Research On Oilfield Produced Water From Asp Flooding Treated By Coagulation And Dewatering Performance Of The Sludge

Large-scale field test and industrial application of alkaline surfactant polymer(ASP) flooding has been carried out in Daqing oilfield. However, wo did not find an effective way to the treatment of the produced water. Most oilfields are still using the old three section process to treat it, or as a pretreatment before the membrane filtration. But because the oilfield produced wastewater has a characteristic of high viscosity, high pH value and emulsification seriously, it lead the dosage of conventional coagulant to be large or the effect of it to be invalid. Simultaneously, the effect of coagulation is poor. Thus, it results in the following consequences: the load of the filtration is heavy, the filter media could harden easily, the cycle of backwashing become shorter and the filtered water can not meet the standard. Consequently, in order to strengthen the coagulation process, we studied the treatment of the oilfield produced wastewater using the method of coagulation. And we studied the effect of chemicals on the dewatering of the chemical sludge, to make the sludge can be treated as well as the oilfield produced wastewater.By the tests of coagulation, four kinds of coagulant were filtered. They are iron(â…¢) chloride hexahydrate(FeCl₃), poly-silicate-ferric-zinc(PSFZn), poly-silicate-ferric(PSF) and polymer aluminum chloride(PAC). The best coagulant is PSFZn, and on this basis, we studied the influence of various factors on the coagulation. The results show that: the best pH value of PSFZn is 5.0, and the best dosage of it is 200mg/L; temperature has a little influence on the coagulation, so we do not need to heat it or cool it; the best hydraulic mixing conditions are as follows: the rapid stirring speed is 200r/min; the rapid stirring time is 1 minutes; the slow stirring speed is 80 r/min and the slow stirring time is 15 minutes; when precipitating 30 minutes in the static test, the removal of the pollutant has a little changes, however, we suggest that it need to extend it appropriately in the dynamic test; it need to add the acidic to adjust the pH value before dosing the coagulant, we can not add the acidic and PSFZn simultaneously. The effect of the PSFZn used alone is better than compounding with the polyacrylamide (HPAM).According to the optimum parameters determined, we conducted a static test to verify it. We designed a mixing-flocculation-sedimentation equipment and used it to do the dynamic test. The test results show that: the turbidity of the supernatant is between 6.2 and 16 NTU; the concentration of HAPM is between 35.86 and 38.71mg/L and the content of oil is less than 15mg / L. It can meet the requirements of the oil content of the injection water, which is injected into the middle permeability layer. Then considering the cost of the pharmacy alone, the cost of treating per ton of wastewater is about 2.423yuan, and it can save 1.447 yuan compared with the cost of pharmacy used in Daqing oilfield. Furthermore, it has some environmental benefits at the same time.Conditioning the sludge by adding chemicals, and using the specific resistance to filtration(SRF) as the main evaluation index, we studied the influence of the chemicals on the sludge dewatering. The results show that: the best pharmacy is the anionic HPAM whose molecular weight is 12×106. And we also analyse its mechanism for sludge conditioning. We believe that its main role is adsorption bridge, and the role of charge neutrality is weak. We also determined the optimal dosage of HPAM by tests, which is 20mg/L. And the optimal concentration of it is 0.5‰; the better stirring speed is 150～180r/min; the better stirring time is 120～150s and the optimal filtration pressure is 0.6～0.66MPa.