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Advancing the approach to meter calibration.

Calibration is fundamental to the operation of any measurement system, in order to demonstrate its continued satisfactory operation to the regulatory authorities, says Craig Marshall, project engineer at NEL

In the oil and gas industry, an emphasis on environmental standards and fiscal accountability means that accurate measurement is a key driver, not only for the regulators that want to be assured of accurate fiscal accountability, but for the operators that also want to maximise business efficiency.

Over the past few decades, metering technology has advanced significantly. However, while flow meters can now record and store a vast amount of data, recalibrations are still both costly and labour intensive. This is particularly so when multiple meters are involved. To keep pace with technological change, and save valuable cost and time for the oil and gas industry, a more innovative calibration approach is now required.

In the UK, the Oil & Gas Authority (OGA, formerly part of Department of Energy & Climate Change (DECC)), has specific requirements which demand that flow meters are regularly calibrated, and these requirements are reflected in other regulatory requirements worldwide.

The OGA's requirements include that the operator must be able to demonstrate that, prior to its installation and on-site commissioning, the meter that takes fiscal measurements is fully operational. The operator must therefore designate within their organisation a responsible authority that will co-ordinate the testing procedure and advise the body of the identity of the representative(s) that will be present during the testing procedure.

For decades in the oil and gas industry, physical witness testing has been the normal method, but it is costly as calibrations may take days to complete. Not only does this take up staff time that could be more productively invested elsewhere in the business, but there are other escalating costs to take into account, such as staff accommodation and subsistence.

Flow meters being calibrated under laboratory conditions

A NEW APPROACH

Remote witnessing is a new approach to calibrations that could be adopted to tackle this issue. This is where Internet-based technology takes the laboratory to the world and no longer requires the world to come to the laboratory.

This means that those delegated to witness calibrations would not have to be physically present. While this new approach has obvious benefits for business efficiency, it would have no negative impact on the accuracy or traceability of calibrations. It could also reduce the cost associated with the physical time of the calibration process. For example, if an anomaly is identified during the calibration process, experts can remotely log in to resolve it. As their physical presence at a test is no longer required, answers can be found more quickly so that calibration downtime is minimised.

Technology could also be used to enhance the productivity of calibration laboratory operations and remove the need for post-processing of data. Currently a calibration is completed and then analysed to identify any problems. It is then repeated once those problems have been addressed. By monitoring the calibration against pre-set criteria in real time, this would allow issues to be immediately flagged and addressed during the original calibration.

As a system like this would store historical calibration data, the current performance could be compared with previous performance at similar conditions to check for shifts or drift between calibrations. Again, by setting performance criteria, unacceptable changes over time could be identified and addressed during the calibration. An exciting development of this capability is the use of historical calibration data to improve the quality of the individual instrument uncertainty values, used to develop an overall system uncertainty.

REALISTIC RESULTS

Currently, calibration is also completed in isolation, with no correlation between in-service operation and calibration periods. Using data, sourced from local Scada (supervisory control and data acquisition) systems, to monitor a meter's output against data gathered during the original laboratory calibration, offers the prospect of improving overall system management.

This new approach could move the calibration process from one based on pre-defined re-calibration intervals to one that is condition-based. This would reduce well operations downtime and save significant amounts of money on calibrating meters which are operating within required limits. In addition, remote access to calibration data from anywhere in the world at any time also positively impacts on business performance by enabling quicker, more accurate decision-making.

One of the oil and gas industry's key goals is to reduce operation downtime considerably, while saving money associated with calibrating meters, and meeting the requirements of government and regulatory bodies.

However, periodic calibration of meters remains typically calendar-based, with intervals often based upon a pre-programmed time period or on the volume of flow that has passed through the meter.

A new approach to the calibration of oil and gas meters is now a real possibility, due to the advancement of technology that is reaching a point where computer processing can be completed in real time. This means that calibration utopia is much closer, as thanks to trending of both calibration data, and data from the field, more accurate meter condition-based rather than time-based calibration can be achieved, significantly reducing both calibration and staff costs.

NEL, part of the TaCV SaCD Group, is a global centre of excellence for flow measurement and fluid flow systems and is the custodian of the UK's National Flow Measurement Standards. They provide services in key areas including measurement consultancy, meter development and calibration, erosion, environmental, CFD modelling, and training and knowledge transfer.

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Publication:Oil & Gas News
Date:Oct 26, 2015
Words:922
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