Red Eye® Multiphase Water-Cut Meter How it WOrks

The measurement is based on near-infrared absorption spectroscopy where water, oil, natural gas and hydrate inhibitors, like methanol, all have unique absorption profiles. Near-infrared is particularly well suited to detect and quantify hydrocarbons and water due to the overtone absorption bands for O-H and C-H bonds. Furthermore, since the signal is based on the water molecule itself, there is no sensitivity to water chemistry issues like salinity.

In the Red Eye 2G water-cut meter, four wavelength bands were measured simultaneously to make the measurement. The new multiphase water-cut meter adds a fifth wavelength band for added water sensitivity and to enable four component differentiations (oil, water, gas and methanol). The figure shows the typical wavelength bands measured but these can be optimized for various applications.

Using sophisticated chemometrics, internal algorithms calculate relative concentrations based on individual component calibrations. For low pressure, less than 500 psi (34.47 bar), the absorption profile for natural gas can be assumed to be 0 for all channels. At higher pressures, gas absorbance starts to play a role but it is linear with pressure and easy to accommodate. Typical changes in gas composition do not affect the measurement.

In high GVF streams the liquid tends to flow along the pipe wall. By positioning the sensor gap at the pipe wall, the Red Eye multiphase water-cut meter can accurately characterize that liquid even when the concentration is low relative to the gas content.

Water-liquid ratio calculations are equal or better than those of expensive multiphase metering systems with integrated water-cut measurement. More importantly, calibrations are robust and need not be repeated for modest density changes in the phases.