EFFECT OF SYNTHESIS PARAMETERS ON THE PROPERTIES OF CALCIUM PHOSPHONATE PRECIPITATES

Phosphonates are commonly used in industry for scale prevention in a w ide variety of water systems. In many of these applications, the phosp honates are able to react with divalent cations such as calcium to for m stable divalent cation-phosphonate precipitates. The focus of this p aper is to identify and study how different precipitating factors will affect the resulting properties of calcium-phosphonate precipitates a nd to show how the formation of different precipitates can be used to enhance scale treatments in oil field applications. The phosphonate us ed in this study was 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). The three precipitating conditions under study were (1) the pH of the precipitating solution, (2) the calcium/ HEDP molar ratio of the prec ipitating solution, and (3) the degree of supersaturation of the preci pitating solution. The results in this paper showed that while the deg ree of supersaturation had a minimal effect on the resulting precipita te properties, the coupled effects of pH and calcium/HEDP molar ratio had a significant effect on the resulting precipitate properties. At t he extreme conditions, two distinct precipitates were synthesized: one comprised of fibrous spindles having a calcium/HEDP molar ratio of 1: 1 and the other comprised of spherical particles having a calcium/HEDP molar ratio of 2:1. Finally, micromodel experiments were carried out to test the performance of these two distinct precipitates with respec t to phosphonate treatments in petroleum production systems. The resul ts showed that the slow dissolution of the spherical particles and the morphology of the fibrous spindles were highly advantageous in slowin g the phosphonate release from a porous medium, ensuring successful ph osphonate treatments in oil field applications.