US 9,399,728 B2  32  31  TABLE D-continued  Formulation D of Cationic Polymer and Stability Testing Results  Additives  Formulation D witb Al  Formulation D witb Fe  Neutralized with CaCO$_{3 }$at 250°  F.  Initial Crosslinking  pH 1.5  pH 2.3  Observation  REDUCED VISCOSITY  REDUCED VISCOSITY  to a pouring fluid  to a pouring fluid  after test witb pH 2.3  after test witb pH 2.9  Neutralized with CaCO$_{3 }$at 275°  F.  Initial Crosslinking  pH 1.5  pH 2.3  Observation  REDUCED VISCOSITY  to a pouring fluid  REDUCED VISCOSITY  to a pouring fluid  after test witb pH 2.4  after test witb pH 2. 8  As shown in the tables, all formulations A through C  showed good crosslinked gel stability at 250°  F. and 275°  F.  with increase in final pH after the tests.  A reduction in crosslinked gel viscosity was observed after  the test in Formulation D with propargyl alcohol and metha› nol as corrosion inhibitor. Both Al-acetate and ferric chloride  crosslinkers showed similar observation with this corrosion  inhibitor.  Corrosion Test Results at 200°  F. and 225°  F.  The corrosion tests were carried out using N-80 coupon in  20% HCl for Al-acetate and ferric chloride crosslinkers at  200°  F., and 225°  F. for 3 hours. The results at respective  temperatures are tabulated in Tables 3 and 4.  All corrosion results are compared against existing ferric  chloride crosslinker. At 200°  F. and 225°  F., both ferric chlo› ride and Al-Acetate crosslinkers passed the corrosion tests.  Need for Improvement Above 20% HCl  Based on the above results, use of 28% HCl in in-situ  gelling acidizing withAl-acetate crosslinkerwas not feasible,  as the increase in crosslinked viscosity with acid spend was  not achievable. This observation was consistent with existing  ferric chloride crosslinker. An optimized 20% HCl withAl› acetate or ferric chloride could deliver the expected perfor› mance and hence followed during entire test matrix.  A cationic polyacrylamide (in invert emulsion form,  30-50% polymer by weight) was hydrated in 28% hydrochlo- ric acid for 3 hours. After hydration, glycolic acid (aq. soln.),  aluminum acetate, and a complexation agent for calcium ions  were added and stirred for 5 minutes. This mixture was then  neutralized at 200°  F. using calcium carbonate (CaCO$_{3}$ ).  Dur› ing neutralization the pH was monitored using a pH meter. As  acid spent with CaCO$_{3}$ ,  a slight increase in crosslinked vis› cosity was observed around pH 1 and with further neutraliza› tion the fluid became a lipping gel, which looked like a solid  goo ball. The lipping gel was very stable in the pH range 1 to  4 at 200°  F. With further neutralization to above pH 4, the  lipping gel started losing its viscosity and formed complete  broken fluid. No precipitation or sludge was observed during  neutralization.  The above system was limited to a concentration of HCl  below about 20%. Without being limited by any theory, it is  believed that at higher HCl concentration (that is, greater than  20% ), the high concentration of ca++ ions generated by the  reaction between the HCl acid and carbonate inhibits suffi› cient cross linking of the polymer. This is manifested by  non-formation of lipping gel in spent 28% HCl, which is  unlike in spent 20% HCI.  It is believed that by including a  complexation agent for calcium ions at least an excess of the  high concentration of calcium ions is complexed, thus not  allowing the excess concentration of calcium ions to interfere  in the cross-linking reaction.As noted above, it is believed the  chemistry and behavior of magnesium ions would be similar.  Addition of Complexation Agent for Calcium or Magne› sium Ions  Based on the above laboratory tests, Al-acetate can replace  ferric chloride in in-situ crosslinking for acidizing of a car› bonate formation. In case the user wants to use a liquid form  of the aluminum crosslinker, an 80% w/v aqueous solution,  for example, can be prepared and used. The performance of  80% aqueous solution was tested and found unaltered after 2  months of preparation.  Al-acetate crosslinker has passed successfully the corro› sion test at 200°  F. and 225°  F. and results were comparable  against existing ferric chloride crosslinker.  A good crosslinked gel stability was observed using Al› acetate crosslinker in in-situ crosslinking for an acidizing  blend with chloromethylnaphthalene quinoline quaternary  amine, isopropanol, and aldehyde as corrosion inhibitor at  250°  F. and 275°  F.  A reduction in crosslinked gel viscosity  was observed after the test with prop argy 1 alcohol and metha› nol inhibitor and this observation was consistent with ferric  chloride crosslinker as well.  TABLE3  TABLE4  Corrosion Tests at 200°  F.  Using N-80 Coupon for 3 Hours  Corrosion Loss  No  Formula  (lb/ft’)  Formulation A with Al  0.0137  2  Formulation A with Fe  0.014  3  Formulation B with Al  0.0055  4  Formulation B with Fe  0.01  5  Formulation C with Al  0.0021  6  Formulation C with Fe  0.0049  7  Formulation D witb Al  0.0027  8  Formulation D witb Fe  0.0046  Corrosion Tests at 225°  F.  Using N-80 Coupon for 3 Hours  Corrosion Loss  No  Formula  (lb/ft’)  Formulation A with Al  0.0018  2  Formulation B with Al  0.0155  3  Formulation C with Al  0.0078  4  Formulation D witb Al  0.01  5  Formulation D witb Fe  0.0147 