Methods and apparatus for sensing wellhead pressure

A method of monitoring wellhead pressure in a subsea petroleum system, comprising

• establishing a secondary fluid separate from a well fluid under said wellhead pressure,
• establishing a barrier between said well fluid and said secondary fluid yieldable within predetermined limits,
• biasing said barrier within said predetermined limits,
• establishing a initial pressure on said secondary fluid as a function of ambient subsea pressure,
• thereafter urging said barrier within said limits and against said secondary fluid in response to said wellhead pressure, and
• deriving an indication of the pressure on said secondary fluid as a function of said wellhead pressure

In a petroleum recovery system having a subsea wellhead and the like containing a petroleum fluid under a primary pressure, apparatus for monitoring said primary pressure comprising

• a secondary fluid chamber adapted to contain a secondary fluid,
• isolator means disposed between said petroleum fluid and said secondary fluid for establishing a secondary pressure in said secondary fluid chamber at a level functionally related to said primary pressure,
• pressure transducing means responsive to said secondary pressure for deriving an indication of said secondary pressure, and
• pressurizing means interconnected with said pressure chamber for subjecting said secondary fluid to an initial pressure of a magnitude functionally related to the ambient subsea pressure.

In a petroleum recovery system having a wellhead containing a petroleum fluid under a primary pressure, apparatus for monitoring said primary pressure comprising

• a secondary fluid chamber adapted to contain a secondary fluid under a secondary pressure,
• isolator means disposed between said petroleum fluid and said secondary fluid and having a movable piston member responsive to said primary pressure and trapping said petroleum fluid within said wellhead and from said secondary fluid,
• measuring means interconnected with said secondary fluid chamber and responsive to said secondary fluid pressure, and
• biasing means within said isolator means for acting on said piston member.

In a petroleum recovery system having a subsea wellhead containing a petroleum fluid under a primary pressure, apparatus for monitoring and controlling said primary pressure comprising

• a secondary fluid chamber adapted to contain a secondary fluid,
• isolator means disposed between said petroleum fluid and said secondary fluid and having barrier means yieldable through predetermined limits for establishing a secondary pressure on said secondary fluid at a level functionally related to said primary pressure,
• measuring means interconnected to said secondary fluid chamber for deriving and indication of said pressure on said secondary fluid,
• biasing means in said isolator means maintaining a force on said barrier means,
• pressurizing means interconnected with said secondary fluid chamber for reducing the force of said biasing means on said barrier means when monitoring said primary pressure, and
• valve means for controlling said primary pressure in response to said indication of said pressure on said secondary fluid.

In a subsea petroleum production installation, apparatus for monitoring the pressure of a primary fluid, comprising

• a control module including control circuitry immersed in a protective fluid,
• pressure transducing means for sensing the pressure of a secondary fluid,
• means for generating an electrical signal representative of said pressure of said secondary fluid and transmitting said signal to said control circuitry,
• isolation means coupled between said primary fluid and said secondary fluid for subjecting said secondary fluid to a pressure functionally related to said pressure on said primary fluid,
• shutoff means for retaining said primary fluid within said production installation in the event of a leak in said secondary fluid chamber, and
• means responsive to said control circuitry for varying selected operating parameters of said subsea petroleum production installation.

In a petroleum installation and the like, apparatus for monitoring a primary pressure on a petroluem fluid comprising

• a module including control circuitry immersed in a protective fluid,
• pressure transducer means within said module for generating a signal in response to a secondary fluid pressure,
• conduit means interconnected with said transducer means for containing a secondary fluid,
• isolator means interconnected with said installation and said conduit means and having piston means slidably separating said petroleum fluids and said secondary fluid and subjecting said secondary fluid to a secondary pressure functionally related to said wellhead pressure, and
• shutoff means within said isolator means for automatically retaining said petroleum fluid within said installation in the event of a leak in said conduit means.

In a subsea petroluem production installation, the combination of:

• a first chamber for containing a quantity of primary fluid and adapted to be connected in a fluid communication with a primary fluid conduit of said installation,
• a second chamber for containing a secondary fluid,
• a control module including control circuitry immersed in a protective dielectric fluid,
• pressure transducing means for sensing variations in the pressure of said secondary fluid, generating electrical signals representative of such variations, and transmitting said signals to said control circuitry, and
• isolation means for subjecting said secondary fluid to a pressure that varies as a predetermined function of the pressure of said primary fluid and providing a static seal between said first and second chambers when the pressure differential therebetween exceeds a predetermined magnitude.

As a subcombination,

• a first chamber for containing a quantity of primary fluid and adapted to be connected in fluid communication with a primary fluid conduit in a subsea petroleum production installation,
• a second chamber for containing a quantity of secondary fluid and adapted to be connected in fluid communication with a pressure sensing means,
• isolation means having a barrier member yieldable through predetermined limits for subjecting said secondary fluid to a pressure that varies as a predetermined function of pressure on said primary fluid,
• shut-off means actuated by movement of said barrier member for providing a seal between said primary fluid and said secondary fluid when the pressure differential between said first and second chambers exceeds a predetermined magnitude, and
• biasing means within one of said chambers for prepositioning said barrier member.

In an apparatus for use in a subsea petroleum production installation, the subcombination comprising

• an elongated housing formed to define a substantially cylindrical interior cavity, said housing having at one end of said cavity a first fluid port adapted to be connected in fluid communication with a primary fluid conduit of said installation and having at the other end of said cavity a second fluid port adapted to be connected in fluid communication with a secondary fluid conduit;
• a longitudinally movable piston dividing said cavity into first and second chambers for separately containing, respectively, a quantity of primary fluid and a quantity of secondary fluid, with said piston being movable in response to primary fluid pressure variations and thereby subjecting said secondary fluid to a pressure that varies as a function of primary fluid pressure;
• an annular seat formed on an internal surface of said second chamber;
• an elongated annular sleeve-like element which includes shut-off means for engaging said seat when the pressure differential between said first and second chambers exceeds a predetermined magnitude;
• and
• biasing means within said cavity acting upon said piston for urging said shut-off means away from said seat.

As a subcombination,

• housing means having an inlet port in fluid communication with a primary fluid in a subsea petroleum installation and further having an outlet port in fluid communication with a secondary fluid,
• a first chamber within said housing means for containing a quantity of primary fluid,
• a second chamber within said housing means for containing a quantity of secondary fluid,
• a barrier member between said first and second chambers yieldable through predetermined limits for subjecting said secondary fluid to a pressure that varies as a predetermined function of pressure on said primary fluid,
• a shut-off seat formed on an internal surface of said second chamber,
• a sleeve member connected to be actuated by said barrier member and having a shut-off end for engagement with said shut-off seat and thereby sealing said primary fluid from said secondary fluid when the pressure differential between said first and second chambers exceed a predetermined magnitude, and
• biasing means within said housing means for urging said barrier member away from said shut-off seat.