Experimental study on rock micro damage evolution caused by heological disturbance effect

In order to study the change rule of micro-structure damage of rock under rheological disturbance,a creep disturbance effect experiment of rock was carried out. The porosity,transverse relaxation T₂ spectrum distribution and NMR image of red sandstone were obtained by testing and analyzing the inner and outer red sandstone in the "disturbance sensitive field" by nuclear magnetic resonance (NMR). The results show that ①when the rock sample is disturbed in the insensitive zone,the porosity change rate decreases and the height of T₂ spectral peak curve decreases with the increase of disturbance times,and the porosity change rate of the first five times is larger; the spectral peak curve does not shift to the right. It reflects that the cumulative deformation of rock samples increases rapidly after the first five times of impact disturbance,and then the deformation tends to decay,and the pore size is restrained.②When the rock sample is in the disturbance sensitive zone,the T₂ spectral peak curve shifts to the right as a whole and the height increases significantly,reflecting that the cumulative deformation of the rock sample is in an accelerated state. At the same time,the pore size expands continuously and the penetration evolves into larger pore size. With the increase of the number of disturbances,the damage degree increases,and the disturbance in the disturbance sensitive zone plays a leading role. ③In the non-disturbance sensitive region,the peak area of macro-pore spectra does not change with the increase of disturbance times,and the total area of the peak is almost unchanged after decreasing gradually five times before disturbance. The total area of spectral peaks in the disturbance sensitive area increases sharply,and the third spectral peak curve appears,which reflects that the pore diameter of rock samples in the nondisturbance sensitive area is compacted,and the large-scale pore penetration in the disturbance sensitive area increases continuously. ④Nuclear magnetic resonance imaging (NMR) can display more intuitively the pore structure characteristics of disturbance sensitive and non-sensitive areas with the increase of disturbance times.