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Appendix B

Contamination check for mud-gas monitoring


Standard gas

We analyzed organic component gas using a GC-NGA, a MCIA, and a PGMS. The standard gas contains methane, ethane, propane, iso-butane, n-butane, and nitrogen. The concentration of each component except for nitrogen is 1%.


Standard gas was connected at the inlet of the mud trap (Fig. BF1). Secondary pressure of standard gas was slightly higher than atmospheric pressure. Pump settings in the mud-gas monitoring laboratory are shown in Table BT1.


MCIA and PGMS were used to analyze standard gases. GC-NGA was applied in the same manner as for mud-gas monitoring (measuring with FID and TCD) during the contamination check.


Gas flow rate injected into devices

During the contamination check, gas flow into the PGMS was controlled at 50 mL/min. For GC-NGA, MCIA, and the radon analyzer, gas flow rate was confirmed (Table BT2). With the pump set at 0.5 L/min, gas flows for devices except for PGMS were not high enough.

Standard gas measurement

To evaluate contamination, standard gas was directly sampled and measured by MCIA and PGMS. These results are shown as a red line in Figure BF2.

MCIA. Standard gas was taken with a gas-tight syringe and measured in syringe injection mode. Results are shown in Table BT3.

PGMS. Standard gas was taken in a sampling bag. Then, the sampling bag was connected to the PGMS and standard gas was measured. Results are shown in Table BT4.

Contamination check

Concentrations measured with MCIA and PGMS are shown in Figure BF2. During the contamination check, oxygen concentrations were lower than 3%, and concentrations of other components were close to certified values. Methane concentrations measured by MCIA were almost the same as the results of syringe injection (see “MCIA”; Table BT3) while sufficient gas flowed into the MCIA. Consequently, the effects of air contamination between the mud trap and pump are probably small.