## 3 Methods
### Instrument Parameter Test  
We tested the instrument parameters in the laboratory before the system was applied to the drilling site, based on the results of the best ionization energy of helium obtained by [PERSON] et al. using a MiniRuedi, which showed that the best ionization energy of helium is 70 eV [34]. The following tests were performed at that energy. Comparing the helium detector described in this paper and the MiniRuedi, both include a quadrupole mass spectrometer, but the difference is that the MiniRuedi detection system uses the membrane balance sampling method and performs measurements in rivers and lakes. The rate of gas penetration through the membrane will be affected by factors such as temperature, flow rate, and membrane aging. During the drilling process, because the drilling speed is usually high, the underground gas will continue to move up rapidly; however, the membrane balance gas penetration rate is too low to allow for the required fast measurements. Compared with the MiniRuedi, the helium detector employed in this study uses a gas pump to send gas into the injection system, and the injection rate is much higher than that of the membrane equilibrium method, allowing for meeting the gas detection requirements of the drilling site. The instrument parameters were tested, starting from a blank sample. As the instrument operated in a dynamic detection mode, it was necessary to test a dynamic blank. This was achieved by measuring the signal when the inlet valve was closed, which is shown by solid red dots in Figure 5. This value was used to calibrate both the sample gas and the standard gas. Moreover, natural gas usually contains hydrocarbons and carbon dioxide. The fact that hydrocarbon and carbon dioxide molecules may produce \({}^{12}\)C\({}^{3+}\) ions during the ionization process, whose mass-to-charge ratio is the same as that of \({}^{4}\)He\({}^{+}\) ions, could potentially affect the measurement results. Therefore, we injected standard hydrocarbons (CH\({}_{4}\): 1.49 \(\times\) 10\({}^{-2}\), C\({}_{2}\)H\({}_{6}\): 1.19 \(\times\) 10\({}^{-2}\), C\({}_{3}\)H\({}_{6}\): 0.991 \(\times\) 10\({}^{-2}\), n-C\({}_{4}\)H\({}_{10}\): 0.245 \(\times\) 10\({}^{-2}\), n-C\({}_{5}\)H\({}_{12}\): 0.255 \(\times\) 10\({}^{-2}\); the complete injection volume was achieved with N\({}_{2}\)) and carbon dioxide (500 ppm; the complete injection volume was achieved with N\({}_{2}\)) into the helium  
Figure 4: Instrument gas flow diagram. The blue, red, and yellow lines represent carrier gas, sample gas, and carrier gas + sample gas, respectively. And (**a**–**d**) represent the first, second, third, and fourth working states respectively. detector for interference peak measurement, and the test results are shown in Figure 5. It can be seen in the figure that the \({}^{12}\)C\({}^{3+}\) signals generated by the hydrocarbons and carbon dioxide molecules were within the same range as those of the dynamic blank. Hydrocarbons and carbon dioxide in the gas will not cause discernible interference with the \({}^{4}\)He measurement results. This study used the external standard method to calibrate the helium concentration in the mud gas [34,38]. We configured helium standard gas samples with concentrations of 11.5 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm, injected and measured them 10 times, and plotted their average concentrations, obtaining a standard curve (Figure 6). It can be seen in the figure that there was a good linear relationship between the concentration of the standard gas and the integrated area, and the R-square of the equation was 0.99903, which is highly acceptable. So, the helium concentration in the tested gas could be deduced by using this concentration standard curve. To test the analytical accuracy of the instrument, we calculated the RSD (Relative Standard Deviation) of the 10 concentrations mentioned above, and the results are presented in Table 1. In the table, it can be seen that the lower the standard gas concentration, the greater the RSD.