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When displacing and completing oil and gas wells in deepwater, contaminants, such as oil-base drilling fluids, drilled solids, pipe dope and other debris found in casing and risers, should be removed quickly and efficiently to avoid excessive operating costs and to minimize formation damage during the completion phase. Synthetic-based invert emulsion drilling fluid debris is considered the most difficult to remove and typically requires excessive rig time to filter brine to appropriate levels of clarity using conventional spacer systems. These unscheduled costs and delays can be avoided if the displacement and clean-up spacers are properly designed.
A properly designed displacement spacer system should remove all foreign debris, completely water-wet all metal surfaces in a single pass of the spacer train and require no more than a single circulation of completion brine. The spacers should also be formulated to (1) have superior detergency at cold seabed and downhole temperatures, (2) prevent viscous emulsions or sludge, and (3) be compatible with the drilling fluid to prevent channeling.
Using mesophase technology which is a surface-active additive package (SAAP), a new spacer system has been developed and tested that does not require the use of common organic solvents or terpenes. Additionally, the new system is simple to apply and reduces non-productive time. This novel two-spacer system has been successful in several deepwater applications, demonstrating its ability to efficiently clean the riser, casing, and wellbore clean-up tools. The displacement spacer system has been successfully applied during direct and indirect displacements of synthetic-based drilling fluids.
This paper will discuss the challenges and successes of displacing synthetic-based mud in deepwater applications and the lessons learned.