Rice University


Contribution to the scientific understanding of scale prediction and control

1.    Unified inhibition model for calcite and NORM scale control and treatment:  Equations, based on common field measurement that can be used to estimate the minimum effective concentrations of each of eight common scale inhibitors has been developed and included in both ScaleSoft and ScaleSoftPitzer.  The predicted minimum effective concentrations are calculated based upon the specific well and production conditions.  Additivity rules for inhibitor blends have also been included. Predictions of these equations are generally found to be reasonable compared to field observations.

2.    Effects of methanol and ethylene glycol on Scale formation: Methanol and ethylene glycol effect on the formation of mineral scale has been measured over a wider range of conditions.  A systematic study of these co-solvents on nucleation kinetics and inhibition has been conducted for BaSO4 and calcite.  The impact on the solubility of BaSO4 is quite large, but the effect on nucleation kinetics and inhibition is even more dramatic and unexpected.

3.    Molecular mechanism of how inhibitor squeeze works and inhibition takes place: Molecular mechanism of scale inhibition has been advanced substantially by detailed tests of the effect of solution condition and inhibitors on the inhibition of barite and calcite.  Due to improved reaction apparatus, experimental design, and theoretical analysis, a very wide range of inhibitor action seems to be explainable for the first time.  This work is potentially the first quantitative answer to why and under what conditions inhibitors work for both the squeeze and the return curve and "minimum effective dose".  A wide range of calcite and barite inhibition was modeled with one single model in both kinetics and equilibrium.  This new molecular-level understanding might permit numerical squeeze inhibition and return modeling as well as predicting the minimum effective dose in a well for the first time.

4.    Chemical properties of scale inhibitors:  The acid/base speciation constants, metal complexation stability constants, and solubility constants of amorphous and crystalline phases for phosphonate inhibitors (NTMP, DTPMP, and BHPMP) and polymeric inhibitors (PPCA) as a function of temperature and ionic strength have been determined.