镁离子对油井水泥石的侵蚀

The erosion of oil well cement by magnesium ions

以硫酸镁溶液为腐蚀介质,对高抗硫酸盐油井水泥进行了腐蚀试验,结果表明,在35℃的硫酸镁溶液中浸泡一年,镁离子使水泥石变得致密,强度升高。镁离子的浓度越高,这种作用越明显。从腐蚀液的pH值变化和浸出的Ca^(2+)浓度变化分析认为,镁离子与氢氧化钙在溶液中反应,生成的氢氧化镁沉淀吸附在水泥石表面,形成一层薄膜,减缓了镁离子对水泥石的进一步侵蚀;其后,镁离子扩散进入水泥石内与氢氧化钙反应,生成的沉淀堵塞了微孔隙,从而使水泥石变得密实,强度升高。实验还发現,镁离子对水泥石的作用受温度的影响较大,在75℃下进行试验,溶蚀型腐蚀显著增强,而镁离子的作用不明显。

The erosion of high sulfate resistant cement was conducted in magnesium sulfate solution in comparison with sodium sulfate solution and distilled water. The pH value and calcium ion concentration of medium, compressive strength and permeability of cement in the corrosion process ranging from 2 days to 1 year were determined. It is shown that the compressive strength of cement in magnesium sulfate solution at 35 ℃ is raised in 1 year, and the higher of the concentration of magnesium ion the higher the compressive strength, but the influence of magnesium ion the compressive strength of cement at 75 ℃ is not obviously.