Metal cup pressure transducer with a support having a plurality of thermal expansion coefficients

An instrument for use in a wellbore to measure a wellbore pressure by receiving an input optical signal, and transmitting an output optical signal which varies in response to changes in the wellbore pressure, the instrument comprising:

• a outer housing having a longitudinal axis, a first end and a second end;
• a swivel support means mounted coaxially within the outer housing, and having an internal swivel surface;
• a swivel member having an axis and being mounted in the swivel support supported by the swivel member having an external swivel surface that engages the internal swivel surface to allow angular adjustment of the swivel member axis relative to the longitudinal axis of the housing;
• the swivel member having a shank extending from the external swivel surface toward the second end of the outer housing, the shank being located in the swivel support and spaced therefrom by an annular clearance;
• a plurality of adjustment members extending laterally from the swivel support, through the annular clearance, and into engagement with the shank to support the swivel member at a selected angular position relative to the longitudinal axis of the housing;
• at least one optical fiber extending through the first end of the outer housing and into the swivel member to provide at least one waveguide for directing the input optical signal into the outer housing, and passing the output signal from the outer housing;
• a lens means mounted within the swivel member for receiving the input optical signal from the at least one optical fiber, passing at least a portion of the input optical signal to an optical pathway, and passing at least a portion of the output optical signal to the at least one optical fiber;
• a light reflector disposed within the outer housing and aligned with the lens means for receiving the portion of the input optical signal from the lens means, and directing the portion of the input optical signal back towards the lens means;
• a pressure responsive means mounted in the second end of the outer housing for at least in part determining an optical transmission distance between the lens means and the light reflector in response to the wellbore pressure;
• and
• the swivel support means having a plurality of coefficients of thermal expansion for providing a plurality of mutually offsetting displacements in response to a temperature change, wherein the mutually offsetting displacements prevent the support means from changing the optical transmission distance in response to the temperature change.

A method for use in a wellbore to determine a wellbore pressure by passing an optical signal through an optical transmission pathway, and detecting a change in a distance across the optical transmission pathway, the method comprising the steps of:

• securing a pressure responsive member and a support means together within a housing, the support means having a support head, a swivel support, and a swivel member which have mutually offsetting coefficients of thermal expansion to prevent a temperature change from changing the distance across the optical transmission pathway, and the pressure responsive member secured within the housing for moving in response to a change in the wellbore pressure;
• securing a lens means and a light reflector within the housing and separated by a gap which defines at least part of the distance across the optical transmission pathway, one of the lens means and the light reflector secured to the support means, and the other of the lens means and the light reflector connected to the pressure responsive member for the pressure responsive member to urge a change in the gap in response to a change in the wellbore pressure;
• positioning a fiber optic cable adjacent to the lens means for passing the optical signal to the lens means, and for receiving at least a part of the optical signal from the lens means;
• adjusting the support means to select an initial distance across the gap, and to align the lens means with the light reflector for passing a portion of the optical signal therebetween;
• securing the housing to a fiber optic cable assembly and a downhole well tool;
• lowering the downhole well tool and housing within the wellbore to a downhole wellbore depth;
• and
• passing the optical signal through the optical fiber and to the lens means, which passes at least a portion of the optical signal across the gap to the light reflector, which then reflects the portion of the optical signal back to the lens means for transmission through the lens means and into the optical fiber for passing through the optical fiber.