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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. 

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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 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. 

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. 

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. 

Addition of Complexation Agent for Calcium or Magne› sium Ions 

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. 

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. 

