MICROBIAL-INFLUENCED SHALLOW-BURIAL DIAGENESIS

This project was funded by the American Chemical Society Petroleum Research Fund and investigates the mechanical and chemical effects of microorganisms on the early diagenesis of mudstones. While microorganisms can be found to depths of >500 meters below the sea floor, little is known about the interactions between microorganisms and sediments. To understand these interactions we use resedimentation experiments with and without microogranisms (iron reducing bacterium) to determine changes in mudstone microstructure, compressibility, porosity, permeability, and pore fluid chemistry. Our hypothesis is that biofilm growth in pore spaces will decrease porosity, permeability, and compressibility. Additionally, the pH and carbonate saturation index should increase due to the effects of iron reduction, potentially leading to precipitation of early diagenetic cements. Recognition of the micro-scale processes that take place during the early stages of mudstone diagenesis, especially those mediated by microbial activity, and their long-term effects on mudstone properties can lead to better identification and more effective production of unconventional hydrocarbon reservoirs.

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We developed a new model that accounts for the pH buffering of clay minerals during sediment diagenesis and shows that clay buffering plays a significant role in the precipitation of authigenic carbonate cements throughout Earth’s history. These results are published in the journal Geology [Mills et al., 2021].

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Further results on this project can be found in Mills et al. [2022].