Estudo da acidificação de rochas carbonáticas utilizando ácidos orgânicos, inorgânicos e blends ácidos

Abstract

In some phases of an oil well's cycle, such as drilling, completion, and production/injection, there is a possibility of formation damage. This damage is tamponades of the pores of the rock, which reduces its permeability and decreases the production of hydrocarbons. To increase the permeability of the carbonate rock producing zone in the vicinity of the well, the matrix acidification technique can be applied, which is a low-cost and high-yield stimulation method compared to hydraulic fracturing. For this type of operation, hydrochloric acid, or organic acids such as acetic or formic, are commonly used. The acid reacts with the rock to form wormholes, which are pathways responsible for connecting the reservoir to the well, increasing oil production. Individually, these acids have negative points, because hydrochloric acid, for example, reacts very fast with carbonate and ends up dissolving the face, while acetic and formic acids react slowly, hindering the formation of wormholes and the production itself. This study investigates the use of acid formulations composed of acetic acid, formic acid, and hydrochloric acid for optimizing acidizing processes in carbonate reservoirs, with a focus on dissolution efficiency and structural damage control. The results of the experimental design indicate that the reaction rate (ν) of calcium carbonate tablets in different acid concentrations ranged from 0.02 to 10.50 g/s, with the most efficient composition being 15 mL of acetic acid, 15 mL of formic acid, and 5 mL of HCl, achieving a reaction rate of 4.38 g/s. In reactive flow tests through porous media, it was observed that for injection rates of 2, 4, and 8 mL/min, the blends presented Pore Volume to Breakthrough (PVbt) values higher than those of 15% HCl, requiring a larger fluid volume to reach breakthrough. However, at an injection rate of 10 mL/min, the PVbt of 15% HCl was higher than that of the blends, indicating a faster and less controlled dissolution process, resulting in narrow and direct channels.