Analysis of Microbes in Hydraulic Fracturing of Montney Tight Gas Formations in Western Canada

Abstract

Abstract Microbes in unconventional gas operations can conceivably contribute to (i) degradation of polymers in hydraulic fracturing fluid, (ii) well plugging, limiting gas flow and (iii) souring and corrosion due to activity of sulfate reducing bacteria (SRB). Flowback waters from a tight gas field in Northern British Columbia were distinct from the fresh water, used for making hydraulic fracturing fluid, by their high salinity, low pH and high ammonium concentrations. Microbial counts of SRB and of acid-producing bacteria (APB) for these flowback waters were significantly lower than for the fresh water used to make the hydraulic fracturing fluid. Determining microbial community compositions by sequencing the 16S rRNA genes in the samples did not indicate the presence of microbes preferring high salt or high temperature conditions in samples of flowback water. These data indicate that these tight gas formations are sterile and that the microbes that are being introduced with the hydraulic fracturing fluid do not thrive downhole. Hence, microbes downhole are unlikely to contribute to well plugging, limiting gas flow. Microbes at or near the surface may cause polymer degradation in hydraulic fracturing fluid, especially when guar gum is used in gel-based fracturing treatments, and may cause souring in the fresh water, used for making hydraulic fracturing fluid, if this contains a significant concentration of sulfate.