A novel sensor for monitoring oilfield fouling in near-real time

The goal of our research was to improve the control of process fouling by developing new monitors that could be used to measure and predict fouling in real time. Such monitors could be used to assure the application of the proper chemical treatment at the proper dosage. Operation of these monitors in real time will provide a direct condition-based assessment of fouling and a means for optimizing the response. One approach to direct fouling measurement taken by Nalco/Exxon is the use of the quartz crystal microbalance (QCM) technique. A QCM is a device that uses a piezoelectric quartz crystal wafer with electrodes bonded to the crystal as a frequency control device, or resonator. We have developed our QCM-based instrumentation, referred to as a thickness-shear mode resonator (TSMR), using an oscillator circuit that minimizes the effects of resonator loss over a wide dynamic range of liquid viscosity and density. Results demonstrate the sensitivity and versatility of the TSMR technique for monitoring both rigid and visco-elastic fouling events in both lab and field environments. The TSMR voltage response to changes in the sample's visco-elastic properties is more sensitive than a standard oscillator circuit design using only frequency measurements. This response characteristic of the TSMR has enabled us to develop a highly sensitive monitor for both rigid and visco-elastic deposits.