Produced water (formation water), separated during the production from the hydrocarbons is collected and treated in a water treatment plant for re-injection in the reservoir. OMV AUT plans the construction of a new water treatment plant, which shall replace the existing plant at Schönkirchen in the northeast of Vienna. In the course of that, the existing gravel filtration as the last step of treatment will be replaced by nutshell filtration. Aim of this work is the definition of optimal filter conditions for a nutshell filter, which are necessary to obtain a specified water quality in the drain, to the able to re-inject the purified formation water in the oil production process. The treated water has to reach an oil content and solids content of 1 mg/l and a WBF of <0.7 according the internal specifications. The WBF (Water Blocking Factor) is an OMV internal index, which gives information about the filterability of the treated formation water. The smaller the WBF is the smaller is the risk of the blocking of rock pores. The filter experiments were carried out using a nutshell filter in bench-scale, to investigate the requirements for the filter material and the procedures. In these experiments several nutshell granules and gradings were tested. Moreover the filtration velocity and the depth of the filter bed were variegated, to obtain the optimal filtration power. Furthermore different types of techniques of conditioning and regeneration were tested.