Method of using sized particulates as spacer fluid

A method of emplacing an aqueous cement slurry into a wellbore containing a drilling mud, which comprises:

• (a) introducing a spacer fluid comprising particulates of a hydratable polymeric viscosifying agent having a particle size distribution such that a minimum of 90% of the particulates are retained on a 20 mesh screen into the wellbore containing the drilling mud, wherein the spacer fluid is introduced into the wellbore prior to introducing the aqueous cement slurry into the wellbore;
• (b) displacing at least a portion of the drilling mud having gelled and solid remnants within from an area in the wellbore into which the cement slurry is to be emplaced with the spacer fluid;
• (c) introducing into the wellbore the aqueous cement slurry, displacing at least a portion of the spacer fluid from the area in the wellbore with the aqueous cement slurry fluid and isolating the drilling mud from the aqueous cement slurry with the spacer fluid;
• and
• (d) permitting the aqueous cement slurry to harden.

A method of displacing at least a portion of a first fluid from a wellbore annulus wherein the annulus is between an external surface of a tubing within the wellbore and a face of a subterranean formation penetrated by the wellbore, the method comprising:

• (a) pumping into the wellbore a second fluid, prior to pumping a cementitious slurry into the slurry, the second fluid comprising particulates of a hydratable polymeric viscosifying agent having a particle size distribution such that a minimum of 90% of the particulates are retained on a 20 mesh screen, wherein the second fluid is pumped down the wellbore and up through the annulus and further wherein viscosification is delayed in the annulus by inclusion of the hydratable polymeric viscosifying agent in the second fluid;
• (b) inducing laminar fluid circulation of the first fluid;
• (c) pumping, after step (b), the cementitious slurry into the wellbore and up through the annulus wherein the second fluid isolates the first fluid and the cementitious slurry;
• and
• (d) displacing at least a portion of the first fluid from the annulus with the cementitious slurry;
• and
• (e) curing the cementitious slurry emplaced in the annulus by the removal of the first fluid.