Laboratory study of the electrochemical pre-oxidation for improving thermodynamic stability of an oilfield produced water

Abstract

Currently, oilfield produced water (OPW) in Haoxian Station, Shengli Oilfield was only treated in a simple physical procedure including sterilization, sedimentation and filtration. The thermodynamic stability of the treated OPW was not satisfied. The concentration of the suspended solid (SS) in the treated OPW would gradually increase in the process of OPW transportation from the station to injection wells. The concentration was over than 32 mg/L in some injection wells. This paper presented a new technology of electrochemistry pre-oxidation for OPW disposal. The effects of pre-oxidation electrical voltage and the pH on the actual treatment result and the corrosion rate of the OPW were investigated, and the optimal conditions were decided as an electrical voltage of 10 V and pH of 7.0. The indexes of the OPW treated with the new technology could completely meet the requirements of C1 grade in the SY/T 5329-94 standard (a criterion of China Petroleum Industry). The concentration of the SS in the OPW did not increase with time and corrosive rate of the treated OPW was only 0.044 millimeter per year (mm/a), less than 0.076 mm/a required by SY/T 5329-94, which implied improvement of the thermodynamic stability. Moreover, the compatibility of the treated OPW with the formation water was greatly improved after pre-oxidation treatment, thus less of formation damage would be made when the OPW was used for waterflooding.