Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering.
Over the last decade, the development, evaluation, and use of multiphase-flow-metering (MFM) systems have been a major focus for the oil and gas industry worldwide. Many alternative metering systems have been developed, but none can be referred to as generally applicable or universally accurate. Both established and novel technologies suitable to measure the flow rates of gas, oil, and water in three-phase flow are reviewed and assessed within this framework. Technologies already implemented in various commercial meters then are evaluated in terms of operational and economical advantages or shortcomings from an operator's point of view. The lessons learned about the practical reliability, accuracy, and use of available technology are discussed. As operators now realize, use of MFM systems (MFMSs) is essential in exploiting marginal fields. A new approach to flow assurance, deepwater developments, downhole/seabed separation systems, and wet-gas fields is foreseen. The authors suggest where additional research to develop the next generation MFM devices will be focused to meet the as yet unsolved problems.
The first commercial MFMSs appeared approximately 10 years ago, as a result of several multiphase metering research projects in the early 1980s. The driving force to develop MFM technology was the forecast decline of production from the major North Sea fields, accompanied by the necessity to tie backfuture smaller discoveries to existing infrastructure. Increasing gas and waterfractions, inherent in a mature producing province, would create more-unstable flow conditions in existing production facilities and require more-flexible multiphase solutions.
In less than a decade, MFM has become accepted in the field and is beginning to be considered as a primary metering solution for new field developments.
Within the oil and gas industry, it is generally recognized that MFM could lead to great benefits in terms of the following.1,2,3
The use of MFMs reduces the hardware needed for onshore, offshore topside, and offshore subsea applications. Of primary importance is the removal of a dedicated test separator for well-testing applications. Use of MFM (with its smaller footprint) for topside applications minimizes platform space and load requirements for well-testing operations. Finally, costly well-testing lines can be stripped from the production facilities, which may be of vital importance for unmanned locations, deepwater developments, and satellite fields.
Conventional test separators are expensive and require much time to monitor each well's performance because of the time required to reach stabilized flow conditions. It is particularly important in deepwater developments, because of the exceptional length of the flowlines. In such cases, production from individual wells connected to the same manifold may be monitored by use of a dedicated test line to avoid shutting down all the wells, then testing them one by one (with considerable production loss). However, the expense of a separate flowline may be prohibitive, hence the advantages of MFM installed in the subsea manifold. Test separators have an accuracy between approximately 5 and10% (currently achievable with MFMSs) but require regular intervention by trained personnel and cannot provide continuous well monitoring. Another disadvantage of conventional well testing with conventional separators is that well performance suffers after shutdown cycles related to well testing. Often, wells tested on a regular basis require more-frequent workovers to maintain their production rates.
Use of MFMSs for exploration-well testing4 provides satisfactory flow measurements without separation of the phases. It is claimed that they can be used to monitor the well during its cleanup flow (traditionally, this flow information is lost because the well stream is not directed through the test separator). Added value is represented by improved control of the drawdown applied to the formation, the pressure transient, and shortened flow periods.
MFMSs provide real-time, continuous data to enable operators to characterize field and reservoir performance better and react faster. Changes in gas/oil ratio or water cut can be detected and quantified immediately, where as traditional test separators provide information about only cumulative volumes at discrete points in time.