Modeling Thickness Shear Mode Quartz Sensors for Increased Downhole Pressure & Temperature Applications

G.R. Kirikera, W. Patton, and S.M. Behr
Geophysical Research Company LLC, Tulsa, OK, USA

Numerous sensors based on various sensing principles are used to measure pressures and temperatures in wellbores. Of all these sensors, piezoelectric quartz is the most preferred means of sensing pressure and temperature and is probably the only sensor to meet stringent downhole measurement requirements. The sensor consists of a quartz piezoelectric resonator hermetically sealed between two quartz end caps. The end caps protect the resonator from harsh wellbore conditions and convey stress from downhole fluids to the resonator. As the resonator senses stress, its resonant frequency changes which can be used to calculate the pressure in the well at that particular depth. Quartz is a complex, anisotropic material and COMSOL Multiphysics software is being used by GRC to understand the shape and importance of the end caps on the resonator. Based on simulated results, a new end cap is being designed, manufactured and tested. Finite element results using COMSOL Multiphysics software will be shown in this article.