Determination of the hydrocarbon content in nanometer size pores adsorbed gas in unconventional reservoir rocks by chemical desorption-gas chromatography

A method for the hydrocarbon content in nanometer size pores adsorbed gas in unconventional reservoir rocks using gas chromatography (GC-FID) has been established in this paper. The experiment of gas desorption from nanometer size pores using a device for preparing nanometer size rock samples and gas desorption has been carried out to determine the most favorite experiment conditions. The result shows that the best desorption time is about 20min with the temperature at 80 degrees C and the sample weight of 20g. The test conditions for gas chromatography are as follows: an OV-101 GC column with carrier gas flow rate at 40mL/min; the temperature of GC oven began at 50 degrees C for 0.5min and then increased to 100 degrees C at 10 degrees C/min, with the final temperature being maintained for 5min. The parallel test shows that the method introduced here is characterized by quickness, accurateness, and high sensibility with relative testing error less than 9.99% (the least is 2.18%). We have tested 19 rock samples from 11 wells of the Songliao Basin, and most desorbed gas contains alkane gases from methane to hexane with total alkane gas content between 233.21 and 49,826.89 mu L/kg. Desorbed gas content is significantly different among different areas and intervals, based on which gas content of unconventional reservoirs can be estimated.