Study On The Integration Of Boron Removal And Flocculation Of Shale Gas Fracturing Flowback Fluid

The hydraulic fracturing technology that can improve the reservoir permeability is often used to exploited shale gas,an efficient and clean unconventional natural gas resource.The fracturing fluid is usually injected into the formation during the fracturing process.In the end of fracturing operation,much of fracturing flowback fluid with high viscosity and complex composition will be produced.The fracturing fluid after treatment can be recycled to realize the recycling of water resources and degrade the environmental pollution caused by fracturing flowback fluid.However,the residual boron in the the treated water will affect the viscosity of the base fluid when the the treated water is used to prepare the fracturing fluid.Therefore,it is significant that exploring the efficient removal of boron during the process of treatment of fracturing flowback fluid for improving reuse rate of shale gas fracturing flowback fluid.In this paper,the fracturing flowback fluid in Northern Shaanxi Province is considered as the research object.After the research about the analysis method of residual boron in the flowback fluid,a coupling treatment process of"boron removal by chemical oxo-precipitation and flocculation sedimentation"is formed.The main conclusions can be summed up as follows:?1?The content of boron in shale gas fracturing flowback fluid was determined by ICP-AES.The detection limit is 0.005 mg/L,the measurement limit is 0.025mg/L,the relative standard deviation is less than 1%,the standard addition recovery rate is between 100.32%¹03.56%;the co-existence of SO₄²-,Ca²⁺,Mg²⁺,suspended matter,oil content and organic matter in shale gas fracturing flowback fluid have little influence on the analysis of boron;The residual boron content in the shale gas fracturing flowback fluid is124.5 mg/L by ICP-AES.?2?The results of the chemical oxo-precipitation showed that the best precipitant and oxidant were BaCl₂ and H₂O₂ respectively.The other conditions for the chemical oxo-precipitation were n?Ba?/n?B?=2.0,n?H₂O₂?/n?B?=4.0,pH_p=9,t_p=30 min,pH_r=10,t_r=360 min.At this time,the boron removal was95.5%,and the boron concentration in the simulated wastewater decreased from 150 mg/L to 6.75 mg/L.?3?When FeSO₄ or Ce₂?SO₄?₃ is added under the optimal conditions,the boron removal is 81.2%and82.7%respectively.In addition,the boron adsorption capacity of the precipitate is 41.2 mg/L and 44.9 mg/L respectively.The addition of FeSO₄ or Ce₂?SO₄?₃ will reduce the boron removal effect of the oxidation process to a certain extent.?4?On the basis of chemical oxygen precipitation,when the dosage of PAC is 400 mg/L and the dosage of PAM with cation degree of 60%is 10 mg/L,the residual boron content in the solution after treatment is2.59 mg/L,and the boron removal is 98.3%.?5?After the treatment of the flowback liquid by the method of"boron removal by chemical oxo-precipitation+flocculation sedimentation",the concentration of residual boron and suspended matter in the water are all lower than 4.0 mg/L,which meets the water quality requirements of the flowback liquid.A shale gas fracturing flowback liquid recycling treatment process integrating"boron removal by chemical oxo-precipitation+flocculation sedimentation"is formed.