不同预制温度煤岩冻融损伤及渗流特性研究

Experimental study on freeze-thaw damage and seepage characteristics of coal rock at different prefabrication temperatures

  • 摘要: 为探究温度对煤岩冻融损伤及渗流特性的影响规律,采用煤岩三轴伺服实验系统对煤样进行加温、加温液氮冻融、加温饱水液氮冻融3种预处理方法开展煤岩细观损伤演化及力学、渗流特征实验。研究结果表明:预热温度越高结构损伤越严重,同一温度下饱水液氮冻融煤样的损伤大于液氮冻融煤样和仅加温煤样,损伤程度与波速呈负相关,与端面损伤合维数呈正相关;不同预处理方法下,三轴抗压强度大的煤样,破坏前变形程度小;3种预处理方法都会导致煤样内部孔裂隙增多易破碎,形成裂隙网络,煤样增透效果为加温饱水液氮冻融大于仅加温和加温液氮冻融。因此,工程实践中可探索使用预热-注水-注液氮冻融的技术实现煤层高效增透,提高瓦斯抽采效果。

     

    Abstract: This experimental study probes into the evolution patterns of fine damage and mechanical and seepage characteristics of coal rocks using the coal rock triaxial servo experiment system by employing three types of pretreatment methods, namely heating, freeze-thawing with liquid nitrogen and freeze-thawing with water, with an aim to investigate the effect of temperature on freeze-thaw damage and seepage characteristics of coal rocks.Results show that higher preheating temperature leads to more severe structural damage, damage to water-filled liquid nitrogen freeze-thawed coal samples at the same temperature is greater than that of liquid nitrogen freeze-thawed coal samples and heated coal samples only, the degree of damage is negatively correlated with the wave speed and positively correlated with the number of joint dimensions of the end face damage; coal samples with high triaxial compressive strength feature low pre-deformation under different pretreatment methods; all three pre-treatment methods lead to an increase in the number of internal pores and fractures in the coal sample, resulting in the formation of a network of fractures.Freezing and thawing the coal sample with warmed water and liquid nitrogen demonstrate more stronger effect than that of freezing and thawing with warmed liquid nitrogen only.Therefore, in engineering practice, preheating-water injection-liquid nitrogen injection freeze-thaw could be employed to achieve efficient coal seam penetration and improve the effect of gas extraction.

     

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