Successful Application of an Engineered Fluid Cement Setting Base for Rigless Abandonment

While abandoning a well from a light well intervention vessel (LWIV), and with no ability to run a mechanical cement-setting tool, a fluid barrier spacer was needed to provide a base for the cement. This barrier required a sufficient rheology to hold a 16.0 lb/gal cement slurry and to limit commingling of the cement and the fluid base, which could prevent the cement from setting and risk an inadequate cement barrier 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 between the 13.3 lb/gal calcium chloride/calcium bromide brine (the current annular fluid) and the cement. This testing 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 to seawater, and the spacer was mixed in a cement batch tank on the vessel. This tank was then used for the cementing operations; there was no requirement to clean the tanks between mixing the cement setting spacer and the cement spacer used to cement the plug. After the pill was mixed, the tubing was punched at 4,100 ft, and a 500 ft thixotropic water-based pill was set in the annulus and outside of the punched tubing. The tubing was punched at 3,600 ft. A cement job was performed with 16 ppg cement; after the wait-on-cement time 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 fluid as a setting base. The thixotropic spacer successfully demonstrated sustained separation and a viable fluid base for setting cement. The result is a reliable method to set cement. This method does not require the mobilization of mechanical cement setting tools; the use of the fluid as the cement base enabled the use of a LWIV and negated the expensive need of mobilizing rig barriers to be set in place.