Development of a Combined Device with High Vacuum and Pulsed Discharge Gas Chromatography and Its Application in Chemical Analysis of Gases from Rock Samples

It is important to determine the chemical composition of gases trapped in rocks. The technique of using carrier gas and chemical analysis to release and collect gases is very time-consuming. There is little reported about Gas Chromatography analysis of rock degassing under high vacuum, and the total amount of gases are not commonly measured. It is difficult to analyze gases with similar molecular weights by Mass Spectrometer and because of these problems, a high vacuum rock sample degassing device has been developed. The vacuum of the device is < 10^-4 Pa. The blank sample pressure is < 0.1 Pa, the accuracy for N₂ in the air is 0.63%, and the minimum measurable quantity is < 1 mm³ at standard temperature and pressure. The high vacuum device is coupled with a Gas Chromatography with a pulsed discharge detector, which gives a high sensitive gas chromatographic analysis of the chemical composition of gases in rocks. The gas released from Wudalianchi volcanic rocks in the Songliao Basin reservoirs and shale samples from the Sichuan basin have been analyzed using this system. The results show that the total amount of gas released from the rock can be directly measured. Less sample weight is needed during stage heating, and gas composition analysis is more sensitive compared with the previous experimental device and method. The analyzed main component targeted is the common component in gas-released rock.