Experimental investigation of salt precipitation behavior and its impact on injectivity under variable injection operating conditions

Abstract

During the CO2 geological sequestration in saline aquifers, salt precipitation issues can diminish reservoir injectivity and significantly escalate injection costs. Variations in the gas supply during injection can lead to fluctuations in CO2 injection rates. These abrupt changes in injection parameters can affect the distribution of reservoir pressures and brine migration behavior, subsequently influencing salt precipitation dynamics. This study employs a designed micromodel with representative geological boundary conditions to investigate salt precipitation behavior under variable injection conditions, and the experimental conditions are at atmospheric pressure and 50 °C. The flow rates of the CO2 injection flow rates range from 0.5 mL/min to 4 mL/min. The findings reveal that under variable injection conditions, changes in gas injection rates can induce fluctuations in the reservoir solution, leading to the formation of “wet salt barriers” characterized by clustered salt growth near the inlet. This phenomenon significantly impairs injectivity. When sufficient supplemental solution is introduced, most of the previously precipitated salt is initially dissolved, eventually reaching a dynamic equilibrium that restricts further salt growth. However, under conditions of limited supplemental solution, salt precipitation predominates, and salt can proliferate, further impacting injectivity. This paper proposes a variable injection strategy to mitigate the impact of salt precipitation on injectivity. It recommends transitioning from low to high flow injection rates as early as possible to prevent the reflow of the solution near the injection interface, thereby minimizing salt accumulation and its adverse effects on injectivity.