Mesoporous Silica Microspheres in a Delayed Gel-Breaking System for High-Temperature Fracturing Fluid

Abstract In high-temperature fracturing operations, the rapid decomposition of strong oxidant breakers causes premature viscosity loss of fracturing fluids, severely impairing proppant placement. Currently, most delayed gel-breaking systems rely on polymeric shell materials to physically encapsulate oxidants. However, such polymer-based systems suffer from a dual failure mechanism at elevated temperatures: (i) the polymer shell softens and swells due to intensified thermal motion, losing its structural integrity; and (ii) the encapsulated strong oxidant (e.g., ammonium persulfate) aggressively attacks the polymer backbone, causing oxidative degradation of the shell material and accelerating burst release. These two synergistic effects render “polymer-encapsulated oxidants” fundamentally unworkable in high-temperature reservoirs. To radically overcome this material bottleneck, we propose for the first time a non-polymeric controlled-release strategy based on the synergistic effect of “inorganic mesoporous confinement and oil-phase isolation.” Rigid hollow mesoporous silica microspheres (HMSS) with nanoscale mesoporous shells are employed as inorganic structural carriers, which exhibit exceptional resistance to both high temperature and strong oxidants. APS is loaded via impregnation, followed by hydrophobic surface modification and dispersion in white oil to construct an emulsion-type release system. This system leverages the rigid silica skeleton for outstanding thermal and chemical stability, while the oil-phase interfacial barrier effectively prevents premature APS-aqueous contact. Results show that at 90 °C with 2.5 wt % hydrophobic particles, the cumulative release reaches 62% over 12 h, demonstrating excellent sustained-release characteristics. At 100 °C, the system extends the complete gel-breaking time to ∼8 h, which is 7 times longer (i.e., an 8-fold increase) than that of directly added APS. By completely abandoning organic polymer shellswhich are both thermally labile and susceptible to oxidative attackand instead employing inorganic mesoporous silica combined with an oil-phase barrier, this work fundamentally resolves the long-standing challenge of premature breaker release under high-temperature oxidizing conditions, offering a nanoscale carrier-based, structurally simple, highly robust, and precision-release paradigm for deep high-temperature reservoir stimulation.