Biogenic methane potential for Surat Basin, Queensland coal seams

Abstract

Produced water samples collected from Surat Basin coal seams in eastern Queensland, Australia were shown to contain viable microbial consortia with the ability to convert native Walloon coal into methane. Methane generation rates of up to 1.0 m3/t coal/day (30 scf/ton/day) were observed, with overall yields up to 6.5 m3/t coal (210 scf/ton); in comparison, total methane reserves for the Surat Basin are typically 4 to 8 m3/t. This is the first direct evidence of real-time biogenic coal-to-methane potential for an Australian coal seam sample. Six of the eight Surat Basin water samples tested positive for biomethane production when H2–CO2 was provided as the sole methanogenic substrate; five produced methane from methanol, but acetoclastic methanogenesis was not observed. An active H2–CO2 pathway could have implications for the conversion of sequestered CO2, if an in-situ source of reduced hydrogen is present in excess. In a simple experiment, biomethane production from a Walloon coal was not enhanced when the bicarbonate concentration in the medium was doubled. It is anticipated that the low surface area/solubility of coals may limit their bioavailability; coal-to-methane rates and final yields increased in proportion to the coal particle surface area. Similarly, when a Zonyl FSN surfactant was added to improve coal bioavailability, the initial methane production rate increased by 240%, and the final methane yield increased by 180% in comparison to a no-surfactant control. Overall, these results suggest an opportunity to enhance Surat Basin coalbed methane reserves via in-situ stimulation of indigenous microbial consortia.