Mechanism Study of Wellbore Scaling for Water Injection System and its Prevention Through Nonmetallic Composite Tubing

Abstract

Water injection has been widely applied in tapping oil and gas resources underground; however, scaling corrosion in water injection system was a universal problem, posing a huge threat to the longevity of downhole tubing and water flooding results. In this paper, the mechanism of scaling and corrosion for the water injection system was analyzed, the nonmetallic composite tubing developed through self-propagating high-temperature synthesis was presented in detail and evaluated in terms of its ability to resist scaling and corrosion, and the field operation was carried out to testify this approach. The results indicated that inorganic scale was formed as a result of Cl⁻, Mg+, Ca+ contained in the injection water under the effect of specific temperature and pressure; the scale could become highly corrosive in the weak acid environment; nonmetallic composite tubing was developed based on self-propagating high-temperature synthesis technique; it was composed of three layers, ceramics inside, ceramic–metal combination middle, metal outside, respectively, and the numerical modeling and experiments outcome demonstrated that nonmetallic composite tubing was corrosion resistant and its scale rate was 1/70 compared to the conventional tubing, meanwhile the mechanical properties was better than its counterpart, field operation was performed in several oilfields demonstrating strong scale and corrosion characteristics, more than 1 million meters composite tubing was applied in the water injection system, and the statistic over 3 years indicated that nonmetallic composite tubing guaranteed the smooth water flooding operation downhole. This paper contributes to better understanding the scale and corrosion for water injection system and its prevention technique of nonmetallic composite tubing, through the pioneering example and profound insights we are able to explore new horizons and yield more benefits to the long-term healthy development of water injection operation.