In order to understand the effect of nutrient amendment on coal consortia stimulation, NETL will be conducting lab-scale bench tests with the future goal for in situ testing and field deployment.
Lab-Scale Bench Tests
It remains unknown whether a successful nutrient amendment will contain limited nutrients (phosphorous, nitrogen), trace metals (Zn, Co, Fe), or an oxidizer to increase bioavailability of coal. Various combinations of these are currently being tested in nutrient amendment experiments.
Initial nutrient amendment experiments are conducted under anaerobic conditions and reservoir temperatures in incubation bottle tests. However, the native microbial consortia is expected to be adapted to subsurface conditions typical of high temperature, high pressure, anaerobic, saline environments. In order to understand the native coal-to-methane producing microbial community and expected changes with nutrient amendment exposure, microbial consortia collected from coal samples must be placed back under subsurface conditions. Successful bottle-tested nutrient amendments are further tested under reservoir conditions in NETL-designed bioreactors. NETL utilizes static and flow-through bioreactors with gas sensors capable of methane and carbon dioxide measurements without sampling disruption. The sensor and the bioreactor are capable of anaerobic conditions, reservoir pressures from 0-1,000 psi, and temperatures from 40-150ºF during operation.
Gas chromatograph (GC) analysis, microbial analysis, and coal characterization are performed on coal samples before and after bioreactor incubation. Results from microbial analysis, coal characterization, and methane measurements will be used to select optimal biogasification sites and nutrient amendment strategies for future field deployment.