In a meeting with engineers from several different departments the number 30 MILLION CUBIC METRES PER DAY was mentioned in relation with the Liquefied Natural Gas (LNG) Plant the oil company was planning to build.

The PETROLEUM ENGINEER, who was supposed to tell how many years the gas production rate could be maintained before another field had to be hooked up, was thinking of a daily average production rate of 30 million normal cubic metres at 0 C and 101325 Pa (as his previous assignment was in the Netherlands) and multiplied the 30 million by 365 to get the yearly average number.

The HEAD OPERATIONS, who was an experienced engineer, thought that it was an average number and immediately re-calculated the number into 35, being stream-day capacity in million cubic metres at standard conditions at 15 C and 101325 Pa (a stream-day capacity is the capacity of the facilities when every thing is up and new) as this represents the capacity of the facilities he would have to operate.

The PROCESS ENGINEER in charge of the field facilities thought that a stream day capacity in cubic metres at standard conditions was meant, as that is what he needed for the design of the field facilities. He also knew that the gas contained 1 mol% water vapour and 2 mol% heavy hydrocarbons that would be knocked out in the field and that 7 for the into pipeline gas volume.

The PIPELINER, who had come the month before from a country using cubic metres at standard condition, had also 15 C and 101325 Pa in mind and added 10% to cater for calculation uncertainties. The number of 33 was thereafter used by him.

The LNG PLANT DESIGNER of the front end part of the LNG plant, who had to give a number to his cryogenics specialist knew that the gas contained 7 mol% CO2 and therefore used the number 28 but by then it was not clear which cubic metre was meant.

The very experienced LNG plant designer in charge of the cryogenic part of the facilities knew that the plant throughput was a matter of capacity of one, two or three trains. He knew that one train could handle 8 million standard cubic metre and that one should always calculate in multiples of 8 to get an optimum LNG scheme. The 8 million though was gas excluding water, H2S, CO2, and heavy hydrocarbon. Therefore 24 million was the number he used but whether this was in line with the 30 million mentioned was not clear to him Also did he know that a decision in an early stage had to be made on whether the gas would or would not contain propane and butane or whether these products were produced as LPG in the front end of the LNG plant.

The MARKETER, who only thought in tons per annum was of course at a complete loss as to how much LNG he could sell.

All numbers : 30, 35, 27, 33, 28 and 24 started living their own life.

When you talk about volumes then take account of : Average versus stream day capacity, m³ (standard) versus m³ (normal), design margins, removal of condensates and water in field facilities, slug-catcher free liquids, water and CO2 and H2S removal in the LNG plant, fuel uses, LNG plant storage tank losses, ships losses, down-time and fouling of equipment, varying heat content, varying composition in time.

THE MORAL IS THAT EVERYBODY SHOULD KNOW WHERE YOU ARE TALKING ABOUT WHEN YOU TALK QUANTITIES AND MAKE IT VERY CLEAR FROM THE START WHAT YOU MEAN.