Hydromechanical Effects of Micro-Organisms on Fine-Grained Sediments During Early Burial
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AbstractMicroorganisms are known to change fluid flow and permeability processes in subsurface environments, but this has only been demonstrated for coarsegrained sediments and fractures. For finegrained sediments (mudstones), little is known about the effects of microorganisms on hydromechanical properties. Here, we investigated the influence of microorganisms on the porosity, permeability, and compressibility of finegrained sediments. We performed resedimentation experiments with and without microorganisms added to two reconstituted, finegrained sediment samples. These sediments were collected from the Ursa and BrazosTrinity Basins in the Gulf of Mexico during Integrated Ocean Drilling Program Expedition 308. Microorganisms caused a systematic, yet small increase in compression index for both sediments. Changes to permeability caused by microorganisms, while relatively minor, were greater for the Ursa sediment than the BrazosTrinity sediment. Additionally, the effect of microorganisms on permeability is greater at higher porosities and lower vertical effective stresses. Differences in permeability behavior between the two sediments are likely due to differences in sediment properties and nutrients for microbial growth. We therefore suggest that the effectiveness of microorganisms at altering fluid flow in finegrained sediments is dependent on burial depth (porosity as a function of vertical effective stress) and the grain size, pore and pore throat size, and specific surface area of a sediment. Characterizing the effects of microorganisms on the hydromechanical properties of finegrained sediments can further our understanding of the controls on pore pressure near the sedimentwater interface in marine environments and aid in bioclogging practices around contaminated sites in terrestrial environments.
