Hydrolysis kinetics of self-degradable diverters for well stimulation

Abstract

Self-degradable diverters have gained increased popularity in well stimulation as an environmentally friendly and robust fluid diversion technology. As of now, limited data and conflicting information exist in the literature regarding the hydrolytic degradation rates of diverters under field-representative conditions, and knowing these rates is crucial for optimizing well stimulation designs. In this work, we systematically measured the degradation rates of commercial self-degradable diverters in aqueous solutions spanning a wide solution pH range of 0.3–13.6 and a wide temperature range of 60–110 °C. We first demonstrated that existing bottle degradation test protocols might return misleading results due to the alteration of solution pH by degradation products, and we developed a more reliable experimental protocol using buffer solutions instead. Using this procedure, we found that as the solution pH increased, the hydrolysis rate of diverters first decreased and then increased, with a minimal degradation rate at around pH = 4. Elevated temperatures yielded faster hydrolysis. The collected kinetic data fit reasonably well to a published kinetic model that was originally developed for pure polylactic acid in deionized water, with an R2 value over 0.98 for all pH and temperature conditions. This comparison suggests that the model can be more widely applied to describe the degradation kinetics of commercial diverters over broad temperature and pH ranges. The test protocol, experimental data, and kinetic analysis in this work provide important guidance on improving the efficiency of fluid diversion and well stimulation operations.