Summary
Barite (BaSO4) is one of the common scales in oil-and-gas production. Extensive work has been conducted to study barite nucleation and inhibition at temperatures below 100°C. However, with the advance in deepwater exploration and production (E&P) which can encounter high-temperature (HT) conditions, a better understanding of barite-scaling risk at HT (e.g., > 150°C) becomes essential. In this paper, a systematic study was conducted to explore barite nucleation kinetics from 70 to 200°C in synthetic brines containing phosphonate (0–10 ppm) or polymeric (5–10 ppm) scale inhibitors. A 2-hour protection time with or without any detectable barite nucleation was used to define the scaling risk. To detect barite nucleation, two novel apparatuses were developed—a modified dynamic flow loop and a batch reactor. The modified dynamic flow loop has a retention time of up to 4 hours and is ideal to carry out experiments at higher than 100°C. Ba concentrations in the effluents were monitored to determine barite nucleation more precisely compared with traditional “tube blocking” technique. The new batch reactor uses our newly developed laser-detection method, a transparent pressure tube, and an oil bath. The transparent pressure tube allows laser light to pass through and can withstand 150-psi pressure at 175°C, therefore providing an efficient approach to study the precipitation kinetics of scales and to evaluate inhibition efficiency of inhibitors at HT. Constant inhibitor-concentration isopleths of diethylenetriamine pentamethylene phosphonic acid (DTPMP) for barite inhibition were constructed on the basis of our experimental data. Finally, a semiempirical model that is based on data of barite nucleation and inhibition kinetics from this study and previous work was built to predict scaling risk of barite at different physicochemical conditions. This model covers a wide range of temperature (from 4 to 200°C) and brine compositions. It also covers the effect of Ba2+–SO42− ratio in solution, common cations (e.g., Ca2+), and thermodynamic hydrate inhibitors on barite precipitation. Model precipitations were found to be consistent with field observations. The results of this study can guide the design of barite-scale treatment for HT oil-and-gas production.
