API Publ 2566:2004 pdf download
API Publ 2566:2004 pdf download.State of the Art Multiphase Flow Metering.
It must be noted however that changes in water salinity also affect other volume fraction determination methods and has to be addressed in any multiphase meter. A Multiple Energy Gamma Ray Absorption (MEGRA) measurement technique has been developed (11-21) to compensate for the salinity changes.
Most dual-energy gamma ray methods use a single radiation source. The “single beam” method has the limitation of being flow-dependent (11-24). Thus, the component fractions derived from the attenuation equation will only represent the actual flow cross section if the oil, water, and gas are “homogeneously” mixed. Reference 11-32 describes the development of a dual energy fraction meter that is flow regime independent. Scanning the flow stream and processing the data at very high rates achieve the flow independence feature.
7.3- MEASUREMENT OF COMPONENT VELOCITIES
Venturi devices and the cross-correlation technique are the most commonly used tools for component velocity measurements. When the flow is well mixed — i.e. using a mixing chamber or device — the Venturi meter has been used to measure the bulk velocity of the mixture. For non-homogeneous flow the Venturi meter can also be used if the gas fraction is known (11-42).
The cross-correlation technique is used either with the Venturi meter or by itself to measure the component velocities. The principle of this technique is shown schematically in Figure 6.
Two sensors, separated by a distance L, are used to measure the variation in some properties of the flowing mixture. Thus, each sensor can be used to measure the variation in density or dielectric properties. The time delay between the outputs of the two sensors seeing similar variations in the fluid properties can be calculated by a correlation function (Rxy(t1) measured over a period of time. The time lag (Tm) at which this correlation function is maximized – i.e. both locations show similar variation in the property – is taken as the transit time of flow between the two sensors. The velocity is then determined by dividing the distance separating the two-sensor (L) to the time lag The accuracy of this technique depends on the validity of the assumptions used to derive the velocity of a particular component in the flow stream from the velocity calculated by the correlation function (11-24).
The cross-correlation method measures the velocity of the dispersed phase in the mixture (11-24). In the case of oillwater/gas mixture, the liquid (oil and water) may be travelling at a different velocity than the gas. This difference in the velocity (slip) must therefore be taken into account. Otherwise, the velocity measurement by cross-correlation becomes inaccurate.
Multiphase measurements systems used in production operations utilize a diverse range of equipment from full three-phase conventional separators to inline multiphase meters that consist of a spool piece with no separation. From the perspective of users, these systems have one common purpose — i.e. to provide accurate flow rates for oil, water and gas. In each system, however, the processes schematically shown in Figure 7 must occur. The processes shown in Figure 7 consist of some type of fluid conditioning, mixture density determination, mixture rate determination, mixture composition determination, and application of a flow model. These functions can be supplied by an instrument or by an assumption in a model (111-4).
The volumetric fraction and component velocity measurement techniques described in sections 8 and 9 are commonly used in these systems. Several references, listed in Appendix 2. have attempted to categorize the multiphase metering systems (11-4, Il-il, 11-18, 11-24, 111-4, Xll-3). Terms such as on-line and off-line have been used to describe various systems. There is considerable confusion and even an argument that the term multiphase meter should only be applied to systems that can make multiphase measurements without the separation process. The following dassification of the multiphase metering systems is proposed as a way to develop a commonly accepted language for multiphase metering. It is proposed that we use the following definitions to designate three types of multiphase metering systems.
