Successful Application of an Engineered Fluid Cement Setting Base forRigless Abandonment

摘要

While abandoning a well from a light well intervention vessel (LWIV), and with no ability to run amechanical cement-setting tool, a fluid barrier spacer was needed to provide a base for the cement. Thisbarrier required a sufficient rheology to hold a 16.0 lb/gal cement slurry and to limit commingling of thecement and the fluid base, which could prevent the cement from setting and risk an inadequate cementbarrier length required for abandonment regulations. Two approaches were investigated: a thixotropic water-based barrier spacer and a high viscosity spacer.Laboratory testing indicated that only the thixotropic barrier spacer maintained good separation betweenthe 13.3 lb/gal calcium chloride/calcium bromide brine (the current annular fluid) and the cement. Thistesting was repeated with 8.7 lb/gal seawater, and the thixotropic barrier again showed excellent separation.Neither spacer could be weighted with barite because of limited deck space; both pills were built at 8.7 ppg. The thixotropic water-based spacer was selected for this application. The annulus was circulated toseawater, and the spacer was mixed in a cement batch tank on the vessel. This tank was then used for thecementing operations; there was no requirement to clean the tanks between mixing the cement setting spacerand the cement spacer used to cement the plug. After the pill was mixed, the tubing was punched at 4,100ft, and a 500 ft thixotropic water-based pill was set in the annulus and outside of the punched tubing. Thetubing was punched at 3,600 ft. A cement job was performed with 16 ppg cement; after the wait-on-cementtime elapsed to verify the barrier, the top of cement was tagged at 2,669 ft and successfully pressure tested. The regulatory required length of the cement barrier was successfully set with the thixotropic spacer fluidas a setting base. The thixotropic spacer successfully demonstrated sustained separation and a viable fluid base for settingcement. The result is a reliable method to set cement. This method does not require the mobilization ofmechanical cement setting tools; the use of the fluid as the cement base enabled the use of a LWIV andnegated the expensive need of mobilizing rig barriers to be set in place.