Method of using resin coated sized particulates as spacer fluid

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

• (a) introducing into the wellbore containing the drilling mud an aqueous fluid comprising:
• (i) water;
• (ii) a weighting agent;
• (iii) a hydratable gellant having a particle size distribution between from about 150 mesh to about 300 mesh;
• and
• (iv) particulates of a resin encapsulated hydratable polymeric viscosifying agent, the particle size distribution of the particulates being such that 100% of the particulates are retained on a 6 mesh screen and at least 90% of the particulates are retained on a 20 mesh screen;
• (b) hydrating the gellant and forming a viscous fluid containing the hydrated gellant, weighting agent and the resin encapsulated hydratable polymeric viscosifying agent particulates;
• (c) degrading the hydrated gellant at a bottom hole circulating temperature (BHCT) less than or equal to T1, wherein T1 is at least 175° F.;
• (d) degrading no more than 20% of the resin encapsulating the hydratable polymeric viscosifying agent at a BHCT less than or equal to T1 and degrading at least 80% of the resin encapsulating the hydratable polymeric viscosifying agent at a temperature of T2, wherein T2 is greater than T1, releasing the hydratable polymeric viscosifying agent into the wellbore upon degradation of the resin and suspending the weighting agent in the released hydratable polymeric viscosifying agent;
• (e) pumping the cement slurry into the wellbore and displacing at least a portion of the aqueous fluid with the cement slurry;
• and
• (f) permitting the cement slurry to harden.

A method of separating an aqueous cement slurry from a drilling mud in a wellbore, the method comprising:

• (a) pumping a spacer fluid into the wellbore, after introducing the drilling mud and before introducing the aqueous cement slurry into the wellbore, the spacer fluid comprising:
• (i) a weighting agent;
• (ii) water;
• (iii) a hydratable gellant having a particle size distribution between from about 150 mesh to about 300 mesh;
• and
• (iv) a suspension agent for the weighting agent, the suspension agent comprising particulates of a hydratable polymeric viscosifying agent encapsulated by a resin, wherein the particle size distribution of the suspension agent is such that 100% of the particulates are retained on a 6 mesh screen and at least 90% of the particulates are retained on a 20 mesh screen;
• (b) hydrating the hydratable gellant and forming a viscous fluid comprising the hydrated gellant, the weighting agent and the suspension agent, the weighting agent being suspended in the viscous fluid;
• (c) degrading the hydrated gellant and no more than 20% of the resin encapsulating the hydratable polymeric viscosifying agent at a bottom hole circulating temperature (BHCT) less than or equal to T1, wherein T1 is at least 175° F.;
• (d) maintaining the weighting agent in a suspended stated after degradation of the hydrated gellant by degrading the resin of the suspension agent and releasing the hydratable polymeric viscosifying agent into the wellbore wherein the resin is at least 80% degraded at a BHCT of T2, wherein T2 is greater than T1;
• and
• (e) maintaining the suspended weighting agent in the viscous fluid until a BHCT of T3 is attained, wherein T3 is greater than T2.