Changes

Samples of gas must generally be extracted from the drilling mud by the gas trap. The gas trap is a metal box immersed in the shale shaker possum belly, preferably in a location of maximum mudflow rate ([[:file:mudlogging-gas-extraction-and-monitoring_fig1.png|Figure 1]]). Ports in the lower part of the trap allow mud to enter and leave the trap. An agitator provides both pumping and degassing of mud passing through the trap. Gas evolved from the mud is mixed with ambient air in the upper part of the trap and is then drawn through a vacuum line to the logging unit for analysis ([[:file:mudlogging-gas-extraction-and-monitoring_fig2.png|Figure 2]]).

Samples of gas must generally be extracted from the drilling mud by the gas trap. The gas trap is a metal box immersed in the shale shaker possum belly, preferably in a location of maximum mudflow rate ([[:file:mudlogging-gas-extraction-and-monitoring_fig1.png|Figure 1]]). Ports in the lower part of the trap allow mud to enter and leave the trap. An agitator provides both pumping and degassing of mud passing through the trap. Gas evolved from the mud is mixed with ambient air in the upper part of the trap and is then drawn through a vacuum line to the logging unit for analysis ([[:file:mudlogging-gas-extraction-and-monitoring_fig2.png|Figure 2]]).

Inside the logging unit, the gas-air mixture is drawn through a sample chamber containing a heated platinum filament forming one arm of a Wheatstone bridge circuit. Catalytic combustion of hydrocarbon gases at the filament (the so-called hot wire) further heats the filament, causing an increase in its electrical resistance. This change in resistance unbalances the bridge, causing an electrical current to flow in proportion to the resistance change and a resulting concentration of gas. The current is displayed by deflection on a milliammeter or may be used to scale the meter or recorder in terms of percentage or “gas units” by calibrating the hot wire periodically with a gas-air mixture of known concentration. A second hot wire detector, set at a lower temperature, allows discrimination of ''total gas'' (all combustible hydrocarbon gases) from ''petroleum vapors'' (combustible hydrocarbon gases other than methane). This aids in identifying the types of hydrocarbons in place (that is, oil or gas).

Inside the logging unit, the gas-air mixture is drawn through a sample chamber containing a heated platinum filament forming one arm of a Wheatstone bridge circuit. Catalytic combustion of hydrocarbon gases at the filament (the so-called hot wire) further heats the filament, causing an increase in its electrical resistance. This change in resistance unbalances the bridge, causing an electrical current to flow in proportion to the resistance change and a resulting concentration of gas. The current is displayed by deflection on a milliammeter or may be used to scale the meter or recorder in terms of percentage or “gas units” by calibrating the hot wire periodically with a gas-air mixture of known concentration. A second hot wire detector, set at a lower temperature, allows discrimination of ''total gas'' (all combustible hydrocarbon gases) from ''[[petroleum]] vapors'' (combustible hydrocarbon gases other than methane). This aids in identifying the types of hydrocarbons in place (that is, oil or gas).

==Extraction efficiency==

==Extraction efficiency==