Degradation Characteristics and Mechanism of Guar Gum by Indigenous Coal Seam Microorganisms

Background Hydraulic fracturing is a widely used stimulation technique for the commercial development of coalbed methane (CBM), in which guar gum is commonly used as a thickening agent. However, under the low-temperature conditions of coal reservoirs, conventional chemical gel-breaking methods often exhibit incomplete gel-breaking and high residue content, which can induce formation damage and ultimately reduce CBM production efficiency.

Methods In this study, coal seam indigenous microorganisms were utilized as functional strains to conduct microbial gel-breaking experiments. The biodegradation characteristics of guar gum were systematically investigated, and the dominant microbial taxa responsible for its degradation were identified.

Results and Conclusions  Guar gum was completely degraded by coal seam indigenous microorganisms, meeting the gel-breaking requirement of a fracturing fluid viscosity ≤5 mPa·s while simultaneously reducing both the residue content and particle size distribution. Guar gum was primarily hydrolyzed by microorganisms into soluble polysaccharides, thereby reducing viscosity and achieving gel-breaking. Microbial community analysis revealed that Bacteroidota and Spirochaetota were the dominant functional phyla involved in guar gum degradation. Functional prediction using PICRUSt2 indicated that the degradation process mainly relied on the synergistic activities of α-galactosidase (EC 3.2.1.22), β-mannosidase (EC 3.2.1.25), and β-mannanase (EC 3.2.1.78). Among these, β-mannanase exhibited the most pronounced increase in gene abundance, suggesting its central role in guar gum gel breaking. Furthermore, environmental factors directly influenced gel-breaking efficiency. The highest degradation efficiency was observed at 45 ℃ and pH 6.0. High salinity inhibited guar gum degradation; however, the microorganisms retained gel-breaking capability even at a salinity of 40 g/L. This research not only elucidates the degradation mechanism of guar gum by coal seam indigenous microorganisms but also defines the impact patterns of environmental factors on their biological gel-breaking performance. The findings provide a theoretical basis for the application of indigenous microorganism-based biological gel-breaking technology in CBM extraction.