In Situ Volume Recovery Method for Non-Seal Gas Pressure Measurement Technology: A Comparative Study

Coal seam gas pressure is one of the basic parameters for coalbed methane resource exploitation and coal mine gas disaster prevention. However, the present coal seam gas pressure measurement technology requires harsh field measurement conditions and a long testing period. In this study, a novel non-seal gas pressure measurement technology is proposed, and this technology is mainly aimed at three different changes before and after the collection of coal samples and realizes the real gas pressure measurement through the compensation of gas leakage, in situ volume recovery of the coal core, and reservoir temperature simulation. The technique not only can measure the original gas pressure of coal seam quickly and accurately but also does not need to seal the measuring hole. This paper focuses on the study of a key factor that affects the accuracy of non-seal gas pressure measurement: the restoration of in situ volume. Based on this, the influence of four different in situ volume recovery methods on the measurement accuracy is compared with the self-developed non-sealing gas pressure measuring system. Experimental results show that the in situ volume of the coal core cannot be completely restored by stress loading. Although the contact injection method can restore the original volume of the coal core, the pressure recovery error is large due to the replacement and displacement of the gas effect of water and the inclusion of the coal body effect of oil. Interestingly, the combination of stress loading and contact oil injection can not only restore the original volume of the coal core but also minimize the pressure recovery error, which is only less than 10%. Finally, based on the abovementioned experimental results, the in situ volume recovery method of non-seal gas pressure measurement technology is improved. Therefore, the research results of this paper provide a scientific basis for the field application of non-seal gas pressure measurement technology.