Rheology on AM/AMPS co-polymer fracturing fluids with ultra-high salinity and their crosslinking processes
The rheological properties of AM/AMPS fracturing fluids in different mineralization levels and salt solutions and their crosslinked gel state and rheological properties as well as crosslinking process at ultra-high mineralization levels were investigated.The results show that the viscosity and elastic modulus of AM/AMPS fracturing fluids decreased in KCl and CaCl2 solutions,and decreased more in CaCl2 solu-tion.The ultra-high mineralization magnesium salt solution has enhanced the viscosity and viscoelasticity of fracturing fluid.AM/AMPS fracturing fluids can form gels with organic zirconium crosslinkers that can be fully picked up in different salt solutions and above salinity,and the strain scan results demonstrate that the fracturing fluid exhibits typical gel characteristics after crosslinking.The cross-linking process of AM/AMPS fracturing fluids in highly mineralized salt solution as well as in aqueous solution at a constant temperature of 30 ℃ with small amplitude oscillations can be described by a four-parameter crosslinking rheological kinetic equation,and metal salt ions can increase the gel strength,and the increase is more significant for divalent salts.The crosslinking process of AM/AMPS fracturing fluid with temperature rise in small amplitude oscillation exists in two stages of slow crosslinking and fast crosslinking,and appropri-ate temperature increase is beneficial to the crosslinking reaction.The crosslinking process of AM/AMPS fracturing fluid in tap water and monovalent salt solution with large amplitude oscillation at elevated tem-perature was similar to that of small amplitude oscillation at elevated temperature,the crosslinking process in divalent salt solutions is strongly influenced by shear,and appropriate increase in shear is beneficial to the crosslinking of AM/AMPS fracturing fluid in the salt solution.The study obtained new system of ultra-high salinity AM/AMPS fracturing fluid,which is expected to provide guidance for the engineering appli-cation of AM/AMPS fracturing fluid.
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