Study and Application on Removal of Silica by Chemical Coagulation Process from the Oil field Produced Water Reused in Boiler

The technology of steam injection on the development of heavy oil and low permeability reservoirs has been successfully applied in the worldwide, and one of the key process is the amount of steam injected. The fresh water can be supplied for steam boiler in ground facilities, but it will cause the shortage of fresh water resources. So produced water reuse as the environmental-friendly technology can both make use of waste and avoid the discharge of produced water in the power generation. However, in the development of special oil field, the produced water often contains large amounts of SiO₂ in the form of ion or colloid, these Silica compound are easy to form dense and rigid Silica scales at high temperature, which is difficult to clean with conventional methods, the heat transfer efficiency and safe operation of the boilers and other process equipment are affected seriously. Accordingly, the reuse of the produced water replace of the fresh water is restricted. So, the removal agent of Silica with main agent of Magnesium Sulfate is developed in this paper. The reaction mechanism, the pH regulation of water, the adsorption, coagulation and precipitation of Silica are considered respectively. The optimum compositions are as follow: C_MgSO4:C_NaOH:C_PAC:C_CPAM=12:24:8:3. The agent is applied in the oil field and the results show that the average Silica content from 248.4 mg/L in incoming water to 47.1 mg/L in effluent water, the removal of Silica efficiency is up to 81%, the treated water achieve the quality goal of boiler feed water. The situation of shortage of fresh water resources can be alleviated effectively. Simultaneity, a variety of potential environmental hazards caused by discharged of high-temperature produced water are eliminated. The study is significantly for save energy and reduce consumption, environment-friendly and sustainable development in crude oil industry.