Companies in the oil and gas industry rely upon acquisition of accurate downhole pressure data for management of reservoir resources. Pressure data must be acquired in extreme environments present in wells, including high pressures, high temperatures, and high levels of shock and vibration. A primary concern of oil and gas companies is that pressure transducers provide reliable data throughout the duration of well-testing jobs. Important performance parameters for well-test pressure gauges include inaccuracy arising from nonlinearity, hysteresis, nonrepeatability, and temperature. Accurate pressure measurements are required for determination of reservoir resources. Sensor output per unit pressure (sensitivity) and the corresponding minimum resolvable pressure (resolution) are important performance considerations. Pressure resolution is the key parameter for dynamic well-test analyses used to determine reservoir properties. Design limits, including maximum allowable pressure over the operating temperature range, also must be known. Pressure transducers must retain acceptable performance characteristics including accuracy, sensitivity, and resolution for long periods of operation to provide reliable data and reduce the frequency and cost of recalibration. This paper describes a unique quartz thickness-shear mode sensor that was developed for downhole pressure measurements. Pressure transducers that use this sensor meet the demanding requirements of downhole testing.

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SUMMARYA new solution technique has been developed to calculate the frequency shifts arising from mechanical stresses in the case of quartz resonators. This solution technique utilizes finite element analysis as an initial step to calculate mechanical stress distributions in quartz resonators. Output from the finite element solution is used in a recently developed program to calculate resonator frequency shifts as the final step. Frequency shifts are calculated via numerical integration of the perturbation integral derived by T i e r~t e n .~~ The solution technique is general in that any combination of mount and resonator geometries may be modelled. Any crystallographic orientation may be chosen and any load or combination of loads may be applied to the resonator. The frequency perturbation calculation includes movement of the mode to any position in the general vicinity of the resonator centre. Experimental results for AT-and SC-cut quartz resonators subjected to diametric forces and inertial loading verify the accuracy of frequency shifts calculated using the new solution technique.