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|+ {{table number|1}}Types of gas that result from the drilling process
 
|+ {{table number|1}}Types of gas that result from the drilling process
 
|-
 
|-
! Type of Gas
+
! Type of Gas || Description
! Description
   
|-
 
|-
| “Zero” gas
+
| “Zero” gas || Gas present in the mud circulating system when the bit is off-bottom and there is no vertical movement of the drill string. This reading results from the liberation of gases from the mud system or from the recycling of previously encountered gases in the wellbore. Although a “zero” gas value will constantly vary, it acts as a starting point for evaluating any subsequent formation gas shows.
| Gas present in the mud circulating system when the bit is off-bottom and there is no vertical movement of the drill string. This reading results from the liberation of gases from the mud system or from the recycling of previously encountered gases in the wellbore. Although a “zero” gas value will constantly vary, it acts as a starting point for evaluating any subsequent formation gas shows.
   
|-
 
|-
| Background gas
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| Background gas || Gas that reflects the geological character of a consistent lithology. Background gas readings incorporate gas contributions due to the formation, but also those included as zero gas. Gas from the formation is due to the crushing of the rock as it is being drilled and typically has a low volume. These gas readings are plotted on the mudlog as background gas and represent the relative baseline against which all other gas shows are compared.
| Gas that reflects the geological character of a consistent lithology. Background gas readings incorporate gas contributions due to the formation, but also those included as zero gas. Gas from the formation is due to the crushing of the rock as it is being drilled and typically has a low volume. These gas readings are plotted on the mudlog as background gas and represent the relative baseline against which all other gas shows are compared.
   
|-
 
|-
| Liberated gas
+
| Liberated gas || Gas that is produced by the drilling process due to the crushing of the rock formation by the drill bit.
| Gas that is produced by the drilling process due to the crushing of the rock formation by the drill bit.
   
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|-
| Connection gas
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| Connection gas || Formation gas that enters the wellbore while drilling and circulation are halted to make a connection. For this condition to occur, the contributing formation must be underbalanced by the mud system at some point within the borehole.
| Formation gas that enters the wellbore while drilling and circulation are halted to make a connection. For this condition to occur, the contributing formation must be underbalanced by the mud system at some point within the borehole.
   
|-
 
|-
| Produced gas
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| Produced gas || Formation gas that enters the wellbore while drilling and circulating. This gas represents an underbalanced formation and, if left alone, will cause a blowout.
| Formation gas that enters the wellbore while drilling and circulating. This gas represents an underbalanced formation and, if left alone, will cause a blowout.
   
|-
 
|-
| Trip gas
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| Trip gas || Formation gas that enters the wellbore when the drill string is being “[[trip]]ped” or pulled out of the wellbore. The contributing formation must be underbalanced at some point within the wellbore; such underbalance is due to the “swabbing” effect caused by pulling the drill string out of the hole.
| Formation gas that enters the wellbore when the drill string is being “[[trip]]ped” or pulled out of the wellbore. The contributing formation must be underbalanced at some point within the wellbore; such underbalance is due to the “swabbing” effect caused by pulling the drill string out of the hole.
   
|-
 
|-
| Recycled gas
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| Recycled gas || Gas that has been previously contributed to the borehole and not completely removed from the mud circulation system by surface equipment (such as a gas trap or degasser). Such gases that remain in the mud system are pumped back down the borehole to be subsequently re-recorded by the gas detection equipment. This recycled gas can usually be recognized because the “show” will be detected one full circulation cycle later than originally encountered and will appear more diffuse in character.
| Gas that has been previously contributed to the borehole and not completely removed from the mud circulation system by surface equipment (such as a gas trap or degasser). Such gases that remain in the mud system are pumped back down the borehole to be subsequently re-recorded by the gas detection equipment. This recycled gas can usually be recognized because the “show” will be detected one full circulation cycle later than originally encountered and will appear more diffuse in character.
   
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