Physical simulation of pore filling pressure gradient at different scales in shale oil reservoirs

Abstract The influence mechanism of filling pressure gradient on pores of different scales is complex. In this paper, firstly, the nuclear magnetic resonance method is used to measure the spontaneous imbibition water and spontaneous imbibition oil of different scale pores in shale, revealing the differences in the multiscale pore‐fluid interaction mechanism in shale oil reservoirs. On this basis, the oil injection volume of different scale pores in shale is quantified using displacement and two‐dimensional nuclear magnetic resonance measurement technology under different injection pressure conditions, and the injection pressure gradient (start‐up pressure gradient) of different scale pores is clarified. Results show that (a) in non‐aqueous calcite and illite systems, when the oil/pore ratio is 27%, shale oil is filled in the pore throats; when the oil/pore ratio is ≤20%, water channels are formed inside the shale oil. (b) The small, medium, and large pores of block shale are basically saturated during 1.2 MPa pressure differential displacement, with a saturation degree of 95% and an average pressure gradient of 39.2 MPa/m; (c) The small, medium, and large pores of rich‐bedding shale are basically saturated with a pressure difference of 0.5 MPa during displacement, with a saturation degree of 95% and a pressure gradient of 14.2 MPa/m.