Seal system for downhole tool

Abstract

A downhole tool may include a tubular member having an axis, a wall with a bore, and an orifice extending radially from the bore through the wall. A piston may be configured to be co-axially mounted in the bore of the tubular member and be axially reciprocated therein, the piston having a piston bore. An aperture may extend radially from the piston bore to the bore of the tubular member. First and second glands formed in an outer surface adjacent the aperture. The first gland may be axially spaced apart from the second gland. In addition, a seal system can be configured to be mounted to the piston. The seal system can include a primary seal for the first gland, a secondary seal for the second gland, and the secondary seal is harder than the primary seal.

We claim: 
     
         1 . A downhole tool, comprising:
 a tubular member having an axis, a wall with a bore, and an orifice extending radially from the bore through the wall;   a piston configured to be co-axially mounted in the bore of the tubular member and be axially reciprocated therein, the piston having a piston bore, an aperture extending radially from the piston bore to the bore of the tubular member, an outer surface and first and second glands formed in the outer surface adjacent the aperture, and the first gland is axially spaced apart from the second gland; and   a seal system configured to be mounted to the piston, the seal system comprising a primary seal for the first gland, a secondary seal for the second gland, and the secondary seal is harder than the primary seal.   
     
     
         2 . The downhole tool of  claim 1 , wherein:
 the primary seal has a hardness in a range of about Shore 60A to about Shore 90D;   the primary seal has a hardness in a range of about Shore 60D to about Shore 90D;   the primary seal comprises an elastomer formed in a continuous ring; or   the primary seal comprises hydrogenated nitrile butadiene rubber (HNBR).   
     
     
         3 . The downhole tool of  claim 1 , primary seal has an inner diameter that is less than an outer diameter of the first gland in a range of about 0.020 inches to about 0.060 inches. 
     
     
         4 . The downhole tool of  claim 1 , wherein the primary seal has an inner diameter with a recess formed therein, and annular legs are formed on each axial side of the recess. 
     
     
         5 . The downhole tool of  claim 1 , wherein the primary seal has an outer diameter, and wherein the outer diameter comprises one or more of:
 a non-planar surface;   an incline in a range of about 5 degrees to about 30 degrees;   a crest that forms a line that circumscribes the primary seal; and   inclines that slope radially inward from a crest, and the crest bisects the outer diameter.   
     
     
         6 . The downhole tool of  claim 1 , wherein the primary seal, in a relaxed state, comprises a radial dimension that exceeds that of the first gland in a range of about 0.004 inches to about 0.020 inches. 
     
     
         7 . The downhole tool of  claim 1 , wherein the secondary seal comprises a metallic split ring. 
     
     
         8 . The downhole tool of  claim 1 , wherein the secondary seal comprises a buffer seal that is configured to quasi-seal between the piston and the bore of the tubular member and allow a leakage rate of less than about 5% of a total flow rate through the tool. 
     
     
         9 . The downhole tool of  claim 1 , wherein the piston further comprises first and second axial ends, third and fourth seals are located adjacent the first and second axial ends, respectively, and the first and second glands are axially spaced apart from the first and second axial ends and the third and fourth seals. 
     
     
         10 . The downhole tool of  claim 1 , wherein the tubular member is a sleeve, the sleeve is mounted coaxially inside a housing, the housing has a housing aperture that axially registers with the orifice, and the housing has an axial length greater than that of the tubular member. 
     
     
         11 . The downhole tool of  claim 1 , wherein the bore of the tubular member comprises a coating having a hardness greater than that of the tubular member itself, the hardness of the coating is in a range of about 45 HRc to about 65 HRc, and the coating comprises one or more of chromium, carbide and ceramic. 
     
     
         12 . The downhole tool of  claim 1 , further comprising a chamfer formed on the tubular member at an interface between the bore and the orifice. 
     
     
         13 . The downhole tool of  claim 12 , wherein the chamfer is formed at an angle in a range of about 10 degrees to about 30 degrees. 
     
     
         14 . The downhole tool of  claim 1 , wherein the orifice comprises a plurality of orifices, each adjacent pair of the orifices is separated by a bar that extends parallel to the axis, and the bar has an inner diameter that is substantially equal to that of the bore. 
     
     
         15 . The downhole tool of  claim 14 , wherein the bar is configured to constrain an outer diameter of the secondary seal. 
     
     
         16 . The downhole tool of  claim 1 , wherein the piston is configured to move axially but not rotationally within the tubular member. 
     
     
         17 . The downhole tool of  claim 1 , wherein the seal system is configured to have a closed position wherein neither the primary seal nor the second seal is in the orifice of the tubular member, a partially open position wherein only the primary seal is located at least partially in the orifice of the tubular member and the second seal is not in the orifice of the tubular member, and a completely open position wherein both the primary seal and the second seal are located at least partially in the orifice of the tubular member. 
     
     
         18 . The downhole tool of  claim 1 , wherein a radial clearance is provided between an outer diameter of the piston and an inner diameter of the tubular member, and the radial clearance is in a range of about 0.001 inches to about 0.010 inches. 
     
     
         19 . The downhole tool of  claim 1 , wherein the secondary seal and the second gland are configured to be closer to the aperture in the piston than the primary seal and the first gland, and the primary seal and the first gland are larger than the secondary seal and the second gland, respectively. 
     
     
         20 . A downhole tool, comprising:
 a tubular member having an axis, a wall with a bore, an orifice extending radially from the bore through the wall, first and second glands formed in bore adjacent the orifice, and the first gland is axially spaced apart from the second gland;   a piston configured to be co-axially mounted in the bore of the tubular member and be axially reciprocated therein, the piston having a piston bore, and an aperture extending radially from the piston bore to the bore of the tubular member; and   a seal system configured to be mounted to the tubular member, the seal system comprising a primary seal for the first gland, a secondary seal for the second gland, and the secondary seal is harder than the primary seal.