Study And Application Of Compound Slow Acid System In Neighborhood Gas Reservoir In Southern

Matrix acidification of sandstone mainly used to remove damage from well drilling and completion, workover and water injection, improve formation permeability, tresume and improve oil production capacity. Hydrofluoric acid/hydrochloric acid system is a common acid system that used for sandstone acidizing. However, the reaction between acid and minerals is so fast that acid cannot reach deep inside the reservoir, therefore operating distance of acid is short, and cannot get acidized actually. Hydrofluoric acid can also react with clay as well as the newly formed secondary precipitation will result in new damages to the reservoir. Due to geological complexity and particularity of Xu 2 gas reservoirs Southwest of Sichuan, and some reasons cause reservoir damage in production process, which eventually led to the gas well production is down, it should make fracturing acidification transformation to improve the single well productivity and the mining efficiency.Based on that, this paper present a deep research on the geology characters of the Southwest of Sichuan Xu 2 gas reservoirs and analyze the damage situation combined with the production practice and test. The objectivity of existing different kinds of potential factors was made definite. According to the characters of the Southwest of Sichuan Xu 2 gas reservoirs, Proposed ammonium bifluoride buffer acid on the basis of variety of acid system for sandstone reservoir and many literatures home and broad. Analyzed acidity properties and retarder mechanism of ammonium bifluoride buffer acid and its acid system.Estimate the intersolubility between fluotitanate complex and potassium ions, sodium ions, while the comparative study of precipitation between fluotitanate complex react with calcium ions and mud acid react with these two ions. Determined the best concentration of ammonium bifluoride buffer acid system through plentiful erosion experiments. Proposed a complete set of compound retarded acid system, including retarded hydrochloric acid, ammonium bifluoride buffer acid, retarded mud acid. Evaluated the wettability, corrosivity, anti-acid-slug ability, and compatibility of compound retarded acid system. Conducted a series of experiments on cores by this system. The consequences had proved that this acid system had good effect for sandstone acidification. According to the characteristics of heterogeneity and a large span between layers,temporary blocking layer acidification was proposed. From Xu 2 gas reservoirs gas well including Zhangjia 001-1 well site construction effectiveness analysis, acidification achieved significant results, obtained substantial industrial gas flow, acidizing effect is remarkable.