干热岩电学数值模拟方法与微观特性分析

Electrics numerical simulation and microscopic property of hot dry rocks

干热岩(HDR)是一种重要的地热资源,研究其高温条件下岩石物理性质对有效开发热储资源具有重要指导意义,利用数字岩心技术研究干热岩电阻率微观响应特征是一个重要途径.首先,采用CT扫描、扫描电镜等实验方法,获取岩心不同分辨率图像,采用多尺度、多组分、高分辨率图像构建干热岩电学模型;然后,基于热力学及电学理论,构建矿物或岩石骨架电阻率与温度的关系;最后,通过构建含裂缝干热岩数字岩心,模拟分析含裂缝数字岩心高温电阻率微观特性.不同温度下的数字岩心微观数值模拟表明,干热岩体电阻率随温度升高而降低;当温度超过300℃时,电阻率变化出现异常拐点,电阻率降低程度会变缓.分析认为,出现该现象可能是由岩心热开裂造成的.研究表明,应用数字岩心技术可以替代部分高温岩石物理实验,分析干热岩高温条件下的电学微观特性,也可为干热岩电阻率测井解释提供微观依据.

Hot dry rock(HDR)is an important geothermal resource,and the study of its petrophysical properties under high temperature conditions is an important guide to the effective development of thermal storage resources.The digital core technology is employed to study the electric properties and microscopic response mechanism of HDR.First,the multi-component high-resolution digital core model is constructed from different resolutions scanning experiments,including X-ray computed tomography(X-ray CT),quantitative evaluation of materials by scanning electron microscopy(QEMSCAN),and 2-D map mosaics by scanning electron microscopy(Maps).Then,the construction of the mineral or rock skeleton resistivity versus temperature based on thermodynamic and electrical theories.Finally,the resistivity of HDR digital cores at different temperatures is calculated by the finite element method(FEM).The resistivity decreases as the temperature increases.When the temperature exceeds 300℃,there exis an anomalous resistivity that decreases nonearly as the temperature increases.Then,we consider thermal cracking behavior and then construct the fractured digital core to clarify the microscopic mechanism of the abnormality.Therefore,the digital core technology may be used for high-temperature HDR reservoirs′physical properties instead of cores rock physical experiments.This study provides a microscopic theoretical basis for HDR log interpretation and geothermal development.