敏感性分析在烃源岩成熟度史模拟中的应用——以川东北地区普光5井古生界海相烃源岩为例

The application of sensitivity analysis in the source rock maturity history simulation: An example from Palaeozoic marine source rock of Puguang-5 well in the northeast of Sichuan Basin

通过分析输入模型的参数对输出结果的影响,可以确定影响烃源岩成熟度史模拟的敏感性参数。本文应用Easy%Ro化学动力学模型,以普光5井为例,对川东北地区各期构造运动剥蚀厚度、古地表温度和古地温梯度进行了相关的敏感性分析。分析结果表明:研究区下寒武统、下志留统、下二叠统和上二叠统烃源岩现今成熟度状态完全受控于燕山运动晚幕—喜马拉雅山运动时期(晚白垩世以来)剥蚀厚度、早白垩世末古地表温度和古地温梯度,与其它地质参数无关;海西期古地温梯度和古地表温度对下寒武统烃源岩成熟度史模拟影响最大;此外,研究区印支运动早幕和燕山运动晚幕—喜马拉雅山运动时期的剥蚀厚度对下寒武统烃源岩成熟度史模拟也有较大影响;下志留统烃源岩成熟度史模拟主要受早二叠世末和晚三叠世末川东北地区古地温梯度的影响;各期构造运动剥蚀厚度、古地表温度和古地温梯度的不确定性对下二叠统和上二叠统烃源岩成熟度史模拟结果影响不大,除了晚三叠世末的古地温梯度10%的不确定性对下二叠统烃源岩进入生油晚期(Ro=1.3%)的时间影响达到16.4Ma,燕山运动晚幕—喜马拉雅山运动时期剥蚀厚度50%的不确定性对上二叠统烃源岩进入干气阶段(Ro=2.0%)的时间影响达到16.7Ma之外,其它地质参数的不确定性对下二叠统和上二叠统烃源岩成熟度史模拟结果影响都不超过15Ma。

By analyzing the influence of input model parameters to the output results, the sensitive parameters in the source rock maturity history simulation can be determined. In this paper,for example of Puguang-5 well, we carry out the sensitivity analysis of erosion thickness during tectonic movements, paleo-surface temperature and paleo-geothermal gradient in the maturity history simulation of the Palaeozoic marine source rock in the northeast of Sichuan Basin,using Easy% Ro chemical kinetic model. The analysis results showed that the present maturity of the Palaeozoic marine source rocks is fully controlled by the erosion thickness during Late-Yanshan to Himalayan movement （since Late Cretaceous ）, paleo-surface temperature and paleo- geothermal gradient during the late Early Cretaceous, while it is nothing to do with other factors. The Lower Cambrian source rocks maturity history simulation is affected by many geological parameters, including the paleo-geothermal gradient and the paleo-surface temperature during Hercynian,the erosion thickness during the Early Indosinian movement and the Late Yanshan to Himalayan movement and so on. The Lower Silurian source rock maturity history modeling is mainly affected by the paleo-geothermal gradient during late Early Permian and Late Triassic in the study area. In compare with the Lower Cambrian and the Lower Silurian source rocks, the maturity history simulation of Lower Permian and Upper Permian source rocks have less affect on the uncertainty of denudation thickness of tectonic movements, the paleo- surface temperature and the paleo-geothermal gradient. Apart from the uncertainty of 10% of paleo-geothermal gradient during the Late Triassic,which results in a 16.4 Ma difference in the time when the Lower Permian source rocks comes into the late oil generation stage（Ro = 1.3 ） ; and the uncertainty of 50% of erosion thickness during Late Yanshan to Himalayan movement, which made a 16. 7 Ma difference in the time when the Upper Permian source rocks comes into the dry gas stage, the uncertainty of other geological parameter affects the maturity history simulation result of Lower Permian and Upper Permian source rock no more than 15 Ma.