Long-term stability and performance characteristics of crystal quartz gauge at high pressures and temperatures

Good long-term stability of high precision quartz pressure sensors are necessary for various applications ranging from pressure transient analysis to permanent monitoring systems for optimal reservoir management in the petroleum industry. A crystal quartz gauge (CQG) is a dual-mode thickness-shear quartz pressure sensor that has been used in the oil-field services for the past eight years. High accuracy, resolution and fast response time of this sensor enable a reliable estimate of formation permeability and helps in reducing the overall cost of oil and gas production. Production statistics of manufactured CQGs show its yield exceeding 85% with excellent performance repeatability. The pressure reading errors of manufactured gauges are less than 6.89 kPa (1 psi) (plus 0.01% of the reading because of the uncertainty of the dead-weight tester). The pressure resolution is better than 20.7 Pa (0.003 psi) over 1 second gate time. An extremely effective dynamic compensation algorithm yields corrected pressure readings with a response time as short as a strain-gauge based pressure transducer while retaining high performance of a quartz gauge. Recent long-term stability tests of CQGs show a negligibly small drift on the order of a few-tenths of a psi (0.1 psi=689 Pa) at 103 MPa (15 kpsi) and 175°C for a period of more than a year. These results confirm that the CQG characteristics exceed the demanding specifications for both the well-tests and permanent monitoring systems