Numerical investigation of single- and two-phase flow in porous media with a bifurcated fracture

Considering that fractures arising from fracturing systems have bifurcation characteristics, mathematical models for single- and two-phase flow in porous media with a bifurcated fracture (BFPM) were established. The phase-field method was adopted to trace the oil–water interface, and the influence of fracture morphology, boundary conditions, gravity, and wettability on imbibition in BFPM was discussed. The results are as follows: (1) during single-phase flow in BFPM, the velocity in the bifurcated fracture was several orders of magnitude greater than that in the matrix. (2) Imbibition in BFPM includes countercurrent imbibition and the combination of co-current and countercurrent imbibition. The bifurcated fracture produces an increase in matrix pores that participate in imbibition, thus increasing the oil recovery factor by approximately 30% during simulation. (3) Closing an outlet of the bifurcated fracture has minimal effect on imbibition during the early stage (approximately the first 6 s) and an inhibitory effect during the middle and late stages (after 6 s), which leads to a decrease in oil recovery factor. (4) When the surface tension value is low (0.1 and 1 mN/m), disregarding the effect of gravity during imbibition results in an overestimated oil recovery factor value, while a large surface tension value (20 and 25 mN/m) produces the opposite effect. (5) Similar to the laws followed in porous media with pure pores and a single fracture, improving BFPM wettability increases the oil recovery factor value. This study can provide guidance for the production of low-permeability reservoirs.