Hydraulic lockout device for pressure controlled well tools

A well tool having a movable valve member responsive to a change in pressure from a pressure source, said well tool comprising:

• a movable mandrel operably coupled to said movable valve member for moving said valve member, said mandrel comprising a piston surface;
• a fluid spring operably coupled to said pressure source for receiving fluid pressure from said pressure source;
• and
• means for communicating said fluid pressure from said pressure source to said fluid spring, and for operably coupling pressure from said fluid spring to said movable mandrel after a predetermined change in pressure at said pressure source.

A method for operating a pressure responsive well tool having a fluid spring and a movable mandrel selectively responsive to said fluid spring, comprising the steps of:

• applying a pressure to a pressure source and communicating said pressure to said fluid spring;
• maintaining said pressure in said fluid spring upon a reduction in pressure at said pressure source;
• and
• selectively communicating said pressure in said fluid spring to said movable mandrel.

A method for operating a well tool having a valve therein, said valve responsive to movement of a movable mandrel, said movable mandrel being movable in response to a fluid spring, said method comprising the steps:

• applying a relatively increased pressure to a pressure source and communicating said pressure through use of a fluid medium to said fluid spring;
• decreasing said pressure at said pressure source while maintaining a relatively increased pressure in said fluid spring;
• and
• communicating said pressure in said fluid spring to said movable mandrel in response to an increase in pressure at said pressure source in excess of said previously applied pressure level at said pressure source.

A pressure responsive well tool for use in a borehole, said well tool having a valve therein, said valve member movable in response to a pressure in said borehole annulus surrounding said tool, said well tool comprising:

• a housing assembly;
• a mandrel assembly inside said housing assembly, said housing assembly and said mandrel assembly at least partially defining a fluid chamber;
• a piston for communicating pressure in said annulus fluid chamber to a body of fluid in said tool;
• a chamber at least partially defined by said housing assembly and said mandrel assembly, said chamber also partially defined by a movable piston, said chamber containing a gas adapted to be compressed in response to movement of said movable piston, said piston movable in response to an increase of pressure in said body of fluid to compress said gas;
• a passage having a check valve therein for communicating pressure in said body of fluid to said movable piston, but not allowing said pressure to subsequently decrease in response to a decrease in pressure in said annulus fluid chamber;
• and
• a pressure-releasable valve responsive to a predetermined pressure differential to selectively communicate said pressure of said gas in said chamber to said movable mandrel to move said valve member between opened and closed positions.