Wellhead Samples of High-Temperature, Low-Permeability Petroleum Reservoirs Reveal the Microbial Communities in Wellbores

Abstract

In order to understand the microbial processes in petroleum reservoirs, most liquid samples are collected directly from wellheads because this method is convenient and causes no interruption to oil production. However, the wellhead fluids include the microorganisms inhabiting the wellbore, which could distort the understanding of the community in the reservoir. Therefore, the wellbore community as a possible contaminator should be investigated beforehand. A new method is proposed in this paper to exploit the extreme conditions of selected reservoirs, including low permeability (<40 × 10–3 μm2) and high temperature (>120 °C), to retain and inactivate the microbes in strata, so that the wellbore community can be cost-effectively investigated by directly sampling wellhead fluids. In three selected reservoirs, the results of 16S rRNA gene clone libraries show that both bacterial and Archaeal domains were dominated by Firmicutes, Proteobacteria, and Euryarchaeota with low richness (number of operational taxonomic unit, 10–15), while no hyperthermophiles (>110 °C) were detected. Combining the environmental adaptability and the significant dissimilarity between the three communities, it is suggested that in these reservoirs the wellhead samples could represent the communities inhabiting the wellbores, instead of the reservoirs. The coexistence of aerobes and anaerobes indicate that petroleum production processes (such as drilling and workover) were continuously introducing substances (biomass and oxygen) from the upper strata and surface into the wellbore. Of these exogenous microorganisms, mesophiles and aerobes could gradually become dominant over time because growth rates are faster than in thermophiles and anaerobes. Therefore, after decades of oil production, the wellbore community (providing a significant temperature variation along the wellbore) would have a great possibility to become distinct from the reservoir community. This could explain some common problems frequently appearing in field studies, such as the unexpected detection of aerobes and/or mesophiles in the wellhead fluids from anaerobic and thermophilic reservoirs.

Complementary DNA/RNA-Based Profiling: Characterization of Corrosive Microbial Communities and Their Functional Profiles in an Oil Production Facility

“…The temperature at the time of sampling in all analyzed locations was approximately 40°C, which could explain the lower abundances of thermophiles in the active communities. Thermophilic microorganisms are commonly associated with native populations in oil reservoirs (Ollivier and Magot, 2005; Song et al, 2017), however, temperature gradients generated during the production process favor the growth of mesophilic microorganisms at lower temperatures (Li et al, 2017b). The effect of the temperature variations on the community structure of active populations has been previously evaluated (Salgar-Chaparro et al, 2019).…”

Responses of Microbial Community Composition to Temperature Gradient and Carbon Steel Corrosion in Production Water of Petroleum Reservoir

“…Although they often occurred in production water of high temperature oil reservoirs ( Guan et al, 2013 ; Li et al, 2016 ; Tian et al, 2017 ), it is also possible that they might come from cool portions of the wellbores not the deep oil reservoirs. And it has been reported that the wellhead samples of high-temperature, low-permeability petroleum reservoirs could represent the communities inhabiting the wellbores, instead of the reservoirs ( Song et al, 2017 ). Desulfovibrio species are metabolically diverse and often coupling hydrogen or volatile fatty acid consumption with sulfate, iron, or nitrate reduction ( Bryant et al, 1977 ).…”

“…Distinct thermal characteristics of subsurface and surface environments can cause a considerable variation of the production fluid temperature in the oil production systems. The production fluids can provide mesophilic (20–40°C at surface of facilities and wellhead), thermophilic (> 45°C, middle part of wellbore) and hyperthermophilic (> 60°C, deep wellbore and reservoir) habitats ( Song et al, 2017 ). Despite the extensive study of petroleum reservoir, information about the potential of microbially influenced corrosion (MIC) of pipeline under the prevailing environmental condition is still lacking.…”

Community Distribution of Biofilms along a Vertical Wellbore in a Deep Injection Well during Petroleum Production

“…This taxonomical change was consistent with the present study. The smaller changes observed in the shallow-well study 12 and the significant changes observed in the deep-well study 48 suggested that the magnitude of the community changes in the biofilms became greater with increasing depth.…”