Oillwell cement and method of it*s production

A versatile hydraulic basic oil well cement, compatible with retarders and most common field additives and able to perform its intended function over a wide variety of downhole conditions, particularly temperature and pressure, comprises a common moderate or high sulfate resistant clinker and a weight ratio of calcium sulfate hemihydrate to insoluble anhydrite of 20:80 to 45:55. It can be made either by adding controlled amounts of gypsum and insoluble anhydrite to the grinding circuit or by blending ground hemihydrate and insoluble anhydrite to ground clinker.