Cement oil-based mud spacer formulation

A method for fluidly isolating a portion of a well bore containing an oil-based fluid using a water-based cement slurry,

• where the well bore is located beneath a surface, is defined by a well bore wall extending from a surface underground, fluidly couples to a first fluid conduit and a second fluid conduit, and contains at least a portion of a tubular having an exterior surface;
• where the first fluid conduit and the second fluid conduit each are separately fluidly connected with the surface and are operable to convey fluids between the well bore and the surface;
• and
• where a well bore annulus is defined as a portion of the well bore between the tubular exterior surface in the well bore and the well bore wall;
• the method for fluidly isolating the portion of the well bore comprising the steps of:
• formulating a spacer fluid composition, such that a measured viscosity of a mixture of the spacer fluid composition and the water-based cement slurry at a first ratio of the water-based cement slurry to the spacer fluid composition is less than a measured viscosity of a mixture of the water-based cement slurry and the oil-based fluid at a second ratio of the oil-based fluid to the water-based cement slurry, where the first ratio and second ratio are substantially the same;
• formulating the spacer fluid composition, such that a measured viscosity of a mixture of the spacer fluid composition and the oil-based fluid at a third ratio of the oil-based fluid to the spacer fluid composition is less than a measured viscosity of a mixture of the water-based cement slurry and the oil-based fluid at the second ratio, 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 oil-based fluid and a measured viscosity of the water-based cement slurry, and where the spacer fluid composition maintains compatibility with both the oil-based fluid and the water-based cement slurry 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 water-based cement slurry at about 25% by volume, and the oil-based fluid at about 25% by volume;
• introducing into the well bore through the first fluid conduit an amount of the spacer fluid composition such that the spacer fluid composition fluidly couples to the oil-based fluid in the well bore, where the spacer fluid composition comprises a chemically modified tannin at a concentration of about 8.5 pounds per barrel, barite at a concentration of about 377 pounds per barrel, a silicone liquid at a concentration of about 0.1 gallons per barrel, and an ethoxylated alcohol at a concentration of about 1.9 pounds per barrel in an aqueous base fluid and is compatible with both the oil-based fluid in the well bore and the water-based cement slurry;
• positioning the spacer fluid composition in the well bore annulus such that the spacer fluid composition fluidly contacts the portion of the tubular exterior surface and a portion of the well bore wall of the well bore annulus, the fluid contact making both surfaces water-wet;
• introducing into the well bore through the first fluid conduit an amount of the water-based cement slurry such that the water-based cement slurry fluidly contacts the spacer fluid composition in the well bore and such that the oil-based fluid does not fluidly contact the water-based cement slurry, where the water-based cement slurry is operable to cure into a solid cement material at well bore conditions with up to about 5% volume of the spacer fluid composition in the water-based cement slurry, such that the water-based cement slurry compressive strength upon setting to the solid cement material is increased by at least about 25% at about 24 hours compared to the water-based cement slurry alone;
• positioning the water-based cement slurry in the well bore annulus such that the water-based cement slurry fluidly contacts the water-wetted surfaces of the tubular exterior surface and the well bore wall;
• and
• maintaining the water-based cement slurry in the well bore annulus until the water-based cement slurry adheres to the water-wetted portions of the tubular exterior surface and the well bore wall and cures into the solid cement material, isolating a portion of the well bore from well bore circulation,
• where the oil-based fluid and the water-based cement slurry are not compatible with one another,
• where during each introduction step an amount of the fluid in the well bore substantially equivalent to the amount of fluid introduced passes from the well bore through the second fluid conduit, and
• where during each introduction step the fluid in the well bore flows non-turbulently through the well bore annulus.

A method for treating a well bore annulus using a spacer fluid composition in preparation for introducing a water-based cement slurry,

• where the well bore is located beneath a surface, contains a fluid, is defined by a well bore wall extending from a surface underground, fluidly couples to a first fluid conduit and a second fluid conduit, and contains at least a portion of a tubular having an exterior surface;
• where the first fluid conduit and the second fluid conduit each are separately fluidly connected with the surface and are operable to convey fluids between the well bore and the surface;
• and
• where a well bore annulus is defined as a portion of the well bore between the tubular exterior surface in the well bore and the well bore wall;
• the method for treating the well bore annulus comprising the steps of:
• formulating a spacer fluid composition, such that a measured viscosity of a mixture of the spacer fluid composition and the water-based cement slurry at a first ratio of the water-based cement slurry to the spacer fluid composition is less than a measured viscosity of a mixture of the water-based cement slurry and the fluid at a second ratio of the fluid to the water-based cement slurry, where the first ratio and second ratio are substantially the same;
• formulating the spacer fluid composition, such that a measured viscosity of a mixture of the spacer fluid composition and the fluid at a third ratio of the fluid to the spacer fluid composition is less than a measured viscosity of a mixture of the water-based cement slurry and the fluid at the second ratio, 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 fluid and a measured viscosity of the water-based cement slurry, and where the spacer fluid composition maintains compatibility with both the fluid and the water-based cement slurry 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 fluid at about 25% by volume, and the water-based cement slurry at about 25% by volume;
• introducing into the well bore through the first fluid conduit an amount of the spacer fluid composition, where the spacer fluid composition comprises a chemically modified tannin at a concentration of about 8.5 pounds per barrel, barite at a concentration of about 377 pounds per barrel, a silicone liquid at a concentration of about 0.1 gallons per barrel, and an ethoxylated alcohol at a concentration of about 1.9 pounds per barrel in an aqueous base fluid and is compatible with both the fluid in the well bore and the water-based cement slurry, and where during the introduction an amount of the fluid in the well bore substantially equivalent to the amount of the introduced spacer fluid composition passes from the well bore through the second fluid conduit;
• and
• positioning the spacer fluid composition in the well bore annulus such that the spacer fluid composition fluidly contacts the portion of the tubular exterior surface and a portion of the well bore wall of the well bore annulus, the fluid contact making both surfaces water-wet and the spacer fluid composition mixing with the water-based cement slurry up to a volume ratio of about 95:5 water-based cement slurry 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,
• where during the introduction step the fluid in the well bore flows non-turbulently through the well bore annulus.