Sulfate-reducing bacteria streamers and iron sulfides abruptly occlude porosity and increase hydraulic resistance in proppant-filled shale fractures

AshaleGeoBioCellmicrofluidic testbed has been used to evaluate the processes by which the growth of sulfate-reducing bacteria (SRB) biofilms and iron sulfide biominerals reduce porosity and increase hydraulic resistance (HR) in hydraulically fractured (fracked) shale reservoirs. These microbe-mineral-water interactions were tracked in real time at 45°C (113°F) within proppant-filled microchannels constructed within Devonian New Albany Shale samples from the Illinois Basin. Metagenomic analyses of the SRBcommunities usedinexperimentation indicate they are composed of Desulfovibrio alaskensis,Aminivibrio sp., and two Synergistaceae sp. The SRB growth and iron sulfide precipitation were trackedwith high-resolution brightfieldmicroscopy and HR measurements. After ∼80-160 hr, exponential increases in HR reached complete clogging after ∼150-230 hr (HR > 0.10 psi/(μl min-1)). Porosity and permeability occlusion was caused by the growth of SRB biofilm streamers encrusted with iron sulfides. Environmental scanning electron microscopy revealed that these large SRB streamers that were hundreds of micrometers in diameter were composed of microbial cells that adhere to each other, attach to proppant surfaces, and extend downstream in and around proppant pore spaces. This indicates that in proppant-filled fracked shales, SRB streamers with iron sulfides readily attach, occlude pore space, and hinder flow. This establishes the shale GeoBioCell as a viable experimental testbed for future determination of the efficacy of microbial biocides and other oil field amendments that are routinely applied to maintain and enhance hydrocarbon production in fracked shale reservoirs.