% of the lubrication system's full capacity and the area containing lubricant should take up aproximately 900,of of the lubrication system's full capacity. The tests were conducted in the manner described below.

Tests A dull 7-7/8 S86F was obtained for use in the test. The bit was cleaned and the old grease in it was flushed out. New diaphragms which were assembled without any type of valve were installed in the bit along with new reservoir caps, O-rings, snap rings and filler plugs. The bit was evacuated with a vacuum pump and filled with fresh grease. While filling with grease, an expansion space was left at the bottom of the reservoir bore. The volume of this space was controlled very carefully. Wax plugs were molded to the shape of the bottom of the reservoir bore. The thickness of these plugs was controlled so that the volume they occupied was known.These plugs were made from Carbowax 1540 ("Carbowax" is a registered Trade Mark) which has a melting point of 115 F. During assembly, the wax plug was placed in the bottom of the reservoir bore. Then the diaphragm and cap were installed. When filling with grease the diaphragm was extended down against the plug. When the bit was full of grease, the greasing fixture was removed from the filler hole and grease was allowed to bleed out until the internal grease pressure equalized with the atmosthere. The system was then closed. The bit was placed in a bucket of oil at room temperature, then heated to 2120F and held there for one hour. As soon as the oil temperature rose to 1 150F the wax plugs would melt and run out through the dome vent hole, thus leaving an expansion space for the diaphgarm.After 1 hour at 212"F the bit and oil were heated to 2500F and held there for one hour. Then it was heated to 3000F and held there for an additional hour. All during these heating periods the internal pressure was monitored with pressure gages attached to reservoir caps. Several tests were run as described above with different sizes of the wax plugs to determine how much expansion space was needed to reliably insure that no internal pressure would build up in the lubricant.

It was determined that if the lubrication system is filled to not less than 5% of its full capacity, the expansion space left between the bottom of the reservoir bore and the diaphragm will be sufficient to prevent any excessive internal lubricant pressures from forming up to 3000F with the particular lubricant used.

Referring now to Figures 4 and 5, another embodiment of the present invention is illustrated. In this embodiment the passageway from the bottom of the reservoir bore to the dome of the bit is eliminated and the O-ring seal 38 shown in Figure 3 is eliminated. For these reasons, the embodiment illustrated in Figures 4 and 5 is considered the preferred embodiment.

Referring first to Figure 4, the structural elements of the lubricant reservoir are illustrated. The lubricant reservoir bore 45 extends into the arm 42 of the bit 41. The lower end of the bore 45 is closed. A lubricant passage 43 extends from the bore 45 to the bearing area. A threaded portion 44 of the lubricant passageway 43 is provided to receive a plug during the welding operation when the ball plug is welded in place. During the welding operation the bit 41 is immersed in water to prevent damaging of any of the elements affected by heat. The plug locked in threads 44 prevents the water from entering the bearing area.

A flexible and resilient reservoir diaphragm 47 is positioned in the bore 45.

The diaphragm is locked in place by the reservoir cap 54. A molded "0" ring type seal 52, being primarily an axial seal and secondarily a radial seal, is compressed by the reservoir cap 54 to provide a positive seal between the flexible diaphragm 47 and the bore 45. The molded O-ring seal 52 is positioned between the reservoir cap 54 and a metal ring 51 to provide a positive seal for the lubricant reservoir. The reservoir cap 54 is locked in place by snap ring 53. A passageway extends through the reservoir cap 54 that provides communication between fluid in the borehole and the flexible diaphragm 47.

A threaded filler passage 56 is provided in arm 42 to allow the lubricant reservoir to be filled with lubricant. The reservoir area 50 will receive the lubricant which will be pumped into place through passage 56. The lubricant will be transmitted to the bearing through the lubricant passageway 43. The flexible and resilient diaphragm 47 in its relaxed condition does not completely fill the bore 45. An expansion space 49 is provided outside the flexible diaphragm 47. As previously explained, it has been found that the expansion space should preferably be not less than 5% of the lubrication system's full capacity. A bonded metal plate 48 is positioned in the end of th flexible and resilient diaphragm 47. A cannister 46 is provided to protect the diaphragm from being ruptured by pressure from fluid in the borehole.

Referring now to Figure 5, the filling of the lubricant reservoir will be described.

A tube 57 is connected to the threaded filler passage 56. A vacuum is applied to the lubricant reservoir system to evacuate the entire lubrication system. Lubricant is then introduced through the tube 57 into the reservoir area 50, the passages to the bearings and the bearing area. Pressure is applied to the lubricant being introduced through tube 57 causing the flexible and resilient diaphragm 47 to be stretched and expanded so that it fills subsantially the entire available area. The flexible diaphragm 47 is shown in its initial position in Figure 4 prior to introduction of the lubricant and is shown in its expanded position in Figure 5 when the pressure is being applied to the lubricant. The pressure is removed from the lubricant.The resiliency of the diaphragm 47 will cause it to return to its original un flexed condition, forcing some of the lubri cant back out through the filler passage 56. This will provide the expansion space 49 as shown in Figure 4 to accommodate any expansion of volume within the lubricant area during the drilling operation. As previously described, it was determined for one particular bit and lubricant that if the expansion space left between the reservoir cap and the diaphragm is not less than 5O. it will prevent any excessive internal lubricant pressures from forming up to 300"F.

WHAT WE CLAIM IS: 1. A method of constructing an earth boring bit, comprising the steps of: provided ing a lubrication system for said bit includ inz a lubricant reservoir cavity in said bit: positioning a flexible diaphragm in said lubricant reservoir cavity, said flexible diaDhraern being resilient and being such that in its relaxed condition it divides the cavity into a lubricant portion and an ex Dansion portion: filling said lubricant portion of said lubricant reservoir cavity with a lubricant and applying pressure to said lubricant so that said flexible diaphragm is stretched into said expansion portion: and removing the pressure from said lubricant allowing said flexible diaphragm to relax and withdraw from the expansion portion.

2. A method according to claim 1 wherein the pressure applied to the lubricant is sufficient to cause the diaphragm to be stretched to substantialy fill said expansion portion.

3. A method according to claim 1 or claim 2 wherein the lubricant reservoir cavity is provided in a bore in said bit, said bore having a closed end and an open end with a cap closing said open end, said flexible diaphragm being positioned in said bore between said cap and said closed end so that the flexible diaphragm divides the bore into the lubricant portion between said closed end of said bore and said flexible diaphragm and the expansion portion between said cap and said flexible diaphragm.

4. A method according to any preceding claim wherein said expansion portion is not less than 5% of the volume of said lubricant system.

5. A method according to claim 4 wherein said expansion portion is approximately 10% of the volume of said lubrication system.

6. An earth boring bit, comprising: a bit body; a lubricant system in said bit body including a reservoir cavity; a flexible resilient diaphragm in said lubricant reservoir cavity, said diaphragm being such that in its relaxed condition it divides the cavitv into a lubricant portion and an expansion portion and such that it may be resiliently stretched from its relaxed condition into said expansion portion by filling said lubricant portion with lubricant and applying pressure to said lubricant: and lucricant filling said lubricant portion of said lubricant reservoir cavity.

7. An earth boring bit according to claim 6 wherein said expansion portion is not less than 5% of the volume of said lubricant system.

8. An earth boring bit according ,o claim 7 wherein said expansion portion is substantialy 10% of the volume of said lubricant system.

9. A method of constructing an earth boring bit, substantialy as hereinbefore described with reference to the accompanying drawings.

10. An earth boring bit, substantially as hereinbefore described with reference to and as shown in the accompanying drawngs.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

will be pumped into place through passage 56. The lubricant will be transmitted to the bearing through the lubricant passageway 43. The flexible and resilient diaphragm 47 in its relaxed condition does not completely fill the bore 45. An expansion space 49 is provided outside the flexible diaphragm 47. As previously explained, it has been found that the expansion space should preferably be not less than 5% of the lubrication system's full capacity. A bonded metal plate 48 is positioned in the end of th flexible and resilient diaphragm 47. A cannister 46 is provided to protect the diaphragm from being ruptured by pressure from fluid in the borehole.

Referring now to Figure 5, the filling of the lubricant reservoir will be described.

A tube 57 is connected to the threaded filler passage 56. A vacuum is applied to the lubricant reservoir system to evacuate the entire lubrication system. Lubricant is then introduced through the tube 57 into the reservoir area 50, the passages to the bearings and the bearing area. Pressure is applied to the lubricant being introduced through tube 57 causing the flexible and resilient diaphragm 47 to be stretched and expanded so that it fills subsantially the entire available area. The flexible diaphragm 47 is shown in its initial position in Figure 4 prior to introduction of the lubricant and is shown in its expanded position in Figure 5 when the pressure is being applied to the lubricant. The pressure is removed from the lubricant.The resiliency of the diaphragm

47 will cause it to return to its original un flexed condition, forcing some of the lubri cant back out through the filler passage 56. This will provide the expansion space 49 as shown in Figure 4 to accommodate any expansion of volume within the lubricant area during the drilling operation. As previously described, it was determined for one particular bit and lubricant that if the expansion space left between the reservoir cap and the diaphragm is not less than 5O. it will prevent any excessive internal lubricant pressures from forming up to 300"F.

WHAT WE CLAIM IS: 1. A method of constructing an earth boring bit, comprising the steps of: provided ing a lubrication system for said bit includ inz a lubricant reservoir cavity in said bit: positioning a flexible diaphragm in said lubricant reservoir cavity, said flexible diaDhraern being resilient and being such that in its relaxed condition it divides the cavity into a lubricant portion and an ex Dansion portion: filling said lubricant portion of said lubricant reservoir cavity with a lubricant and applying pressure to said lubricant so that said flexible diaphragm is stretched into said expansion portion: and removing the pressure from said lubricant allowing said flexible diaphragm to relax and withdraw from the expansion portion.
2. A method according to claim 1 wherein the pressure applied to the lubricant is sufficient to cause the diaphragm to be stretched to substantialy fill said expansion portion.
3. A method according to claim 1 or claim 2 wherein the lubricant reservoir cavity is provided in a bore in said bit, said bore having a closed end and an open end with a cap closing said open end, said flexible diaphragm being positioned in said bore between said cap and said closed end so that the flexible diaphragm divides the bore into the lubricant portion between said closed end of said bore and said flexible diaphragm and the expansion portion between said cap and said flexible diaphragm.
4. A method according to any preceding claim wherein said expansion portion is not less than 5% of the volume of said lubricant system.
5. A method according to claim 4 wherein said expansion portion is approximately 10% of the volume of said lubrication system.
6. An earth boring bit, comprising: a bit body; a lubricant system in said bit body including a reservoir cavity; a flexible resilient diaphragm in said lubricant reservoir cavity, said diaphragm being such that in its relaxed condition it divides the cavitv into a lubricant portion and an expansion portion and such that it may be resiliently stretched from its relaxed condition into said expansion portion by filling said lubricant portion with lubricant and applying pressure to said lubricant: and lucricant filling said lubricant portion of said lubricant reservoir cavity.
7. An earth boring bit according to claim 6 wherein said expansion portion is not less than 5% of the volume of said lubricant system.
8. An earth boring bit according ,o claim 7 wherein said expansion portion is substantialy 10% of the volume of said lubricant system.
9. A method of constructing an earth boring bit, substantialy as hereinbefore described with reference to the accompanying drawings.
10. An earth boring bit, substantially as hereinbefore described with reference to and as shown in the accompanying drawngs.