How to improve measurement systems

SHORTCOMINGS OF METERING CONTROL SYSTEMS

1: METERING SUPERVISORY COMPUTERS ARE JUST ANOTHER HMI

Metering control systems consist of flow computers, a supervisory computer and sometimes a PLC. Most metering control systems are built like any other control system and provide a graphical user interface for the daily operation of the metering system. Other users (than the operators) may occasionally use the system to look at the actual process data and to access historical reports. But what about all the other activities that are necessary to ensure accurate and reliable custody transfer of oil and gas assets? Why isn’t a metering control system used to monitor and control the quality of measurement?

2: SMART METERING DEVICES ARE NOT USED TO THEIR POTENTIAL

Flow meters, transmitters, process analyzers and proving systems are all becoming smart devices. They are able to check their own health, to communicate with other devices and more and more provide additional fluid property information such as temperature, density and velocity of sound. In most custody transfer systems this wealth of information is not used at all leaving the responsible metering staff unaware of potential issues. Metering control systems only acquire process data that is required for the daily operation from the metering equipment. In the best case the metering control system generates an alarm that something is wrong (or might be wrong) with the measurement, which requires a specialist to travel to metering site and to connect into the metering device to troubleshoot the issue. Why don't metering control systems provide remote access to this wealth of information?

3: MEASUREMENT DATA GETS LOST OVER TIME

Measurement data is not only about the meter ticket as printed by the flow computer. As clearly defined in API MPMS Chapter 21.1 and 21.2 measurement data is about both the quantity and quality of measurement.  Besides of the batch, daily and hourly reports measurement data involves changes to configuration settings, re-calibration of metering equipment and any activities and events that relate to the metering system. Flow computers store their measurement data for a particular period e.g. 3 months.  After the retention period the data gets flushed from the flow computers and is lost forever. Measurement data that is not captured by the flow computers is either not recorded at all or stored separately from the metering control system in logbooks and computer files. Metering control systems interact with all metering equipment and the users, so why don't they properly acquire and archive all this crucial measurement data?

4: QUALITY OF MEASUREMENT IS UNKNOWN MOST OF THE  TIME

Flow measurement is a continuous process. Metering systems generate measurement data 24/7. Measurement errors can lead to serious repercussions and the accuracy of the measurement is a continuous concern of the stake holders. Unfortunately, the verification of most field instrumentation is a costly and labor-intensive activity and therefore only performed a few times a year. For the same reason metering audits are scheduled even more infrequently. A smart metering control system can continuously monitor the health of metering equipment and validate measurement data in real-time, e.g. by cross-checking redundant and parallel measurements and applying statistical control. By applying self-diagnostics on both device and system level the control system can warn the user in real-time for (upcoming) measurement issues.

5: CORRECTION FOR ERRORS IS COSTLY AND INACCURATE

Depending on the financial impact a measurement error may or may not require a correction to the meter ticket. When the issue is revealed only after some time, e.g. at a calibration or an audit, then faulty meter tickets may already have been used for one or more invoices that were sent to the customer. It may take several days before measurement analysts have been able to quantify the measurement errors and to correct all the individual meter tickets. The accuracy of the correction very much depends on the availability of additional information, the resolution of the quantitative data and the applied correction method. In fact accurate correction is only possible with redundant measurement information, high-resolution metering data and a sophisticated correction method. All data required for corrections can be acquired and stored by the Metering Control System, so why not use this system for automated error corrections?

Spirit IT's solution: Measurement data from well to awareness