Microbiology in Hydraulically Fractured Shales
Our understanding of the causes, forecasting and simulation of microbiological oilfield reservoir souring isn’t limited to conventional onshore, offshore and subsea reservoir environments.
In association with Natural Environment Research Council (NERC) Research Fellow, Dr Sophie Nixon, and her team in the Department of Earth and Environmental Sciences at The University of Manchester, we are actively investigating the microbiology of hydraulically fractured shales.
Over the past decade, the production of natural gas from onshore shale reservoirs has increased significantly around the globe. At the same time, research has confirmed the existence of active microbial communities in fractured shale environments.
New microbial habitats
Similar to conventional oil production, where the introduction of sulfate-containing water during secondary recovery can propagate microbial life, the presence of bacteria in injected fluids can assist the creation of new microbial habitats in the hydraulically fractured subsurface. As evidence, a growing number of studies have identified the presence of potentially financially damaging microbial communities in production fluids.
During the hydraulic fracturing process, the injected freshwater can interact with salts and brines within the rock, resulting in brine-level salinity in produced waters and salt-tolerant microorganisms which are able to endure extreme downhole conditions over hundreds of days, often remaining viable long after the recovery of fractured fluids.
The opportunity for biofouling
The drilling and hydraulic fracturing for shale gas introduces the microorganisms, energy sources, water and space necessary for microbial life – and it is the microbiological life forms which inhabit fractured shale formations that can result in biofouling, with higher production costs, reduced efficiency, as well as the potential for environmental damage.
Biofouling includes the formation of corrosive metabolic by-products, particularly sulfide and organic acids, as well as the clogging of fractures and reduced sensitivity to biocides. As a powerful corrosive agent, sulfide sours gas. More difficult to eradicate than in oilfield souring, it is also highly toxic and flammable, with the potential for environmental and equipment damage, and the need for enhanced injection chemistry. Whilst normally less corrosive than sulfide, organic acids, common by-products of carbohydrate fermentation, also assist corrosion.
Gaining a better understanding
Although the microbial communities collected from flowback and produced fluids are well documented, it is extremely challenging to study their activity in-situ. Our work with the Department of Earth and Environmental Sciences aims to provide a better understanding of the behaviour of these communities, including whether or not their colonization of fractures reduces total gas yields, what effect pressure and temperature (P/T) have on microbial metabolic processes, the potential interaction of pyrite with oxidising additives – and if shale geochemistry has the potential to sustain microbial communities long after additives have depleted.
Over the past decade, the production of natural gas from onshore shale reservoirs has increased significantly around the globe.