PR-015-09603-R01 LNG Measurement Uncertainty Analysis

The U.S. natural gas industry is expected to import increasing amounts of liquefied natural gas (LNG) in the near future. When an LNG tanker ship arrives at an LNG terminal, the quantity of LNG transferred to the terminal is found by measuring the changes in static volume within the ships tanks. The LNG volume is inferred from measurements of the liquid height, along with tables of tank characteristics predetermined by a method known as “tank strapping.” Once transferred, the LNG is then regasified at the terminal before being sent to limited distribution companies (LDCs) or power plants. There is concern that the basis for uncertainty estimates in the energy content of the transferred LNG (typically taken as ±0.5% to ±0.6%) may underestimate the true magnitude of measurement uncertainties. Dynamic methods of liquid flow measurement, gas flow measurement, product sampling, and composition determination used elsewhere in the energy industry may reduce the measurement uncertainties at the LNG terminal, as they relate to terminal balances. Measurement uncertainties for conventional meters and equipment placed into LNG service may lead to more accurate LNG measurement and reduced lost-andunaccounted for (LAUF) quantities at receipt terminals. This report describes research to evaluate the measurement uncertainties associated with both static and dynamic methods of determining LNG volumes and energy content delivered to, processed by, and shipped from, LNG terminals. This was performed to determine whether dynamic methods are potentially more effective than existing static methods for accurate measurements and LAUF determination at LNG terminals. Another objective of the research was to establish which methods offer the most potential for reducing custody transfer measurement uncertainty and LAUF within LNG receipt terminals.