Polyphosphino Carboxylic Acid (PPCA) polymeric scale inhibitor is widely used for downhole application in oilfield squeeze treatments. Like all scale inhibitors (SI), it must perform the dual role of inhibiting scale formation at low concentration levels (~2 to 20ppm) while giving acceptably long return curves at the wellbore. Both of these properties of polymeric scale inhibitors, inhibition efficiency and retention, are thought to be the functions of the molecular weight. PPCA is often applied in the field as a "precipitation squeeze" treatment and the molecular weight also has an important effect on the solubility of the polymer complex which is precipitated. In this work, we present several results on the phase behaviour and properties of PPCA when it is applied in precipitation squeeze. In particular, we present new results, which explain the behavior of PPCA in terms of the molecular weight distribution (MWD) of the PPCA, as follows:
(i) MWD results (Mw, Mn and PDI) were determined for different fractions of PPCA including the stock solution as well as the Precipitate (P) and Supernatant (S) of the PPCA/Ca complex.
(ii) The PPCA Precipitate (Mw = 4900) is shown to be composed of mainly higher molecular weight components which explains the corresponding high Inhibition efficiency of this fraction. As a corollary, the Supernatant PPCA fraction (Mw = 1300) shows poor Inhibition Efficiency and contains much less high molecular weight material.
(iii) The implications of the MWD on the assay of PPCA concentration by wet chemical (Hyamine/C18) methods and by ICP are also discussed.
The MWD results for the PPCA polymer have given us some significant insights into the precipitation/dissolution mechanisms, which are occurring in polymer precipitation squeeze processes. We believe that these results are the most detailed to be published in the literature on the PPCA system and that they are of general significance and application for all polymeric scale inhibitor precipitation squeeze treatments.