Microscopic pore controls on seepage behavior in varied coal structures based on dual-scale digital core analysis

Area of Science:

• Geology
• Petroleum Engineering
• Materials Science

Background:

• Tectonic deformation significantly modifies coal's pore-fracture structure, impacting fluid flow and gas outburst risks in coalbed methane (CBM) reservoirs.
• Understanding these multiscale structural changes is crucial for effective CBM reservoir management.

Purpose of the Study:

• To investigate the influence of geometric and topological parameters on coal seepage behavior at micron and submicron scales.
• To compare the flow characteristics between primary coal (PC) and tectonically deformed coal (TC).

Main Methods:

• Integration of micron and submicron-scale X-ray computed tomography (CT) for detailed structural analysis.
• Application of pore network modeling (PNM) to simulate seepage behavior and analyze flow dynamics.
• Correlation analysis to identify scale-dependent controls on permeability.

Main Results:

• Primary coal (PC) exhibits continuous, moderately connected fractures and uniform submicron pores, leading to smooth, stable flow.
• Tectonic coal (TC) shows increased fracture connectivity but spatial heterogeneity, with complex submicron pores, resulting in direction-dependent flow and preferential migration pathways.
• Permeability control shifts from geometric/topological effects at the micron scale to connectivity/throat-size sensitivity at the submicron scale.

Conclusions:

• Coal's pore-fracture morphology, altered by tectonic deformation, dictates multiscale seepage behavior.
• Scale-dependent analysis reveals distinct flow regimes and permeability controls in primary versus tectonic coals.
• Findings are critical for predicting fluid migration and mitigating gas outburst risks in CBM exploration and production.