摘要
为进一步研究液氮循环冻融煤体渗透率演化规律,采用核磁共振仪、电子万能试验机和煤岩芯渗透率自动测试系统,分析了不同液氮循环冻融次数前后煤体内部温度、孔隙分布、力学特性和渗透率的演化规律;基于立方定律和循环冻融煤体损伤本构关系,建立了液氮循环冻融煤体渗透率计算模型。结果表明:液氮冻结过程中,煤体内部温度变化分为0~9 min,9~30 min两个阶段,不同时间段内温度下降关系为ΔT_(阶段二)>ΔT_(阶段一),升温解冻时,煤体温度呈指数关系上升,升幅逐渐减小;液氮循环冻融作用下,煤体孔隙结构得到明显改善,微小孔隙数量增加,部分相互贯通扩展,逐渐转化为中大孔隙。随着冻融循环次数的增加,微小孔隙占比减小,中大孔隙占比显著增大;煤体孔隙度增量、孔隙度变化率呈正幂函数增加,渗透率增量、渗透率变化率呈正指数增加;煤体单轴抗压强度与弹性模量呈直线型降低,单轴抗压强度变化率、弹性模量变化率均呈负线性相关。所建立的液氮循环冻融煤体渗透率计算模型的计算结果与实验测试值绝对误差为0.006~0.016 mD,相对误差为1.61%~6.41%,计算模型在试验范围内的渗透率预测值与实际测量值基本一致。
To further explore the evolution law of coal permeability under liquid nitrogen cycle freezing and thawing,nuclear magnetic resonance(NMR)instruments,universal testing machine,and a coal-rock core permeability automatic testing system were adopted to analyze the temperature distribution,pore distribution,mechanical characteristics,and permeability changes inside the coal bodies before and after different cycles of liquid nitrogen freezing and thawing.Based on the cubic law and the damage constitutive relationship of circulation-freeze-thaw coal bodies,a permeability calculation model was es-tablished for circulation-freeze-thaw coal bodies with liquid nitrogen.The results indicate that during the liquid nitrogen freezing process,the internal temperature changes of the coal body can be categorized into two stages of 0-9 minutes and 9-30 minutes.The temperature reduetionsaifesΔT_(stage2)>ΔT_(stage1).In the process of warming-up and thawing,the coal body temperature increased exponentially,but the rise degree gradually decreased.Under the liquid nitrogen cycle freezing and thawing,the pore structure of the coal body was significantly improved,and the number of tiny pores increased,some of which were interconnected and gradually transformed into medium and large pores.With the increase of freezethaw cycles,the proportion of tiny pores decreased,and the proportion of medium and large pores significantly increased.The increment of pore volume and the rate of pore volume change showed an increasing polynomial function,as well as an increasing exponential function for the permeability.The uniaxial compressive strength and elastic modulus of coal bodies decreased linearly.The rate of changes in the uniaxial compressive strength and the elastic modulus were negatively linearly correlated.Compared to experimental testing values,the proposed permeability calculation model for the liquid nitrogen circulation-freeze-thaw coal body had merits within an absolute error of 0.006-0.016 mD and a relative error of 1.61%-6.41%,which had a good consistence between the calculation model and the experimental data.
作者
林海飞
王裴
李树刚
李博涛
罗荣卫
秦雷
LIN Haifei;WANG Pei;LI Shugang;LI Botao;LUO Rongwei;QIN Lei(College of Safety Science and Engineering,Xi'an university of science and technology,Xi'an,Shannxi 710054,China;Ministry of Education,Key Laboratory of Mine Mining and Disaster Prevention and Control,Xi'an university of science and technology,Xi'an,Shannxi7i 10054,China)
出处
《采矿与安全工程学报》
EI
CSCD
北大核心
2023年第5期1067-1077,共11页
Journal of Mining & Safety Engineering
基金
国家自然科学基金重点项目(51734007)
国家自然科学基金项目(51874236)
陕西省杰出青年基金项目(2020JC-48)。
关键词
液氮循环冻融
孔隙分布
力学特性
渗透率模型
liquid nitrogen cycle freezing and thawing
pore distribution
mechanical properties
permea-bility model
