Cement compositions and process of cementing wells

Claim 1

IN THE METHOD OF CEMENTING A CASING IN A WELL WHICH COMPRISES PUMPING A CEMENT COMPOSITION AQUEOUS SLURRY COMPRISING A HYDRAULIC NATURAL CEMENT INTO THE ANNULAR SPACE BETWEEN THE WELL CASING AND THE BOREHOLE AND INTO CONTACT WITH SAID CASING AND AN EARTH FORMATION PENETRATED BY SAID BOREHOLE, THE STEP OF ADDING TO THE CEMENT COMPOSITION AQUEOUS SLURRY SMALL WEIGHT PERCENTAGES OF THE WEIGHT OF SAID DRY HYDRUALIC NATURAL CEMENT OF AN AMOUNT OF A CEMENT THICKENING TIME EXTENDING AND WATER LOSS REDUCING AGENT SUFFICIENT TO REDUCE THE WATER LOSS PROPERTIES OF SAID SLURRY, SAID AGENT BEING SELECTED FROM THE GROUP CONSISTING OF ACID CARBOXYALKYL HYDROXYETHYL CELLULOSE MIXED ETHERS IN WHICH THE ALKYL GROUP CONTAINS ONE TO TWO CARBON ATOMS, THE TOTAL SUBSITUTION PER ANHYDROGLUCOSE UNIT OF THE CELLULOSE OF CARBOXYALKYL AND HYDROXYETHYL GROUPS IS BETWEEN 0.5 TO 1.75, THE HYDROXYETHYL SUBSTITUTION IS FROM 0.35 TO 1.35, AND THE CARBOXYALKYL SUBSTITUTION IS FROM 0.15 TO 1.2, AND SALTS OF SAID MIXED ETHERS, AND A SMALL BUT EFFECTIVE AMOUNT OF A CEMENT THICKENING TIME REDUCING AGENT HAVING SUBSTANTIALLY NO EFFECT ON SAID WATER LOSS CONSISTING OF AN ALKALI METAL SILICATE HAVING A SILICON DIOXIDE TO ALKALI METAL OXIDE MOL RATION OF FROM 1 TO 2.5.