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Nanomaterials for enhanced oil recovery （EOR） have gained more and more attention from petroleum researchers. However， the research mainly focuses on the properties of spherical nanomaterials， and the research on two-dimensional nanosheets is insufficient. In this paper， the amphiphilic MoS2 nanosheets （active MoS2 nanosheets） were independently synthesized to significantly enhance the oil recovery after water flooding in reservoirs. The spreading law of active MoS2 nanosheets on a solid surface was studied， and the mechanism of active MoS2 nanosheets on an oil film of a solid surface was elucidated. Based on the measurement of the gas-water-solid three-phase contact angle， it is determined that the equilibrium contact angles of water droplets remain unchanged at 90° after oil-wet quartz is immersed in an oil displacement system of active MoS2 nanosheets for 120 h. Eventually， the wettability of the quartz surface changes from oil-wet to neutral-wet. Both formation water and SiO2 nanofluid （mass fraction of 0.15%） fail to make the oil film produce wedge film on the solid surface. However， the oil displacement system of active MoS2 nanosheets （mass fraction of 0.005%） could form a prominent wedge film in the oil-water-solid three-phase contact area， then form structural disjoining pressure and eventually strip the oil film from the solid surface. Moreover， it is found that the oil film could form two contact lines （inner line and outer line） during the contraction process on the solid surface in the oil displacement system of active MoS2 nanosheets （mass fraction of 0.005%）. The contraction velocities of the inner contact line and the outer contact line are 0.661 7 × 10-5 and 8.581 7 × 10-5 cm/s， respectively. From the perspective of thermodynamics， the Gibbs free energy increment of the oil-water-solid mixture system is negative in the contraction process of oil film， which proves that the contraction of the oil film in the oil displacement system of MoS2 nanosheets is spontaneous. The research results show that the oil displacement system of MoS2 nanosheets （mass fraction of 0.005%） has high oil displacement efficiency.

The wettability of the proppant is crucial in optimizing the flowback of fracturing fluids and improving the recovery of the produced hydrocarbons. Neutral wet proppants have been proven to improve the fluid flow by reducing the interaction between the fluid and the proppant surface. In this study, a lightweight amphiphobic proppant (LWAP) was prepared by coating a lightweight ceramic proppant (LWCP) with phenolic resin, epoxy resin, polytetrafluoroethylene (PTFE), and trimethoxy(1H,1H,2H,2H-heptadecafluorodecyl)silane (TMHFS) using a layer-by-layer method. The results indicated that the LWAP exhibited a breakage ratio of 2% under 52 MPa (7.5 K) closure stress, with an apparent density of 2.12 g/cm3 and a bulk density of 1.21 g/cm3. The contact angles of water and olive oil were 125° and 104°, respectively, changing to 124° and 96° after displacement by water and diesel oil. A comparison showed that the LWAP could transport over a significantly longer distance than the LWCP, with the length increasing by more than 80%. Meanwhile, the LWAP displayed notable resistance to scale deposition on the proppant surface compared to the LWCP. Furthermore, the maintained conductivity of the LWAP was higher than that of the LWCP after displacement by water and oil phases alternately. The modified proppant could minimize production declines during hydrocarbon extraction in unconventional reservoirs. [ABSTRACT FROM AUTHOR]

Polymer flooding is an effective development technology to enhance oil recovery, and it has been widely used all over the world. However, after long-term polymer flooding, a large number of oilfields have experienced a sharp decline in reservoir development efficiency. High water cut wells, serious dispersion of residual oil distribution and complex reservoir conditions all bring great challenges to enhance oil recovery. In this study, the method of enhancing oil recovery after polymer flooding was studied by taking the S Oilfield as an example. A surfactant–polymer system suitable for high-permeability heterogeneous oilfields was developed, comprising biogenic surfactants and polymers. Microscopic displacement experiments were conducted using cast thin sections from the S Oilfield, and nuclear magnetic resonance was employed for core displacement experiments. Numerical simulation experiments were also conducted on the S Oilfield. The results show that the enhanced oil recovery mechanism of the surfactant–polymer system is to adjust the flow direction, expand the swept volume, emulsify crude oil and reduce interfacial tension. Surfactant–polymer flooding proves to be effective in improving recovery efficiency, significantly reducing the time of flooding and further enhancing the strong swept area. The nuclear magnetic resonance results indicate a high amplitude of passive utilization of residual oil during the surfactant–polymer flooding stage, highlighting the enormous potential for an increased recovery ratio. Surfactant–polymer flooding emerges as a more suitable technique to enhance oil recovery in the post polymer-flooding stage in high-permeability heterogeneous oilfields. [ABSTRACT FROM AUTHOR]

Geochemical reactions are crucial for in situ CO2 mineralization underground associated with CO2‐enhanced oil recovery (CO2‐EOR) in a hydrocarbon reservoir. However, the presence of formation water and adsorbed oil on rocks generates physical barriers to CO2's access to mineral surfaces, which may yield impedance to CO2 mineral trapping that has yet to be accounted for. In this study, we mimic the dynamic oil detachment process using molecular dynamic (MD) simulation and analyze the influence of an adsorbed oil film on supercritical CO2 (scCO2) diffusion toward the mineral surface in the presence and absence of a water phase. Our results demonstrated a negative impact of water on oil film detachment by scCO2, which may weaken mineral reactions and is unfavorable for mineralized CO2 storage underground. Plain Language Summary: Carbon dioxide emission has been identified as one of the primary factors influencing global climate change. Storing CO2 underground while enhancing oil recovery is a promising technology that can effectively reduce costs for carbon capture, utilization, and storage (CCUS). Mineral trapping, that is, converting CO2 to carbonate minerals through CO2‐water‐mineral surface reactions, is one of the major mechanisms for CO2 storage. However, residual oil adsorbed on rock surfaces after CO2 injection into an oil reservoir yields a physical barrier for CO2 approaching mineral surfaces. CO2‐water‐oil‐mineral interactions have yet to be thoroughly understood. Therefore, we conducted a series of molecular dynamics simulations to mimic the dynamic oil detachment process and unveil the impact of water on oil film detachment by supercritical CO2. We found that the presence of water strengthens the interactions between the oil and rock surface, which may give rise to a substantial delay in oil film detachment and weaken mineral reactions. Our results provide significant implications for the mineralized storage of CO2 in a depleted oil reservoir and CO2‐enhanced oil recovery and its consequent sequestration. Key Points: CO2‐water‐oil‐rock interactions are investigated using molecular dynamics simulationsscCO2 can collapse the oil film and channel out a path for CO2 diffusionWater exhibits a negative impact on oil film detachment by scCO2 [ABSTRACT FROM AUTHOR]

The Henan Oilfield's medium-permeability blocks face challenges such as high temperatures and severe heterogeneity, making conventional flooding systems less effective. The starch gel system is an efficient approach for deep profile control in high-temperature reservoirs, while the nano-MoS2 system is a promising enhanced oil recovery (EOR) technology for high-temperature low-permeability reservoirs. Combining these two may achieve the dual effects of profile control and oil displacement, significantly enhancing oil recovery in high-temperature heterogeneous reservoirs. The basic performance evaluation of the combination system was carried out under reservoir temperature. Displacement experiments were conducted in target blocks under different permeabilities and extreme disparity core flooding to evaluate the combination system's oil displacement effect. Additionally, the displacement effects and mechanisms of the starch gel and nano-MoS2 combination system in heterogeneous reservoirs were evaluated by simulating interlayer and intralayer heterogeneity models. The results show that the single nano-MoS2 system's efficiency decreases with increased core permeability, and its effectiveness is limited in triple and quintuple disparity parallel experiments. After injecting the starch gel–nano-MoS2 combination system, the enhanced oil recovery effect was significant. The interlayer and intralayer heterogeneous models demonstrated that the primary water flooding mainly affected the high-permeability layers, while the starch gel effectively blocked the dominant channels, forcing the nano-MoS2 oil displacement system towards unswept areas. This coordination significantly enhanced oil displacement, with the combination system improving recovery by 15.33 and 12.20 percentage points, respectively. This research indicates that the starch gel and nano-MoS2 combination flooding technique holds promise for enhancing oil recovery in high-temperature heterogeneous reservoirs of Henan Oilfield, providing foundational support for field applications. [ABSTRACT FROM AUTHOR]

The CO2-responsive Pickering emulsions employed have garnered considerable attention across enhanced oil recovery agents, delivery of crude, and oilfield-produced fluid treatment. This study focuses on the design of an innovative type of Janus nanoparticle (JNP) and its application in the construction of CO2 stimuli-responsive Pickering emulsions. The emulsion stabilized by JNPs demonstrates swift phase separation subsequent to the injection of CO2. Furthermore, the mechanism of the CO2-stimulated responsiveness enabled by the JNPs was proposed. Based on the Schiff reaction, the synthesis of JNPs was achieved successfully via the Pickering emulsion template method. The properties of the JNPs were studied using various analytical techniques such as Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, etc. The developed responsive system, composed of JNPs and sodium oleate surfactant, showed high interfacial activity at the oil/water interface. The study revealed that the responsive system-stabilized Pickering emulsions could remain stable at 70 °C and room temperature for 24 and 120 h, respectively. Furthermore, the introduction of CO2 for 1.5 min resulted in phase separation because the nanoparticles lost the amphiphilic nature, triggering a significant decrease in interfacial activity and the protonation of sodium oleate surfactant inactivation. Then, the particles started to desorb from the interface. This study proposes a convenient, simple, and cost-effective approach for preparing fast CO2-responsive Pickering emulsions. It provides novel insights into the advancement of oilfield-produced fluid treatment, transportation of crude oil, and enhanced oil recovery. [ABSTRACT FROM AUTHOR]