Although the story of the apple falling on Isaac Newton’s head isn’t true, Newton’s Law of Gravity is a very relevant lesson for the oil & gas operator. We know that gravity causes oil to stratify in a tank, which means the API and BS&W will vary at different levels of the tank (BS&W generally increases as you move toward the bottom of the tank).

Another relevant law in the testing and sale of oil is Newton’s Law of Centrifugal Gravity…

Sir Issac Newton

When computing the BS&W of a tank of oil, we use a centrifuge. And, we’ve put together a quick check list of things you should remember next time you’re determining a tank’s “shakeout”.

Tip 1: When samples are taken from the oil thief and placed in your centrifuge tube, neither the pumper (nor the purchaser) should run his centrifuge for more than 3 minutes.

Why? 

When oil is centrifuged for more than 3 minutes, valuable (read: saleable) matter like asphaltene and paraffin is centrifuged out of your sample… this works in the purchaser’s favor.

Tip 2: If you have access to a heated centrifuge, use it. Heated centrifuges keep paraffin in a liquid state (ie you get paid for it!).

The same logic is used behind the quick turn-around of a tank that has just been hot oiled. Not only does a quick sale keep the paraffin from congealing and causing problems in the tank, but acting fast will also enable us to collect money on our paraffin when it is removed from the system.

Tip 3: Although many crude oil purchasers use an electric centrifuge, it’s a good idea to make sure the purchaser’s centrifuge is properly calibrated. If the RPMs of the centrifuge are higher than stated, the seller will lose (also, keep in mind that if the RPMs are lower than stated, this works in the Operator’s favor).

RPM is calculated as follows:

RPM=257(RCF^(1/2)/D)

where

RPM = Revolutions per minute
RCF = Relative centrifugal force (should be between 500 and 800)
D = Diameter* measured between the tips of the tubes when rotating

*careful, we’ve seen lots of different sized testing tubes… if/when diameter is doubled, the centrifugal force is increased by 4X!

Tip 4: Finally, when trying to reduce water content below the required/contracted 1%, be sure to use “cold treating” chemicals. Also, try and bring the level of water just below the 1% mark… Anything below 0.8% or 0.9% is a waste of money (friends, we don’t get paid for a higher quality, more heavily treated crude ;-).

Got any other tips? Share the wealth! Leave ’em in the comments below…