砂岩酸化过程中铁离子沉淀研究

Research of iron precipitation in sandstone acidizing

关键词:  酸化  砂岩  铁沉淀  多氢酸 

Key words:  acidizing  sandstone  iron precipitation  multi-hydrogen acid

摘要:

酸化可有效疏通地层渗流通道,改善地层流体渗流能力,实现油气井增产、注水井增注。但酸化过程中铁离子的存在容易在地层中形成沉淀,堵塞地层孔隙喉道,影响酸化效果。针对砂岩储层,开展了常规土酸、氟硼酸、多氢酸三种酸液体系中铁离子沉淀机理研究。研究结果表明:在砂岩储层酸化中,铁离子以多种复合物的形式存在于沉淀产物中,不同于碳酸盐岩储层采用盐酸酸化时铁离子以Fe(OH)₃沉淀的形式出现。对于不同酸液体系,铁沉淀形成的条件不同。常规土酸在较低的pH值条件下即出现沉淀,且在pH值为1.2时完全沉淀, 氟硼酸形成铁沉淀的pH值较土酸大。多氢酸对金属离子具有较好的螯合作用,使得其在一个较小的pH值范围内才会出现铁的沉淀,而且出现沉淀时pH值较大,采用该酸液体系进行砂岩储层酸化,形成铁离子沉淀的风险较小。 

Abstract:

Acidizing can dredge formation seepage channels effectively, and improve the seepage ability of formation fluid, which achieves the production stimulation of oil, gas and water-injection wells. But the iron ions precipitates can be easily formed in formation during acidizing, which will block pore throats and impact acidizing effect. Aiming at sandstone formation, precipitation mechanisms of iron ions in mud acid, fluoboric acid and multi-hydrogen acid are researched in this paper. The research results show that in sandstone formation acidizing, iron ions exist in precipitates as various of composites, which is different from the form of Fe(OH)₃ precipitate when carbonate reservoir acidized by hydrochloric acid. Formation conditions of iron precipitates are different in different acid systems. In mud acid, iron precipitates are formed in low pH value and completely precipitate while pH=1.2. In fluoboric acid, iron precipitates are formed in higher pH value than in mud acid. Multi-hydrogen acid has good chelation to metal ions. So in multi-hydrogen acid, iron precipitates can be formed only in a smaller pH value range as well as in higher pH value. The risk of iron precipitates formation is low when adopting multi-hydrogen acid in sandstone formation acidizing.