Abstract
Hydrous and anhydrous isothermal experiments on n-pentane and n-octadecane were conducted at 300–375℃ for durations up to 1094 h to evaluate the cracking and hydrolysis of hydrocarbons, using fused silica capillary capsules as micro-reactors. The chemical compositions of the gaseous products during cracking of n-octadecane at 350 and 375℃ were methane, ethane, propane, and n-butane. The aqueous product in the hydrolysis of n-pentane and n-octadecane at 300–375℃ was alcohol. Alkenes and hydrogen were not detected throughout all the isothermal experiments. Results showed that the gaseous yields were characterized by higher contents of wet gas than those in natural gas accumulations. Mechanisms regulating the enrichment of methane in reservoirs should be further studied. The hydrolysis and oxidation of hydrocarbon were relatively limited in the absence of iron-bearing mineral buffers, suggesting that hydrocarbons might be more stable in iron-poor reservoirs (e.g. carbonate and quartz arenite) than in iron-bearing-mineral-rich ones (e.g. mudstone and arkose) under deep burial conditions. The absence of hydrogen was ascribed to its high diffusion rate in fused silica than in gold tube; any hydrogen produced in the reaction tends to diffuse out of the fused silica capsule with no or limited hydrogen accumulation, similar to those in geological environment. The diffusion of hydrogen should be considered during calculating the volume and pressure changes in the thermal cracking of oil to gas in reservoirs, because the loss of hydrogen would result in a decrease in the conversion rate of oil to gas.
Highlights
Knowledge on the stability of petroleum in deep sedimentary basins is important for petroleum exploration
Hill et al (2003) proposed an oil cracking scheme based on their experimental observations using pyrolysis of crude oil combined with gas chromatography–mass spectrometry (GC–MS) analysis
This study indicated that the pyrolysis of n-octadecane produced a considerable amount of wet gas
Summary
Knowledge on the stability of petroleum in deep sedimentary basins is important for petroleum exploration. The cracking of petroleum appears to be a potential source for natural gas accumulations in sedimentary basins. To investigate the origin of oilcracking gases and the corresponding geochemical identification criteria, many experiments were conducted, those related to the study of the products and the kinetics of the cracking of petroleum and long-chain alkanes Chen et al, 2014, 2016; Feng et al, 2002; Guo et al, 2011; He et al, 2013; Jiang et al, 2009; Liu et al, 2016; Ma, 2016; Shuai et al, 2012; Teinturier et al, 2003; Tian et al, 2006; Uguna et al, 2016; Wang et al, 2015; Xiong et al, 2016; Zhang et al, 2009; Zhao et al, 2008). The gaseous products usually contain a certain amount of alkenes, which are not expected in natural gases (e.g. Feng et al, 2002; Jiang et al, 2009; Jiao et al, 2011; Zhang et al, 2009)
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