Companies extracting gas and oil from the North Sea use a shared network of sub-sea pipelines to carry their products to dry land. So they need to know what they are putting into the pipelines at the wellhead in order to lay their claim when the oil comes ashore.
The flow from an oil well consists of a mixture of crude oil, natural gas and water, all of which move at different rates. Proportions vary from field to field and over the life of a field. The flow may contain additives, such as corrosion inhibitors.
At the moment, measuring the amount of oil and gas involves diverting the flow from production for up to eight hours, separating out its constituents and measuring each one. Typically, this is done once a month. Now AEA Technology, the contract research arm of the United Kingdom Atomic Energy Authority, has developed a meter, mounted outside the pipeline, that can measure and analyse its contents without interrupting the flow.
The meter sends out a pulsed neutron beam that counts passing hydrogen, carbon and oxygen atoms. A short burst of radiation then 'activates' the oxygen atoms, enabling the meter to track them and measure the velocity of flow through the pipeline. By combining these measurements, the composition and rate of flow can be determined. The meter will work through steel pipes up to 4ins thick.
'AEA's meter will help improve the economics of marginal fields by reducing the investment and disruption required to measure oil flow,' says Peter Surridge, project manager at AEA.
He estimates that the neutron beam meter would cost pounds 10m to install and run for 10 years, compared with pounds 25m for the existing type of meter.
The meter would improve safety, because it could be installed on the sea-bed and send back readings automatically. In addition, it would provide more accurate measurements than the current method, simplifying management and accounting for oil flows within the complex pipeline networks in the North Sea.
Oil production companies also need information on flow from the well to manage extraction. The ability to recover the maximum amount of oil and gas from a field is a function of how it is exploited.
'Using the neutron beam meter, production could be tweaked each day rather than just being adjusted monthly,' Mr Surridge says.
AEA Technology has developed the meter as part of a move to diversify away from the nuclear industry. According to Mr Surridge: 'The nuclear industry is interested in detecting and monitoring things that are not accessible, and the North Sea oil industry has similar problems.'
The development of the meter has been funded by two oil companies and the DTI's Offshore Supplies Office. AEA Technology is at present building a laboratory-scale oil rig at its Harwell site to test the flow meter. Mr Surridge says these tests will be followed by a field demonstration programme in the North Sea.