Abstract: Microcracks have increased the permeability of pores in limestone formations to varying degrees. In order to clarify the impact mechanism of different development of microcracks on the ability of drilling waste to be reinjected during the reinjection process and ensure the safe implementation of drilling waste reinjection, firstly, X ray CT (computed tomography) scanning was used to digitally reconstruct the limestone core collected from a certain gas field to obtain its matrix model, and the migration and sedimentation mechanism of waste particles in the pores were studied. Then, based on numerical algorithms, a fracture-matrix model is constructed, and the fracture connectivity coefficient and fracture orientation factor are introduced to quantitatively characterize the connectivity and orientation of fractures, and to reveal the influence of fracture opening on the permeability of reinjected formations and the ability of waste reinjection. The results have shown that as the crack direction factor increases, the lateral tortuosity shows a decreasing trend, with a maximum decrease of 35.21%, while the longitudinal tortuosity shows an increasing trend, with a maximum increase of 21.59%. The larger f (fracture connectivity coefficient), the more likely the fracture matrix model is to exhibit dominant channel effects (especially significant when f≥0.7), and the higher the permeability and particle escape rate. Compared with the matrix model, the permeability increases by 0.671 3  μm2, and the particle escape rate increases by 15.06%.

Key words: drilling cuttings, reinjection；limestone；microfracture, connectivity； strike； slurry seepage, matrix model