Dual-seal drill bit pressure communication system

A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

• a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;
• an annular primary seal disposed between said leg and said roller cone;
• an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;
• and
• an annular space formed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolation from said bearing cavity, said annular space having a chamber pressure, wherein said chamber pressure can be altered by allowing the passage of fluid from said annular space to the borehole and from the borehole to said annular space.

A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

• a bit body having at least two bit components said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;
• an annular primary seal disposed between said leg and said roller cone;
• an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;
• and
• an annular space formed between said annular primary seal and said annular secondary seal, said annular space having a chamber pressure and at least partially containing fluid, said annular space being in substantially absolute fluid isolation from said bearing cavity, wherein said fluid migrates from said annular space to the borehole when said chamber pressure is greater than the borehole pressure and wherein said fluid migrates from the borehole to said annular space when the borehole pressure is greater than said chamber pressure.

A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

• a bit body having at least two bit components said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;
• an annular primary seal disposed between said leg and said roller cone;
• an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;
• and
• an annular space formed between said annular primary seal and said annular secondary seal, said annular space having a chamber pressure and at least partially containing fluid, said annular space being in substantially absolute fluid isolation from said bearing cavity, wherein said fluid migrates from said annular space to the borehole when said chamber pressure is greater than the borehole pressure.

A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

• a bit body having at least one leg, said leg including an exterior surface and a journal segment;
• a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;
• an annular primary seal disposed between said leg and said roller cone;
• an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;
• an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially including fluid and being in substantially absolute fluid isolation from said bearing cavity;
• an opening in said exterior surface of said leg;
• and
• a passage disposed in said leg and extending from said opening to said annular space, said passage allowing fluid communication between said annular space and the borehole.

A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

• a bit body having at least one leg, said leg including an exterior surface and a journal segment;
• a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;
• an annular primary seal disposed between said leg and said roller cone and forming a substantially absolute seal therebetween;
• an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;
• an annular space disposed between said annular primary seal and said annular secondary seal, said annular space in substantially absolute fluid isolation from said bearing cavity;
• an opening in said exterior surface of said leg;
• a passage disposed in said leg and extending from said opening to said annular space, said passage being filled with incompressible fluid;
• and
• a plug disposed in said opening.

A method for communicating fluid pressure between a borehole at least partially containing drilling fluid and the annular space formed between first and second annular seals in a dual-seal drill bit, the drill bit including a bit body having at least two bit components, the bit components including at least one leg having a journal segment, the bit components further including a roller cone rotatably mounted upon the journal segment and forming at least one bearing cavity therebetween, the first annular seal disposed between the leg and the roller cone, the second annular seal disposed between the leg and the roller cone and between the annular primary seal and the borehole, including:

• providing an absolute seal between the first annular seal and the bit components;
• fluidly isolating the annular space between the first and second annular seals from the bearing cavity;
• filling the annular space between the first and second annular seals with incompressible fluid;
• permitting the passage of said incompressible fluid from the annular space to the borehole;
• and
• permitting the passage of said drilling fluid from the borehole to the annular space.