Abstract:
An optical method for measuring the water and oil content using mid-IR (1.6–2.4 $\mu$m) LEDs and a wideband photodiode is suggested for the first time. This method is developed based on the absorption spectra of pure water, dewatered oil, and water—oil emulsions (cut oil) with different content of water and uses 10 types of LEDs in the spectral range 1.6–2.4 $\mu$m. It is shown that pure water heavily absorbs the LED radiation in the spectral range 1.85–2.05 $\mu$m, oil absorbs in the range 1.67–1.87 $\mu$m, and the LED radiation with a maximum at 2.20 $\mu$m is equally weakly absorbed by water and oil. An optical cell of the water-and-oil analyzer is designed on the basis of a three-element diode array with radiation maxima at 1.65 (detection of oil), 1.94 (detection of water), and 2.2$\mu$m (reference signal) wideband photodiode covering the spectral range 1.3–2.4 $\mu$m. A calibration curve is derived that represents the dependence of the water concentration in oil on the amplitude of the reduced signal obtained by processing three signals from the LEDs. This optical method of measuring the water content in oil underlies a portable analyzer making possible online measurements directly in an oil well.
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