Subterranean well safety valve with reference pressure chamber

Claim 2

In a subterranean well tool having a shiftable member, reciprocal in response to a force differential between opposite surfaces of said shiftable member, the force on one surface of said shiftable member comprising a force generated by the pressure of a gas; the improvement comprising a barrier fluid relatively impervious to the passage therethrough of the gas, said barrier fluid being located between said gas and a region at a pressure differing from the pressure of said gas, said barrier fluid being at a pressure in excess of said reference pressure to retard passage of said gas into said barrier fluid.

Claim 3

The subterranean well tool of claim 1 further comprising a second shiftable member between said reference pressure chamber and said barrier fluid, said second shiftable member being biased so that the pressure of said barrier fluid is greater than said reference pressure.

Claim 4

The subterranean well tool of claim 2 wherein said second shiftable member is spring biased.

Claim 5

The subterranean well tool of claim 3 wherein the force exerted by said barrier fluid on said second shiftable member is equal to the sum of the force exerted by the reference pressure and the spring force acting on said second shiftable member.

Claim 6

The subterranean well tool of claim 2 wherein said second shiftable member is adjacent to and movable relative to said first mentioned shiftable member with resilient sealing means establishing sealing integrity along adjacent surfaces of said first and second shiftable members between said reference pressure chamber and said barrier fluid.

Claim 7

The subterranean well tool of claims 2, 3, 4 or 5 wherein said first and second shiftable members comprise pistons longitudinally movable relative to a stationary cylindrical member, the surfaces defining said reference pressure chamber comprising surfaces on said first and second shiftable members and said stationary cylindrical member.

Claim 8

The subterranean well tool of claim 6 wherein said barrier fluid is contained in a barrier fluid chamber, other surfaces on said first and second shiftable members and said stationary cylindrical member comprising surfaces defining said barrier fluid chamber.

Claim 9

The subterranean well tool of claim 3 further comprising a floating piston in said reference pressure chamber initially movable under the action of an external force to change the volume of said reference pressure chamber to determine said reference pressure.

Claim 10

The subterranean well tool of claim 8 wherein said floating piston is movable in response to subterranean well conditions.

Claim 11

The subterranean well tool of claim 9 further comprising locking means engagable to stabilize the pressure acting on said floating piston and prevent further changes in said preference pressure.

Claim 12

In a subterranean well tool having a shiftable member, reciprocal in response to a force differential between opposite surfaces of said shiftable member, the force on one surface of said shiftable member comprising a force generated by the pressure of a gas in a reference pressure chamber; the improvement comprising a barrier fluid relatively impervious to the passage therethrough of the gas in said reference pressure chamber, said barrier fluid being located between said reference pressure chamber and a region at a pressure differing from the pressure in said reference pressure chamber, said barrier fluid being at a pressure in excess of said reference pressure to retard passage of said gas into said barrier fluid.

Claim 13

In a subterranean well tool having a shiftable member, reciprocal in response to a force differential between opposite surfaces of said shiftable member, the force on one surface of said shiftable member comprising a force generated by the pressure of a gas in a reference pressure chamber; the improvement comprising a barrier fluid relatively impervious to the passage therethrough of the gas in said reference pressure chamber, said barrier fluid being located between said reference pressure chamber and a region at a pressure differing from the pressure in said reference pressure chamber, said barrier fluid being at a pressure in excess of said reference pressure to retard passage of said gas into said barrier fluid.

Claim 14

The subterranean well tool of claim 11 further comprising a barrier fluid chamber, said barrier fluid filling said barrier fluid chamber.

Claim 15

The subterranean well tool of claim 12 further comprising resilient sealing means on opposite sides of said barrier fluid chamber.

Claim 16

The subterranean well tool of claim 11 further comprising resilient sealing means between said reference pressure chamber and said barrier fluid.

Claim 17

The subterranean well tool of claims 13 or 14 wherein said resilient sealing means comprise means for establishing sealing integrity along a surface of said shiftable member.

Claim 18

The subterranean well tool of claim 11 wherein said shiftable member is movable in response to variable pressure, said barrier fluid being located between the reference pressure chamber and a region of variable pressure.

Claim 19

The subterranean well tool of claim 16 wherein a surface on said shiftable member is exposed to said region of variable pressure, said shiftable member moving in response to pressure variations in said region.

Claim 22

The apparatus of claim 18 wherein said biasing means comprise spring means.

Claim 23

The apparatus of claim 18 wherein said first piston is movable with said second piston.

Claim 24

The apparatus of claim 18 wherein the gas in said reference pressure chamber is compressed having a pressure in excess of atmospheric pressure.

Claim 25

The apparatus of claim 18 wherein the force acting on said first piston comprises the sum of the reference pressure force and the force exerted by said biasing means.

Claim 26

The apparatus of claim 22 wherein said barrier liquid comprises a relatively incompressible liquid, the sum of the reference pressure force and the force exerted by said biasing means being transmitted from said second piston through said barrier fluid to said first piston.

Claim 27

The apparatus of claim 18 wherein said first and second seal means comprise resilient seal means.

Claim 28

The apparatus of claim 18 wherein said first piston means comprises a first surface defining said reference pressure chamber.

Claim 29

The apparatus of claim 25 wherein said second piston means comprises a second surface defining said reference pressure chamber.

Claim 30

An improved flow control apparatus for use in a subterranean well in which a piston is movable in response to the pressure differential between the gas in a reference pressure chamber and the pressure in the well; the improvement comprising: a sealed member comprising the lower surface of said reference pressure chamber; a barrier fluid, relatively impermeable to the passage of gas therethrough located on said sealed member at the bottom of said reference pressure chamber; an upper seal at the top of said reference pressure chamber; a cavity below said upper seal and separate from said reference pressure chamber containing a barrier fluid, relatively impermeable to the passage of gas therethrough; and biasing means acting on said barrier fluid in said cavity in addition to the pressure in said reference pressure chamber with the resultant pressure on said barrier fluid in said cavity being greater than the pressure of gas in said reference pressure chamber, whereby said barrier fluid acts to prevent the passage of the gas in said reference pressure chamber past the seals at the top and bottom of said reference pressure chamber.

Claim 31

An improved flow control apparatus for use in a subterranean well in which a piston is movable in response to the pressure differential between the gas in a reference pressure chamber and the pressure in the well; the improvement comprising: a sealed member comprising the lower surface of said reference pressure chamber; a barrier fluid, relatively impermeable to the passage of gas therethrough located on said sealed member at the bottom of said reference pressure chamber; an upper seal at the top of said reference pressure chamber; a cavity below said upper seal and separate from said reference pressure chamber containing a barrier fluid, relatively impermeable to the passage of gas therethrough; and biasing means acting on said barrier fluid in said cavity in addition to the pressure in said reference pressure chamber with the resultant pressure on said barrier fluid in said cavity being greater than the pressure of gas in said reference pressure chamber, whereby said barrier fluid acts to prevent the passage of the gas in said reference pressure chamber past the seals at the top and bottom of said reference pressure chamber.

Claim 32

The apparatus of claim 27 wherein said biasing means is located within said reference pressure chamber.