Emulsion Phase and Electrical Measurement
Literature since the early 1920s describes the two physical phases of an oil and water emulsion. One is similar to the Turkey gravy; cornstarch helps to maintain a viscous water-in-oil phase. If just water were added to the Turkey oil, it would settle out into the two discrete phases very easily. An oil-in-water emulsion exists and is physically described as oil surrounded by water.
If we use a coaxial line to establish the RF (radio frequency) or microwave energy waves with a bare center rod and a metal outer pipe, this becomes the electromagnetic structure to make our water cut measurement.
The Oil Continuous Emulsion Phase (water-in-oil) is non-conductive since the oil is insulating. The saltwater bubbles are uniformly spaced throughout the oil and the salinity does not matter at the frequencies Phase Dynamics operates (100 to 300 MHz).
When the emulsions invert to the Water Continuous Phase (oil-in-water), then a path can be drawn from the center conductor of the coaxial line to the outer pipe wall. Since saltwater is conductive and the measurement is electromagnetic in nature, the conductive liquid attenuates the electrical energy. A correction for the conductivity must be made to know where 100% water is on the electrical curves.
Phase Dynamics uses the fact that when the emulsions are in the water continuous phase (where salinity does matter), the RF or Microwave energy is absorbed to a much higher degree than in the oil continuous phase. This information is used to determine the emulsion of the phase of the liquids. The difference in attenuation of the signal between the oil continuous phase and the water continuous phase is great enough that a line of demarcation can be drawn between the two attenuation curves for all salinity of the water.
Phase Dynamics senses the phase of the liquids at each measurement of 2 seconds in time. It will respond to emulsion phase changes at any water cut (from approximately 30% to 100% water cut). The calibration on a flow loop is done for both emulsion phases across the entire salinity calibration range. This is true even though the calibration runs go only to 50% water cut for water continuous emulsions. The calibration runs stop at 50% water cut only due to the stability of the water emulsion with the oil used to make this phase's calibration. Phase Dynamics has proven that the correct phase will be selected from the attenuation power curves generated during the water continuous calibrations, even for emulsions below 50%.
The equipment furnished by Phase Dynamics makes a continuous emulsion phase determination oat ever measurement point. This is unlike other vendors where the emulsion phase is determined by a fixed value of water cut to select between the curves. Only Phase Dynamics' dynamic determination of the emulsion phase will give accurate water cut measurements. The emulsion phase is a dynamic event, which will change at each cycle of the well and with any change in temperature, salinity, or oil properties. Instrumentation used must be capable of instantaneous determination of the phase of the emulsions for an accurate measurement.
Personally Pulling the Sample to Test Emulsion Phase
The emulsion phase cannot be determined easily by examination of the liquids. Once the sample is pulled from the flowing stream the emulsion phase becomes unknown due to the change in temperature and flow rate. Temperature directly determines phase because it is energy added or subtracted, flow rate is an indirect contributor.
Flow rate contributes energy to the emulsion phase depending upon the Reynolds Number of the flow region, which contributes to the shear of the liquid. Shear adds energy as mechanical and thermal energy. If a good sample can be obtained, the phase is determined by a microscopic examination of the emulsion itself or by viscosity comparisons to know emulsions of the same makeup. Extreme care must be taken to assure not to disturb the emulsion type during preparation and examination. Phase Dynamics give us an unusual insight into the emulsion type of the fluids at a temperature and actual flowing conditions. This information can be used to aid in the evaluation and control of the reservoir.
If you require references on emulsion science, please contact us via. Email.