A reversible emulsion drill-in fluid can exhibit the drilling benefits of conventional oil-based emulsion muds and still show cleanup characteristics equivalent to or better than biopolymer calcium carbonate water-based drill-in fluids. After exposure to the reversible emulsion drill-in fluid and an acid cleanup procedure, laboratory tests have demonstrated satisfactory retained permeabilities through sandstone cores in both the production and injection directions. Tests on aloxite disks show that the reversible invert emulsion filter cakes are stable during displacement of the drill-in fluid with brine. Clean up of the filter cakes shows that the destruction of the reversible invert emulsion filter cake containing calcium carbonate is easily attained with acid treatment through a simulated gravel pack.
The reversible emulsion drill-in fluid had higher retained permeabilities in both the injection and production directions when compared to the xanthan-based calcium carbonate fluids. The cleanup treatments for the reversible emulsion fluid and the xanthan carbonate fluids varied from a 10% acetic acid solution to a 10% hydrochloric acid solution. Tests of the reversible invert emulsion drill-in fluid filtercake stability on aloxite disks in a stirred filtration cell showed that the filter cakes are quite stable to calcium chloride displacement brine. Placement of gravel packing sand over the filter cakes and subsequent clean up of the filter cakes through the gravel pack showed that good clean up of the cakes could be achieved through the pack.
Lab work presented here has been validated by application of this reversible emulsion drill-in fluid in West Africa, where both production and injection wells have exceeded what was expected from use of a conventional invert emulsion. In addition, the wells were completed with less rig time and lower cost for the completion and clean up.