| 摘要 |
<p>The present invention relates to systems for retarding setting in an oilfield well cement slurry constituted by a solution of a phosphonate selected from methylene phosphonic acid derivatives and a phosphate, in particular selected from the following salts or the corresponding acids: mono-phosphates (ortho-phosphates PO42-, meta-phosphates PO¿3?-), acyclic poly-phosphates (pyrophosphates P¿2O7?4-, tripolyphosphates P¿3O10?5-) or cyclic poly-phosphates. The system preferably may also comprise a retarder booster and is more particularly applicable to cementing at low or medium temperatures.</p> |
