Calibrating and validating a numerical model concept for microbially enhanced coal bed methane production with batch and column data

Microbially enhanced coal-bed methane (MECBM) production is an innovative idea to stimulate biogenic coal-bed methane production by providing nutrients to the native microbial community. Through additional substrate in the subsurface, a stimulation of microbes occurs, which leads to an increased methane production. Experimental studies, performed at Montana State University, provide the basis for modelling MECBM production with two-phase multi-component transport processes using the numerical simulator DuMuX [1].

We will present the calibrated and validated numerical batch model. The conceptual model comprises a food-web that includes two types of bacteria and three types of archaea representing substrate-specific members of the community with the corresponding biogeochemical reactions. These are derived from experimental studies [2]. The model is able to capture the interactions between different microbial groups, coal bioavailability, biofilm growth and decay as well as CH4 production.

The numerical batch model is extended to simulate column studies [3]. The model is being used to test hypotheses on different processes e.g. coal bioavailability and retardation or filtering effects when adding substrate. The numerical model provides a more detailed understanding of the relevant processes involved in MECBM production as well as a general understanding of biogeochemical reactions coupled with possibly changing flow and transport conditions in the subsurface. This model will be an instrumental tool in further development of a more sustainable method of harvesting methane from unmineable coal-beds.

[1] Koch, Timo, et al. "DuMu^X3--an open-source simulator for solving flow and transport problems in porous media with a focus on model coupling." arXiv preprint arXiv:1909.05052 (2019).
[2] Davis, Katherine J., et al. "Biogenic Coal-to-Methane Conversion Efficiency Decreases after Repeated Organic Amendment." Energy & fuels 32.3 (2018): 2916-2925.
[3] Davis, Katherine J., et al. "Biogenic coal-to-methane conversion can be enhanced with small additions of algal amendment in field-relevant upflow column reactors." Fuel 256 (2019): 115905.