Modeling, estimation and optimization in coreflooding experiments for coalbed methane production

• Coal coreflooding experiments for biogenic methane production were modeled.
• The coupled kinetics and transport model was validated against experimental data.
• Methane production was optimized by varying nutrient injection characteristics.
• Model reduction was performed based on active and exhausted reactions and modes.
• The model reveals that much of the methane produced is from the nutrient, tryptone.

We extend a previously derived kinetic model for coal bioconversion and couple it with a transport model to simulate coreflooding experiments with packed crushed coal, which are representations of a coalbed methane (CBM) reservoir at the laboratory scale. We apply a tanks-in-series model to simulate plug flow in the core, and the nonlinear model is regressed against experimental data using particle swarm optimization. The validated model is used to analyze CBM production at different operating conditions and subsequently for the optimization of gas production. Model-based experimental design is applied to improve the accuracy of parameter estimation, and computational singular perturbation analysis is applied to develop a better understanding of the important species and reaction at each stage of the coreflooding experiment, and to develop reduced order kinetic models that can be used in process optimization.