The loss of hippocampal interneurons has been considered as one reason for the onset of temporal lobe epilepsy (TLE) by shifting the excitation-inhibition balance. Yet, there are many different interneuron types which show differential vulnerability in the context of an epileptogenic insult. We used the intrahippocampal kainate (KA) mouse model for TLE in which a focal, unilateral KA injection induces status epilepticus (SE) followed by development of granule cell dispersion (GCD) and hippocampal sclerosis surrounding the injection site but not in the intermediate and temporal hippocampus. In this study, we characterized the loss of interneurons with respect to septotemporal position and to differential vulnerability of interneuron populations. To this end, we performed intrahippocampal recordings of the initial SE, in situ hybridization for glutamic acid decarboxylase 67 (GAD67) mRNA and immunohistochemistry for parvalbumin (PV) and neuropeptide Y (NPY) in the early phase of epileptogenesis at 2 days and at 21 days after KA injection, when recurrent epileptic activity and GCD have fully developed. We show that SE extended along the entire septotemporal axis of both hippocampi, but was stronger at distant sites than at the injection site. There was an almost complete loss of interneurons surrounding the injection site and expanding to the intermediate hippocampus already at 2 days but increasing until 21 days after KA. Furthermore, we observed differential vulnerability of PV- and NPY-expressing cells: while the latter were lost at the injection site but preserved at intermediate sites, PV-expressing cells were gone even at sites more temporal than GCD. In addition, we found upregulation of GAD67 mRNA expression in dispersed granule cells and of NPY staining in ipsilateral granule cells and ipsi- and contralateral mossy fibers. Our data thus indicate differential survival capacity of interneurons in the epileptic hippocampus and compensatory plasticity mechanisms depending on the hippocampal position.

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The implementation of highly effective polishing filter technologies plays a key role in polymer EOR where reservoir characteristics require extremely good water qualities. Few filter technologies are capable of handling volatile inlet fluid conditions such as back-produced polymer concentrations up to 420 ppm and OIW contents up to 70 ppm while targeting treated water qualities of less than 5 ppm OIW. A fully integrated field trial was set up in the Matzen field in Austria where producing wells from EOR operations provide sufficiently high polymer concentrations for technology evaluations. A three-phase separator and a multi-chamber flotation unit were used as upstream treatment to supply produced water to the different filtration technologies under evaluation. With this setup, a broad range of entry criteria like OIW, solid content, polymer concentration and oil droplet size could be adjusted to challenge each filtration technology to its limit. None of the tested technologies such as nutshell filters, conventional multi-media-filters, coated media, or vendor specific technologies were able to handle the challenging inlet water conditions while providing the required water qualities for polymer flooding projects. A new concept was developed, combining conventional multi-media filtration design with a type of media that, thus far, was not common in the oil and gas industry. A system-specific operating envelope was developed, describing the strong impact of inlet water conditions such as oil droplet size D50 values down to 15 micron, OIW concentrations up to 70 ppm, solid contents up to 10 mg/l and viscosities up to 3 cp. Where state-of-the-art technologies did not fulfill the performance criteria, it was possible to achieve less than 5 ppm at the filter outlet. Not only the filter performance but also the crucial aspect of effective media regeneration was solved with a novel filter backwash design, since known backwash systems completely failed with the newly implemented media.

Cost-effective treatment of produced water is crucial for the implementation of EOR technologies. A multi-chamber flotation unit was tested under real-field conditions for a polymer flood of the Matzen field, Austria. The operating conditions, performance, and potential for cost-effective separation were successfully assessed with HPAM polymers for a concentration up to 800 ppm. In order to evaluate the performance of the flotation technology, a comprehensive test matrix for a widespread operating envelope was defined. Characteristics of the feed water were varied by selecting specific production wells from the Torton reservoir. Consequently, a wide range of retention times, oil-in-water contents, oil droplet size distributions, and EOR polymer concentrations were tested. The unit was operated with and without the application of a water clarifier. Performance was evaluated by measuring inlet and outlet water quality parameters via laboratory analyses and an in-line monitoring device. The impact of EOR polymer on the treatment efficiency clearly indicated a turning-point of treatment efficiency dependent on polymer concentration. Produced water conditions of polymer flooding operations are considered harsh due to the impact on oil droplet coalescing behavior and impacted viscosity. The influence of oil droplet size and shearing of polymer versus the impact of retention time on effectiveness was assessed. On-site core-flood tests were performed to evaluate the injection behavior of treated water with different HPAM polymer concentrations and in combination with and without a water clarifier.