沙埝油田采油井井筒结垢的物相组成及形成机制

Study on the scale composition and formation in the production well of Shanian Oilfield

在江苏油气区，沙埝油田结垢腐蚀尤为严重。在对沙19—31油井井筒结垢物进行系统取样的基础上，利用X荧光光谱、X射线衍射分析、扫描电子显微镜和能谱仪等方法全面分析了结垢物的化学组成、矿物成分、微观形貌等，发现结垢物的化学组成以铁、钙质为主，铁元素含量超过50％。结晶态的铁质化合物主要为复硫铁矿、铁硫矿、菱铁矿、纤铁矿、氢氧化铁，钙质化合物则主要为文石、方解石，少量出现石膏和硬石膏。铁质垢为腐蚀成因，与细菌活动、酸性气体一井壁氧化还原作用和无机盐的腐蚀有关；钙质垢则主要由采出流体在上升过程中的物理条件变化引起。

In Shalian area of Jiangsu Oilfield,the scaling is serious .Based on a systematic sampling of the scales from S19-31 production well, X-ray diffraction （XRD）, X-ray fluorescence （XRF） spectrometric analysis and scanning electronic microscopy coupled with X-ray energy dispersive microanalysis （SEM -EDX） were employed to investigate the chemical composition, mineral assemble and surface morphology of the scales. The results show that ferruginous and calcareous precipitations are the main chemical composition. The iron bearing minerals consist of ferric hydroxide/oxides, greigite, mackinawite, siderite and lepidocrocite. Calcareous phases include aragonite, calcite, gypsum and a small amount anhydrite. Finally, the probable mechanism of scaling was discussed. Ferruginous scales are mainly corrosion products, which probably caused by the activities of bacteria and the redox reactions between acidic gases, salt and well walls. Precipitation of calcareous scales is attributed to the physiochemical changes of the production fuids.