Abstract: Due to acidizing problems present in high-temperature carbonate reservoirs from conventional acids, such as rapid acid-rock reaction, short effective action distance and difficulty in achieving deep acidizing, a new type of solid granular acid has been developed. The solid acid was prepared by taking sulfonic acid as the core material and using organic sulfonic acid/ethyl cellulose composite as capsule materials, and it could be solidified and granulated by adopting a spray drying process. The capsule material can be dissolved gradually and then an acid solution can be released at a certain temperature, so as to increase the action distance of acid. Experimental evaluation showed that the developed solid acid could release an acid solution gradually at a temperature range of 80 to 90 ℃, the complete release time at 120 ℃ was 25 min, and the effective acid concentration was up to 10.3%. Due to the low reaction rate, it can be carried into the deep fractures by liquid media. Field testing of solid granular acid has been conducted in the well THX of the Tahe Oilfield, and the daily oil production capacity was greatly improved. Studies indicated that the solid granular acid could effectively communicate with distal reservoirs, and provide a new technical means for the efficient development of carbonate reservoirs.