Research And Application Of Boron Removal Agent For Fracturing Flow-back Fluid

With the increasing demand for energy,the development of unconventional oil and gas reservoirs is becoming more and more vigorous.Fracturing technology has become an important stimulation measure in the process of unconventional oil and gas reservoir exploitation.After the fracturing operation is completed,a large amount of fracturing flow-back fluid will be generated.Reuse after fracturing flow-back fluid which is purified is the main way out.Borax and organic boron are usually used as crosslinking agent for fracturing fluids.After fracturing process,the residual boron in the flow-back fluid will cause premature crosslinking and blockage of fracturing fluid pipeline when fracturing flow-back fluid is reused after treatment.The determination method of boron content is studied in the paper,and a fast and accurate method for the determination of residual boron content in fracturing flow-back fluid is determined.The effect of XSC-700 boron specific resin on the removal of boron from pre-treated fracturing flow-back fluid is explored.The main conclusions are as follows:1.With bromocresol green-methyl red-phenolphthalein mixed solution as indicator and mannitol dosage of 7 g/100mL,the determination range of boron content by titration is 50～300 mg/L.The relative standard deviation of the method is 0.78%.The recovery rate is 99.09%～100.69%.It has good precision and high accuracy.The coexistence of Ca2+,Mg2+,SO42-,suspended solids and oil in the flow-back fluid has little influence on the determination results.2.The range of determination of residual boron by curcumin spectrophotometry is 0.02～10 mg/L,regression equation A=0.2644C-0.0026,R2=0.9999,detection limit is 0.02 mg/L.The coexistence of Ca2+,Mg2+,suspended solids in the flow-back fluid has great influence on the determination results.3.The adsorption performance of XSC-700 boron specific resin on boron is affected by time,initial borate concentration,resin dosage,temperature,pH and rotational speed.Add 2.5g/100mL XSC-700 boron specific resin in boric acid solution with pH 9 and initial borate concentration of 50 mg/L.At room temperature,200r/min oscillates for 1 h,and the removal rate can reach above 90%.The pseudo-second-order model appears to be more suitable to describe the adsorption kinetic data than pseudo-first-order model,indicating that the adsorption is a chemical adsorption.Isothermal adsorption line is more consistent with Freundlich isothermal adsorption model.The coexisting ions of Ca2+,Mg2+,SO42-,CO32-had little effect on the adsorption performance of the resin,and the removal rate of the new resin remained at 85%after five cycles of regeneration.4.The residual boron content of fracturing flow-back fluid in Yan’an area is 47.15 mg/L and the pH is 6.0 after pre-treatment such as oxidative,flocculation and sedimentation.The residual boron content in flow-back fluid can be reduced to 3.67 mg/L by adding about 2.5 g XSC-700 boron resin to 100 mL water sample.The removal rate of boron can reach 92.22%,which meets the requirement that the residual boron concentration in flow-back fluid is less than 5 mg/L.5.Initial borate concentration,resin volume and sample flow rate are closely related to the dynamic adsorption process of boron on resin.When the sample flow rate is 1.5 mL/min,resin volume is 10 mL and injection concentration is 50 mg/L,the residual boron concentration of boric acid solution,simulated fracturing flow-back fluid and field fracturing flow-back fluid can be reduced to less than 5 mg/L.