API RP 86:2005 pdf download

API RP 86:2005 pdf download.API Recommended Practice for Measurement of Multiphase Flow.
4.1 GENERAL
As mentioned earlier in Scope, it is not intended that this Recommended Practice be used alone, but in conjunction with other similar documents to guide the user toward good measurement practice in upstream production applications.
Having said this, it is important to recognize that well rate determination is the single most important task which is to be undertaken in the measurement of oil and gas production and the subsequent allocation to individual wells and reservoirs, and for this reason, ii is crucial to examine in great detail the various methods used for this task, and how each is influenced by its environment.
This section is an overvicw of thc multiphase flow mcasuremcnt environment, and of some of the methods employed to measure multiphase flow.
4.2 MULTIPHASE FLOW IN PIPES
In contrast to the case of single-phase flow, because the constituents of multiphase flow vaiy in their physical properties (density. viscosity, chemical composition, etc.), describing multiphase flow characteristics is usually quite difficult.
One typically identifies the various ways in which the constituents travel through the pipe in terms of theirflow regime. This simply means the geometrical distribution in space and time of the individual phase components, i.e. oil, gas. water, any injected chemicals, and so on.
Which flow regime is assumed in a particular instance is not simply a function of the relative proportions of the individual constituents, but to other factors such as orientation of the pipe and the velocity of flow, among others.
Specific information regarding the kinds of flow regimes possible and the conditions in which they normally exist is provided in Section 5.
Another complication which must be recognized in attempting to characterize multiphase flow is the possibility that a change of the physical state of the flowing medium may occur. A multiphasc fluid is made up of natural gas. hydrocarbon liquids, water, other fluids (some of which may have been injected into the stream), or any combination of these. Because pressure and temperature conditions may differ at various locations along the flow path between reservoir and points downstream, the fluid may exist solely as a vapor (gas). solely as a liquid, or as a mixture of both gas and liquid. Furthermore, these conditions can be expected to change over the lifetime of the reservoir is produced. The problem of measurement is raised to a new level of difficulty when compared to more traditional measurement of separated and stabilized gas and liquids.
4.3 APPROACHES TO WELL RATE DETERMINATION
The determination of flow rates of oil, gas, water, and other constituents can be accomplished in a number of ways. five of which shall be considered here:
Single-Phase Meters with Full Separation. The traditional method of measuring multiphase flow has been to separate the flow into either multiple single-phase streams (three phase separation) or a gas and liquid stream (two.phase separation). Single-phase meters are then used to measure the flow of the separated streams. This method ordinarily uses gravity separation in the fomi of a large vessel, but alternatively can employ a compact separator if total separation can be achieved. While these means of measurement can be accomplished using meters on a production separator, in the case of commingled flows from several wells a common embodiment is to use one or more specialized test separators periodically to test all the wells connected to a production platfonn. Because (I) such tests are by definition periodic, and (2) the length and path characteristics between the well and the test separator can vary between different wells, this approach inherently increases the uncertainty of the measurement.
Meters Used with Partial Separation. Recent years have seen the introduction of a number of innovative devices for phase separation. Although not as efficient at full separation as traditional devices, they offer certain advantages, such as smaller size and faster response For metering applications, they may enhance the use of multiphase and wet gas meters by creating more favorable conditions to measure the partially separated streams, i.e. gassy liquid and wet-gas streams.