基于核磁共振的煤岩孔裂隙应力变形特征

为探讨煤岩孔裂隙应力变形特征，设计不同围压（0，2，4，6，8，10 MPa）下的核磁共振实验，并基于弯曲变形理论对煤岩孔裂隙应力变形问题进行理论分析。实验得到各煤样孔裂隙在不同围压下的核磁共振T2谱图，绘制了各煤样不同围压下不同孔径的孔裂隙核磁信号衰减率图，推导出煤岩应力变形时孔裂隙截面积弹性减小率公式。实验显示：煤岩孔裂隙应力变形存在差异性：相同围压下，裂隙变化最显著，大中孔次之，微小孔变化微弱；对孔隙（或裂隙）而言，孔径大者变化程度大；但无烟煤样不同孔径孔裂隙应力变形差异性不明显。理论分析表明：相同应力作用下，孔径越大，孔裂隙应力变形越严重。煤岩孔裂隙在实验中通过加载围压发生的“被动式”变形与实际排水降压生产过程中在有效应力作用下的“部分主动式”变形存在一定差异，需引起注意。

Characteristics of the stress deformation of pore-fracture in coal based on nuclear magnetic resonance

In order to study the characteristics of deformation in coal pore-fracture system under the stress，a series of NMR experiments，which were designed under different confining pressures (0，2，4，6，8，10 MPa），were conducted.A theoretical analysis on the deformation problem was also made.Experiments show a series of NMR T2 spectrograms，and also the attenuation rates diagrams of magnetic signal intensity of coal samples under different confining pressures.The elastic strain reduction rates of cross-sectional areas of pore-fracture under different stresses are derived.Experiments show that as the confining pressure increases，fracture changes significantly，followed by the macropore and mesopore，while the micropore hardly changes.For high rank coal (Ro>3%)，the difference of stress deformation between different sizes of pore is not obvious.The theoretical analysis of pore-fracture deformation indicates that，based on the theory of bending deformation and the consideration on the micro elastic deformation of the pore-fracture system，under the same effective-stress，the greater the pore or fracture，the heavier the stress-deformation damage.By loading confining pressure in the laboratory，the deformation of pores and fractures of coal is “passive” deformation，while the effective-stress deformation of pore-fracture system of coal reservoir in actual production process is “partly-active” deformation.There are differences between these two kinds of deformations，which needs to be further investigated.