A Dual-Mode Thickness-Shear Quartz Pressure Sensor for High Pressure Applications

Pressure measurements are vital for the development and completion of oil and gas wells for hydrocarbon production. High precision pressure measurements provide accurate estimates of the reservoir pressure, permeability, and gas/oil/ water interfaces in reservoirs that help in an optimal completion of wells for oil and gas production. This is based on identifying small differences in hydrostatic gradients caused by differences in mass densities of the gas, oil, and water. This differentiation can be accomplished by high resolution pressure measurements on the order of a few mpsi. Deeper oil and gas wells require pressure sensors that can operate up to 210 MPa (30 kpsi) and 210 °C or more. A dual-mode thickness-shear quartz pressure sensor has been commercialized to meet these high pressure and high temperature requirements for the deep drilling projects. This pressure sensor uses a doubly-rotated Stress-compensated for the B-mode, and temperature compensated for the C-mode (SBTC)-cut disc resonator sandwiched between two matching end caps. Hydrostatic pressure applied on the outside of the cylindrical probe transmits in-plane, compressive stresses to the sensing resonator and is a key feature of this design for high pressure applications. Optimal design of a bi-convex SBTC-cut resonator operating in the fundamental Band C-modes of vibration has led to the resonator having a Q*f product of about 9.18e11 for the B-mode and 5.02e12 for the C-mode. The metrological performance of this dual-mode thicknessshear over the target pressure and temperature ranges shows a calibration accuracy to be within 0.014 MPa (2 psi); a pressure resolution of about 20 Pa (0.003 psi), and stability of 0.003 MPa/week (0.5 psi/week).