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

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.

Advances in Tools to Monitor Souring and Corrosion in Oil and Gas Fields

“…There is no evidence of this in this study as indicated also elsewhere (Elliott et al, 2014). The high temperatures of Montney shale gas fields (70-100°C), caused by their location at depths of 2500 mbs or more, combined with the high salinity (Ͼ2 Meq of NaCl) and a low pH of this environment prevents microbial growth.…”

“…Samples were obtained from a shale gas field in the Montney formation in NE BC, located at 2500 m below the surface (mbs), where the resident temperature is 75-100°C (Elliott et al, 2014). Samples were also obtained from a shale oil field in the Bakken formation, located at 1000 mbs with a resident temperature of 30-35°C.…”

“…This field is injected with water drawn from a nearby shallow subsurface formation. Shale gas samples obtained included a sample from a fresh water storage pond (M_SW), used to formulate fracturing fluid, as well as two samples of produced water retrieved from a well separator and two samples from a high total dissolved solids water storage pond (Elliott et al 2014). These four samples will collectively be referred to as Montney produced waters (M_PW).…”

Geochemistry and Microbiology Predict Environmental Niches With Conditions Favoring Potential Microbial Activity in the Bakken Shale

“…Hydrocarbon resources represent an important global energy source, currently providing over 75% of primary energy in the United States (U.S. Department of Energy et al, 2020b), and also play an essential role in other countries including Canada and the United Kingdom (Stevens, 2013;Elliott et al, 2014;Rivard et al, 2014). The majority of fossil fuels are currently extracted from unconventional wells using advanced technologies, including horizontal drilling and hydraulic fracturing (U.S. Department of Energy et al, 2020a).…”

Biogenic versus Thermogenic H2S Source Determination in Bakken Wells: Considerations for Biocide Application

“…Most studies report the presence of bacteria in produced water, 2−4,9,12−15 although a number of studies have found few to no bacteria present. 6,8 Of those studies in which bacteria were found, the Marcellus shale formation shows an eventual dominance by halotolerant sulfidogenic organisms, 2,3 while other shale plays seem to exhibit highly diverse microbial consortia. 4,9,12,13,15 H 2 S gas may also arise from geochemical sources 18 and has been shown to originate from the interaction of hydrocarbons with sulfur-bearing minerals such as anhydrite (CaSO 4 ), at 284 °F, 19 via the following reaction:…”