Experimental Method For The Gas Composition Measurement In The Shale And A Primary Application

Residual gas in shale is an important part for the study on gas storage, and it is of great significance for the assessment on the shale-gas resources and the identification of core area. At present, there is not a available systematic experimental method to determine the chemical composition and carbon isotopic composition in residual gas in shale. In this paper, crushing and heating samples for different time and temperature were used to extract gases stored in samples, and the chemical and isotopic compositions of the released gas were determined by mass spectrometry or chromatography. Based on the results from different methods of shale gas extraction and analytical methods, we obtain the effective method in determing the gas composition in shale. The main understanding is as follows:1. Based on the advantages and disadvantages of current experimental methods on the gas storage in shale, we propose that mechanical crusing is an effective method to extract gases stored in shale; Mass spectrometry can measure the absolute concentration of gases.2. A set of high vacuum mechanically crushing device to release gas was developed and improved, and an analytical system was designed to match it. This device and method has the merits of high vacuum, thoroughly broken degree, short operation time, low process temperature, and the injection without water, and has good analytical stability, reliability and maneuverability.We design a series of conditional tests such as different crushing degree and background values, and the comparison of the results under different analytical methods according to the analytical requirements for residual gas in shale, and determine the specific experimental process and parameters.3. The multiple sets of parallel experiments show that the application of the device and method can obtain better repeatability and low standard deviation.4. More gas geochemical information can be got after shale desorption. The amount of released gas is more than6ml indicating that residual gas in shale is high. Gas contains the main hydrocarbon and nonhydrocarbon components. The volume percentage of hydrocarbon gas increases significantly, up to more than65%; Carbon isotopic values from C1to C3of samples can be detected stably. 5. Desorbed gas obtained from developed crushing device and method can truly reveal the gas geochemical characteristics of source rock, and prove a approach for experiment measurement of shale gas and the assessment on the shale-gas resources.6. The gases stored in core shale samples from Qianqian No.1well in lower Silurian formation in Sichuan basin, west China have been extracted and determined using the developed crushing device and method. The results of chemical and isotopic compositions of gases show high precision, the gas content and organic showed a positive correlation, residual volume in contrast. And the data from this method are close to that of the actual logging, and it have good correlation with the source rocks, indicating the reliability of this device and method.