Corrosion Inhibitive Cement Slurry and Supporting Techniques for Cementing the Luohe Aquifer in Changqing Oilfield

Corrosion of the cement sheath sealing off the Luohe aquifer has caused the permeability of the cement sheath to increase, resulting in severe corrosion of the casing string in the aquifer section. Corrosion boring in the casing string has resulted in problems such as increase in the water cut of the produced fluid, low utilization of water flooding from water injectors and maladjustment of the injection and production well pattern. To solve the corrosion problem, an epoxy emulsion nonpenetrating agent and a corrosion inhibitor formulated with an anti-rust agent and a bacteria inhibitive agent, were mixed with conventional oil well cement. In this way the corrosivity and permeability of the cement slurry can be reduced, and hence corrosion to the casing string be mitigated. It was found in testing the permeability of the cement slurry samples that when a low-density cement slurry was treated with 10% nonpenetrating agent and 2% corrosion inhibitor, the permeability of the set cement was reduced from 0.075 mD to 0.021 mD. When a cement slurry of normal density was treated with 10% nonpenetrating agent and 2% corrosion inhibitor, the permeability of the set cement was reduced from 0.041 mD to 0.0009 mD. Experiment on the corrosion resistance of the set cement showed that when a cement slurry was treated with 10% nonpenetrating agent and 2% corrosion inhibitor, the corrosion resistance of the set cement was increased by a factor of 6, meanwhile, compared with the untreated conventional cement, the thickening time of the treated cement slurry and the compressive strength of the treated set cement were kept unchanged. A set of optimized operating tools and measures were used with the treated cement slurry in oil well cementing operation. The cement slurry and the supporting techniques have provided a powerful means of dealing with corrosion inhibition for the Luohe aquafer.