镜质体反射率剖面反演中的不确定性分析——以鄂西渝东茶园1井为例

UNCERTAINTIES IN THE INVERSION OF VITRINITE REFLECTANCE PROFILE—A CASE STUDY OF WELL CHAYUAN 1, WEST HUBEI AND EAST CHONGQING

王玮 周祖翼

Wang Wei Zhou Zuyi

同济大学, 海洋地质国家重点实验室, 上海, 200092

State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China

由于镜质体反射率与地层温度史之间的高度非线性关系,镜质体反射率剖面反演中存在着不确定性;同时输入参数的误差会进一步导致反演结果的不确定性。反演的不确定性可以借助马尔科夫链—蒙特卡洛(MCMC)方法进行描述和分析。对于鄂西渝东茶园1井,反演结果不确定性表现为:(1)镜质体反射率剖面只能对地层经历最高古温度时的地温梯度及相应的剥蚀量进行有效的约束;(2)对于可接受的反演结果,剥蚀量和古热流之间存在负相关关系;(3)岩石骨架热导率、古地表温度和孔隙度—深度关系等输入参数的误差增加了反演结果的不确定性。反演结果表明,中新生代以来鄂西渝东热流下降约20%,从145 Ma时的(57±4.7)mW/m2到现今的45 mW/m2,相应的剥蚀量约为(3.4±0.4)km。

Uncertainties in the inversion of vitrinite reflectance profile are resulted from the strongly nonlinear relationship between strata temperature history and vitrinite reflectance,and as well as the parametric errors further cause the uncertainties.This uncertainties can be described and analyzed by means of Markov Chain Monte Carlo(MCMC).As for the inversion of vitrinite reflectance profile in Well Chayuan 1,the uncertainties can be summarized as:(1) Only when the strata experience the maximum paleotemperature,can vitrinite reflectance profile provide valid constraints on the geothermal gradient and corresponding denudation thickness;(2) For acceptable results,there is negative correlation between the geothermal gradient and the eroded thickness;(3) Errors in input parameters,such as thermal conductivity of rock,ancient surface temperature and relationship between porosity and depth,increase the uncertainties.The inversion results show that the heat flow of this area has decreased by about 20% since Meso-Cenozoic,from(57±4.7) mW/m2 at 145 Ma to 45 mW/m2 at present,and the corresponding denudation thickness is(3.4±0.4) km.

国家自然科学基金(40572075,40621063)

https://doi.org/10.11781/sysydz200803292