Aeration desulfurization of offshore oilfield produced water used for preparation of polymer solutions

Abstract

It is an inevitable trend to reuse treated oilfield produced water to prepare polymer solutions due to the shortage of freshwater resources in offshore platforms. The presence of S2− in produced water reduces the viscosity of the prepared polymer solution, which proves unfavorable for oil displacement. In this study, the aeration and sedimentation techniques were employed to desulphurize the produced water of an offshore oilfield in the Shengli Oil Field. The oxygen mass transfer coefficient was directly proportional to the aeration rate and the concentration of micromolecular organics, but inversely proportional to the concentration of petroleum hydrocarbons. Raising the air-water ratio from 0.1 to 2 increased the removal rate of S2− from 16% to 100%. The high temperature of produced water could enhance the oxidation of S2−, the products of which principally comprised elemental sulfur and thiosulfate at a low air-water ratio, but sulfate and sulfite at a higher ratio. An 8 h static sedimentation of the aerated produced water led to a significant decrease in the concentration of dissolved oxygen (DO), which was consumed by the low-valence sulfur-containing substances and reactive organic matters. When the hydraulic retention time was 20 min and the air-water ratio was 1, both S2− and DO were not detected in the produced water after sedimentation, which was qualified for confection of polymer solutions. Findings in this research is expected to provide a theoretical basis for optimization of parameters in the processes of aeration and sedimentation.