A quartz thickness shear mode transducer for utilization in a borehole environment is presented. The pressure sensor is a direct conversion device which utilizes a non-cylindrical shell to convert and transmit forces to the quartz crystal resonator. A brief conceptual description of the transducer is given. Both laboratory and field examples are presented which illustrate the exceptional performance of the quartz thickness shear mode transducer.
In today's oil and gas industry there is an increasing demand for higher quality measurement of various physical parameters. One of the parameters of interest is the precise determination of pressure, For various well testing applications, a petroleum engineer needs accurate pressure information to adequately characterize a reservoir and thus make proper decisions in economically marginal cases or to maximize recovery of oil and gas. The pressure information needed includes both absolute accuracy as well as fine resolution of changes in pressure.
Prior to the advent of surface read out type pressure gauges and electronic memory gauges, pressure gauges were generally mechanical devices. Most of these contained a bourdon tube which extended and contracted to cause a stylus to scribe a line on a coated brass chart. A mechanical clock mechanism was used to drive the chart and thus provide pressure versus time. This chart was then read with the aid of a traveling microscope. These devices are still widely used.
Modern pressure transducers in common usage today can be categorized into three basic types. The first of these are strain gauges. There are four types of strain gauges. Of these, the only ones widely used in downhole applications are (1) bonded foil strain gauge transducers and (2) sputtered strain gauges. The basic concept of these devices are the same. A resistor pattern on an insulator is bonded to or deposited directly on the force summing element which is typically a metal diaphragm. The diaphragm is exposed directly to the pressurized fluid. The resistor pattern is arranged to form an active bridge which is incorporated into the electronics. Typical accuracies quoted for strain gauges of this type are 0.1% of full scale output.