急剧冷却后粗粒花岗岩渗透率和孔隙结构演化规律研究

Evolution Patterns of Permeability and Pore Structure of Coarse-Grained Granite After Sharp Cooling

开发深层地热能是实现“双碳”目标的一种重要途径。由于成岩环境的不同,深层花岗岩的矿物组成和细观结构与浅层花岗岩有较大差异。选取代表深层热储的山西芦芽山粗粒花岗岩为研究对象,在急剧冷却的方式下,利用三轴渗流测量系统,采用压力脉冲击和压汞法分别研究了不同围压、热处理温度和循环次数下粗粒花岗岩试样渗透率和孔隙结构的演化规律。结果表明:在无约束且缓慢升温条件下,粗粒花岗岩渗透率的阈值温度为250℃;多次“升温-冷却”循环可以提高渗透率和孔隙率,但随着循环次数的增加,增幅逐渐降低;提高热处理温度和增加“升温-冷却”循环次数均有利于超大孔和大孔的形成,当热处理温度达到400℃时,微孔开始生成;粗粒花岗岩的物性和温度敏感性均有利于深层热储的开发。

The development of deep geothermal energy is an important way to realize the goal of"double carbon".Due to the difference in diagenetic environments,the mineral composition and fine structure of deep granites are quite different from those of shallow granites.The coarse-grained granite of Luya Mountain,Shanxi Province,which represents a deep geothermal reservoir,was selected as research object.Using a three-axis seepage measurement system,the evolution laws of permeability and pore structure were systematically studied under rapid cooling with pulse pressure impact method and mercury intrusion method.It is found that the threshold temperature for permeability of coarse-grained granite is 250℃ under unconfined and slowly heating conditions.Multiple"heating-cooling"cycles can increase permeability and porosity,but the increase decreases as the number of cycles increases.Increasing the heat treatment temperature and the number of"heating-cooling"cycles are conducive to the formation of oversized holes and large holes.When the heat treatment temperature reaches 400℃,the microporous start to generate.Both the physical properties and temperature sensitivity of the coarse-grained granite are favorable for the development of deep geothermal reservoirs.