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Nanofluid flooding, as a new type of oil displacement technology in low permeability reservoirs, has attracted more and more attention due to its advantages of good injection, low reservoir damage, strong oil displacement ability, and intelligent response. Compared with spherical nanoparticles, Janus sheet nanomaterials have lower interfacial free energy and more limited rotation, can further prevent the diffusion of internal and external phase molecules, and form solid particle films with higher interfacial strength, showing excellent oil displacement performance. Janus nanosheets have a large specific surface area and abundant surface chemical groups, which have great application potential in enhancing oil recovery. Because of its sheet structure and unique physicochemical properties, molybdenum disulfide (MoS2) has attracted wide attention in enhancing oil recovery, but there is relatively little research on the Janus modification of MoS2nanosheets. In this article, amphiphilic Janus molybdenum disulfide nanosheets (JSMS) were prepared by a one-pot method, and their microstructure and physicochemical properties were characterized and analyzed. Finally, through a core flooding experiment and microscopic displacement test, the ability and mechanism of JSMS nanofluids to enhance oil recovery were evaluated. The results showed that the JSMS had excellent interface properties because of its Janus structure. It can produce a strong, elastic interfacial film. At the same time, the JSMS nanofluid can realize wetting reversal of rock surfaces. The results of the core flooding experiments showed that JSMS had a good oil displacement effect. The JSMS nanofluid enhanced oil recovery effectively by 4.7% with low concentration (0.005 wt %). This work demonstrated the feasibility of the Janus MoS2for enhanced oil recovery.

To address low viscosity of CO2in supercritical CO2fracturing, the authors studied silicon-based thickeners for a supercritical CO2fracturing fluid. Two silicon-based thickeners, namely, PMSQ-VAc and PDMS-VAc, were prepared by solution polymerization and emulsion polymerization, respectively; for each of the thickeners, molecular structural characterization, observation of dissolution in supercritical CO2with a pco.dimax cs1 high-frequency microscope camera, and exploration of viscosity-enhancing mechanisms were performed; a differential pressure method for fluid flow in a high-pressure delivery pipe was used to calculate viscosity and frictional drag coefficient of the supercritical CO2fracturing fluid, and rheological behavior and frictional drag behavior of the fracturing fluid under different experimental conditions were evaluated. The test results show that, by solution polymerization, the PMSQ-VAc thickener could be prepared from vinyl acetate and polymethylsilsesquioxane at a mass ratio of 13.95:7.51, with a yield of 84%, a molecular weight of 49,170 g/mol, and a viscosity of 12.86 mPa·s; by emulsion polymerization, the PDMS-VAc thickener could be prepared from dimethylcyclosiloxane, vinyltriethoxylsilane, and vinyl acetate at a mass ratio of 2:1:3, with a yield of 93%, a molecular weight of 76,190 g/mol, and a viscosity of 21.47 mPa·s; in the absence of any cosolvent, both silicon-based thickeners had a good solubility and viscosity-enhancing effect in supercritical CO2, among which PDMS-VAc had a better solubility and viscosity-enhancing effect, enabling the viscosity of supercritical CO2to be up to 10.12 mPa·s; after being incorporated with the silicon-based thickeners, the supercritical CO2fracturing fluid exhibited rheological behavior in agreement with shear behavior of pseudoplastic fluid and thus belongs to non-Newtonian fluid; the viscosity of the supercritical CO2fracturing fluid varied in a nonlinear manner with increasing temperature and pressure, i.e., increasing and then decreasing, and with increasing thickener concentration, the viscosity increased and then tended to be stable; the frictional drag coefficient of the fracturing fluid in pipe flow decreased gradually with increasing flow rate and pipe diameter and increased gradually with increasing viscosity of the fracturing fluid; two fracturing fluid systems consisting of silicon-based thickeners and supercritical CO2barely or weakly damaged the reservoir core. The silicon-based thickeners are practicable to some extent during supercritical CO2fracturing and likely to become high-performance, low-cost, pollution-free supercritical CO2thickeners.