The paper presents a microwave sensing method to detect and quantify the presence of water or saline water in natural gas pipelines. Efficient and safe operation of natural gas production lines depends on intelligent monitoring capabilities of specific chemicals harmful to the operations and to the environment. For example, high salinity formation water will erode the steel pipelines, thus requiring immediate actions. Quantifying such contents is as important as detecting them. Real-time, in-situ quantification of water fraction and salinity in the flow leads to reduced production cost and improved equipment safety. The gas pipe in this work is modeled as a waveguide that is filled with gas and different fractions of water. By measuring the magnitude and phase of the reflected and transmitted signals over a broad spectrum, the water fraction can be calculated using waveguide model. With water fraction increasing, signal magnitude changes and cutoff frequency shifts. Both signal magnitude and frequency shift can give accurate estimation of the water fraction inside.
The advantage of using microwaves is the ability to cover the whole cross section area of the pipe, without missing any water droplet inside. Other methods, like electrochemical, resistivity or capacitance probes, only capture local variations. HFSS software was used to simulate the wave characteristics for different water volume fractions inside the pipe and the experimental data showed that a water fraction as low as 1% can be quantified. A repeatability study was done in this work and it showed that measurements have good repeatability.
Index Terms — Microwave Spectroscopic Sensing, NDT testing, Natural gas industry, Petroleum industry, Water fraction.