Organic amendments for enhancing microbial coalbed methane production

Abstract

Coalbed methane (CBM) is natural gas found in subsurface coal beds and supplies approximately 4-6% of the annual U.S. natural gas requirements. Many unmineable coal beds contain CBM produced by native microbial communities. Enhancing the microbial processes for coal-to-methane conversion can increase the rates of CBM production and the amount of extractable natural gas in these coal beds. Strategies for enhancing microbially-produced CBM must be logistically attainable and economically practical. The goal of this dissertation work was to determine a feasible methane enhancement strategy using organic amendments to increase microbial coal-to-methane conversion. Four organic amendments were tested in coal-containing batch microcosms. Increased coal-to-methane conversion was demonstrated with small amounts of amendment addition, and all four tested amendments increased methane production similarly. Subsequent amendment addition produced smaller amounts of additional methane which appeared to be primarily due to amendment-to-methane conversion. 13 C-labeled algal and yeast amendments were used in coal systems for tracking carbon for methane production. It was shown that <22% of the amendment carbon was converted to methane. By tracking amendment carbon, it became clear that carbon sources besides coal and amendment are utilized for methane production; these carbon sources potentially include organic and inorganic carbon in the formation water and inoculum. Amendment strategies tested in batch systems were scaled up and applied to column reactors. Methane production from coal increased with small amounts of 13 C-labeled algal amendment addition. However, unlike in batch experiments, methane production rates in the column flow reactors did not slow or cease after 60-90 days, and methane was still being produced after 176 days when the study was terminated.