Novel Class of Retarded, Newtonian, Single-Phase HCl-Based Stimulation Fluids - A Laboratory Characterization

The current industry incumbent compositions of retarded acids have certain drawbacks: (1) environmentally harmful, (2) unstable at high temperatures or shear rates, (3) excessive frictional pressure losses due to high viscosity, (4) high-cost additives, (5) complicated mixing procedures, etc. This work reports the development and laboratory characterization of the novel class of retarded acid that contains 15 wt% HCl but overcomes all the disadvantages mentioned above. A rotating disk apparatus (RDA) was used to determine the dissolution rate of calcite-marble in the novel class of retarded acids and 15 wt% HCl solution. Experiments were performed at a temperature of 250°F, disk rotational speed of 587 rpm, and pressure of 1,150-1,300 psig. The dissolution rate of calcite-marble was calculated from the calcium ion concentrations in the samples of the solutions withdrawn during the RDA tests. Corrosion rates of Cr13, L80, P110, and T95 steel coupons have been measured using an autoclave at a temperature of 250°F, and a pressure of 450 psig, for 6 hours. Kinematic viscosity was measured using a capillary viscometer at a temperature of 73-200°F. The novel class of retarded acids contains 15 wt.% HCl, and is a single-phase, Newtonian, low-viscosity, i.e., water-like liquid. The acid is adjustable, i.e., has the capability to fine-tune the reactivity from 1.2 to 9200 times slower than 15 wt.% HCl at 250°F. Besides tunable reactivity, no significant corrosion of steel coupons is observed without adding any corrosion inhibitor and/or corrosion inhibitor aid. The measured corrosion rates were 0.00001 to 0.05061 lb/ft2 in 6 hours. Moreover, novel acid packages act as an H2S scavenger and can be used in sour wells. This work reports the development of innovative retarded acid packages that exhibit tunable reactivity, low corrosion rate on many steel grades, high-temperature stability, and multifunctionality. Such acid packages are of great interest for the oil and gas industry, CO2 storage, and geothermal projects around the world.