In the last decade, the world of petroleum industry multiphase measurement has evolved from its infancy in research to operational equipment. Virtually all the endeavors were focused on the predominantly liquids aspect of multi-phase, mainly in the low GOR, low water cut regimes. With considerable time and money spent on development, the technology has evolved to cover both water and oil-continuous flows of 0-100% water and to GVF (Gas Volume Fractions) upwards of 90%.
With the advancement of technology and the increase in natural gas usage, the demand for "wet gas" metering has become more apparent. Wet gas is roughly defined as production or pipeline streams with GVFs above 95% gas at the point of measurement.
This paper presents a discussion of the equipment currently available and/or in development and the efforts put forth to perform this type of multi-flow measurement.
Measurement of gas well production has been primarily left to the orifice plate, recognizing that the resulting flow calculations were in error because of the associated liquids (water and condensate). Several attempts have been made (with little or no success) to quantify the degree of error in orifice plate measurement with variouspercentages of liquids.
Well testing of gas well production is predominantly accomplished by two or three phase well test separators, often with little concern for testing of liquid carryover in the gas, entrained and solution gas in the liquids, water carryover in the oil, and oil carryover in the water. Wells that surge or have slugging flow patterns often flood normally sized (for average flow) test separators, because the average liquid flow is considerably less than the liquidslug flow rates. Likewise, a well may tend to produce considerably more water as the well ages, and the test separator, by its internal design, is incapable of handling to 10 times the usual amount of water that can be experienced from one well test sequence to another. The range ability of a well test vessel and/or separator level control system is difficult to change in the field. A better, less expensive, lighter weight, portable and more accurate "mouse trap" was needed.
Virtually any and all multi-phase measurement technology has its limitations within different flow regimes. Considerable use is made of combining several technologies into a given high gas fraction (wet gas) multi-phase meter. Those technologies include:
In addition to the existing or near operational technologies in wet gas metering additional approaches, such as nuclear activation, polymer solubility, and radioactive isotopes, are in the research and design phases in both Europe and the United States.