Patent Number: 
Section: description

At ambient temperature, 50 ml of a 10 wt % dibasic acid (DBA) acid solution (glutaric acid 51-61 wt %; succinic acid 18-28 wt %; adipic acid 15-25 wt %) was poured into a 100 ml beaker that contained a magnetic stirring bar. Reagent grade calcium carbonate powder (10.00 g) was weighed in a weighing boat. The calcium carbonate powder was slowly added in small increments to the beaker while stirring until the acid fluid just became cloudy. The remaining calcium carbonate powder was reweighed, and the amount dissolved was calculated by difference. By this method, 50 ml 10 wt % DBA acid was found to dissolve 2.7 g, which is equivalent to 0.45 lb/gal. This Example illustrates that DBA acid will dissolve calcium carbonate. Since DBA acid alone does not dissolve silicates, DBA acid was used together with ammonium fluoride to generate hydrofluoric acid at high temperature. The test procedure was as follows: 1. A 1 inch diameter (2.54 cm), 400 mesh (37 micron) stainless steel screen, which is dry and weighed, was placed onto the surface of a one-inch diameter (2.54 cm) sandstone core, then the screen and core were put into a core holder; 2. A fluid which contains 2.5 wt % 400 mesh Rev Dust in water (components of Rev Dust: 12 wt % quartz; 7 wt % cristobalite; 4 wt % illite; 29 wt % mixed layer clay; 26 wt % kaolinite; 22 wt % chlorite) was pumped to plug the screen and damage the core; 3. The screen with Rev Dust on it was removed, and the screen was dried and weighed; 4. The screen was replaced back onto the core surface and the core was heated to 300xc2x0 F. (149xc2x0 C.); 5. A fluid of 10 wt % DBA plus 1.5 wt % hydrofluoric acid, generated from ammonium fluoride, and a corrosion inhibitor was pumped into the screen and core at 3 ml/min for 24 minutes; the core was then soaked for 12 minutes at 300xc2x0 F. (149xc2x0 C.); 6. The core was cooled to room temperature, the screen was removed from the core holder, and the screen was dried and reweighed. After pumping 72 ml of the DBA:HF fluid described above, 0.5 g of Rev Dust on the screen was removed, which is equivalent to 0.058 lb Rev Dust dissolved per gallon of acid at 300xc2x0 F. (149xc2x0 C.). Tables I through VI report corrosion inhibitor test results mentioned previously. All tests were run at 2000 psi pressure (14 MPa), and corrosion inhibitor aid 3% NH4Cl was present in the formulations. The steel alloys used were 22-Cr chromium steel and coiled tubing of N-80 steel (CT). With respect to the corrosion rate, 0.05 lb/ft2 (2.4 kg/m2) is the maximum acceptable. The pitting index is a measure of corrosion, where pits are small pockets of localized corrosion about 0.1 mm in diameter or less usually caused by relatively low corrosion inhibitor concentration or galvanic currents. The pitting index definitions are as follows: In the foregoing specification, the invention has been described with reference to specific embodiments thereof, and has been demonstrated as effective in providing an acidizing treatment fluid that has low corrosivity with respect to the iron-alloy materials and equipment it comes into contact with. However, it will be evident that various modifications and changes can be made thereto without departing from the broader spirit or scope of the invention as set forth in the appended claims. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, specific combinations of dicarboxylic acids and other components falling within the claimed parameters, but not specifically identified or tried in a particular composition or under specific conditions, are anticipated to be within the scope of this invention.