Study On Chemical Treatment And Recycling Of Biological Polymer Fracturing Waste Liquid System

Fracturing technology is an important measure to increase production of oil and gas wells and injection wells.However,the fracturing backflow contains a large number of refractory polymers and pollutants,If these pollutants are not treated in time,they will enter the ecological cycle,destroy the ecological environment around the well site,affect the condition of the surrounding surface water system and the life and health of residents.Therefore,it is urgent to develop efficient,practical,fast and recyclable treatment agents and processes to solve the difficult problems of refractory fracturing fluids,harmful organic compounds,metal ion pollutants.In view of the problems of high suspended matter content,high COD,high ammonia nitrogen value,difficult removal of mineral ions,high turbidity and high viscosity of fracturing fluid in Changqing Oilfield,this paper focuses on the analysis of suspended matter,chemical oxygen demand,high ammonia nitrogen content,high turbidity,main organic matter straight-chain alkanes in water and a small amount of aromatics with benzene ring structure organic compounds and nitrogen compounds in well Su 14-13-51 of Changqing Oilfield..Thereby,zeolite supported nano-titanium dioxide catalyst and nano-zero-valent iron with in-situ intercalation of montmorillonite composite treatment agent were designed and prepared.The morphology,particle size,specific surface area and element composition of nanocomposites were tested and analyzed,and the existing sewage treatment process was improved.The process of“flocculation--pre-oxidation--nano-TiO₂ozone-catalyzed oxidation--nano-zero-valent iron adsorption”was proposed.The mechanism of flocculation,catalytic oxidation and adsorption for advanced treatment of fracturing return fluid was studied,and the treatment method of fracturing return fluid reuse was explored.The flocculation-preoxidation system was designed,the optimum conditions for COD removal rate of fracturing backflow fluid treated by flocculant polyferric sulfate?PFS?are p H=8 and dosage of 0.4%,which can produce the best bridging and adsorption bridging performance.At the same time,it is found that Fenton oxidation reagent has a significant effect on COD removal rate,while H₂O₂has a weak effect.The maximum COD removal rate was 88.2%at p H=3 and the ratio of Fe SO₄.7H₂O:H₂O₂?30%?=1:6?molar ratio?The nano-titanium dioxide catalytic oxidation system was designed.The average particle size of catalyst is 2.5 um,and the average particle size of nano-titanium dioxide is 10-20 nm,which is uniformly dispersed on the surface of zeolite.Its catalytic oxidation performance is 25%higher than that ozonation alone.The prepared montmorillonite intercalated nano-zero-valent iron is spherical or ellipsoidal with an average particle size of 20-50 nm,and its specific surface area of 34.378 m²/g is larger than that of reduced iron powder of 0.1121 m²/g.The catalytic effect of 0.1%of the catalyst and 5 min of ozone entrance time was the best,while that of 5.0 g/L of zero-valent iron and 4 h of adsorption time was the best.The final effluent COD value of comprehensive treatment is stable below 100 mg/L,and ammonia nitrogen concentration is lower than 15 mg/L,the Ca²⁺,Mg²⁺and Fe³⁺concentrations that affected the salinity of the wastewater decreased significantly,which met the first level discharge requirement of National Sewage Comprehensive Discharge Standard?GB8978-1996?.The reusability of treated fracturing fluid was also explored.The base fluid viscosity,salt resistance,temperature resistance,shear resistance,static filtration loss?initial filtration loss,filtration coefficient,filtration rate?,residue content and surface tension of gel breaking fluid of the fracturing fluid system met the requirements of industry technical indicators.