Mud Gas DefinitionsFor definition purposes the level of gas in...

Mud Gas Definitions

For definition purposes the level of gas in the mud is due to one or a
combination the following:-

Background Gas
The general level of gas carried by the mud purely
as a function of circulating in open hole.

Drilled Gas
Gas which has entered the mud due to the actual
drilling of the formation. i.e. the gas contained in the
matrix of the rocks which have been drilled.

Connection Gas
The gas which enters the mud when a connection is
made due to reduction in hydrostatic due to loss of
ECD and due to swabbing while pulling back.

Swabbed Gas
The gas which enters the well due to swabbing . This
may be caused by tripping or by simulating tripping.

Trip Gas
The gas which enters the mud during a trip which is
measured after a trip has taken place.

Pump Off Gas
The gas which enters the mud due to turning off the
mud pumps and removing ECD from the
hydrostatic pressure on the bottom of the well.

It is imperative for pore pressure estimation that the gas levels in adrilling mud are correctly interpreted and the above definitions adhered to.

Pore pressure can only be definitively assessed on the basis of observations of trip gas , connection gas , swab gas and pump off gas.

If any of these are observed then pore pressure levels are close to mud hydrostatic.

Increasing background gas levels can indicate increasing pore pressure if correctly determined and analysed - it is important that drilled gas level
content of background gas is understood.