The Fastest Capillary Flow in Root-like Networks under Gravity

The Carbon Dioxide Enhanced Coalbed Methane (CO2-ECBM) technique significantly enhances clean energy extraction and mitigates climate change. Central to this process is the dynamic evolution of rough fracture networks within coal seams, influencing the migration of CO2 and natural gas. However, existing research lacks a comprehensive, quantitative approach to examining the micro-evolution of these fractures, including fracture roughness, fracture density, fracture touristy, and fracture size, particularly under thermo-hydro-mechanical effects. Addressing this gap, our study introduces an innovative, fractal model for quantitative analysis. This model intricately characterizes fracture networks in terms of number, tortuosity, length, and roughness, integrating them with fluid dynamics affected by external disturbances in CO2-ECBM projects. Upon rigorous validation, the finite element method analysis reveals significant impacts of micro-parameters on permeability and natural gas extraction. For instance, increasing CO2 injection pressure from 4 to 6 MPa changes fracture network density by up to 6.4%. A decrease in fracture density (Df) from 1.6 to 1.5 raises residual gas pressure by 2.7% and coal seam stress by 9.5%, indicating crucial considerations for project stability. Applying the proposed interdisciplinary model to assess CO2 emissions in Australia, it is can be obtained that when Df decreases from 1.6 to 1.5, the total amount of CO2 storage reduces by 17.71%–18.04%. Our results demonstrate the substantial influence of micro-fracture behaviors on CO2-ECBM projects, offering a ground-breaking solution for efficient greenhouse gas reduction and clean energy extraction, with practical implications for the energy sector's sustainability.

A novel interdisciplinary model for optimizing coalbed methane recovery and carbon dioxide sequestration: Fracture dynamics, gas mechanics, and its application

Ye,

Liu,

Gao

et al. 2024

Fractal analysis of dimensionless permeability and Kozeny–Carman constant of spherical granular porous media with randomly distributed tree-like branching networks

Li,

Gao,

Xiao

et al. 2024

The seepage of porous media has garnered significant interest due to its ubiquitous presence in nature, but most of the research is based on the model of a single dendritic branching network. In this study, we derive a fractal model of the dimensionless permeability and the Kozeny–Carman (KC) constant of porous media consisting of spherical particles and randomly distributed tree-like branching networks based on fractal theory. In addition, three different types of corrugated pipes are considered. Then, the relationships between the KC constant, dimensionless permeability, and other structural parameters were discussed in detail. It is worth noting that the KC constant of the porous media composed of three types of pipes decreases sharply first and then increases with the increase in the internal diameter ratio, while the dimensionless permeability has the opposite trend and conforms to the physical law. In addition, empirical constants are not included in the analytical formulas of the present model, and the physical mechanism of fluid flow in spherical granular porous media with randomly distributed tree-like branching networks is clearly revealed.

Fractal study on the permeability of power-law fluid in a rough and damaged tree-like branching network

Zhang,

Gao,

Xiao

et al. 2024

In the field of fractal theory, the study of permeability in tree-like branching networks has always been rather popular. However, most of the studies have been focused on the permeability models of common fluids. In this study, based on fractal theory and the theory of power-law fluid, a fractal model of the permeability of power-law fluid in a damaged tree-like branching network considering roughness is derived. This study discusses the effects of power-law index, roughness level, damage degree, branching layer number, and length ratio on permeability. The results show that the permeability decreases with an increase in the power-law exponent, roughness, damage degree, bifurcation layer number, and length ratio when the diameter ratio is relatively small; on the contrary, with an increase in the diameter ratio and the power-law exponent, the permeability will increase with an increase in the bifurcation layer number; the permeability will decrease with an increase in the bifurcation layer number when the diameter ratio is large and the power-law exponent is small. The proposed model can be used to analyze the permeability of power-law fluid in a rough damaged tree-like branching network.