A Novel Eco-Friendly Solid Acid for Deep Diversion during Matrix Acidizing of Injection Wells

The development of heterogeneous reservoirs presents a significant challenge to effective acid stimulation, as conventional acid systems tend to preferentially flow through high-permeability channels while bypassing tighter zones. This study addresses the issue by developing a novel temperature-responsive deep-diversion acidizing system (DDA) that enables efficient redirection of acid into low-permeability formations. The system combines organic acid salts, acid-releasing precursors, buffers, and dispersants into a single formulation capable of in situ phase transformation. Under downhole temperatures ranging from 60 °C to 70 °C, the precursor generates hydrogen ions that trigger the formation of insoluble organic acid particles. These particles temporarily plug high-permeability pathways, allowing the acid to penetrate deeper into the formation. Once the diversion is complete, the generated organic acids gradually dissolve on the carbonate scale, thereby restoring flow channels and achieving a self-cleaning effect. Laboratory tests demonstrate that the DDA system maintains low viscosity under surface conditions for injectability and rapidly converts to a solid-phase plugging agent upon heating, with over 90% of the particles actively contributing to diversion. This study proposes a two-stage injection strategydiverter followed by acidto maximize the plugging effect. The system's ability to combine deep placement, temporary plugging, and post-treatment self-dissolution offers a highly effective and operationally feasible solution for enhancing stimulation in heterogeneous water-injection wells.