Settable spotting fluid compositions and methods

An improved settable spotting fluid composition for use in cementing wells comprising:

• a hydraulic settable component comprising ASTM Class F fly ash;
• hydrated lime present in said composition in an amount of about 5% by weight of said hydraulic settable component in said composition;
• a fluid loss control additive comprising a graft polymer having a backbone of lignite and grafted groups of 2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile and N,N-dimethylacrylamide or their salts present in said composition in an amount in the range of from about 0.4% to about 0.75% by weight of said hydraulic settable component in said composition;
• a gel strength inhibiting additive comprising a copolymer of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid present in said composition in an amount in the range of from about 0.4% to about 0.75% by weight of said hydraulic settable component in said composition;
• a set retarding additive comprising the calcium salt of a sulfomethylated lignin present in said composition in an amount in the range of from about 0.1% to about 2% by weight of said hydraulic settable component in said composition;
• and
• water selected from the group consisting of fresh water and salt water present in an amount sufficient to form a slurry having a density in the range of from about 12 to about 15 pounds per gallon.

An improved method of cementing a pipe string in a well bore containing drilling fluid with a cement composition comprising the steps of:

• (a) preparing a settable spotting fluid composition comprised of a hydraulic settable component selected from the group consisting of ASTM Class C or the equivalent fly ash and ASTM Class F or the equivalent fly ash together with a source of calcium, a fluid loss control additive, a gel strength inhibiting additive, a set retarding additive and water selected from the group of fresh water and salt water present in an amount sufficient to form a slurry having a density in the range of from about 12 to about 15 pounds per gallon;
• (b) pumping said settable spotting fluid composition into said well bore to displace at least a portion of said drilling fluid out of said well bore thereby preventing said drilling fluid from remaining in fractures or other permeable zones in said well bore and progressively increasing in gel strength over time therein;
• (c) running said pipe string to be cemented into said well bore whereby said pipe string and well bore are at least partially filled with said settable spotting fluid;
• (d) pumping and displacing said cement composition through said pipe string and into the annulus between said pipe string and the walls of said well bore whereby said drilling fluid and said settable spotting fluid composition in said pipe string and said annulus are displaced therefrom except for portions of said settable spotting fluid composition which may remain in fractures or other permeable zones therein;
• and
• (e) allowing said cement composition in said annulus and any settable spotting fluid composition remaining in said fractures or other permeable zones therein to set into hard impermeable masses therein.