基于相控原则和随机森林算法的沉积微相对渗透系数空间分布控制机理研究

In order to characterize quantitatively the relationship between sediment environment and hydraulic conductivity, the first and second aquifers of 136 drill in north China plain (NCP) were selected to calculated hydraulic conductivity using the Archie equation, subsequently, under the condition of Facies-controlled Modeling theory, based on considered the micro-influencing factors, such as effective diameter of grain size, distribution structure, and mineral compositions, Random Forest was employed to establish inversion model of hydraulic conductivity for each sediment micro-facies unit. The effects of each micro influencing factor on hydraulic conductivity was different, which could be quantitatively described according to coefficient of inversion model; the macro controlled factors combined with micro influencing factors that were used to characterize quantitatively the relationship between sediment and hydraulic conductivity; the spatial variation of hydraulic with depth in vertical direction was discussed by this work, which play an important role for the deep groundwater resources exploitation in the coming years.

目前沉积微相对渗透系数的控制机理多以定性研究为主。为定量刻画二者间的相关性，本课题以华北平原山前-滨海区136个钻孔内第一和第二含水层为研究对象，根据物探测井曲线计算钻孔内含水层渗透系数，进而以相控建模原理为指导，利用随机森林算法，构建不同沉积微相内关于粒度大小、粒度分布结构和矿物成分的渗透系数反演模型。根据反演模型内的因子系数，定量表征各微观因子在不同微相内对渗透系数影响的差异性，并探究在不同微相内渗透系数的概率密度函数和变差函数模型；通过相控建模原理，研究各微相内“粒度大小-粒度分布结构-矿物成分-渗透系数”体系的组成和空间分布特征，从而实现对沉积微相与渗透系数相关性定量刻画的目的，这对于后期渗透系数空间变异性的研究具有重要意义。

以华北平原山前-滨海区89个标准水文地质钻孔为研究对象，以粒度、沉积韵律、生物痕迹等资料为基础，识别出辫流线、边滩、天然堤、决口扇、陆上天然堤、河漫滩6种沉积微相，通过粒度分布、矿物组分、化学成分、有机碳微观参数，利用结构方程模型，定量刻画宏观沉积微相对于微观渗透系数的影响。项目主要研究成果如下：.1、在第一含水层组内，从华北平原山前-中部平原-滨海区内平均粒径呈显著递减趋势；在第二含水层组内并无此趋势；.2、从辫流线、边滩、陆上天然堤、决口扇、天然堤到河漫滩，平均粒径和砂粒含量呈递减趋势，代表水动力条件逐渐减弱，粘粒和粉粒含量逐渐增高的趋势；辫流线微相内渗透系数远大于其它5种微相，这主要是由于在该微相内颗粒较粗、粘粒含量较少，从而导致该区域内具有较大渗透系数；.3、在上述6种微相内，平均粒径、粘粒、砂粒、有机碳含量对于渗透系数空间分布具有重要影响；.4、在上述6种微相内，渗透系数主要以对数正态概率分布，其变差函数拟合模型主要为高斯分布；.5、边滩、陆上天然堤、天然堤对于渗透系数具有显著的控制作用，决口扇和河漫滩对于渗透系数的影响较小；.通过本项目的研究，定量刻画了沉积微相对于渗透系数的影响，并查明了在不同微相内渗透系数的主控因子和其统计分布特征函数，为渗透系数空间分布模型的建立提供基础数据，为华北平原地下水资源合理开发利用提供科学依据。