Biomass thermal decomposition induced hydrogen sulfide blooming in thermal recovery reservoirs

High concentration of secondary hydrogen sulfide (sH₂S) in thermal recovery reservoirs of Liaohe Oilfield, NE China was concluded to originate from thermochemical sulfate reduction (TSR), and no biotic source of H₂S under abundant biomass has been reported in these presumed steam sterilized reservoirs ever before. In this study, we propose a new mechanism, biomass thermal decomposition for sulfur compounds (BTDS), to interpret the increasing of sH₂S. Sulfur of cells’ dry weight took 0.20%–1.92% of the active strains isolated from the in-situ thermal recovery reservoirs of Liaohe Oilfield. When microbial organic sulfur compounds (MOSC) in biomass were exposed to injected steam, it resulted in the BTDS process. The isolated Bacillus subtilis D3 (G+) and Pseudomonas aeruginosa XJ14 (G−) were chosen to simulate this process. About 36% of sulfur in MOSC emitted as H₂S in steam chamber by BTDS. The δ³⁴S of H₂S from produced gas ranged from 8.7‰ to 17.0‰, close to the δ³⁴S of H₂S 11.2‰ from BTDS simulation experiment. It provides new insight into the contribution and sulfur cycle made by subterranean microorganisms on H₂S formation.