This paper reviews multiphase flow meter development for application in the oil industry against basic theoretical concepts involved in the flow measurements.
Several metering concepts for the mass flow rate measurement of oil/water/gas mixtures in oil pipelines have been proposed. Determination of components, volumetric fraction is an integral and essential part of such a meter and reported methods of its measurement are also reviewed here.
Although a number of multiphase flow concepts have been patented and a number of prototype models built. no patented and a number of prototype models built. no extensive field trials of a multiphase flow meter have been reported.
Improved reservoir management and affordable exploitation of marginal offshore fields are some of the tangible consequences of the on-line metering of pipeline multiphase flows. pipeline multiphase flows. The current multiphase flow metering field practice is first to separate the flow into its individual components (phases). Following flow separation, gas flowrate is measured and flared or recompressed for enhanced oil recovery or transportation to the processing plant. Water flow rate is also measured and processing plant. Water flow rate is also measured and is usually disposed of close to, or at the separation site, while metered crude is pumped to the processing plant often in a separate line. plant often in a separate line. Separation close to a well enables appropriate allocation control and monitoring of the excisable production rates of each well. The need for production rates of each well. The need for separators, test and production lines, in addition to separate flow monitors, constitute considerable capital cost investment which often renders marginal fields uneconomic to exploit.
Multiphase flow meters installed in each well riser close to or at the top of the 'Christmas tree' would considerably simplify the flow transportation and result in significant reduction of capital costs. In some offshore installations, they would help render obsolete the costly production platforms.
These, among other economic and operational incentives, have led to world wide research into ways to monitor flowrates of multi-component pipeline mixtures. On-line flow meters capable of simultaneously measuring flow rates of oil, water and gas have been under intense development in a number of countries including Norway, UK, USA, Japan, Canada and Australia. This paper reviews some of these developments. paper reviews some of these developments.
Multiphase mass flow rate measurement essentially involves, for a given total volumetric flow rate, the determination of volumetric flow fraction and densities of the constituting components. However, the volumetric flow rate, if not given, is often determined from flow velocity measurement and knowledge of pipe geometry.
The analytical background for the multiphase mass flow measurement is developed below. For mass flow rate M, volumetric flow rate Q for oil, water and gas (o, W, g),
and since M = Q
then, M = oQo + wQw + gQg