| Inhibitor solution chemistries and their efficiencies toward BaSO 4 nucleation inhibition have been quantitatively evaluated under simulated field conditions, with the aid of molecular models and electrostatic theory.;The acid-base and metal complexation chemistry of inhibitors has been described using a general 1:1-type charge neutralization model. With this model and electrostatic theory, the constants for proton and Ca2+ dissociation/association of PPCA can be expressed as: pKH = (4.856--0.984•I 1/2 + 0.2534•I-198.7/T) + f•thetau and pK Ca = (3.968--2.671•I1/2 + 0.750•I-1102.3/T) + 2 f•thetau, respectively, with f = 2.778--1.081•I 1/2 + 0.226•I; where I, T and thetau stand for ionic strength (m), temperature (K) and dissociated fraction of PPCA, separately. Similarly, dissociation constants pKM for other M2+-PPCA's (Mg2+, Sr2+, Ba2+, Cu 2+ and Zn2+) and pKH for NTMP, DTPMP and BHPMP have also been determined.;A semi-empirical method to define the solubility product of CaPPCA has been proposed and the solubility product constant has been expressed as: Ca 2(A_A_A_A) ↔ 2Ca2+ + (A_A_A_A)4-- with pK sp = 12.11--1506.0/T (T > 323°K) where T refers to temperature (K) and A refers to a monomer unit of PPCA. Similarly, the solubility product of CaBHPMP has also been formulated: H2Ca4BHPMP (cr) ↔ 2H+ + 4Ca2+ + BHPMP10-- , with pKsp = 55.600--2.985I1/2--2508.7/T where I stands for ionic strength.;The efficiency ([mg/Kg H2O]--1) of PPCA to inhibit BaSO4 nucleation in brine has been derived as: b PPCA0 = (--0.365•SI0.917 + 322.7/T)•theta u + 23.356•SI--5.696•thetaCa and in the presence of methanol and/or ethylene glycol, bPPCA m-EG = (2.85--0.93•SI + 14.06•Cmethanol+ 9.31•CEG)•thetau + (--0.92 + 17.82•SI --3 + 26.50•Cmethanol)•theta Ca (at 25°C), where SI stands for BaSO4 supersaturation index; Cmethanol and CEG are methanol and ethylene glycol (EG) concentration (Kg/Kg H2O), respectively. Methanol has been observed to accelerate BaSO4 nucleation. PPCA in the absence of Ca2+ can induce new fiber type BaSO4 crystals. A new complexing-binding-bridging model has been proposed to interpret nucleation inhibition mechanisms. The efficiency of BaSO4 inhibitors is: HEDP > PPCA > NTMP and the extent of the effect of Ca2+ is different, because of different Ca2+ enhancing mechanisms. Effects of Mg2+, Cu2+ and Zn2+ have also been investigated. |
