High-Order Models for Gas Transport in Multiscale Coal Rock

Area of Science:

• Geosciences
• Computational Mechanics
• Petroleum Engineering

Background:

• Coal reservoirs display complex multiscale pore/fracture heterogeneity and anisotropy.
• Accurate real-time prediction of microgaseous flow in such media is computationally challenging and currently unavailable.

Purpose of the Study:

• To develop and validate a multiscale approximate solution for predicting coalbed methane (CBM) transport in macro-microscopic two-scale porous media.
• To establish a detailed finite element algorithm for analyzing gas flow and pressure fields.

Main Methods:

• Constructing multiscale approximate solutions using first- and second-order auxiliary cell functions and homogenized pressure field derivatives.
• Employing finite element algorithms for numerical simulations.
• Validating solutions by comparing with direct numerical simulation results.

Main Results:

• Homogenized solutions offer rough macroscopic pressure evolution.
• First-order solutions partially capture macro-microscopic pressure oscillations.
• Second-order solutions accurately predict pressure profiles and evolution in complex media, demonstrating high accuracy and efficiency.
• Developed models predict microgaseous flow with pronounced slippage effects at low reservoir pressures.

Conclusions:

• The second-order multiscale approximate solution provides accurate and efficient predictions for CBM transport.
• The developed models are applicable to hierarchical matrix-fracture systems in CBM and shale gas reservoirs.
• This research enhances understanding of gas transport in multiscale networks, crucial for optimizing hydraulic fracturing in tight reservoirs.