Progress of Kerogen Pyrolysis for Hydrocarbon Generation Using Molecular Simulation
[Significance]Kerogen is the most abundant source of natural organic matter in the world. It is important to study the pyrolysis of kerogen for the exploitation and utilization of oil shales. The traditional pyrolysis experiment cannot easily reveal the mechanism of kerogen pyrolysis,but the molecular simulation method can expose the micro-scopic mechanism of kerogen pyrolysis at the atomic and molecular level,which is an important research method.[Progress]In this study,the research progress of molecular simulation of kerogen pyrolysis was systematically re-viewed. Combined with the experimental results,the effects of temperature,heating rate,water,pressure,and shale mineral composition on kerogen pyrolysis were described. The results showed:(1) The most commonly used method for constructing a kerogen molecular structure model is based on the elements,functional groups,and structural pa-rameters obtained from experimental analysis methods. (2) Temperature,heating rate,water,pressure,and shale mineral components all have varying degrees of influence on the molecular number and components of kerogen pyroly-sis products. In general,the number of molecules undergoing kerogen pyrolysis increases with the increase in tempera-ture. High temperature is not conducive to the direct pyrolysis process but helps to fully conduct the reaction in the hydropyrolysis process. An increase in heating rate increases the temperature at which kerogen begins to pyrolyze. The number of molecules produced by the pyrolysis of kerogen increases with the increase in heating rate,but a high heating rate reduces the number of molecules produced by pyrolysis. Choosing the appropriate temperature and heat-ing rate can maximize the yield of shale oil. (3) Water molecules can provide more hydrogen radicals to participate in the reaction,thereby promoting the cracking of kerogen and heavy shale oil,hindering the formation of C-C crosslink-ing structure,and improving the formation of light shale oil and gas yields. (4) Compared with the experimental re-sults,molecular simulation has significant advantages in the quantitative description,whereas it is slightly insuffi-cient in the qualitative description. (5) Molecular simulation increases the simulation temperature to shorten the reac-tion time to compensate for the geological thermal evolution time,which is one of the shortcomings of molecular simu-lation at present. (6) The high-temperature simulation of kerogen produces a large amount of C2H4,which is not con-sistent with the experimental facts and geological situation,which is also a deficiency of the current molecular simula-tion.[Prospects]Future studies on molecular simulation of kerogen pyrolysis concentrating on the following aspects will be beneficial. (1) The machine learning method is used to quickly construct a kerogen molecular structure model with a relative molecular weight of millions,reflecting both the chemical structure and pore structure of kerogen. (2) A multi-scale and complex kerogen model rich in shale mineral components,formation water,organic acids,and inorganic salts is established. (3) The effects of heating rate,water phase,formation water,pressure,mineral composition and different thermal evolution degree on kerogen pyrolysis are studied. (4) Combined with the actual geological situation,the mechanism of kerogen pyrolysis to generate hydrocarbon at low temperatures is explored to bridge the gap between experiment,geology,and theory,providing important reference information and theoretical guidance for the exploration and development of shale oil and gas.
kerogenmolecular structure modelpyrolysis mechanismmolecular dynamics simulationReaxFF force field
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