Regular HCl has been used as the main acidizing fluid. At high temperatures, rapid spending of the acid with carbonates prevents deeper penetration of the acid into the formations. Alternatives such as acetic and formic acid have lent themselves to retarded reaction rates, low corrosivity and reduced tendency to form acid/oil sludge in asphaltene-rich crudes. The same problem of high reaction rate is still observed with organic acids at very high temperatures.
Complex thermodynamics equilibrium and reaction kinetics have been cited as issues apparent in selecting suitable organic acid as a stimulation fluid for specific acidizing treatment. Chelating agents, with the added advantage of complexing with carbonate to form a water-soluble product, have been introduced as stimulation fluids. Glutamic acid diacetic acid (GLDA), is a polycarboxylic acid with this property.
To predict the spending of GLDA relative to the organic acids, the kinetics of dolomite dissolution in organic acids and GLDA solution was investigated. The rotating disk apparatus was used to compare the reactivity of these solutions by varying the disk rotational speed from 100 to 1500 rpm and for 0.886N solutions at 120°C. Samples of the reacted acids, from the reactor, were collected and analyzed with Inductively Coupled Plasma.
Experimental results indicated that dolomite dissolution rates increased in all the acid solutions as the disk rotational speed increased at 120°C. At disk rotational speed of 1000 rpm and higher; the dissolution rate of dolomite in formic acid remained the same. Hence, the prevailing reaction regime in the acid solutions were mass transfer limited processes until the process shifted to reaction kinetics controlled at 1000 rpm in formic acid. Compared to the organic acids, GLDA demonstrated the lowest reactivity with dolomite at the same acid molarity and reaction conditions.