Supramolecular-Structure-Associating Weak Gel of Wormlike Micelles of Erucoylamidopropyl Hydroxy Sulfobetaine and Hydrophobically Modified Polymers

The properties of a new supramolecular-structure-associating weak gel (SAWG) are discussed in this paper. On the basis of a hydrophobically modified polymer thickener (HMPT), the thickening system formed a gel with wormlike micelles of the erucoylamidopropyl hydroxy sulfobetaine (EHSB) surfactant by experimental design. The resultant gel contained very efficient physical cross-links between the HMPT and EHSB, generating viscoelasticity. To describe the performance of the SAWG, we investigated its high-temperature and shear-rate tolerance properties, suspension behavior, and rheological and structural thermal stabilities. Furthermore, scanning electron microscopy and transmission electron microscopy images of the solution microstructure revealed a supramolecular network honeycomb structure in the gel, which was formed with strong hyperbranched compound structures through extremely efficient non-covalent interactions. Meanwhile, an envisioned gelation mechanism model was proposed to facilitate rational discussion of the results. Moreover, the gel-breaking properties and formation damage were studied. The results of the steady shear viscosity and static-column tests showed that the optimized formula of the SAWG was obtained at 0.5 wt % EHSB, which can effectively satisfy the tight gas reservoir at approximately 150 degrees C. The results of the rheological experiments demonstrated that the salt-absorption capacity and charge-shielding effect of the surfactant micelles co-determined the solution structure and rheological properties. Differential scanning calorimetry data showed that temperatures reached their maximum during the SAWG structure transition point. The structural thermal stability evaluation of the SAWG showed that the temperature disaggregates the long rod wormlike micelles into spherical micelles and results in the tendency toward a supramolecular structure that was connected by spherical micelles containing on average two hydrophobic monomers suspended in the copolymer at 0.5 wt % EHSB. The thermodynamic study also demonstrated that this supramolecular structure had the lowest activation energy, generated the highest thermal stability, and had the most stable network structure of the optimized formulation. The SAWG could be completely broken with almost no water-insoluble residue, and its formation damage was 20% less than that of the guar fracturing fluid.