Simulation of shale gas generation by using different experimental systems: A case study from Chang7 shale in the Ordos Basin

In this study, open system and closed system laboratory pyrolysis are conducted on a low maturity shale sample from Yanchang Formation of the Ordos Basin. The kinetics parameters in different experimental systems were calculated and extrapolated to geological conditions to predict the yield of hydrocarbon gases and the hydrocarbon generation history. In addition, the amount of hydrocarbon gases expelled during generation was estimated by using hydrocarbon gas generation kinetics extrapolation and the residual gas measurement of the shale. Moreover, the desorbed gas in 98 shale core samples from 4 drilling wells were measured and the ratio of desorbed hydrocarbon gases to generated hydrocarbon gases was calculated. The yield and transformation ratio of methane (C1) in the study area ranged from 22.80 to 36.52 ml/g·TOC and 0.07 to 0.31, respectively. The yield and transformation ratio of hydrocarbon gases (C1-C5) in the study area ranged from 36.13 to 59.28 ml/g·TOC and 0.12 to 0.34, respectively. During the generation process, shale gas was expelled in quantities ranging from 4.68 to 27.83 ml/g·TOC. The average ratios of desorbed hydrocarbon gases to generated hydrocarbon gases in 98 shale samples ranged from 33.78% to 55.79%; however, the ratios of samples for 4 different drilling wells were different, suggesting different adsorption capacities in shales from different parts of the southeastern Ordos Basin.