Subject: Return Gas
From: [email-masked]
To: [email-masked]
Cc: [email-masked], [email-masked], [email-masked]
Date: Thu, 7 Jun 2001 06:25:16 -0700 (PDT)

Les/Gene,	

With regard to determining the BTU's of Return Gas for custody transfer, I am not aware of any facility that actually measures the flow of gas to the ship.  Such low pressure flow meters would not provide reliable readings.  Other companies, such as PERTAMINA's CIF Trade with Japan, account for return gas by measuring the volume of LNG offloaded from the ship, then calculating the BTU's of the gas returned to the ship based upon measured temperature and pressure on the ship at the end of ship unloading, and assuming a composition equivalent to 100% methane.   Actual return gas will be a composition containing N2, C1, and C2, and probably have a GHV slightly less than 100% methane, depending upon the amount of Nitrogen in the LNG in storage. Presently, SLNG does not have any sample points for boiloff gas, and no plans for installing any.

With regard to the FERC Tariff Calculation, the Return Gas is accounted for in what is termed, LAUF (losses and unaccounted for) gas, an amount determined by differential storage volume.  When comparing expected BG Return Gas vs Enron Return Gas, the volume of Return Gas should be directly proportional to the volume of gas delivered, as pressure and temperatures at the end of unloading should be essentially equivalent (pressure must be sufficient to allow LNG from the manifolds to drain back into the tanks). Willful operator intervention would likely have to take place to significantly increase the pressure and therefore the mass of the return gas. Therefore, it is recommended that we not press for a special accounting for the Return Gas in the Definitive Agreement with El Paso.  For accounting purposes, we should also track the Return Gas for Enron deliveries, just in case it does become an issue.  Should either EPME or BG push for specific Return Gas accounting, we should not oppose, as it is easily calculated utilizing measured volume, temperature, and pressure with an composition of assumed 100% methane.

Regards
James