Erosive effects of SO42? and HCO3? on oil well cement stone

The corrosion products, microstructure and compressive strength of corroded cement matrix were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and strength test instrument. Corrosion of oil well cement stone by sulfate (SO42?) and bicarbonate (HCO3?) during enhanced oil recovery (EOR) in adjustment wells was analyzed. The erosive effects on the compressive strength were studied to provide theoretical foundation for reasonably designing corrosion resistance cement system. The results show that the main corrosive products of cement cooperatively eroded by SO42? and HCO3? were gypsum, ettringite and calcite under the temperature between 38 ~60 ℃, which has changed the material composition and microstructure of cement. Otherwise, the compressive strength of cement stone eroded by both of SO42? and HCO3? were much lower than that singly eroded by SO42? or HCO3? for all samples. When the corrosion time reached or exceeded 21 d, the compressive strength of corrosive cement was lower than that of un-corroded stone. The compressive strength of corrosive cement paste matrix precipitously declined with the increase of corrosion time and concentration of blend liquid of SO42? and HCO3?. When the corrosion time was within 14 d, compressive strength of the corrosive cement paste matrix increased with the rise of corrosion temperature. And when the cement was eroded over than 21 d, compressive strength decreased with the increase of temperature.