help with engineering/math riddle

[Zero Cool]

I received an email from a man who uses a unique message in his signature. It is in the form of a math equation. To the left of the equal sign is S_W. I did some brief checking online and did not find an equation using S_W. I don't want to publish the entire equation so that someone else solves the message before me. Any help would be appreciated.

Possible clues:

1. he is a "petrophysical advisor" who works with an engineering firm

2. the equation is next to a picture of an oil derrick

 

If you have an idea what the equation might be used for but need an extra hint, I will provide more information.

Thank you.

[Sensei]

If it is physical equation you can figure out units used in it..

Like e.g. E=m_ec²

m_e has unit kg

c has unit m/s

Therefore c² has unit m²/s²

so E has unit kg m²/s²

 

Edited June 4, 2019 by Sensei

[Endy0816]

Possibly a reference to Entropy.

[Zero Cool]

Thank you, I will look into those suggestions.