Electronic SOI Gauges

The downhole environment is very stressful to sensors. The following basic requirements were used during the development of the Analog and Digital Pressure/Temperature Sensors so that reliable data was assured:

• Wide operating temperature range - Must be capable of surface and downhole.
• Large output signal on the Transducer - Simplifies the processing and minimizes the effect of measurement circuit errors.
• Repeatability - Under pressure and temperature cycling, the sensor output for given input conditions should be the same each time the conditions are applied.
• Stability - Under constant pressure and temperature, the transducer output should not change.
• Resistant to mechanical shock and vibration - Minimal error during operation and no long term degradation.
• Resistant to gases and liquids produced or placed downhole, whether naturally occurring (CO₂, brine, H₂S) or from well treatment (acids, alkalis).

Transducer

The design incorporates a Piezo Resistive transducer which incorporates a Silicon on Insulator type diaphragm. A silicon chip (approx. 0.1 inch square) is micro machined with a cavity on the underside to form a pressure-sensing diaphragm. The depth of the cavity determines the pressure range. Four resistors are defused into the surface, located so that two are in compression and two are in tension. The diaphragms are fabricated in quantity on wafers using integrated circuit production methods. The sensor is made when the diaphragm is fused to a silicon substrate.

Basics of Operation

The Piezo Resistive transducer converts a pressure into a change in resistance. The strain of the applied pressure is measured across an active four wire resistive bridge and the temperature is measured from a secondary of the main bridge.

The purpose of the temperature measurement is so that the pressure transducer output can be compensated for temperature induced errors ('temperature compensated' for increased pressure accuracy over a broad temperature range, 15°C to 125°C ( 59°F to 257°F).

The designs incorporate minimal electronics that decreases infant mortality commonly experienced in other designs.

Instrumentation, Data Interface and Communications

mPOD™ and sPOD™ Gauge WSMS Interface

The CS7X™ wellsite management system is an Internet-ready, modular, scalable system designed to provide real time process control and monitoring of oil and gas production facilities. The advantage of the CS7X well site management system (WSMS) is that it has been designed with built-in applications that minimize reconfiguration requirements. An integral web server supports direct viewing of process data using off-the-shelf browsers such as Microsoft® Internet Explorer or Netscape®. A flash file system supports FTP file transfer of system configuration and HTML files. Internal data Logging and IO capabilities are standard functionality of the WSMS.

sPOD Gauge Interface

A surface interface for the sPOD single-point digital gauge, the ePRO™ data process system has data storage and pressure-signal output that provides an ideal solution for single well applications. The system can output a pressure control signal to variable speed drive controllers to automate artificial lift equipment and be installed world-wide with no special considerations for venting or heating. The ePRO system offers compact size with ease-of-use. Designed for ruggedness, the system can be pole mounted or building enclosed.