“Connection Gas” is distinct increase of gas above a normal background gas level when bottom up occurs after a connection. If you see a small high gas peak in short period of time and when you calculate back you will see that it comes from every connection, you can suspect that this is the Connection Gas.
While we are drilling, there is a stable gas reading that is not connected with either bottoms up gas or drilled gas is generally called “Background Gas”. The background gas always shows every time while drilling and it is not a sign of considerable risk to well control situation. Nevertheless, we must always check changes in background gas value because it is able to help recognize underbalance situation while drilling, especially drilling into high pressure zone.
Remember – PLEASE ALWAYS KEEP TRACKING YOUR BACKGROUND GAS
Reference book: 
Well Control Books
While drilling, there will be a certain amount of the gas in cuttings entering into drilling fluid when we drill through porous formations that contain gas. The gas showing on the surface due to drilling through formations is called “Drilled Gas”.
When gas from the cutting comes into drilling fluid, it will expand as it is circulated out of hole, hence, you will see the gas from the monitors at the flow line. Even though we have overbalance hydrostatic pressure exerted by mud column, gas showing on the surface by this mechanism always happens. You cannot rise mud weight up to make it disappear.
Shut in Well Procedures
The shut in procedure must be developed and practiced for every rig activity such as:
• Shut in while drilling
• Shut in while tripping
• Shut in while running casing, tubing, completion, etc.
• Shut in while performing workover operation
• Shut in while logging
• Shut in while performing drill stem test
What is the main reason why we need to have the shut in procedure and frequently practice it?
This is the second part of the possible kick indications that I would like to share with you.
Decrease in d-Exponent Value
Normally, trends of d-Exponent will increase as we drill deeper, but this value will decrease to lower values than what we expect in transition zones. By closely monitored d-Exponent, d-Exponent chart will be useful for people on the rig to notify the high pressure transition zones.
Read and understand about d-Exponent and learn how to calculate d-Exponent and normalized d-Exponent (corrected d-Exponent)
