Downhole tool control

Abstract

A method of operating a downhole tool in a no-flow configuration in which a piston and a flow-restriction cooperate to occlude a tool throughbore. The tool is reconfigured to an intermediate configuration by flowing fluid through the tool at an intermediate flow-rate lower than an operating flow-rate and axially translating the piston to an intermediate position in which the piston and flow-restriction cooperate to define an intermediate flow area. Axial translation of the piston between a no-flow position and the intermediate position includes an occlusional stage of a first axial extent during which the piston and the flow-restriction occlude the tool throughbore, and a transitional stage of a second axial extent during which the piston and the flow-restriction cooperate to provide a step-change in flow area. The tool is reconfigured to an operating configuration by flowing fluid through the tool at the operating flow-rate and axially translating the piston.

What is claimed is: 
     
         1 . A method of operating a downhole tool, the method comprising:
 providing a downhole tool in a no-flow configuration in which an axially movable tubular piston and a flow-restriction cooperate to substantially occlude a tool throughbore;   reconfiguring the tool to an intermediate configuration by flowing fluid through the tool at an intermediate flow-rate lower than an operating flow-rate and axially translating the piston to an intermediate position in which the piston and the flow-restriction cooperate to define an intermediate flow area, wherein axial translation of the piston between a no-flow position and the intermediate position comprises an occlusional stage of a first axial extent during which the piston and the flow-restriction substantially occlude the tool throughbore and a transitional stage of a second axial extent during which the piston and the flow-restriction cooperate to provide a step-change in flow area;   holding the tool in the intermediate configuration by flowing fluid through the tool at the intermediate flow-rate; and   reconfiguring the tool to an operating configuration by flowing fluid through the tool at an operating flow-rate and axially translating the piston to an operating position in which the tool defines an operating flow area.   
     
     
         2 . The method of  claim 1 , wherein the second axial extent is less than the first axial extent. 
     
     
         3 . The method of  claim 1 , comprising providing the tool in the no-flow configuration and then reconfiguring the tool to the intermediate configuration by pumping fluid through the tool at the intermediate flow-rate and axially translating the piston from the no-flow position to the intermediate position, the axial translation of the piston comprising an initial occlusional stage and a secondary transitional stage. 
     
     
         4 . The method of  claim 3 , comprising subsequently reducing the flow-rate to return the tool to the no-flow configuration. 
     
     
         5 . The method of  claim 3 , comprising subsequently increasing the flow-rate to the operating flow-rate to reconfigure the tool to the operating configuration. 
     
     
         6 . The method of  claim 1 , comprising providing the tool in the operating configuration and then reconfiguring the tool to the intermediate configuration by reducing the flow-rate through the tool from the operating flow-rate to the intermediate flow-rate and permitting the piston to assume the intermediate position. 
     
     
         7 . The method of  claim 1 , comprising reconfiguring the tool from the no-flow configuration to the operating configuration by increasing the flow-rate directly from zero to the operating flow-rate. 
     
     
         8 . The method of  claim 1 , comprising reconfiguring the tool from the operating configuration to the no-flow configuration by decreasing the flow-rate directly from the operating flow-rate to zero. 
     
     
         9 . The method of  claim 1 , wherein reconfiguring the tool to the operational configuration involves a degree of translation of the piston from the no-flow position greater than the degree of translation of the piston from the no-flow position to the intermediate position. 
     
     
         10 . The method of  claim 1 , comprising removing the flow-restriction from the tool. 
     
     
         11 . The method of  claim 1 , comprising controlling the sequence of reconfiguration of the tool by a cam arrangement. 
     
     
         12 . The method of  claim 1 , comprising:
 flowing fluid through the tool at the operating flow-rate and with the tool in a first operating configuration;   reducing the flow through the tool to the intermediate flow-rate and reconfiguring the tool to the intermediate configuration; and   increasing the flow through the tool from the intermediate flow-rate to the operating flow-rate and reconfiguring the tool from the intermediate configuration to a second operating configuration.   
     
     
         13 . The method of  claim 12 , comprising reducing the flow-rate directly from the operating flow-rate to zero and reconfiguring the tool directly from the first operating configuration to the no-flow configuration, and then increasing the flow-rate directly from zero to the operating flow-rate to reconfigure the tool to the first operating configuration. 
     
     
         14 . The method of  claim 12 , further comprising:
 ceasing fluid flow through the tool and reconfiguring the tool from the second operating configuration to the no-flow configuration.   
     
     
         15 . The method of  claim 12 , further comprising:
 ceasing fluid flow through the tool and reconfiguring the tool from the first operating configuration to the no-flow configuration.   
     
     
         16 . A downhole tool having utility in an operator-selectable intermediate configuration and in an operating configuration, the tool comprising:
 a tubular body;   a piston axially movably mounted in the body, the piston being movable between a no-flow position, an intermediate position and an operating position; and   a flow restriction cooperating with the piston to vary a flow area of the tool;   wherein, in the no-flow position, the piston and the flow-restriction cooperate to substantially occlude the through bore;   wherein, in the intermediate position, the piston and the flow-restriction cooperate to define an intermediate flow area, axial translation of the piston between the no-flow position and the intermediate position comprising an occlusional stage of a first axial extent during which the piston and the flow-restriction cooperate to substantially occlude the through bore and a transitional stage of a second axial extent during which the piston and the flow-restricting member cooperate to provide a step-change in flow area; and   wherein, with the piston in the operating position, the tool defines an operating flow restriction.   
     
     
         17 . The tool of  claim 16 , wherein the piston is biased towards the no-flow position. 
     
     
         18 . The tool of  claim 16 , wherein the flow restriction includes an elongate flow-restricting member mounted in the body. 
     
     
         19 . The tool of  claim 18 , wherein the flow-restricting member is coaxial with the piston. 
     
     
         20 . The tool of  claim 18 , wherein the flow-restricting member is received within the piston. 
     
     
         21 . The tool of  claim 18 , wherein the flow-restricting member includes a substantially cylindrical portion which is received in a complementary passage in the piston when the piston is in the no-flow position and during the occlusional stage of translation between the no-flow position and the intermediate position. 
     
     
         22 . The tool of  claim 16 , wherein the flow restriction includes an elongate flow restriction mounted on the piston which cooperates with a complementary restriction in the body. 
     
     
         23 . The tool of  claim 16 , wherein the piston defines a piston flow restriction, such that increasing flow through the piston creates an increasing axial fluid pressure force on the piston. 
     
     
         24 . The tool of  claim 23 , wherein the piston flow restriction cooperates with a body-mounted flow-restricting member. 
     
     
         25 . The tool of  claim 16 , wherein the piston and body cooperate to define a differential piston, wherein an area of the piston is exposed to internal tool pressure and an oppositely directed area of the piston is exposed to external tool pressure. 
     
     
         26 . The tool of  claim 16 , comprising a cam arrangement for controlling the movement of the piston relative to the body. 
     
     
         27 . A method of reconfiguring a downhole device between a no-flow configuration, a first flow configuration and a second flow configuration, the method comprising:
 providing a device in a no-flow configuration;   flowing fluid through the device at an operating flow-rate and reconfiguring the device to a first flow configuration;   maintaining fluid flow through the device at the operating flow-rate and maintaining the device in the first flow configuration;   reducing the fluid flow through the device from the operating flow-rate to an intermediate flow-rate lower than the operating flow-rate and reconfiguring the device to an intermediate flow configuration between the no-flow configuration and the first flow configuration; and   increasing the fluid flow through the device from the intermediate flow-rate to the operating flow-rate and reconfiguring the device from the intermediate configuration to a second flow configuration.   
     
     
         28 . The method of  claim 27 , further comprising:
 stopping fluid flow through the device and reconfiguring the device from the second flow configuration to the no-flow configuration, or   stopping fluid flow through the device and reconfiguring the device from the first flow configuration to the no-flow configuration.   
     
     
         29 . The tool of  claim 16 , wherein the piston is a tubular piston defining a throughbore and the flow area varied by the flow restriction cooperating with the piston is a flow area of the throughbore of the tool. 
     
     
         30 . The tool of  claim 22 , wherein the elongate flow restriction mounted on the piston is received in a complementary restriction in the body when the piston is in the no-flow position.