Study On Treatment And Reuse Technology Of High-salinity Oilfield Produced Water

The development of water treatment and reuse technology for high-salinity oilfield produced water is highly beneficial to the reduction of the production cost, the improvement of the oil recovery and the decrease of the surrounding environment pollution in the exploration and production of offshore oilfields as well as many onshore oilfields.In this work the high-salinity oilfield produced-water treatment and reuse technology was investigated via the approach of lab simulation experiment, theoretical deduction, and field trial. The main contents and results obtained are as follows:1) Taking the advantage of the advanced detection equipments such as dynamic colloidal stability analysis, this thesis investigated the oil-in-water(o/w) emulsion, corrosion and scaling tendency of the high-salinity oilfield produced water. The results show that: the content of the emulsified oil in high-salinity oilfield produced water was influenced by the type and content of the dissolved salts. The presence of the multi-charged ions will decrease the influence brought by the double electrical layers, which will decrease the stability of the o/w emulsion. While for the oilfield produced water with scaling tendency, the stability of the o/w emulsion will be improved. With the rise of the temperature, the corrosion rate of the high-salinity oilfield produced water will be increased. As for the oilfield produced water with scaling tendency, the rise of temperature will inhibit the electrochemical corrosion. The presence of the dissolved oxygen will dramatically enhance the corrosion of the oilfield produced water. Since the precipitated scales contain a significant amount of dissolvable salts, more scale from the high-salinity oilfield produced water is expected than the theoretical prediction.2) Based on the molecular design, dodecydimethylamine, dimethylamine and ethylenediamine were used as starting materials to prepare the star-like polymer of quaternary ammonium salt ( SPQA) and partially crosslinked polyquaternary ammonium. They were used as the main ingredients for the prototype polyquaternary ammonium reverse demulsifier. The examination of the holding time during the synthesis, the ratio of ingredients, the dosage of the chemicals and the sedimentation time on the demulsifier performance indicates that all four factors influence the performance of the reverse demulsifier. The oil removal rate can reach as high as 97.6% by dosing 15mg/L of demulsifier.3) Analytical equipments such as laser particle size analyzer were used to study the demulsification mechanism and the results show that the reverse demulsifier can enable the emulsion droplets aggregate and flocculate within 1-2 mins, thus the demulsification mechanism is attributed to its multiple functionalities of charge neutralization, substitution and adsorption bridging.4)By analyzing the water quality, oil quality, corrosion products and characteristics of the technology, the developed technology of the corrosion and bacteria inhibitor and reverse demulsifier can cope with the complex corrosion brought by the H2S, CO2, dissolved salt and SRB bacteria,and attaining a corrosion rate less than 0.02 mm/a, can control the sewage discharge at OIW<25mg/L in the marine heavy oil exploitation,and <20mg/L in the lubrication oil exploitation.5)The simulated experiments shows that with the 10mg/L dosage of the complex formulation of maleic anhydride copolymer and organic phosphoric acid, the scale inhibiting efficiency of the mixed injection of the sea water and the high-salinity oilfield produced water can be >93%, safe for reuse.