Synthesis And Performance Evaluation Of Clean And Low-damage Emulsion Variable Viscous Slick Water

Slick water fracturing fluid is widely used in shale gas exploitation and stimulation,and the effect of increasing production was directly affected by its performance.At present,the geological conditions of unconventional oil and gas resources are becoming more and more complex,so the performance of slick water fracturing fluid needs higher requirements.There are some problems in slick water fracturing fluid,such as low viscosity,easy sand removal,poor flow-back reuse,great damage to the reservoir,complicated liquid distribution process on site,and high friction.In this paper,a clean and low-damage variable viscosity slick water is synthesized,which has the features of short dissolution time,low friction resistance,easy flow-back,strong sand carrying capacity and less residue content.Polymer POE was synthesized by inverse emulsion polymerization with AM,AMPS,AA and self-made monomer AOPE,and its structure was characterized.At the same time,the performance evaluation,pilot production and field application of the slick water system are carried out.(1)Two functional monomers AIPE and AOPE were prepared by acryloyl chloride and fatty alcohol polyoxyethylene ether compounds.The infrared spectra were tested and the structural characterization results were analyzed.The monomers were introduced into the polymerization reaction.The results indicate that the introduction of AOPE into the polymerization reaction has the advantages of short emulsification time,high apparent viscosity and good stability of the water-in-oil pre-emulsion system.The process parameters of functional monomer AOPE introduced into the system will be further optimized and studied.(2)The effects of monomer content,emulsifier dosage,oil-water ratio,initiator dosage,aqueous phase pH,monomer molar ratio,reaction temperature and time,type and dosage of phase inversion agent on the polymerization process of inverse emulsion polymer POE were studied by single factor method.The optimum technological parameters were determined as follows:monomer content was 30%,emulsifier dosage was 3.0%,oil-water ratio was 0.65:1,initiator dosage was 0.03%,aqueous phase pH=7.0,monomer molar ratio n(AM):n(AA):n(AMPS):n(AOPE)=3:2:0.2:0.002,reaction temperature was 40～45℃,reaction time was 4 h,NP-10 phase inversion agent dosage was 4%,(3)The synthesized polymer POE was tested by infrared spectroscopy and NMR hydrogen spectroscopy,and the structure was consistent with the expected molecular structure.The long chain structure of polymer POE molecules in water was observed by scanning electron microscope,and the spatial arrangement between molecular chains in brine was more compact and complex,XRD analysis shows that the structure is amorphous,and the polymer is mostly in a random coil state.The particle size of the emulsion before polymerization was 11.00 μm,and the particle size of the emulsion after polymerization was 7.604 μm.The particle size distribution of the polymer emulsion was concentrated and uniform.The relative molecular mass of the polymer with different monomer content was tested.When the monomer content was 30%,the molecular weight reached more than 14 million,the molecular weight of the polymer was larger,and the macroscopic performance was higher apparent viscosity.(4)The performance test of the polymer POE for variable viscosity slick water fracturing.POE is completely dissolved within 40s.In 10%standard brine,the viscosity retention rate of POE is still higher than 80%.When the temperature rises to 120℃ and 90℃,the apparent viscosity of POE is respectively 60.27 mPa·s and 56.45 mPa·s in water and 10%standard brine.The end viscosity of POE after shearing for 1 h in water and 10%standard brine is 54.64 mPa · s and 55.84 mPa·s,respectively.The G’ of the system is greater than G",which is dominated by elasticity and has good viscoelasticity.The drag reduction rate of the drag reducer solution with a concentration of 0.1%reaches the maximum and is greater than 70%.The static sand suspension data at room temperature and 90℃show that the system has good sand suspension performance.The surface tension of POE after gel breaking was 27.48 mN/m,and the residue content was 137.5 mg/L.The core damage rates of 2 h,7 d and 20 d were 19.0%,21.7%and 23.5%,respectively.Polymer POE has the characteristics of difficult to sand out,low friction,easy to break,clean and low damage.(5)Comparing the performance of pilot product and the laboratory product,the consequence is basically the same.The synthesis process is repeatable and suitable for industrial production.The clean and low-damage emulsion variable viscosity slick water fracturing fluid system was successfully fractured in Well 68 and Well 47 of Changqing Oilfield.The construction process was normal and stable,and the construction effect was good.