Cement oil-based mud spacer formulation

A spacer fluid composition for use between a first fluid and a second fluid, the spacer fluid composition comprising:

• a base aqueous fluid comprising fresh water,
• a viscosifier comprising a chemically modified tannin,
• a weighting agent comprising barite,
• an antifoaming agent comprising a silicone-based liquid, and
• a non-ionic surfactant comprising an alkoxylated alcohol,
• where a measured viscosity of a mixture of the first fluid and the spacer fluid composition at a first ratio of the first fluid to the spacer fluid composition is less than a measured viscosity of a mixture of the second fluid and the first fluid at a second ratio of the second fluid to the first fluid, where the first ratio and second ratio are substantially the same, and where the second fluid comprises an oil-based fluid and the first fluid comprises a water-based cement slurry,
• where a measured viscosity of a mixture of the second fluid and the spacer fluid composition at a third ratio of the second fluid to the spacer fluid composition is less than a measured viscosity of a mixture of the second fluid and the first fluid at the second ratio of the second fluid to the first fluid, where the third ratio is substantially the same as the first ratio and the second ratio,
• where a measured viscosity of the spacer fluid composition is less than a measured viscosity of the first fluid and a measured viscosity of the second fluid, and where the spacer fluid composition maintains compatibility with both the first fluid and the second fluid during heavy contamination when the volume percent of the spacer fluid composition is about 50% by volume in a mixture comprising the spacer fluid composition, the first fluid at about 25% by volume, and the second fluid at about 25% by volume, and
• where the first fluid is operable to mix with the spacer fluid composition up to a volume ratio of about 95:5 first fluid to spacer fluid composition, such that the water-based cement slurry compressive strength upon setting to a solid cement is increased by at least about 25% at about 24 hours compared to the water-based cement slurry alone.