Preparation And Study On Drag Reduction Mechanism Of Nano-SiO₂ Modified Polymer Slickwater

Due to the advantages of the low cost and low damage,slickwater fracturing fluid has been widely used in the development of unconventional oil and gas resources such as shale gas.But in the process of application,the problem of poor shearing resistance and high friction is also daily prominent because of the high discharge velocity of slippery water.In present study,the macromoleclar polymer is still the most ideal additive in slickwater fracturing fluid,but polymer drag reduction and shear resistance is an urgent need to reconcile the contradictions.In order to improve the effect of shear resistance and drag reduction of slickwater,it is needed to develop polymers with suitable molecular weight and excellent performance of shear resistance and slickwater fracturing fluid is prepared on this basis.This is of great significance to develop reservoirs with low low porosity and low permeability.In this paper,a kind of nano-SiO₂ modified polymer slickwater fracturing fluid system was developed.First of all,the hydrophilic nano-SiO₂ was modified by KH-570 and the modified nano-SiO₂ and acrylamide were used as the reaction monomer.The nano-SiO₂modified polymer was finally synthesized by relying on the REDOX initiator system（ammonium persulfate-sodium bisulfite 1:1）to initiate free radical polymerization at low temperature and optimizing the polymerization reaction condition such as temperature,initiator,p H,monomer concentration,etc.Then,the slickwater system was constructed by selecting the types and proportions of drag reducing agent,drainage aid agent and clay stabilizer in slickwater fracturing fluid.And the performance of the slickwater system was evaluated by experimental methods of drag reduction apparatus,dynamic light scattering,rheological test and physical simulation.Finally,the effect factors and regulation of drag reduction in slickwater fracturing fluid are revealed,and the drag reduction mechanism of slickwater fracturing fluid is clarified.This provides theoretical and technological support for the application of nano-SiO₂modified polymer slickwater fracturing fluid.Based on the results of solubility and drag reduction,nano-SiO₂ modified polymer（SAM1-90）was selected as drag reduction agent for slickwater fracturing fluid.The formulation of slickwater system was finally optimized:0.05-0.1 wt%polymer SAM1-90+0.15-0.2 wt%dodecyl polyoxyethylene ether+0.1-0.2 wt%polyepichlorohydrin diethanolamine.The performance evaluation results show that SAM1-90 has better drag reduction effect compared to pure polyacrylamide（The maximum drag reduction rate is 72.60%）and commercial J2 drag reducer（The maximum drag reduction rate is 75.52%）,and the maximum drag reduction rate can reach 78.09%.The slickwater system offers better temperature and shear resistance（up to 90℃）and water quality adaptability(110000 mg·L^-1salinity).The experimental results of the regulation of drag reduction show that the drag reduction ability of slickwater is improved with the increase of molecular weight.When the molecular weight exceeds 1.5 million,the maximum drag reduction rate will no longer change.With the increase of salinity of water,the hydrophobic association is weakened due to a large amount of cationic adsorption between molecules of drag reducer,resulting weaken drag reduction effect.It is high temperature has a significant effect on drag reduction.When the temperature is less than 50℃,the maximum drag reduction rate almost does not change.When the temperature is 100℃,the retention rate of drag reduction rate is over 88%.The results of pipe diameter and discharge velocity affecting drag reduction show that the best drag reduction effect can be achieved when the slickwater works in the condition of 40·L·min^-1 discharge velocity and the pipe diameter of 10 mm.The drag reducer mainly depends on the structure to increase viscosity and elastic energy storage to reduce drag.The test results of steady-state shear show that the system has good effect on viscosity increasing and high viscosity retention rate.The viscoelastic test results show that the system has good viscoelasticity.