EFFECT OF PHOSPHONATE INHIBITORS ON CALCITE NUCLEATION KINETICS AS A FUNCTION OF TEMPERATURE USING LIGHT-SCATTERING IN AN AUTOCLAVE

Phosphonates are some of the more popular inhibitors used in the oil i ndustry to prevent formation of calcite scale. Only recently has it be en shown that compounds with a direct P-C bond are forming naturally. The effect of phosphonate on calcite precipitation kinetics was studie d using a Hastelloy autoclave fitted with sapphire windows so that lig ht scattering measurements could be made in situ. As temperature incre ased from 25 degrees to 200 degrees C the induction time for calcite n ucleation following CO2 degassing decreased from more than an hour to a few minutes. The ability of chemical inhibitors (phosphonates) to de lay nucleation also decreased with increasing temperature. One of the inhibitors, diethylenetriamine-pentamethylenephosphonate (DETPMP), was able to disperse the calcite precipitate, when used in concentrations sufficient to precipitate ''calcium phosphonate''. It is still not cl ear whether phosphonates affect calcite precipitation kinetics by mono layer adsorption, or by surface precipitation.