Extraction and numerical simulation of gas–water flow in low permeability coal reservoirs based on a pore network model

ABSTRACT

This study aimed to investigate the effects of pore structure on gas–water permeability in low permeability coal reservoirs. A 3D digital coal model with macropores (>13.85 μm) was constructed by using a μCT225kVFCB test system and Avizo image processing software. An equivalent pore network model (EPNM) was extracted on the basis of the 3D model. PoreFlow was used to simulate the micro-flow process of gas and water in the EPNM. A control variable method was used to analyze the influence of pore structure on relative permeability. Results showed a sensitive zone in the relative permeability of the non-wetting phase in the low permeability coal reservoir. In this zone, the relative permeability of the gas phase showed remarkable variations, and the changes of the pore throat ratio (PTR) were minimal. In addition, a critical throat radius (TR) was established in the low permeability coal reservoir with water saturation (S_w) of less than 48.33%. Gas fluidity was poor when TR reached its critical value. The water phase relative permeability (K_rw) increased with the increase of PTR. The variation of K_rw was minimal as the coordination number (CN) increased. The influence of the pore throat structure on K_rw was ranked as PTR>TR>CN.

KEYWORDS:

• Micro-CT scan
• image processing
• digital coal
• network model
• two-phase flow simulation

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (No. 41772319).

Notes on contributors

Ya-Feng Han

Ya-Feng Han is a PhD candidate at the school of Civil Engineering, Chongqing University, China. He holds Msc in Mining Engineering, BTech in Mining Engineering. His main research interests include mining engineering, data mining in energy, information security, image processing and Geotechnical engineering.

Xiao-Yang Cheng

Xiao-Yang Cheng is an assistant researcher at the China Coal Technology and Engineering Group Chongqing Research Institute, Chongqing, China. His main research interests include mining engineering and exploitation of coalbed methane.

Xin-Rong Liu

Xin-Rong Liu is a Professor at the school of Civil Engineering, Chongqing University, China. His main research interests include mining engineering and Geotechnical engineering. He holds Bsc, Msc and PhD in Mining Engineering. He has over 160 publications relevance to his research interest.

Lei-Lei Zhao

Lei-Lei Zhao is a PhD candidate at the school of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing). He holds Msc in Mining Engineering. His main research interests include Mining Engineering and Solid Mechanics.

Jun He

Jun He is an assistant researcher at the China Coal Technology and Engineering Group Chongqing Research Institute, Chongqing, China. He received his Msc degree at the school of Energy Science and Engineering, Henan Polytechnic University, China, in 2012. His main research interests include mining engineering and exploitation of coalbed methane.

Jie Miao

Jie Miao received his Msc degree in mining engineering from Henan Polytechnic University in 2017. His main research interests include data mining in energy and exploitation of coalbed methane.