|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Journal Paper|
|Title||Orifice Metering of Two-Phase Flow|
|Authors||Mattar, Louis, U. of Calgary; Nicholson, Murray, U. of Calgary; Aziz, Khalid, U. of Calgary; Gregory, G.A., U. of Calgary|
|Journal||Journal of Petroleum Technology|
|Volume||Volume 31, Number 8||Pages||955-961|
Several correlations for two-phase flow through orifice meters are reviewed and verified experimentally, using air and oil mixtures in a 2-in. (5.08-cm) orifice meter. A simple, empirically determined relationship is shown to be valid for a limited range of oil/gas ratios when separator tests are possible. For predictive purposes, however, a more complex relationship is recommended.
The flow of two-phase mixtures in a single pipeline is becoming more common. To determine the rates of flow in such systems, the phases are separated first, and the flow rate of each phase is measured individually. In many instances, we need to know the flow rates without having to separate the phases. A typical example would be when continuously (automatically) monitoring sour gas fields, where retrograde condensation occurs before measurement by an orifice meter. Sometimes existing installations, which were once producing dry gas, now are producing in two-phase flow, and satisfactory interpretation of these orifice meter readings is desired. Another application of interest is the determination of steam quality during the flow of wet steam when the total mass flow rate (boiler feed rate) is known. This study tries to obtain a relationship between the orifice-meter differential reading and the flow rates of the individual phases, using air and oil as the flowing fluids.
Review of the Literature
Most investigations into two-phase flow-rate measurement with orifices have been concerned with the flow of wet steam. Occasionally, air/water systems were studied. There are few papers relating to natural gas/oil flow.
All correlations presented in the literature are based on the single-phase, orifice-meter equation, which may be written as
James, working with geothermal steam wells, used Eq. 1, but replaced the density with an effective two-phase mixture density. He obtained this density by raising the mass dryness fraction to the empirically determined power of 1.5. In another approach, Smith and Leang used a "blockage factor" to modify the coefficient of discharge, Kd, and expressed it as a function-of-dryness fraction. Smith and Leang and Smith et al., reviewed and evaluated several published correlations. Murdock, Bizon, and Chisholm and his coworkers took a different approach from those mentioned before. They related the two-phase pressure drop to that obtained by flowing the gas and liquid pressure drop to that obtained by flowing the gas and liquid separately. Murdock and Bizon assumed there was no interfacial shear between the gas and liquid phases (no slip model) and derived the relationship,
We show in the Appendix that / is proportional to the liquid-to-gas ratio. When there is no proportional to the liquid-to-gas ratio. When there is no liquid flowing, the liquid-to-gas ratio is zero, and must equal one. Eq. 2 then becomes equivalent to that reported by Wichert,
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