Natural gas is bought and sold based on the level of its energy content. Gas transmission plays a critical role in ensuring these natural gas resources are safely transported, measured, and recorded before reaching their final destination point. Increasing variations in the sources of natural gas, such as unconventional shale gas, is making it harder to ensure that the gas entering the network meets the company’s specifications and that the assumptions regarding metering conditions always hold true. If the gas is not analyzed properly or if the gas quality changes dramatically, the accuracy of the flow measurement and energy calculations will be compromised. If the flow and energy measurements on the inlet and outlet of the transmission network do not match, the lost energy across the network results in lost revenue.
Proper calibration can yield savings of 0.4% over the typical 25-year life of a large natural gas transfer metering system, equaling $120-330 million of extra revenue for the system examined, depending on commodity pricing. Determining early that meters are properly calibrated is key to realizing these savings.
Traditional methods for auto sampling with online Chromatographs (GCs) make use of pressure reduction stations in order to collect a sample to perform an online analysis. Due to the required pressure reduction, there is a potential for condensation as described by the gas specific pressure/temperature phase boundary diagram. As soon as condensation occurs, the sample cylinders collect two‐phase flow and the sample can be considered unrepresentative. Moreover, it is not just the bulk of the gas stream that should be considered, but also the individual components in order to prevent a degrading of the sample being analysed. Apart from the amount of training and expertise required to operate an online GC, they tend to have a high failure rate and require frequent re‐calibrations on a daily or weekly basis in order to remain accurate within the desired operational levels.
Using spectroscopy can eliminate the need for pressure reduction by arranging the light to enter and exit the gas at pipeline pressure. Also other then cleaning, little maintenance or calibration will be required.
- LNG metering
The nature of liquefied natural gas (LNG) raises many challenges when it comes to the measurement and reporting of its composition for the purpose of ship loading and unloading. LNG’s extreme temperature, and the difficulty with keeping it in liquid form, introduces unique sample-handling issues, while the batch-handling operation makes reporting difficult. At the same time, the accuracy and reliability of the LNG measurement is uniquely critical since the loading and unloading operations are highly time-sensitive with no second chances. Delays in loading or unloading because of measurement issues are not tolerable, when the costs of keeping a ship in port are considered. For example, one LNG operator had two measurements systems fail right before the docking of a large tanker. The problem resulted in significant penalties. Additionally, disparities in the measurement are often not known until after the unloading is complete at the destination and comparisons to the load report are made.
Gas Chromatographs need to calibrated every time they are turned on, which happens only periodically in LNG applications. Spectroscopy based instruments don’t need frequent calibration. To use a GC the gas must be vaporized. The vaporization process must start with pure liquid phase and must add sufficient heat to the liquid phase to convert to the gas phase without causing sample fractionation. It will be possible to pass the light through a liquid sample thus not needing vaporization and allowing on line continuous measurement.
- Water in Oil
Stable water-in-oil emulsions may form during the production of crude oil, as co-produced water is mixed with the oil from reservoir to separation facilities. Such emulsions introduce technical challenges, as they must be resolved to provide the specified product quality. Asphaltenes and resins indigenous to the oil are acknowledged as the most important components in respect to stabilization of the interface against coalescence. Fine solids may also contribute to the stabilization, as may the presence of naphthenic acids. Combined, this creates a complex picture of several contributing mechanisms, and it is established that the pressure conditions will influence the behavior of active components and the properties of the interface. In order to successfully mitigate the problems of stable emulsions, a thorough knowledge of component properties, behavior, interactions and effect on water/oil interfacial properties must be developed for pressures ranging from ambient to high.
Water has a distinctly different spectral signature then hydrocarbons, therefore it will be possible the use spectroscopy to measure the amount of water by passing the light through a thin sample of the mixture.