Shiliang He

The inhibition of gypsum and barite nucleation in NaCl brines at temperatures from 25 to 90°C

Abstract The inhibition of gypsum and barite nucleation in NaCl brines by phosphonates and polycarboxylates was studied at 25, 50, 70 and 90°C in terms of the prolonged induction period. Hexamethylene-diaminetetra (methylene phosphonic) acid (HDTMP) was found to be an effective inhibitor for the scaling of calcium sulfate dihydrate. Hydroxyethylene-1, 1-diphosphonic acid (HEDP) and phosphinopolycarboxylic acid (PPPC) were found to be effective inhibitors for barium sulfate scaling. The inhibition of nucleation through prolongation of the nucleation induction period likely resulted from an increase in the interfacial tension between the crystal and aqueous solution due to the presence of the inhibitors. It was observed that the inhibition of nucleation depends highly on the lattice cation/anion molar ratio and the pH of the solution as well as the degree of supersaturation and temperature for a given inhibitor.

Inhibition of calcium carbonate precipitation in NaCl brines from 25 to 90°C

Abstract The nucleation induction period of CaCO3 in NaCl brines in the absence and presence of scale inhibitors was experimentally measured at temperatures from 25 to 90°C. A semi-empirical mathematical inhibitor model is presented for the CaCO3 scale control in industrial processes based upon nucleation theory and experimental observations. Results show that the minimum inhibitor dosage (Cinh) may be obtained from: Cinh=f(s)/binh log [tinh/t0], where tinh is the inhibition time, e.g., 20 min, t0 is the nucleation induction period in the absence of inhibitors, binh is the inhibitor efficiency, and f(s) is the safety factor, e.g., 2. Important factors for the kinetics of both nucleation and inhibition have been incorporated in this model including the calcite saturation index (SI), temperature (T), and the molar ratio of Ca to HCO3 alkalinity (R). In this paper, model parameters are presented for commonly used inhibitors, including 1-hydroxyethylidene-1,1-diphosphonic-acid (HEDP) and nitrilotri(methylene phosphonic) acid (NTMP). Results show that HEDP and NTMP are the best inhibitors for calcite scaling in the systems examined.

Inhibition of Mineral Scale Precipitation by Polymers

The inhibitory efficiency of polymeric inhibitors against the precipitation of common mineral scales in industrial processes could be described quantitatively using a semi-empirical model based on nucleation theory and laboratory experimental observations. The minimum effective inhibitor concentration (Cinh, mg/1) which is needed to prevent precipitation at a given degree of supersaturation can be estimated by: Cinh = (l/binh) log (fStp/t0), where binh is the efficiency of the inhibitor (l/mg), tp is the inhibition time or protection time needed for the system (seconds), t0 is the nucleation induction period for the mineral at a given condition in seconds, and fS is the safety factor (e.g., 2). Model parameters have been measured for typical scale minerals such as calcite and barite with eight scale inhibitors which have been commonly used in industrial processes, including polyacrylates and their derivatives (PAA, SPA, and PPCA) and poly-phosphonates (HEDP, NTMP, HDTMP, DTPMP, and BHPMP). This semi-empirical model has been demonstrated to be accurate in predicting the minimum effective inhibitor concentrations needed to protect a system from scaling comparing to both laboratory experimental simulation results using a high-temperature/high-pressure flow-through apparatus and preliminary observations in oil and gas production systems.