Downhole tool control

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.

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.