(28d) Efficient Displacement of Synthetic or Oil-Based Mud and Transitional Phase Inversion

Effective displacement of a synthetic or oil-based mud (S/OBM) to completion brine is extremely important in order to minimize non-productive time (NPT), to lower brine filtration costs, reduce waste volume, to prevent cement failures and to reduce the risk of completion tool complications during the completion of a well. A good displacement spacer system should remove the S/OBM and debris, prevent viscous emulsions or sludge, be compatible with the drilling fluid in order to prevent channeling and should completely water-wet all metal surfaces in no more than a single circulation of completion brine.

The key spacer properties to obtain an effective displacement of the S/OBM are (1) high detergency or oil removal, (2) good mud/spacer compatibility without noticeable increase of viscosity at the fluids interface and (3) ability to change wettability of the rock and metal from oil-wet to water-wet.

Spacer fluids with such required properties need to have good microemulsification of the nonpolar components of the S/OBM and produce a transitional phase inversion from oil-continuous phase to water-continuous emulsion.

This paper discusses the phase behavior of microemulsion spacer systems, the transitional phase inversion, and the interfacial properties that result in successful displacements of synthetic-based drilling fluids in deepwater applications.