Application of Electrochemical Treatment Technology of Produced Water of a Heavy Oil Field, via Boron Doped Diamond BDD Electrode

Abstract

Electrochemical technologies are a promising alternative for the Oil Industry, for the treatment of formation water containing organic and inorganic contaminants. The main advantages of these technologies include environmental compatibility, versatility, energy efficiency, health & safety and selectivity. However, the effectiveness of the electrochemical approaches depends significantly on the electrode material and the cell parameters. Recently, BDD electrodes have shown a growing interest due to their unique ultra-wide electrochemical window with highest O2 and H2 over-potentials. The current approach based on the application of boron doped diamond (BDD) electrode to treat electrochemically production water (PW) coming from a heavy oil field, was investigated in one-compartment electrolytic batch cell. Formation water is increasing more and more with the depletion of pressure and the age of many oil and gas fields. This formation water is characterized by high initial chemical oxygen demand (COD) due to their high level of organic content. Proper elimination of the high COD content from PW to be re-usable water streams for beneficial purposes such as irrigation water or correct disposal is becoming increasingly important for an environmental and human health in the Oil Industry. The influence of primary settling treatment step and several operating parameters such as applied current density, supporting electrolyte (NaCl or Na2SO4), agitation and temperature on the COD removal efficiency from PW were investigated and the corresponding energy consumption value was also evaluated. The estimated COD removal efficiency was achieved with and without settling step between 90 and 100 % within treatment time of 5h - 7h by using applied current in the range of 5 - 12.5 mA/cm2, but the minimum absolute value of COD for the resulting water with and without settling step was achieved to be less than 0.09 mg/l and 75 mg/l, respectively by adding 3.5 g/l NaCl. However, the energy requirement for high removal efficiency without adding NaCl was 2.5 more than with NaCl into PW. Adding NaCl into PW decreases the energy consumption and increases the oxidation efficiency by promoting the electro-generation of active chlorine species in addition to hydroxyl radical. On the other hand, only 67 % removal efficiency of COD was achieved by adding 5.1 g/l Na2SO4 into PW which affect negatively the COD removal efficiency compared to PW without any supporting electrolyte. The integration of electrochemical treatment step based on BDD electrodes after settling primary step, which is commonly used in industry, as a novel secondary treatment step will create a hybrid stable electrochemical system combining different electrochemical removal mechanism by BDD electrode as anode and cathode such as electro-oxidation, - reduction [1], -flotation, - coagulation and -disinfection simultaneously.