Removing oil-based drilling fluid residue is crucial to developing an excellent cement bond between casing and formation. A good cement bond leads to proper zonal isolation, improved casing integrity, and reduces annular gas migration. The development of an effective displacement spacer to remove oil residue is paramount in creating an effective cement bond. Typically mixtures of several different components consisting of solvent and surfactant combinations have to be run for an effective displacement from oil-based fluid to cement. Microemulsions offer an attractive alternative to the use of solvent/surfactant combinations. Microemulsion forming surfactant solutions can solubilize large volumes of oil like a solvent while simultaneously water wetting the casing and formation.Laboratory testing led to the development of a surfactant-based microemulsion forming cement spacer. The microemulsion spacer water wets more effectively than previously used solvent/surfactant spacers, eliminating the use of solvents in the cement spacer. The elimination of solvents can allow for a more environmentally friendly solution. Mixing this spacer with oil-based drilling fluid does not change the wettability of the bulk mud, allowing it to be re-mixed with the remaining fluid.Several different field trials in the Rocky Mountain region have been run showing improved cement bond logs. Operational personnel identified that the surfactant package replaced the use of two existing surfactant packages, eliminating mixing errors and minimizing logistical issues. Initial lab tests were done with local field mud samples to compare wettability results. Improved wettability was achieved on different mud systems, diesel based and synthetic oil based. The operator approved the use of a new microemulsifier on several wells. After the operator had run bond logs, results were compared to wells with similar job designs and wellbore conditions. Improved bonds were shown in the wells where the new surfactant package was applied.
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