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

Abstract The many purposes and benefits of tubing pickling include iron control, scale removal, sludge prevention, removal of damaging pipe dope, asphaltene or paraffin deposit, elimination of spent acid, prevention of sulphur species deposition, improvement in stimulation and reduction in overall treatment cost. Corrosive hydrochloric or acetic acid is the common pickling solution. Additionally they often contain hazardous organic solvent and surfactant to remove asphaltene or wax deposit and pipe damaging dope residue. The major problem of acid based system is safety concern as pickle acid systems are classified as hazardous materials before pickling and upon return to the surface after treatment. The near neutral pickling fluid is an environmentally favourable derusting fluid which has the capability of reacting with rust, mill scale and steel substrate producing a protective phosphate film that coats the metal surface to provide a corrosion protection through passivity mechanisms. Near neutral pickling fluid has been successfully applied in some workover risers in the Niger Delta at low seabed temperature. Results of the applications are very impressive and these shall be discussed in this paper. Also to be discussed is the application of the near neutral fluid in the fishing of a 2-3/8″PXN plug which got stuck at the XN-nipple in an old tubing making it impossible to set an A-5 dual completion parker. All previous attempts to retrieve the fish for over 72 hours had failed but the fish (23ft long) was recovered with slick line after soaking well with the near neutral fluid over night.