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.
GDN Price at posting:
0.0¢ Sentiment: Buy Disclosure: Held