不同温度作用下砂岩微观结构变化与演化规律实验研究

Experimental study on the microstructure change and evolution law of sandstone under different temperatures

深部煤层的高地应力以及地下气化过程中产生的高温热应力的共同作用会对岩石造成损伤,破坏煤层围岩的稳定性。采用扫描电子显微镜、X射线衍射、CT扫描等实验手段对砂岩试样不同温度(25℃,200℃,400℃,600℃,800℃,1000℃)下微观结构及矿物成分变化情况进行研究。结果表明:温度变化对砂岩的微细观结构具有重要影响。砂岩的孔隙率整体上随温度的升高而增大,1000℃的砂岩孔隙率最大,25℃的砂岩孔隙率最小。砂岩不同孔径的孔隙数量总体上随温度的升高而减少,但1000℃砂岩的微孔数量最多,25℃砂岩其他孔径的孔隙数量最多。加热后砂岩开始产生微裂纹,当温度超过600℃时,试件产生的微裂纹的数量明显增加,微裂纹长度、宽度及密度随着温度的升高进一步扩展。试件的矿物成分衍射强度及矿物的含量随温度的变化各不相同,超过600℃时各类矿物成分衍射强度变化发生转折,超过400℃时,砂岩内部矿物成分发生物理化学反应,晶体之间发生转化,随温度的升高,石英矿物含量逐渐增加,长石矿物逐渐减少;试件表观形态变化的临界温度为400℃。

The combination of high ground stress in deep coal seams and high temperature thermal stress in underground gasification will cause rock damage and destroy the stability of the coal seam surrounding the rock.This research investigated the relationship between temperature(25℃,200℃,400℃,600℃,800℃,and 1000℃)with the microstructure and mineral composition of sandstone through the application of scanning electron microscopy,X-ray diffraction,and CT scanning.The results suggests that the temperature has a significant impact on sandstone microstructure because an increase in the temperature can improve the total porosity.The porosity of sandstone at 1000℃is the maximum and the minimum at 25℃.The number of pores of different sizes decreases with the increase in the temperature.However,the number of tiny pores at 1000℃is the most,and the number of pores at other sizes at 25℃is the most.After heating,the sandstone begins to produce microcracks.When the temperature exceeds 600℃,the number of microcracks increases significantly,and the length,width and density of microcracks further expand with the increase in the temperature.The diffraction intensity and mineral composition of the sandstone vary with the temperature.When the temperature is higher than 600℃,the diffraction intensity of various mineral compositions takes a turning point.When the temperature exceeds 400℃,a physical and chemical reaction occurs in the mineral composition of sandstone,and a transformation occurs between crystals.With the increase in temperature,the quartz mineral content gradually increases,and the feldspar mineral gradually decreases.The critical temperature of the specimen's apparent morphology change was 400℃.