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

Abstract

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.

Study of Changes in Apparent Permeability in Shale’s Complex Microfracture Networks

“…16− 18 Many researchers assumed that fractures resembled a forked symmetric fracture network through referral to fracture fractal theory and to characterize the complex bifurcated fracture network structure based on simple mathematical iteration. 10,19,20 However, the above research was constructed on a static fractal dimension, which was inconsistent with the actual situation. Porosity varied during the shale gas production process under the influence of various factors, 21 indicating that the pore's heterogeneity, including pore size, also differed and was not constant; therefore, the fractal dimension characterizing the pore's heterogeneity should reflect change.…”

“…Shale being a typical dual-porosity structure, researchers have amalgamated gas flow, deformation, matrix-fracture interaction, and heat transference to develop a dual-porosity permeability model in order to investigate the interaction between the matrix-fracture microstructure and macroscopic behavior . However, none of the above studies considered the complex features of the fracture bifurcation structure, which over time has revealed that fractures in shale’s low permeability reservoirs possess bifurcation characteristics similar to a tree network pattern. – Many researchers assumed that fractures resembled a forked symmetric fracture network through referral to fracture fractal theory and to characterize the complex bifurcated fracture network structure based on simple mathematical iteration. ,, However, the above research was constructed on a static fractal dimension, which was inconsistent with the actual situation. Porosity varied during the shale gas production process under the influence of various factors, indicating that the pore’s heterogeneity, including pore size, also differed and was not constant; therefore, the fractal dimension characterizing the pore’s heterogeneity should reflect change.…”

Mesoscopic Study on Seepage Characteristics with Shear Displacement in a Single Fracture

“…Starting from the fluid inlet, when the shear displacement is 0 (the contact area is minimal), the pressure drops in a "wave" shape (Zhu et al 2021). With the increase of shear displacement (the contact area after the increase of the shear displacement is larger than the contact area when the shear displacement is 0 mm), the flow velocity near the contact parts change greatly, resulting in the change of the pressure (Fig.…”

Experimental Study on Waterflooding Characteristics of a Large-Scale Physical Low-Permeability Model Based on a Similarity Criterion

“…Researchers employed both physical and numerical simulation methodologies to assess the influence of distinct fracture–matrix systems on the development of low-permeability oil and gas resources. − The utilization of indoor physical simulation methods offers a more faithful reproduction of actual reservoir conditions and oil displacement processes. This facilitates an analysis of the displacement phenomena and oil displacement mechanisms.…”