摘要
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。
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.
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2015年第6期1415-1421,共7页
Journal of China Coal Society
基金
国家科技重大专项资助项目(2011ZX05038-001)
国家自然科学基金资助项目(41272175)
关键词
核磁共振
孔裂隙
应力变形
煤储层
NMR
pore-fracture system
stress-deformation
coal reservoir
