Abstract:
Objective Self-generated heat gas is an effective approach to solving the gel-breaking issue of fracturing fluids in low-temperature reservoirs. However, there is a problem that the acid catalyst in the self-generated heat system is incompatible with the alkaline fracturing fluid, and the addition of a sufficient amount of catalyst during fracturing at once may lead to excessively rapid gel breaking, making it difficult to achieve precise control.
Method In this study, a double-emulsion solvent evaporation method was employed to encapsulate the acid catalyst of the self-generated heat gas system, using polyvinyl alcohol (PVA) as a stabilizer and ethyl cellulose (EC) as the shell material, thereby enabling controlled and delayed gel breaking of fracturing fluids under low-temperature conditions. Single-factor analysis and orthogonal experiments were conducted to optimize the gel-breaking microcapsule system. The microstructure and particle size distribution of the microcapsules were characterized using scanning electron microscopy (SEM) and laser particle size analysis, and their gel-breaking performance was evaluated.
Result The optimal microcapsule formulation was achieved with 2.5 g EC, 4.50% emulsifier, 1.0% Tween-60, and 2% PVA stabilizer, resulting in microcapsules with an average particle size of 201.88 μm, a uniform particle size distribution, high sphericity, and an encapsulation efficiency of 46.76%.
Conclusion When combined with the self-generated heat gas system, the porous shell structure of the microcapsules facilitates the slow release of hydrogen ions, enabling effective gel breaking of the fracturing fluid within 2 h at 40 ℃. The microcapsules exhibited remarkable delayed gel-breaking performance. This study is of great significance for ensuring effective gel breaking in low-temperature reservoir fracturing operations and expanding the application scope of microencapsulation technology.
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