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Sulfur is usually contained in existing gel breaker systems for fracturing fluids, which leads to the generation of hydrogen sulfide gas. In the process of fracturing development. The presence of hydrogen sulfide gas would cause equipment corrosion and environmental pollution. In this paper, a system of sulfur-free gel breaker agents for association fracturing fluid was constructed by evaluating the gel-forming and breaking properties of the fracturing fluid applied with this formula. The results showed that the combinations of 0.02% chlorine dioxide and 0.12% to 0.2% citric acid were chosen as the sulfur-free gel breaker formulas at 80 to 100°C. The polymer molecular chains were broken by synergistic effects of low concentration chlorine dioxide and citric acid to reduce the viscosity of association fracturing fluid, achieving gel-breaking. Simultaneously, the influence of hydrogen sulfide on the development process could be inhibited through bactericidal and oxidation actions of chlorine dioxide. The viscosity of the sulfur-free fracturing fluid remains above 50 mPa·s within 60 minutes, the value of the flow regime index was between 0.2593 and 0.3125, and the settling rate in this system was 0.024 to 0.042 mm/s. The temperature resistance, shear resistance, rheological properties, and sand carrying capacity of the sulfur-free fracturing fluid were not inferior to that of the conventional fracturing fluids, which guaranteed the effect of fracturing reformation. This study is of great significance to not only the development of environmental-friendly fracturing fluid but also the prevention and control of toxic and harmful gases, promoting sustainable development of oilfields.

Construction of sulfur-free gel breaker agent system and investigation on gel-breaking mechanism for association fracturing fluid