Investigation Of Analysis And Control Methods Of Suspended Solids In Oilfield Wastewater

At present, water flooding, as the secondary oil recovery technology is still used in oilfield in Xin Jiang province, and most wastewater after treating by joint station is reinjected. Since this region is low-permeability oilfield, the standard of injected water quality is strict. It will probably block the formation and badly influence the oil-production efficiency if the suspended solids(SS) content exceed standard. This research starts on analysis of the SS content, source, and components of wastewater in production area A&B. Meanwhile, the content of oil, iron and scaling ion which can influence to SS content directly are analyzed. Combined with components analysis of the adsorbates in the filtering tank, scaling tendency prediction and components analysis of the pipeline scale, the reason why it’s hard to make the SS qualified will be found. Thereby, the SS content will reach the standard of injected water quality with the help of wastewater treatment process and rational use of water treatment chemicals.The analysis of the SS, oil, and iron showed that the oil content in separator outlet water of production area A is about 200~300mg·L-1, and that there are some close relationship between oil and SS content. The SS content will increase if the oil is badly treated. The iron content in production area B wastewater exceeds 100mg·L-1, and the main influence factor to SS content is the oxidation of iron.The components analysis of SS and adsorbates in the filtering tank indicates that there are strong interactions between SS and strong polarity compositions(such as petroleum acid etc). And these interactions will influence the effect of water treatment agent and removement of SS. The components analysis of the SS in production area B indicates that half of inorganic substance is insoluble in HCl, and these compositions are mainly scale of Ba SO4 and Sr SO4.The results of pipeline scaling tendency prediction indicates scaling tendency of Ca CO3, Ca SO4 is not existened, and the scaling tendency of Ba SO4 is slight. But the scaling tendency of Sr SO4 is significant. The XRD analysis of pipeline scale sample showed what constitute the scale sample are oil scale, Ba SO4 and Sr SO4 scale and iron compounds. It is inferred that the pipeline scale results from the deposition of SS for a long time. The deposited SS will form crystal nucleus, and intensify scaling process.The results of water treatment agent experiment showed that the floc is difficult to sink because of the high oil content in production area A wastewater. Therefore, in order to control SS content, the SS should be wrapped by floc, and floating after adsorbing oil, then recovered with waste oil in the top of the settling tank by adding a small amount of organic flocculants and some inorganic coagulants. The water treatment agents in the preoxidization technology are evaluated synthetically in production area B. The results showed that the dosage of the oxidants and adjustments are main factors to the effect of the preoxidization technology. The dosage of the oxidants and adjustments are 60mg·L-1 and 30mg·L-1 respectively. In order to control SS content, 30 percent of Fe2+ are oxidized to Fe(OH)3 which makes the SS flocculated and sedimented with the help of adding a small amount of organic flocculants and iron removers.After technology adjustment, the content of SS in production area A&B are determined and the rate of reaching the standard is 100 percent.