Study On Enhanced Coagulation Pretreatment Of Oil And Gas Field Wastewater

In the process of exploitation and exploitation of oil and gas resources,a large number of produced waters,fracturing fluid,drilling wastewater will be produced.This wastewater will endanger the surrounding environment and soil and water resources,and affecting the further development of oil and gas fields.This kind of waste water is caused by mining technology and water mixed with formation water or even mud,usually high COD,high oil content,high salt content,high suspended solids content and contains a large number of chemical additives and so on.Moreover,the water quality and composition in the solution are complex and varied according to the process and the local formation conditions.Therefore,there is no fixed treatment technology.Oil and gas field wastewater treatment is often based on the characteristics of its water quality using a variety of different processes to form a joint treatment,to satisfy the relevant standards of reinjection,reuse or discharge.Foam fracturing flowback fluid in gas field is a kind of difficult to treatment in oil and gas field wastewater.And foam fracturing technology will be used in the middle and later stage of gas field development.Therefore,there are not many researches and applications on Foam fracturing flowback fluids in gas field.This topic is based on national science and technology major projects,Environmental Protection Technology Integration and Key Equipment for Oil and Gas Development.Taking Foam fracturing flowback fluid in gas field as research object,Coagulation and enhanced coagulation treatment were carried out.Through a series of influencing factors test and enhanced coagulation process experiments,the best coagulation condition and effective enhanced coagulation method were determined.In addition to saving the dosage of coagulants,the removal efficiency of the main pollutants in the foam drainage is improved.Enhanced coagulation as a pretreatment process,it can effectively relieve pressure for foam drainage and subsequent treatment of similar oil-gas field wastewater.The main contents and achievements of the study are as follows:(1)According to hydraulic condition experiment and influence factor orthogonal experiment,The best level of each factor is: The dosage of coagulant is 4000mg/L;The dosage of coagulant aid is 60mg/L;pH is 5;the temperature is 60℃;at the mixing stage,Stirring rate is 250r/min,Stirring time is 120s;at the Flocculation reaction stage,Stirring rate is 40r/min,Stirring time is 450 s.The influence degree of each factor on coagulation treatment is determined: pH;Coagulant;temperature;Coagulant aid.(2)Through a series of experiments on coagulating factors and experiments on Coagulant adding points separately,The influence mechanism of PAC on the electric neutralization of pollutants as the dominant coagulation process was determined.And PAM as aid coagulant,its adsorption bridging effect is mainly in the flocculation stage to help coagulation treatment.Combined with the mechanism and the development of coagulation technology,to Analyzed and demonstrated.The results show that,There are a lot of metal ions and natural organic matter in the Foam fracturing flowback fluid in gas field.This is also one of the main reasons for the high concentration of COD,suspended solids and soluble solids in effluent.(3)Through A series of intensified coagulation experiments with changing processes for Foam fracturing flowback fluid in gas field.The effect of coagulation treatment is enhanced,the removal rates of all major pollutants in the solution are improved.The mechanism of aeration oxidation and Coagulant adding point to enhance coagulation efficiency is determined respectively: Aeration can cause oxidation reaction of pollutants in solution,Breaking the emulsion state of solution,And destroy the stability of colloid,It makes the suspended solids,organic substances and colloidal particles in solution more easily adsorbed and coagulated by coagulants and occurs flocculation reaction,So as to enhance coagulation efficiency;The addition of drugs at different points can make PAC and PAM play their biggest roles in different stages,Using PAC neutralization as the mechanism of action to promote coagulation and flocculation in the mixed stage,The adsorption and bridging mechanism of macromolecule polymer promotes the aggregation of flocs in flocculation,So as to enhance coagulation efficiency.