古龙油页岩干酪根热解特性分子动力学模拟

Molecular dynamics simulation of kerogen pyrolysis of Gulong shale

古龙页岩油在开发过程中面临油气同出、油品差异大等问题,成烃演化后储层中流体组分组成是影响其有效开发的首要问题。针对上述问题,利用分子动力学模拟建立了古龙油页岩典型的干酪根基质模型,并在此基础上开展了不同温度下的干酪根热解模拟,分析了干酪根热解产物组成以及干酪根基质孔隙结构变化。结果表明:在不同热解温度下,干酪根热解产物中的C1—C5短碳链烃类比例较高,对应着较高的气油比,这与古龙页岩油在实际开发过程中所得到的结果一致;干酪根热解效果随温度的升高而增强,而过高温度反而会抑制干酪根的热解,2500K为最佳热解温度;干酪根热解生成的大量产物堵塞干酪根基质孔隙且伴随着干酪根骨架的坍塌导致基质孔隙度降低,但伴随着后续排烃的进行使得孔隙度大幅上升,从而有利于干酪根热解的进一步开展。研究成果为古龙页岩油的赋存和运移以及实际现场开发中的有效动用提供了理论指导。

During the development of Gulong shale oil,several challenges arise such as co-production of oil and gas and significant variation in oil quality.Fluid composition resulting from hydrocarbon generation evolution in reservoir is the foremost concern affecting its effective development.In response to aforementioned challenges,a typical kerogen matrix model of Gulong oil shale is established via molecular dynamics simulation.Subsequently,simulations of kerogen pyrolysis at different temperatures are performed,enabling analysis of pyrolysis product composition and variations in pore structure of kerogen matrix.The result shows that at different pyrolysis temperatures,kerogen pyrolysis products are characterized by high proportion of C1-C5 short-chain hydrocarbons,corresponding to high gas-oil ratio.This finding aligns with the results obtained during actual development of Gulong shale oil.Kero-gen pyrolysis efficiency increases with temperature rise,however,excessively high temperature inhibits pyrolysis process.The study determines optimal pyrolysis temperature of 2500 K.Large amount of products generated from kerogen pyrolysis tend to clog pore spaces within kerogen matrix,with collapse of kerogen skeleton causing matrix porosity reduction.Nevertheless,subsequent hydrocarbon expulsion process increases porosity significantly,facili-tating further kerogen pyrolysis.The research provides theoretical guidance for study on occurrence and migration of Gulong shale oil and effective producing in field development.