Non-Intrusive Level Measurement Using Guided Elastic Waves

Abstract

Abstract Accurate level measurement in process vessels is important for safety, production optimization and control as well as for optimization of chemical additives. Most of the level measurement sensors used in oil and gas production today are Differential Pressure (DP) transmitters, displacers and, sometimes, Guided Wave Radar (GWR). More advanced profiler-type sensors are used more rarely and most often only for process analytics. Almost all of the commercially available level measurement instruments are intrusive, meaning that they require a flange or penetration for installation and maintenance. In practice, this implies that installation and maintenance on an existing installation have to be conducted during a turnaround. This makes such a project prohibitively expensive considering the cost of turnaround time and the fact that a turnaround on an offshore platform is only performed once every 1-4 years. This work describes pilot trials with a novel non-intrusive level measurement system that utilizes Guided Elastic Waves (GEW) for attenuation tomography. Pilot experiments were carried out in a model separator with an internal diameter of 1.00 m and length 3.75 m. The pilot separator which was filled to pre-determined levels with tap water, mineral oil and construction sand. Flow of water was induced in some of the experiments. Phase levels were recorded manually through a sight glass and compared to readings generated by the novel measurement system. Experiments showed that the novel level measurement system is able to detect levels of sand and liquid as well as clean water/oil interface levels with very high accuracy. Flow had no significant influence on the measurement results and the sensor output remained stable over the cause of one month. After the successful testing, the system has been qualified for its first trial on an offshore installation. In addition to an offshore pilot, more R&D needs to be conducted in order to develop capabilities to measure emulsion and foam interface layers as well as to determine how fouling by scale, waxes and other impurities present in a full-scale separator influence the measurement.