GB2418439A

GB2418439A - Rock-bit and rock-bit seal

Info

Publication number: GB2418439A
Application number: GB0518765A
Authority: GB
Inventors: Sudarsanam Chellappa; Zhou Yong
Original assignee: Smith International Inc
Current assignee: Smith International Inc
Priority date: 2004-09-28
Filing date: 2005-09-14
Publication date: 2006-03-29
Anticipated expiration: 2025-09-14
Also published as: GB2418439B; US20060065445A1; CA2519745A1; GB0518765D0

Abstract

A seal (80) is disposed radially between a cone (11) and a leg (16) of a rock bit. A footprint (96) defines an area of contact between the seal (80) and the leg. Compression of the seal (80) generates a contact pressure between the seal (80) and the leg. An axial centreline (98) evenly bisects the footprint (96) into a mud side and a grease side. A contact pressure profile (110) defines the contact pressure over the footprint (96), wherein the contact pressure on the mud side of the footprint (96) is greater than the contact pressure on the grease side of the footprint (96).

Description

ROCK-BIT AND ROCK-BIT SEAL

The present invention relates to a rock bit and to a seal for a rock bit.

The present invention relates generally to sealed bearing earth boring drill bits, such as rotary cone rock bits. The present invention also generally relates to seal rings for use in rotary cone rock bits. In embodiments, the present invention relates to journal bearing seal rings used to isolate a lubricated bearing area from abrasive wellbore fluids.

Rock bits are employed for drilling wells in subterranean formations for oil, gas, geothermal steam, minerals, and the like. Such drill bits commonly have a body connected to a drill string and three cutter cones mounted on the body. The cutter cones are rotatably mounted on steel journals or pins integral with the bit body at its lower end. A lubricated bearing is often used to support rotation of the cutter cone about the journal pins. Journal bearing seal rings are used to isolate the lubricated bearing from abrasive fluids moving through the well.

Journal bearing seal rings are often constructed from an elastomer or rubber material and have a symmetric axial cross-sectional geometry. The particular geometric configuration of the seal surfaces produces a given amount of seal deflection that defines the degree of contact pressure or "squeeze" applied by the dynamic and static seal surfaces against respective journal bearing and cone surfaces.

The contact pressure generated by the journal bearing seal ring is the force that protects the journal bearing from wellbore fluids. Failure of the journal bearing seal ring can allow wellbore fluids to contaminate the journal bearing and can lead to failure of the bearing. Once the bearing fails, or becomes severely worn, the cutter cone may no longer operate properly and the drill bit will have to be replaced. Replacement of a drill bit can be a time consuming process, because it requires a cessation of drilling operations and removal of the entire drill string from the wellbore. Therefore, any improvement that maximizes the life of a drill bit is beneficial.

Conventional journal bearing seals perform best within a narrow range of contact pressures and fluid conditions.

Because the seal bears against a rotating surface between the seal and the leg, lubricant is often used to decrease the friction forces in this sealing area. If the contact pressure is too high, lubricant will not be able to reach the sealing interfaces and the heat generated by sliding contact of the seal and the leg will increase. If the contact pressure is too low, abrasive particles can enter the sealing interfaces and increase wear of both the seal and the leg. In either condition, the life of the seal will be greatly reduced over a seal operating with proper lubrication and without abrasive particles.

Thus, there remains a need to develop journal bearing seal rings that overcome some of the foregoing difficulties while providing more advantageous overall results.

According to a first aspect of the present invention, there is provided a rotary cone rock-bit comprising: a bit body; a leg extending from said bit body; a cone rotatably mounted to said leg; a seal disposed radially between said cone and said leg; a footprint defining an area of contact between said seal and said leg, wherein compression of said seal generates a contact pressure between said seal and said leg; an axial centreline that evenly bisects said footprint into a mud side and a grease side; and, a contact pressure profile defining the contact pressure over said footprint, wherein the contact pressure on the mud side of said footprint is greater than the contact pressure on the grease side of said footprint.

According to a second aspect of the present invention, there is provided a bit for drilling a borehole into earthen formations, the bit comprising: a bit body; a journal shaft extending from said bit body; a rolling cone cutter mounted on said journal shaft and being adapted to rotate about a cone axis; a seal gland between said shaft and said cone and comprising a first seal-engaging surface on said shaft and a second seal-engaging surface on said cone; an annular seal disposed in said gland, said annular seal comprising: a radially inner surface sealingly engaging said first seal-engaging surface, and a radially outer seal surface sealingly engaging said second seal- engaging surface; and, a seal footprint on one of said seal-engaging surfaces, said footprint being defined by the portion of said seal contacting said one seal-engaging surface, said footprint having a footprint length measured axially relative to said cone axis and being bisected by a footprint centreline that is perpendicular to said cone axis; wherein said seal creates a pressure profile on said one seal- engaging surface axially along said footprint, said pressure profile being asymmetric relative to said centreline.

According to a third aspect of the present invention, there is provided a rotary cone rock-bit seal comprising: a seal in contact with a rotating surface along a footprint; wherein: a centreline through the midpoint of the footprint divides said seal into a drilling fluid side and a lubricant side; and, a contact pressure profile formed between said seal and the rotating surface is asymmetric about said centreline.

The preferred embodiments of the present invention are directed toward sealing arrangements for a rotary cone rock-bit comprising a leg extending from a bit body and a cone rotatably mounted to the leg. A seal is disposed radially between the cone and the leg. A footprint defines an area of contact between the seal and the leg.

Compression of the seal generates a contact pressure between the seal and the leg. An axial centreline evenly bisects the footprint into a mud side and a grease side. A contact pressure profile defines the contact pressure over the footprint, wherein the contact pressure on the mud side of the footprint is greater than the contact pressure on the grease side of the footprint.

In certain embodiments, a bit for drilling a borehole into earthen formations comprises a journal shaft extending from a bit body and a rolling cone cutter mounted on the journal shaft and being adapted to rotate about a cone axis. A seal gland is formed by the shaft and the cone and comprises a first seal engaging surface on the shaft and a second seal engaging surface on the cone. An annular seal is disposed in the gland. The annular seal comprises a radially inner surface sealingly engaging the first seal engaging surface and a radially outer seal surface sealingly engaging the second seal engaging surface. A seal footprint on one of the seal engaging surfaces is defined by the portion of the seal contacting the one seal engaging surface. The footprint has a footprint length measured axially relative to the cone axis and being bisected by a footprint centreline that is perpendicular to the cone axis. The seal creates a pressure profile on one of the seal engaging surface axially along the footprint, the pressure profile being asymmetric relative to the centreline.

Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a prior art rock bit;

Figure 2 is a partial cross-sectional view of the rock bit of Figure 1; Figure 3A is a partial cross-sectional view of a prior art seal; Figure 3B illustrates the seal of Figure 3A disposed in a seal gland; Figure 3C illustrates the contact pressure profile of the seal of Figure 3A; Figure 4A is a partial cross-sectional view of an example of a seal constructed in accordance with an embodiment of the invention; Figure 4B illustrates the seal of Figure 4A disposed in a seal gland; Figure 4C illustrates the contact pressure profile of the seal of Figure 4A; Figures 5A-B through 9A-B are partial cross-sectional views of and contact pressure profiles generated by radial seals that have asymmetric external features; Figures lOA-B through 12A-B are partial cross- sectional views of and contact pressure profiles generated by radial seals that have asymmetric internal features; Figures 13A-B through 22A-B are partial cross sectional views of and contact pressure profiles generated by radial seals that have a combination of internal and external asymmetrical features; Figures 23A-B through 26A-B are partial cross sectional views of and contact pressure profiles generated by radial seals having multiple material interfaces; Figures 27A-B through 31A-B are partial cross sectional views of and contact pressure profiles generated by symmetrical radial seals disposed within asymmetrical seal glands.

Figure 32A is a partial cross-sectional view of an example of a seal constructed in accordance with an embodiment of the invention; Figure 32B illustrates the seal of Figure 32A disposed in a seal gland; Figure 32C illustrates the contact pressure profile of the seal of Figure 32A; Figures 33A-33F are cross-sectional views of examples of O-ring seals constructed in accordance with embodiments of the invention; Figures 34A34D are cross-sectional views of examples of composite O-ring seals constructed in accordance with embodiments of the invention; Figure 35 is a cross-sectional view of an example of a dual seal assembly constructed in accordance with embodiments of the invention; and, Figure 36 is a cross-sectional view of an example of a dual seal assembly constructed in accordance with embodiments of the invention.

Referring now to Figure 1, a rock bit comprises body having three cutter cones 11 mounted on its lower end.

A threaded pin 12 is at the upper end of body 10 for assembly of the rock bit onto a drill string. A plurality of hardened inserts 13 are pressed into holes in the surfaces of cutter cones 11 for bearing on the rock formation being drilled. Nozzles 15 in body 10 introduce drilling fluid into the space around cutter cones 11 for cooling and carrying away formation chips drilled by the bit. - 9 -

Figure 2 is a partial longitudinal cross-section of the rock bit, extending radially from the rotational axis 14 of the rock bit through one of the three legs on which the cutter cones 11 are mounted. Each leg includes a journal pin 16 extending downwardly and radially inwardly of the rock bit body 10. Journal pin 16 includes a cylindrical bearing surface 17 including lubrication gap 18.

Cuter cone 11 comprises an inner cavity with a cylindrical bearing surface 21. Bearing surface 21 interfaces with bearing surface 17 to form the journal bearing that supports rotation of cutter cone 11. The bit may also comprise ball bearings 24 that carry thrust loads tending to remove cone 11 from the journal pin 16 and thereby retain the cone on the journal pin.

Grease, or another appropriate lubricant, lubricates the bearing surfaces between the journal pin 16 and the cone 11. A supply of grease is provided by a grease reservoir in cavity 29. Grease is supplied to the bearing surfaces through lubricant passages 31 and 32. Grease is retained in the bearings by a radial seal 33 between cone 11 and journal pin 16. A pressure compensation subassembly, including bellows 37, is included in the grease reservoir in cavity 29, and acts to maintain the pressure of the grease within a desired pressure range.

Referring now to Figure 3A, one example of a radial seal 40 comprises a rectangular body 42 and symmetrical, curved end surfaces 44 and 46. Radial seal 40 is formed from a resilient material and may have end portions 48 formed of a second resilient material having different properties from the material forming body 42. End portions 48 are moulded to body 42 along straight, symmetrical interfaces 49.

Figure 3s shows radial seal 40 disposed within a seal gland 50 formed by a seal groove 52 and a cylindrical sealing surface 54. Radial seal 40 is compressed within seal gland 50 and forms a contact footprint 56 on cylindrical sealing surface 54. Footprint 56 is bisected by axial centreline 58 such that linear dimensions 60 and 62 are equal. For purposes of this discussion, axial centreline 58 divides the seal into an abrasive side 64 and a lubricant side 66. Axial centreline 58 may or may not mark the physical interface between the abrasive fluid on one side of the seal and the lubricating fluid on the other side of the seal.

Referring now to Figure 3C, the contact pressure profile exerted by radial seal 40 on sealing surface 54 is represented by curve 70. Curve 70 is divided by centreline 58 into an abrasive-side area 72 and a lubricant-side area 74, which are symmetrical about centreline 58. The abrasive-side peak contact pressure 76 and the lubricant- side peak contact pressure 78 both occur at point 79, which is located on centreline 58.

Radial seal 40 thus provides a distribution of sealing contact pressure along sealing surface 54 that is symmetric about centreline 58. Seals that generate a symmetrical contact pressure distribution, such as seal 40, perform best within a narrow range of contact pressures. If the contact pressure is too high, lubricant will not be able to reach the sealing interfaces and the heat generated by sliding contact of the seal and the cone will increase.

Similarly, if the contact pressure is too low, abrasive particles can enter the sealing interfaces and increase wear of both the seal and the cone. In either condition, the life of the seal will be greatly reduced over a seal operating with proper lubrication and without abrasive particles.

Referring now to Figure 4A, a radial seal 80 comprises a rectangular body 82 and an asymmetrical, curved end surface 84 having a protruding portion 86. Radial seal 80 is formed from a first resilient material and end portion 88 is formed of a second resilient material having different properties from the material forming body 82.

End portion 88 is moulded to body 82 along an asymmetrical interface 89 such that the region of end portion 88 adjacent to protruding portion 86 has a greater thickness of the second resilient material.

Figure 4B shows radial seal 80 disposed within a seal gland 90 formed by a seal groove 92 and a cylindrical sealing surface 94. Radial seal 80 is compressed within seal gland 90 and forms a contact footprint 96 on cylindrical sealing surface 94. Footprint 96 is bisected by axial centreline 98 such that linear dimensions 100 and 102 are equal. For purposes of this discussion, axial centreline 98 divides the seal into an abrasive side 104 and a lubricant side 106. Axial centreline 98 may or may not mark the physical interface between the abrasive fluid on one side of the seal and the lubricating fluid on the other side of the seal.

Referring now to Figure 4C, the contact pressure profile exerted by radial seal 80 on sealing surface 94 is represented by curve 110, which illustrates that the contact pressure profile is asymmetric about centreline 98.

Asymmetric end portion 88 of seal 80 helps to generate the asymmetric contact pressure profile by having an increased volume of seal material on one side of the seal. Contact pressure profile curve 110 is divided by centreline 98 into an abrasive-side 112 and a lubricant-side 114.

The area under contact pressure profile curve 110 represents the total contact pressure applied to the seal.

The asymmetric contact pressure profile created by seal 80 results in the area under curve 110 on abrasive-side 112 being greater than the area under curve 110 on the lubricant-side 114. In some embodiments, the area under curve 110 on the lubricant-side is 95% of the area under curve 110 on abrasive-side 114. In some embodiments, the area under curve 110 on the lubricant-side is 75% of the area under curve 110 on abrasive-side 114. In general, the ratio is preferably in the range greater than 50% and less than or equal to 95%. The asymmetrical contact pressure profile curve 110 translates into less contact pressure on lubricant-side 114 and more contact pressure on abrasive side 112. The asymmetrical distribution encourages increased lubrication and reduced interaction with abrasive particles.

The peak contact pressure 116 on abrasive-side 112 is also higher than the peak contact pressure 118 on lubricant-side 114. The highest peak contact pressure may indicate the interface between the abrasive fluids and the lubricating fluids. By shifting the highest peak contact pressure toward abrasive-side 112, less of footprint 96 is exposed to abrasive fluids.

Thus, the asymmetrical contact pressure profile 110 has a peak contact pressure point 116 that is shifted toward abrasive side 104, causing a sharp increase in contact pressure on the abrasive side and a more gradual increase in contact pressure on lubricant side 106. The high contact pressure on abrasive side 104 acts to prevent abrasive particles from entering the sealing interface.

The lower contact pressure profile on lubricant side 106 allows lubricants to more easily enter the sealing interface.

Some of the performance advantages of seal 80 can be seen by comparing the contact pressure distribution shown in Figure 3C with that of Figure 4C. By shifting the peak contact pressure 116 more toward the abrasive side of the seal, as opposed to the centred location of peak contact pressure 76, the surface area of the seal that is exposed to the abrasive fluid is reduced. Providing a lower magnitude, gradually increasing contact pressure profile on lubricant side 114, as opposed to lubricant side 74, a greater surface area of seal 80 will be exposed to lubricant. Both of these conditions allow for reduced friction between seal 80 and sealing surface 94. With reduced friction comes longer sealing life and more reliable performance.

Generation of a desirable contact pressure distribution profile is not limited to seals similar to seal 80, but may be achieved a variety of seal configurations. As illustrated by seal 80, the external geometry of the seal and/or the geometry of the internal material interface may be asymmetric. Non-composite and single material seals may also be used. The sealing surfaces on either, or both, the cone and the leg may also be shaped so as to generate an asymmetric contact pressure distribution. Further, the asymmetric contact pressure distribution is not limited to that shown in Figure 4C and may be any distribution that provides desirable performance.

Figures 5A-B through 31A-B illustrate a variety of sealing arrangements that provide asymmetrical contact pressure distributions. Figures 5A-B through 9A-B illustrate radial seals that have asymmetric external features. Figures lOA-B through 12A-B illustrate radial seals that have asymmetric internal features. Figures 13A- B through 22A-B illustrate radial seals that have a combination of internal and external asymmetrical features.

Figures 23A-B through 26A-B illustrate radial seals having multiple asymmetrical material interfaces. Figures 27A-B through 31A-B illustrate symmetrical radial seals disposed within asymmetrical seal glands.

Referring now to Figures 5A-B through 9A-B, Figures 5A-9A illustrate a radial seal that has asymmetrical external features and Figures 5B-9B illustrate exemplary asymmetrical contact pressure distributions that are generated by each respective seal. In Figures 5A- 8A, although only one end of each seal is shown, it is understood that the opposing end of each seal may have a different construction or the same construction as the illustrated end of the seal. Figure 9A illustrates a full cross-section of a radial seal. In each illustration, the lower edge of the seal is the grease (lubricant) side and the upper edge of the seal is the mud (abrasive drilling fluid) side.

Referring now to Figures 5A and 5B, radial seal 100 comprises end portion 102 that has a ridge 104 of increased thickness on the mud side of the seal so as to generate contact pressure profile 106 that is asymmetrical about centreline 108 of the seal contact footprint.

In Figures 6A and 6B, radial seal 110 comprises end portion 112 that has two ridges 114 of increased thickness, with the ridge on the mud side of the seal having a greater thickness than the one on the grease side. Seal 110 generates contact pressure profile 116 that is asymmetrical about centreline 118 of the seal contact footprint.

In Figures 7A and 7B, radial seal 120 comprises end portion 122 that has multiple ridges 124 of increased thickness. Seal 120 generates contact pressure profile 126 that is asymmetrical about centreline 128 of the seal contact footprint.

In Figures 8A and 8B, radial seal 130 comprises a radial groove 132 on body 134 that reduces the volume of seal material on the grease side of the seal. Seal 130 generates contact pressure profile 136 that is asymmetrical about centreline 138 of the seal contact footprint.

In Figures 9A and 9B, radial seal 140 has a tapered cross-section such that end portion 142 is larger than end portion 144. End portion 144 is offset toward the mud side of the seal so as to increase sealing force on the mud side. Seal 140 generates contact pressure profile 146 that is asymmetrical about centreline 148 of the seal contact footprint.

Figures lOA-B through 12A-B illustrate radial seals that have asymmetric internal features. Referring now to Figures lOA-B through 12A-B, Figures lOA-12A illustrate one end of a radial seal that has asymmetrical internal features found on the interface between two materials used to form the seal. Figures lOB-12B illustrate exemplary asymmetrical contact pressure distributions that are generated by each respective seal. Although only one end of each seal is shown, it is understood that the opposing end of each seal may have a different construction or the same construction as the illustrated end of the seal. In each illustration, the lower edge of the seal is the grease (lubricant) side and the upper edge of the seal is the mud (abrasive drilling fluid) side.

In Figures lOA and lOB, radial seal 150 comprises end portion 152 that has asymmetrical material boundary 154 shaped so as to provide a thicker region of the end portion material on the mud side of the seal. Seal 150 generates contact pressure profile 156 that is asymmetrical about centreline 158 of the seal contact footprint.

In Figures llA and llB, radial seal 160 comprises end portion 162 that has asymmetrical material boundary 164 having two regions of increased thickness, with the thicker of the two regions on the mud side of the seal. Seal 160 generates contact pressure profile 166 that is asymmetrical about centreline 168 of the seal contact footprint.

In Figures 12A and 12B, radial seal 170 comprises end portion 172 that has asymmetrical material boundary 174 that has multiple regions of increased thickness. Seal 170 generates contact pressure profile 176 that is asymmetrical about centreline 178 of the seal contact footprint.

Figures 13A-B through 22A-B illustrate radial seals that have a combination of internal and external asymmetrical features. Figures 13A22A illustrate one end of a radial seal that has asymmetrical internal and external features and Figures 13B-22B illustrate exemplary asymmetrical contact pressure distributions that are generated by each respective seal. In Figures 13A-16A and 18A-21A, although only one end of each seal is shown, it is understood that the opposing end of each seal may have a different construction or the same construction as the illustrated end of the seal. In each illustration, the lower edge of the seal is the grease (lubricant) side and the upper edge of the seal is the mud (abrasive drilling fluid) side.

In Figures 13A and 13B, radial seal 180 comprises an asymmetrical, curved end portion 182 that also has asymmetrical, V-shape material boundary 184. End portion 182 and boundary 184 are shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 186 that is asymmetrical about centreline 188 of the seal contact footprint.

In Figures 14A and 14B, radial seal 190 comprises an asymmetrical, curved end portion 192 with two ridged protrusions, wherein the protrusion that is closer to the mud side of the seal is larger. Seal 190 also comprises an asymmetrical, V-shape material boundary 194, wherein the deepest part of the V-shape is toward the mud side of the seal. Seal 190 is shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 196 that is asymmetrical about centreline 198 of the seal contact footprint.

In Figures 15A and 15B, radial seal 200 comprises an asymmetrical, curved end portion 202 with multiple ridged protrusions, wherein the protrusion that is closer to the mud side of the seal is the largest. Seal 200 also comprises an asymmetrical, V-shape material boundary 204, wherein the deepest part of the V-shape is toward the mud side of the seal. Seal 200 is shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 206 that is asymmetrical about centreline 208 of the seal contact footprint.

In Figures 16A and 16B, radial seal 210 comprises an asymmetrical, curved end portion 212 and a groove 213 on the lubricant side of the seal body. Seal 210 also comprises an asymmetrical, V-shape material boundary 214, wherein the deepest part of the V-shape is toward the mud side of the seal. Seal 210 is shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 216 that is asymmetrical about centreline 218 of the seal contact footprint.

In Figures 17A and 17B, radial seal 220 comprises an asymmetrical, curved end portion 222 that is larger than opposite end portion 223. End portion 223 is offset toward the mud side of the seal so as to increase sealing force on the mud side. Seal 220 also comprises an asymmetrical, V-shape material boundary 224, wherein the deepest part of the V-shape is toward the mud side of the seal. Seal 220 generates contact pressure profile 226 that is asymmetrical about centreline 228 of the seal contact footprint.

In Figures 18A and 18B, radial seal 230 comprises an asymmetrical, curved end portion 232 that also has an asymmetrical, curved material boundary 234. End portion 232 and boundary 234 are shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 236 that is asymmetrical about centreline 238 of the seal contact footprint.

In Figures l9A and l9B, radial seal 240 comprises an asymmetrical, curved end portion 242 with two ridged protrusions, wherein the protrusion that is closer to the mud side of the seal is larger. Seal 240 also comprises an asymmetrical, curved material boundary 244, wherein the deepest part of the end portion is toward the mud side of the seal. Seal 240 is shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 246 that is asymmetrical about centreline 198 of the seal contact footprint.

In Figures 20A and 20B, radial seal 250 comprises an asymmetrical, curved end portion 252 with multiple ridged protrusions, wherein the protrusion that is closer to the mud side of the seal is the largest. Seal 250 also comprises an asymmetrical, curved material boundary 254, wherein the deepest part of the end portion is toward the mud side of the seal. Seal 250 is shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 256 that is asymmetrical about centreline 258 of the seal contactfootprint.

In Figures 21A and 21B, radial seal 260 comprises an asymmetrical, curved end portion 262 and a groove 263 on the lubricant side of the seal body. Seal 260 also comprises an asymmetrical, curved material boundary 264, wherein the deepest part of the end portion is toward the mud side of the seal. Seal 260 is shaped so as to provide a thicker region of the end portion material on the mud side of the seal so as to generate contact pressure profile 266 that is asymmetrical about centreline 268 of the seal contact footprint.

In Figures 22A and 22B, radial seal 270 comprises an asymmetrical, curved end portion 272 that is larger than opposite end portion 273. End portion 273 is offset toward the mud side of the seal so as to increase sealing force on the mud side. Seal 270 generates contact pressure profile 276 that is asymmetrical about centreline 278 of the seal contact footprint.

Figures 23A-B through 26A-s illustrate radial seals having multiple asymmetrical material interfaces formed between a plurality of component material layers. Figures 23A-26A illustrate one end of a composite radial seal and Figures 23B-26B illustrate exemplary asymmetrical contact pressure distributions that are generated by each respective seal. Although only one end of each seal is shown, it is understood that the opposing end of each seal may have a different construction or the same construction as the illustrated end of the seal. In each illustration, lower edge of the seal is the grease (lubricant) side and the upper edge of the seal is the mud (abrasive drilling fluid) side.

In Figures 23A and 23B, radial seal 280 comprises an end portion 282 formed from two layers of seal material having different properties such that the mud-side layer 283 provides a higher contact pressure than lubricant-side layer 284. Seal 280 generates contact pressure profile 286 that is asymmetrical about centreline 288 of the seal contact footprint.

In Figures 24A and 24B, radial seal 290 comprises an end portion 292 formed from two layers of seal material having different properties such that the mud-side layer 293 provides a higher contact pressure than lubricant-side layer 294. The boundary 295 between end portion 292 layers 293 and 294 and the seal body is also asymmetrical so that seal 290 generates contact pressure profile 296 that is asymmetrical about centreline 298 of the seal contact footprint.

In Figures 25A and 25B, radial seal 300 comprises an end portion 302 formed from two different seal materials having different properties such that the embedded region 303 has a higher elastic modulus and/or hardness than the surrounding region 304. Seal 300 generates contact pressure profile 306 that is asymmetrical about centreline 308 of the seal contact footprint. - 23

In Figures 26A and 26B, radial seal 310 comprises a plurality of layers 312 of seal material having different properties arranged such that the mud-side layer 313 provides a higher contact pressure than lubricant-side layer 314. Seal 310 generates contact pressure profile 316 that is asymmetrical about centreline 318 of the seal contact footprint.

Figures 27A-B through 31A-B illustrate radial seals disposed within asymmetrical seal glands. The radial seals are shown as being symmetrical seals but could also be asymmetrical seals, such as those described above. Figures 27A-31A illustrate the radial seal disposed in a seal gland and Figures 27B-31B illustrate exemplary asymmetrical contact pressure distributions that are generated by each respective seal arrangement. In each illustration, lower edge of the seal is the grease (lubricant) side and the upper edge of the seal is the mud (abrasive drilling fluid) side.

In Figures 27A and 27B, radial seal 320 is disposed within seal gland 322 comprising seal groove 324 and engages seal surface 325. Seal surface 325 is angled, or curved, across a portion of the face of seal 320 such that the mud side of the seal is compressed more than the lubricant side of the seal. Seal 320 generates contact pressure profile 326 that is asymmetrical about centreline 328 of the seal contact footprint.

In Figures 28A and 28B, radial seal 330 is disposed within seal gland 332 comprising seal groove 334 and engages seal surface 335. The bottom of seal groove 334 is angled, or curved, such that the mud side of seal 330 is compressed more than the lubricant side of the seal. Seal 330 generates contact pressure profile 336 that is asymmetrical about centreline 338 of the seal contact footprint.

In Figures 29A and 29B, radial seal 340 is disposed within seal gland 342 comprising seal groove 344 and engages seal surface 345. Seal surface 345 and the bottom of seal groove 344 are angled, or curved, such that the mud side of seal 340 is compressed more than the lubricant side of the seal. Seal 340 generates contact pressure profile 346 that is asymmetrical about centreline 348 of the seal contact footprint.

In Figures 30A and BOB, radial seal 350 is disposed within seal gland 352 comprising seal groove 354 and engages seal surface 355. Seal surface 355 is angled, or curved, across the entire face of seal 350 such that the mud side of the seal is compressed more than the lubricant side of the seal. Seal 350 generates contact pressure profile 356 that is asymmetrical about centreline 358 of the seal contact footprint.

In Figures 31A and 31B, radial seal 360 is disposed within seal gland 362 comprising seal groove 364 and engages seal surface 365. Seal surface 365 and the bottom of seal groove 364 are angled, or curved, such that the mud side of seal 360 is compressed more than the lubricant side of the seal. Seal 360 generates contact pressure profile 366 that is asymmetrical about centreline 368 of the seal contact footprint.

An asymmetrical contact pressure profile may also be generated by an Oring type seal. Referring now to Figure 32A, an O-ring seal 370 has a generally circular cross- section with a flattened face 372 on one side of the seal.

Figure 32B shows seal 370 disposed within a seal gland 374 formed by a seal groove 376 and a cylindrical sealing surface 378. Face 372 of seal 370 is disposed on the mud- side of the seal gland and toward sealing surface 378.

Seal 370 is compressed within seal gland 374 and forms a contact footprint 380 on cylindrical sealing surface 378.

Footprint 380 is bisected by axial centreline 382 such that linear dimensions 384 and 386 are equal. For purposes of this discussion, axial centreline 382 divides the seal into a mud side 388 and a grease side 390. Axial centreline 382 may or may not mark the physical interface between the mud on one side of the seal and the grease on the other side of the seal.

Referring now to Figure 32C, the contact pressure profile exerted by radial seal 370 on sealing surface 378 is represented by curve 392, which illustrates that the contact pressure profile is asymmetric about centreline 382. The abrupt contour change at face 372 generates a peak contact pressure 394 on the mud side 388 of centreline 382. Contact pressure profile 392 is divided by centreline 382 into a mud-side area 394 and a grease-side area 396.

Although centreline 382 runs through the middle of footprint 380, it divides the area under curve 392 into a mud-side area 396 that is larger and provides a higher gradient of contact pressure than a grease-side area 398.

Figures 33A-33F illustrate a number of alternative embodiments of O-ring type seals having asymmetric cross- sections. Figure 33A shows seal 460 having a flat region 462, where, when installed, the flat region is oriented on the mud-side of the dynamic sealing interface. Figure 33B shows seal 464 having flat sides 466 for fitting into the rectangular sides of a groove and a flat region 468 that is oriented on the mud-side of the dynamic sealing interface.

Figure 33C shows seal 470 having flat face 472, and curved face 474, which has an increased diameter. Figure 33D shows seal 476 having flat face 478, and multiple curved faces 486, each with a different radius of curvature.

Figure 33E shows seal 488 having curved groove 490. Figure 33F shows seal 492 having multiple flat faces 494.

In each of these seal designs, the portion of the seal that has material removed is oriented toward the mud-side of the dynamic sealing surface. The removed material creates a stress concentration that generates a peak in the contact force on the dynamic sealing surface toward the mud-side of the seal. Although the features of Figure 33A F are only shown on side end of each seal, it is understood that in some applications the asymmetric features may be on more than one side of the seal. The embodiments shown are not exclusive and many other configurations and variations of asymmetric profile seals may also be created.

Figures 34A-34D illustrate a number of alternate embodiments of composite O-ring type seals having asymmetric cross-sections or asymmetric boundaries between the two component materials. Figure 34A illustrates seal 496 comprising a first material 498 and a second material 500 with an asymmetric material boundary 502. Boundary 502 is formed such that the depth of second material 500 is greater on one side so as to create a peak in the contact force on the mud-side of the dynamic sealing surface.

Figure 34B shows seal 504 having first material 506 and second material 508 joined at an asymmetric boundary 510.

Figure 34C shows seal 512 having first material 514 and second material 516 joined at an asymmetric boundary 518.

Figure 34D shows seal 520 having first material 522 and second material 524 joined at boundary 526. Second material 524 also has flat surface 528. Although the features of Figure 34A-D are only shown on side end of each seal, it is understood that in some applications the asymmetric features may be on more than one side of the seal. The embodiments shown are not exclusive and many other configurations and variations of asymmetric profile seals may also be created.

Figure 35 shows a dual seal assembly 600 comprising a symmetric seal 602 and asymmetric seal 604. Seal assembly 600 creates a seal between cone 606 and leg 608 forming a barrier between a mud side 610 and a lubricant side 612.

Symmetric seal 602 forms a contact pressure profile 614 along leg 608 that is symmetrical about a centreline bisecting the profile. Asymmetric seal 604 forms a contact pressure profile 616 along leg 608 that is asymmetrical about a centreline bisecting the profile.

Figure 36 shows a dual seal assembly 620 comprising a first asymmetric seal 622 and second asymmetric seal 624.

Seal assembly 620 creates a seal between cone 626 and leg 628 forming a barrier between a mud side 630 and a lubricant side 632. The first asymmetric seal 622 forms a contact pressure profile 634 along leg 628 that is asymmetrical about a centreline bisecting the profile. The second asymmetric seal 624 forms a contact pressure profile 626 along leg 628 that is asymmetrical about a centreline bisecting the profile.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting by size, shape and/or directionality of the rotating body against the stationary body. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Claims

1. A rotary cone rock-bit comprising: a bit body; a leg extending from said bit body; a cone rotatable mounted to said leg; a seal disposed radially between said cone and said leg; a footprint defining an area of contact between said seal and said leg, wherein compression of said seal generates a contact pressure between said seal and said leg; an axial centreline that evenly bisects said footprint into a mud side and a grease side; and, a contact pressure profile defining the contact pressure over said footprint, wherein the contact pressure on the mud side of said footprint is greater than the contact pressure on the grease side of said footprint.

2. A bit according to claim 1, wherein the contact pressure on the grease side of said footprint is less than 95% of the contact pressure on the mud side of said footprint.

3. A bit according to claim 1, wherein the contact pressure on the grease side of said footprint is less than 75% of the contact pressure on the mud side of said footprint.

4. A bit according to any of claims 1 to 3, wherein the maximum contact pressure is on the mud side of said footprint.

5. A bit according to any of claims 1 to 4, wherein said seal comprises: a body constructed from a first resilient material; and, an end portion constructed from a second resilient material, wherein said end portion is connected to said body along an interface.

6. A bit according to claim 5, wherein said end portion has an asymmetrical outer surface arranged such that a greater volume of the second resilient material is disposed on the mud side of said seal.

7. A bit according to any of claims 1 to 6, comprising a second seal disposed radially between said cone and said leg, wherein said second seal is adjacent to and on the mud side of said first seal.

8. A bit for drilling a borehole into earthen formations, the bit comprising: a bit body; a journal shaft extending from said bit body; a rolling cone cutter mounted on said journal shaft and being adapted to rotate about a cone axis; a seal gland between said shaft and said cone and comprising a first seal-engaging surface on said shaft and a second seal-engaging surface on said cone; an annular seal disposed in said gland, said annular seal comprising: a radially inner surface sealingly engaging said first seal-engaging surface, and a radially outer seal surface sealingly engaging said second seal engaging surface; and, a seal footprint on one of said seal-engaging surfaces, said footprint being defined by the portion of said seal contacting said one seal-engaging surface, said footprint having a footprint length measured axially relative to said cone axis and being bisected by a footprint centreline that is perpendicular to said cone axis; wherein said seal creates a pressure profile on said one seal-engaging surface axially along said footprint, said pressure profile being asymmetric relative to said centreline.

9. A bit according to claim 8, wherein said seal divides a lubricant side from a drilling fluid side, and wherein said pressure profile includes a maximum pressure peak located on said drilling fluid side.

10. A bit according to claim 8 or claim 9, wherein a curve representing the pressure profile on the lubricant side defines an area that is less than 95% of an area defined by a curve representing the pressure profile on the drilling fluid side.

11. A bit according to claim 8 or claim 9, wherein a curve representing the pressure profile on the lubricant side defines an area that is less than 75% of an area defined by a curve representing the pressure profile on the drilling fluid side.

12. A bit according to any of claims 8 to 11, wherein said seal comprises: a body constructed from a first resilient material) and, an end portion constructed from a second resilient material, wherein said first portion is connected to said body along a first interface.

13. A bit according to claim 12, wherein said end portion has an asymmetrical outer surface arranged such that a greater volume of the second resilient material is disposed on the drilling fluid side of said centreline.

14. A bit according to claim 12 or claim 13, wherein the first interface is asymmetric.

15. A bit according to any of claims 8 to 14, wherein said seal creates a pressure profile on said second seal engaging surface.

16. A rotary cone rock-bit seal comprising: a seal in contact with a rotating surface along a footprint; wherein: a centreline through the midpoint of the footprint divides said seal into a drilling fluid side and a lubricant side; and, a contact pressure profile formed between said seal and the rotating surface is asymmetric about said centreline.

17. A seal according to claim 16, wherein said contact pressure profile on the drilling fluid side of said seal defines an area larger than an area defined by said contact pressure profile on the lubricant side of said seal.

18. A seal according to claim 16 or claim 17, wherein said contact pressure profile comprises a peak contact pressure that is located on the drilling fluid side of said centreline.

19. A seal according to any of claims 16 to 18, wherein said seal is constructed of a resilient material, wherein a majority of the resilient material is located on the drilling fluid side of said seal.

20. A seal according to any of claims 16 to 18, wherein said seal is constructed of a first material and a second material bonded along a boundary that is asymmetric about the centreline.

21. A seal according to any of claims 16 to 20, wherein said seal has an asymmetric surface profile in contact with the rotating surface.

22. A seal according to any of claims 16 to 21, further comprising: a second seal in contact with a rotating surface along a second footprint, wherein said second seal is adjacent to the drilling fluid side of the first seal; wherein: a second centreline through the midpoint of the second footprint divides said second seal into a drilling fluid side and a lubricant side; and, a second contact pressure profile is formed between said second seal and the rotating surface.

23. A seal according to claim 22, wherein said second contact pressure profile is asymmetric about said second centreline.

24. A seal according to claim 23, wherein said second contact pressure profile on the drilling fluid side of said second seal defines an area larger than an area defined by said second contact pressure profile on the lubricant side of said second seal.

25. A seal according to claim 23 or claim 24, wherein said second contact pressure profile comprises a peak contact pressure that is located on the drilling fluid side of said second centreline.

26. A seal according to any of claims 23 to 25, wherein said second seal is constructed of a resilient material, wherein a majority of the resilient material is located on the drilling fluid side of said second seal.

27. A seal according to any of claims 23 to 25, wherein said second seal is constructed of a first material and a second material bonded along a boundary that is asymmetric about the second centreline.

28. A seal according to claim 22, wherein said second contact pressure profile is symmetric about said second centreline.

29. A rotary cone rock-bit, substantially in accordance with any of the examples as hereinbefore described with reference to and as illustrated by Figures 4 to 36 of the accompanying drawings.

30. A seal for a rotary cone rock-bit, substantially in accordance with any of the examples as hereinbefore described with reference to and as illustrated by Figures 4 to 36 of the accompanying drawings.