Application of Near Neutral Pickling Fluid in Workover Riser Pickling andFishing Operation in the Niger Delta: Case Histories

摘要

The many purposes and benefits of tubing picklinginclude iron control, scale removal, sludge prevention,removal of damaging pipe dope, asphaltene or paraffindeposit, elimination of spent acid, prevention of sulphurspecies deposition, improvement in stimulation andreduction in overall treatment cost.Corrosive hydrochloric or acetic acid is the commonpickling solution. Additionally they often containhazardous organic solvent and surfactant to removeasphaltene or wax deposit and pipe damaging doperesidue. The major problem of acid based system issafety concern as pickle acid systems are classified ashazardous materials before pickling and upon return tothe surface after treatment. The near neutral picklingfluid is an environmentally favourable derusting fluidwhich has the capability of reacting with rust, mill scaleand steel substrate producing a protective phosphate filmthat coats the metal surface to provide a corrosionprotection through passivity mechanisms.Near neutral pickling fluid has been successfully applied insome workover risers in the Niger Delta at low seabedtemperature. Results of the applications are veryimpressive and these shall be discussed in this paper. Alsoto be discussed is the application of the near neutral fluidin the fishing of a 2-3/8''PXN plug which got stuck at theXN-nipple in an old tubing making it impossible to set anA-5 dual completion parker. All previous attempts toretrieve the fish for over 72 hours had failed but the fish(23ft long) was recovered with slick line after soaking wellwith the near neutral fluid over night.