Multiphase Flow Metering: Current Status and Future Developments

Abstract

Abstract The history of some of the early developments in multiphase flow metering is briefly described, leading to an explanation of the technical principles of the currently available technology. The impact on flow measurement of the flow patterns expected to be found in the offshore industry is discussed. The status of the current developments in relation to the target uncertainties required by end users is reviewed and the likely future technologies which may be applied to meet more stringent uncertainty criteria are described. Some of the practical problems of offshore and subsea deployment are explained, and the progress in resolving these problems described. 1. Introduction As the oil industry develops smaller and more marginal reservoirs the demand for compact and more cost effective solutions for production and monitoring of these wells has increased. The demand comes from companies working offshore, and particularly those in the North Sea. Many multiphase flowmeter development projects were instigated during the mid 1980's in response to this need and these development projects have made use of many differing technological approaches. The progress achieved by projects aimed at developing multiphase flowmeters for applications in the oil industry has been varied. Early approaches took one of two directions, either attempting to develop completely new technologies or adapt existing techniques utilised in single-phase flows. The limitations of attempting to adapt existing technology to more compact equipment were illustrated by multiphase flowmeters developed by Texaco and by NELISGS. Both of these projects made use of compact separation technology, but the development of each project was halted by problems associated with foaming and emulsion formation. Projects which have developed or applied new technologies have advanced from similar levels of accuracy to those using existing technology and now approach those of good test separators. Non-intrusive techniques, such as measurement of bulk capacitance or dielectric constant for derivation of water content, have advanced steadily and significantly over the past five years to the point where 'real world' applications have been made. In deed it is now true to say that multiphase flow metering is 'coming of age' with several new applications of multiphase meters recently reported, for both topsides and subsea installation. 2. Flow Conditions The multiphase flow conditions likely to be found at a flowmeter installation can cover virtually the full range of flow patterns. The prevailing flow pattern is governed by the proportions, physical properties and velocities of each phase present. Process conditions and orientation of the flow play a significant role in determining flow pattern as do the nature of the continuous and dispersed media. Characteristics of the mixture, such as the propensity to form emulsions or foams, the up- and downstream pipework configurations, and the 'history' of the flow also influence the flow pattern at a particular location.