There is NEVER EVER just one gas composition one has to design for.
There is NEVER EVER just one temperature one has to design for.
There is NEVER EVER just one pressure one has to design for.
There is NEVER EVER one gas/oil ratio one has to design for.
There is NEVER EVER one gas volume one has to design for.

DESIGNERS that have received just one composition, one temperature, one pressure and one gas/oil ratio as basic design parameters may make the mistake to only design for these conditions.

S P E C I F Y    R A N G E S    B E T W E E N    W H I C H
I N P U T    A N D    O U T P U T    D A T A    M A Y    V A R Y .
(but do not specify the range too wide as that will cost money)

Day - Night, Summer - Winter, Dry season - Wet season, Surface temperature - Sea-bed temperature, Buried lines - Surface lines, Start up - Normal operation, and pressure drops (even in long pipelines) cause T E M P E R A T U R E    V A R I A T I O N S that will influence the design and operation of facilities. Your plant should not shut down every day in summer for three month in a row between 13 and 14.00 hours because the propane does not condense any more!! But you may want to accept a shut-down once a year when that temperature is at maximum possible peak, as designing for that peak would have been very costly!! FIND THE OPTIMUM !!

BE ALWAYS PREPARED FOR CHANGES not only in temperature. It is unavoidable that changes take place particularly in the early stage of a project. Anticipate potential changes in gas/oil ratios, volumes and composition. Estimate the importance of changes.

Even after freezing the data one should be able to make changes provided the project manager agrees. He must always check whether it is economic to do so as the change will 9 out of 10 cases cost money and time. Consequential losses due to delays are often very high.

Variations in temperature do influence crude viscosity and therefore can cause decreased oil flow rates at night, so does a tropical rain storm. Because of reduced oil flow rate and lower separator temperature the (associated) gas production can be considerably lower in volume than average and different in gas composition and molar mass. This is very important for centrifugal compressors!! Therefore, as a designer, get up early and gather data at the site before you design your facilities and do not go only at the easy hours of the day but also at 03.00 AM.

The phenomenon mentioned above is particularly true for heavy oil where the casing is connected with the flow line. The gas production from the casing can even stop at night when the back-pressure in the flow line increases. At 10 AM however a surge of gas production, factors more than average, can be expected. (Venezuelan Laguna crude was an example).

Surface Natural Gas Liquids (NGL) lines can also cause tremendous surges as a result of day-night temperature variations. At night the gas-part of the line content condenses and reduces the end of the line output significantly (in Iran the flow stopped for some hours at night and at 10 AM the flow increased manyfold). A proper design pressure will solve this problem.

When starting up and shutting down the facilities the

P L A N T    S H O U L D    A L S O    B E    O P E R A B L E ! !

G O    I N    Y O U R    M I N D    T H R O U G H    A L L    T H E

S T E P S    F R O M    A    C O L D    ( O R    H O T )    A N D

N E W    P L A N T    T O    N O R M A L    O P E R A T I N G

C O N D I T I O N S    A N D    B A C K    T O     A    S H U T -

D O W N    S I T U A T I O N.