Recent developments in high precision quartz and Langasite pressure sensors for high temperature and high pressure applications

Pressure measurements provide reliable estimates of the reservoir pressure, permeability and oil/water interface in reservoirs that help in optimal completion of wells for oil and gas production. Pressure sensors with high accuracy, resolution, and fast response time are necessary for characterizing highly permeable reservoirs. High precision pressure sensors are generally, made of crystalline quartz because of its excellent stability under temperature and pressure cycling, high material Q, and minimal hysteresis under loading and unloading. The capability of a thickness-shear resonator to experience pressure and temperature induced shifts in its resonance frequency is utilized in the design of high precision quartz pressure sensors. It is well known that the frequency changes in a thickness-shear quartz resonator caused by changes in the temperature, pressure or externally applied forces are strongly dependent on its crystalline orientation, resonator geometry, and mounting supports. Two types of quartz pressure sensors are currently used for different applications in the oil and gas industry. The first one uses a single-mode thickness-shear quartz resonator as the sensing device; and the other one employs a dual-mode thickness-shear quartz resonator. A drawback of the single-mode design is that a temperature sensing device is not co-located with pressure sensing resonator and reliable temperature compensated pressure output is possible only after temperature equilibration between the temperature and pressure sensing devices. In contrast, both the temperature and pressure sensing resonators in a dual-mode design are physically the same sensing element and helps in obtaining temperature compensated output in the presence of temperature gradients. Lately, there has been an increasing demand for high precision sensors operating at temperatures as high as 210 degC and pressures up to 210 MPa. This paper describes applications of new quartz crystalline orientations and efforts that led to the development of a new dual-mode pressure sensor to achieve the target metrological performance at high pressures and temperatures. In addition, we present computational results to show the presence of stress, and temperature compensated loci for Langasite and its isomorphs, which can be promising candidates for geothermal applications when the operating temperatures are greater than 300 degC.