Investigation on Flowback Behavior of Imbibition Fracturing Fluid in Gas–Shale Multiscale Pore Structure

To investigate the influence of flowback time and difference on behavior shale fracturing fluid, we carried out permeability test experiment Longmaxi Formation under different pressure gradients analyzed retention characteristics water phase in pores fractures after by nuclear magnetic resonance (NMR) instrument. The results indicate that gradient ranges 0.06~0.18 MPa/cm, content retained samples from 9.68% to 16.97% fluid does not decrease with increase difference. Additionally, increasing will reduce damage rate, but rate is still above 80%. After flowback, mainly stays pore space D < 100 nm, especially 2~10 nm 10~50 nm. It extremely difficult for flow back out. experimental show critical particle migration rock powder fracture surface 0.09 MPa/cm. research have important guiding significance gas well flowback.