Influence of the Bacterial Factor on the Change in Formation Permeability During Produced Water Reinjection

On Danish fields in the North Sea, a large amount of produced water is generated. The problem of disposing of this volume is a major challenge for the oil and gas sector in general. Produced water is a complex mixture of dispersed and dissolved components. The former includes dispersed oil and solids, while the latter can consist of water-soluble organic compounds, dissolved salts, and production chemicals (Dudášová et al., 2014). According to a report by the Danish Energy Agency (2023), 30.8 million cubic meters of produced water are extracted annually. One method of disposing of this volume is discharging produced water into the North Sea. However, this approach is a primary source of ocean pollution with crude oil and PAHs, affecting the populations of biota in the water column (Beyer et al., 2020). Additionally, produced water contains heavy metals and radioactive materials (Hansen and Davies, 1994), which can impact food security in the discharge region (Milenkovic et al., 2019). As an alternative, the process of reinjecting produced water is used to maintain reservoir pressure and displace hydrocarbons from production wells (Saripalli et al., 2000). Produced water undergoes a purification process that includes degassing, oil separation, biological treatment, coarse purification, and deoxygenation, after which it is injected into the reservoir (Fakhru'l-Razi et al., 2009). However, this method is associated with several disadvantages. As operator practices show, the decline in permeability during the reinjection of produced water leads to a rapid decrease in reservoir permeability, necessitating additional measures to control oil and gas inflow. The decline in permeability during the reinjection of produced water poses a significant obstacle for oil and gas companies in the North Sea region. The presence of total suspended solids (TSS) (Ye et al., 2013), total dissolved solids (TDS) (Hosseinzadehsadati et al., 2024), oil content (Zyleyka, 1999), and bacterial growth (Gandler et. all, 2006) can accelerate the decline in injectivity in injection wells. In the context of reinjecting produced water into chalk reservoirs, the fluid composition, temperature, and presence of organic contaminants play a more significant role due to the very low permeability (typically less than 2 mD) and high porosity (more than 20%) of chalk formations (Childs and Reed, 1975).