火成侵入体对相邻烃源岩成熟度影响的模型研究

摘要

This study presents a numerical investigation of the thermal effect of an igneous dike on organic -rich host rocks based on four types of different heat conduction models which are classified in terms of the different intrusion mechanism and the consideration of evaporization of pore water. A 0.9m thick intrusion dike in the Jurassic siltstone section Isle of Skye, northwest Scotland is selected as an example. Results indicate: 1) the influence of different intrusion mechanism on the prediction of maturation of organic matter in host rocks is remarkable. The vitrinite - reflectance ( Ro) computed by the model of instantaneous intrusion is much higher than the Ro computed by the model of finite - time intrusion, and the highest deviation between them can reach 2.13% ~ 2. 59% ; 2) in case of the same intrusion mechanism, the Ro predicted by the model which considers evaporization of pore water is obviously lower than that predicted by the model which does not consider evaporization of pore water. The deviation between them can reach 0.71% -0.91%, which is far below the influence of different intrusion mechanism; 3 ) the model of finite - time intrusion without pore - water evaporization closely matches with the measured vitrinite reflectance. This demonstrates that magma intruded into the strata in finite time and that the evaporization and escape of pore water is insignificant.%根据不同的岩浆侵入地层方式以及围岩内孔隙水是否发生气化建立了四种热传导模型,以苏格兰西北部Skye岛的辉绿岩岩墙为实例分别采用这四种热传导模型数值模拟了侵入体相邻泥质烃源岩有机质的成熟度.模拟结果显示:(1)岩浆的侵入方式能显著地影响热传导模型对侵入体围岩成熟度的预测,岩浆有限时间侵入方式的假设下热传导模型所预测的镜质体反射率(Ro)与假设岩浆瞬间侵入方式的模型相比,最大偏差处低2.13%～2.59%;(2)当岩浆侵入方式相同时,考虑孔隙水气化的模型预测的Ro普遍低于不考虑孔隙水气化的模型.孔隙水气化引起Ro的最大偏差达0.71%～0.91%,明显低于岩浆的侵入方式对围岩成熟度预测结果的影响;(3)不考虑围岩内孔隙水的气化且假设岩浆有限时间侵入地层的热传导模型所预测的Ro与实测值十分吻合,说明岩浆侵入方式应为有限时间侵入且围岩孔隙水的气化作用不显著,该模型是否适用于其他地区,还有待于进一步研究.