Method of enhancing stability of cement slurries in well cementing operations

1. A method of cementing a pipe or casing in a well having a bottom hole temperature of at least 200° F. which comprises:

(a) pumping into the well a cement slurry comprising cement and particulates of a hydratable polymeric viscosifying agent wherein the particle size of the hydratable polymeric viscosifying agent particulates is such that a minimum of 90% of the hydratable polymeric viscosifying agent particulates is retained on a 20 mesh screen;

(b) placing into the well the cement slurry;

(c) allowing the slurry to harden to a solid mass at the bottom hole temperature of at least 200° F.; and

(d) cementing the pipe or casing in the well with the cement slurry to form a cement sheath

wherein non-separation of the cement from the cement slurry after being pumped into the well is enhanced and thermal thinning of the cement slurry is minimized during placement of the cement slurry into the well by the particle size of the hydratable polymeric viscosifying agent particulates.

2. The method of claim 1 , wherein the bottom hole temperature of the well is at least 300° F.

3. A method of decreasing settling of cement particles in a cement slurry during the cementing of a pipe or casing in a well, the method comprising pumping into the well a cement slurry containing a viscosifying agent adsorbed onto a water-insoluble adsorbent, water and cement particles, wherein the amount of viscosifying agent in the cement slurry is between from about 15 to about 50 pounds per 1,000 gallons of water in the cement slurry and further wherein the viscosifying agent exhibits a 90% retention on a 20 mesh screen, wherein settling of the cement particles from the cement slurry is decreased during the cementing of the well until after the cement slurry is pumped into a targeted location within the well and further comprising cementing the pipe or casing in the well with the cement slurry to form a cement sheath.

4. The method of claim 3 , wherein the viscosifying agent is a selected from the group consisting of hydroxyethyl cellulose, methylhydroxyethyl cellulose, hydroxyethylmethyl cellulose, ethylhydroxyethyl cellulose, ethylmethylhydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethylpropyl cellulose, dialkyl carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and carboxymethyl cellulose and mixtures thereof.

5. The method of claim 3 , wherein the water-insoluble adsorbent is diatomaceous earth.

6. The method of claim 5 , wherein the hydratable polymeric viscosifying agent is an ammonium or alkali metal salt of an acrylamidomethylpropanesulfonic acid and mixtures thereof.

7. A method of delaying viscosification of a cement slurry during the cementing of a well and after pumping the cement slurry into the well, the method comprising:

(a) pumping into the well a cement slurry, the slurry comprising cement and a hydratable polymeric viscosifying agent, wherein the hydratable polymeric viscosifying agent is an ammonium or alkali metal salt of an acrylamidomethylpropanesulfonic acid and mixtures thereof, wherein the particle size of the hydratable polymeric viscosifying agent is such that a minimum of 90% of the hydratable polymeric viscosifying agent is retained on a 20 mesh screen;

(b) delaying viscosification of the cement slurry; and

(c) cementing the pipe or casing in the well with the cement slurry containing the hydratable polymeric viscosifying agent to form a sheath wherein viscosification of the cement slurry is more delayed than when a substantially similar cement slurry is pumped into the well, the substantially similar cement slurry containing a hydratable polymeric viscosifying agent having a particle size such that less than 90% of the hydratable polymeric viscosifying agent is retained on a 20 mesh screen and further wherein the substantially similar cement slurry only differs by the particle size of the hydratable polymeric viscosifying agent.