The titled acidizing fluid containing 12-20% HCl is prepared with an acid and salts tolerant unique additive VPH 110 (3%), corrosion inhibitor, Fe ions stabilizer, backflow aid and other additives introduced. It is characterized by specific performance: the fresh acid has low viscosity and forms highly viscous gel on etched rock surfaces at pH≥2.5 in acid rock reaction processes which forces the fresh acid squeezed to penetrate more deeply and diverts the acid to lower permeable zones; the gel entirely breaks down in contact with the reservoir crude (hydrocarbons) and turns to thin spent acid easily flown out of the zones treated. The basic formulations are given. The performance properties of a VPH 110 treated 20% HCl acid of a standard formula (VPH 110 acid) are investigated in comparison with a common 5% HCl acid of normal formula (HCl acid). VPH 110 acid of pH=0.5 has viscosity 4 mPa·s, of pH=2.5 - viscosity 1 440 mPa·s and this high viscosity is kept unchanged at pH>2.5. In experiments on 2 sets of 3 parallel cores of low permeability and small permeability difference (0.05,0.04 and 0.03 μm 2 approximately),treating medium and low permeable cores with VPH 110 acid results in more increase in permeability and much longer acid passages than that by HCl acid and the injecting pressure of VPH 110 acid goes through a maximum, indicating deep peretration and diverting. The permeability damage rate caused by broken down spent VPH 110 acid of pH=7 accounts only 0,1.57%, and 0.79% for the high, medium and low permeable cores, respectively. Similar viscosities are observed at 20-80℃ for spent VPH 110 acid and HCl acid of pH=7.
hydrochloric acidizing fluid
in situ gelation
protecting reservoir formations