High Temperature Self-Regenerative Granular Hydrogels for Fracture Treatments During Subsurface Energy Recovery.

The uses of granular hydrogels to assemble macroscopic bulk hydrogels display numerous distinct advantages. However, prior assembly of bulk hydrogels is accomplished by interparticle linking strategy, which compromised mechanical property and thermal stability under hostile conditions. To expand their applications as engineering soft materials, self-regenerative granular hydrogels via a seamless integrating approach to regenerate bulk hydrogels is highly desirable. Herein, covalent regenerative granular hydrogels (CRHs) are prepared at low-temperature synthetic conditions and re-construct bulk seamless hydrogels at high-temperature aqueous environments. The re-formed bulk hydrogels display rubber-like viscoelastic behaviors over a wide range of temperatures from 90 to 150 °C, where the covalent re-crosslinking reactions homogeneously occurr along the periphery and in the matrix of granular hydrogels, accounting for the increased structural integrity at high temperatures. The bulk hydrogel shows increased elasticity and long-term thermal integrity at 150 °C for more than six months in the confined fractures. Moreover, regenerative granular CRH-based bulk hydrogels significantly improve mechanical robustness under destructive pressure. Thus, high temperature water induced regenerative granular hydrogels present the paradigm to treat engineering scenarios such as large fractures for hydraulic fracturing, drilling operation, and disproportionate permeability reduction under extremely hostile conditions during subsurface energy recovery.

A Self-Healing Gel with an Organic-Inorganic Network Structure for Mitigating Circulation Loss.

Lost circulation control remains a challenge in drilling operations. Self-healing gels, capable of self-healing in fractures and forming entire gel block, exhibit excellent resilience and erosion resistance, thus finding extensive studies in lost circulation control. In this study, layered double hydroxide, Acrylic acid, 2-Acrylamido-2-methylpropane sulfonic acid, and CaCl2 were employed to synthesize organic-inorganic nanocomposite gel with self-healing properties. The chemical properties of nanocomposite gels were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy and thermogravimetric analysis. layered double hydroxide could be dispersed and exfoliated in the mixed solution of Acrylic acid and 2-Acrylamido-2-methylpropane sulfonic acid, and the swelling behavior, self-healing time, rheological properties, and mechanical performance of the nanocomposite gels were influenced by the addition of layered double hydroxide and Ca2+. Optimized nanocomposite gel AC6L3, at 90 °C, exhibits only a self-healing time of 3.5 h in bentonite mud, with a storage modulus of 4176 Pa, tensile strength of 6.02 kPa, and adhesive strength of 1.94 kPa. In comparison to conventional gel, the nanocomposite gel with self-healing capabilities demonstrated superior pressure-bearing capacity. Based on these characteristics, the nanocomposite gel proposed in this work hold promise as a candidate lost circulation material.

Highly Robust Nanogels from Thermal-Responsive Nanoparticles with Controlled Swelling for Engineering Deployments.

Regular nanogels have been demonstrated their inefficiency for subterranean oil recovery due to their intrinsic drawbacks of fast swelling within minutes, thermal instability, and salinity vulnerability. Prior deployment of swelling delayed nanogels mainly depended on the reservoirs at a relatively higher temperature. To address the issues encountered during engineering deployment, hereinwe devised an integrative approach to in situ form swelling delayed robust nanogels by introducing radically active monomers with thermally sensitive moieties. The nanoparticles with hydrophobic cores in brine in response to thermal input in situ generated well-dispersed hydrophilic nanogels, which showed a pronounced delayed swelling of a week compared to traditional nanogels showing swelling kinetics within minutes. Furthermore, the formation of swelling-delayed nanogels could occur at ambient temperature. This behavior was radically different from that of temperature-controlled labile cross-linkers containing nanogels, requiring temperatures greater than 50 °C for volume increase thanks to ester hydrolysis. In addition, the in-situ formed nanogels displayed long-term thermal stability and salinity tolerance under hostile media at temperatures up to 130 °C. The release of an acidic proton under aqueous conditions has been demonstrated to control the microenvironment for various scenarios. The nanotechnology of converting hydrophobic nanoparticles to hydrophilic nanogels could be applied in a wide range of practical applications such as plugging materials and foaming stabilizers for in-depth conformance control during water and CO2 flooding.