Preparation and Field Application of Slow-Release Solid Acidifier ZY-Y

Conventional acidizing fluids have a limited effective stimulation radius due to their rapid reaction, resulting in ineffective stimulation of reservoirs far from the wellbore or even acid wastage. In addition, existing solid acids suffer from poor retarding performance, insufficient high-temperature resistance, and potential environmental risks. A slow-release solid acidifier ZY-Y was prepared by synthesizing solid acid particles from carbamide and oleum and then spray coating the particles with degradable materials to address the above issues. Laboratory performance tests revealed that at 90 °C, the acid-rock reaction with ZY-Y lasted for 350 min, 7.1 times as long as that with gelled acid, while the dissolution rate exceeded 93%. These results indicated that ZY-Y had excellent resistance to dilution by formation water, allowing it to effectively stimulate reservoirs in far-wellbore regions. Moreover, it produced pronounced nonuniform etching, thereby enhancing fracture conductivity. Field applications in eight wells deeper than 6 500 m in an oilfield in western China demonstrated an average oil production increase rate of 51.6%. In a typical well, cumulative incremental oil production exceeded 12 000 t, showing a 21.9% overall reduction in acidizing stimulation costs. Laboratory research and field applications verify the outstanding retarding performance, high dissolution efficiency, environmental friendliness, and economic benefits of the slow-release solid acidifier ZY-Y. Capable of effectively stimulating the deep sections of carbonate reservoirs, ZY-Y is suitable for plug removal and production enhancement in formations at intermediate and far distances from mature wells and has great potential for large-scale application.