No abstract

In this study, a thermo-responsive temporary plugging agent was developed with the property of solution (sol)− gel−sol transition behavior at different temperatures. At low temperature, the material is in the sol state, while increasing temperature led to a stable gel formation, but the gel can transform to sol again upon further heating. This unique behavior was characterized by a series of SEM, FT-IR, XRD, rheology, and viscoelasticity measurements. All scientific results showed noncovalent interactions between the components, which play an important role for the supramolecular gel formation. These findings provide that this system can be applied as a temporary plugging agent by the idea of temperature-induced smart material with the advantages of cross-linker and gel-breaker free. Physical simulation experiment results showed that the material is a solid free fluid with good fluidity at room temperature. After injecting to formation, the fluid gradually transformed to a hard gel around 90 °C with sufficient strength to block cracks. Upon further heating by formation, the hard gel would collapse to a sol around 110 °C without adding additional gel breakers, leading to the flow conductivity restoring of fractures. This novel temporary plugging agent has potential use in diverting fracturing, network fracturing, drilling, well completion, well cleaning, etc.

A thermoresponsive in situ generated proppant based on liquid−solid transition of a supramolecular selfpropping fracturing fluid was developed. At lower temperatures (below gas/oil reservoir temperature), the supramolecular fracturing fluid is in the liquid state; with the increase of temperature, the self-propping fracturing fluid becomes a solid proppant during the phase transition. This particular conversion was characterized by scanning electron microscopy, nuclear magnetic resonance, viscosity, viscoelasticity, leak-off, friction, mechanical properties, and conductivity tests. All test results indicated that noncovalent interactions between the components led to the supramolecular proppant generated. These scientific findings showed that the self-propping fracturing fluid is a proppant solid-particle-free liquid with good fluidity at lower temperatures. After injection to a fracture in reservoir formation, the self-propping fracturing fluid gradually transformed into solid proppant particles with good mechanical strength stimulated by the reservoir high temperature. The critical phase transformation temperature and time could be adjusted by a change in the composition. This novel self-propping fracturing fluid is solid ceramsite and quartz proppant free, and there is no need to add thickeners and cross-linkers. Comparisons with existing proppant-carrying fluid mixture of a solid proppant and high viscosity fracturing fluid, damage by fracturing fluid gel residues, abrasion of the pumping equipment and tubes are reduced. Besides, the self-propping fracturing fluid could enter any narrow fracture, increasing the effective propped area. All experimental results proved that the novel fracturing fluid has potential use in conventional reservoir fracturing and unconventional reservoir network fracturing.