Cement mixing and pumping system and method for oil/gas well

A method of mixing and pumping a cement slurry into an oil or gas well, comprising:

• pumping water through a first control valve into a tub at the well;
• conducting dry cement through a second control valve into the tub;
• mixing the water and dry cement into a cement slurry in the tub;
• recirculating cement slurry out of and back into the tub;
• pumping cement slurry out of the tub into the well;
• controlling the first control valve in response to a desired water flow rate and an actual water flow rate;
• controlling the second control valve in response to a desired slurry density and an actual slurry density;
• controlling the pumping of cement slurry in response to a desired downhole pump rate and an actual downhole pump rate;
• and
• defining the desired water flow rate, the desired slurry density and the desired downhole pump rate from an interrelated common data base of predetermined operating conditions.

A method of mixing and pumping a cement slurry into an oil or gas well, comprising:

• controlling, with a computer, a flow of water into a mixing tub, a flow of dry cement into the mixing tub, and a flow of resultant mixture from the mixing tub into the well;
• entering into the computer a plurality of operating characteristics for a plurality of different mixtures;
• and
• sequentially performing said controlling step for at least two of said plurality of different mixtures so that the at least two different mixtures are sequentially prepared in the mixing tub and placed in the well.