Low pressure responsive downhole tool

An annulus pressure responsive downhole tool valve apparatus, comprising:

• a housing;
• a power piston having first and second sides, said power piston being slidably disposed in said housing and movable between first and second positions relative to said housing;
• valve means, attached to said power piston, said valve means being movable between closed and open positions corresponding to said first and second positions, respectively, of said power piston, said closed position of said valve means being such that a flow passage of said valve means is closed;
• a power passage means for communicating a well annulus with said first side of said power piston;
• a low pressure zone, defined within said housing, and communicated with said second side of said power piston;
• and
• pressure relief means, communicated with said low pressure zone, for relieving from said low pressure zone a volume of fluid sufficient to permit said power piston to travel from said first position thereof to said second position thereof, said travel being in a direction from said first side toward said second side of said power piston.

A method of operating an annulus pressure responsive downhole tool of the type including a power piston slidably disposed in a housing and first and second pressure conducting passages communicating a well annulus with first and second sides of said power piston, said method comprising the steps of:

• applying an increase in annulus fluid pressure to an annulus fluid in said well annulus;
• communicating said increase in annulus fluid pressure to said first side of said power piston through said first pressure conducting passage;
• delaying communication of a sufficient portion of said increase in annulus fluid pressure to said second side of said power piston a sufficient time to allow a pressure differential from said first side to said second side of said power piston to move said power piston from a first position thereof to a second position relative to said housing;
• and
• relieving from said second pressure conducting passage a volume of fluid sufficient to permit said power piston to travel to its said second position.

A method of operating an annulus pressure responsive downhole tool of the type including a power piston slidably disposed in a housing, a valve means operatively associated with said power piston, first and second pressure conducting passages communicating an annulus of a well with first and second sides of said power piston, and a pressure relief means disposed in said second pressure conducting passage, said power piston being movable between first and second positions relative to said housing corresponding to closed and open positions, respectively, of said valve means, said method comprising the steps of:

• running said tool down into said well with said valve means in its said closed position closing a flow passage of said valve means, and with said power piston in its said first position;
• resiliently biasing said power piston toward its said first position with a resilient biasing means;
• sufficiently balancing well annulus pressure across said power piston as said tool is run into said well so that a pressure differential from said first side to said second side of said power piston is never sufficient to overcome said resilient biasing means and prematurely move said power piston to its second position as said tool is being run into said well;
• setting a packer means, connected to said tool, in said well to separate said well annulus into upper and lower portions, said first and second pressure conducting passages being communicated with said upper portion, and said flow passage of said valve means being communicated with said lower portion of said well annulus;
• applying an increase in annulus fluid pressure to an annulus fluid in said upper portion of said well annulus;
• communicating said increase in annulus fluid pressure to said first side of said power piston through said first pressure conducting passage;
• delaying communication of a sufficient portion of said increase in annulus fluid pressure to said second side of said power piston a sufficient time to allow a pressure differential from said first side to said second side of said power piston to move said power piston to its said second position;
• opening said pressure relief means during said time of delayed communication;
• moving said power piston from its first position to its second position;
• relieving from said second pressure conducting passage, as said power piston moves from its first position to its second position, a volume of fluid sufficient to permit said power piston to travel to its said second position;
• and
• thereby moving said valve means to its said open position opening said flow passage of said valve means as said power piston is moved to its said second position.