Abstract:Conventional water-swelling gels lack re-crosslinking ability，making them susceptible to displacement from loss zones under pressure fluctuations，which reduces their pressure resistance and leads to poor plugging performance. Aiming at these problems，a self-healing gel was synthesized using chitosan as a physical crosslinker，combined with acrylamide（AM），acrylic acid（AA）and stearyl methacrylate（SMA）monomers. The gel’s structure was characterized through infrared spectroscopy， thermogravimetric analysis and scanning electron microscopy. Its swelling capacity，rheological properties，self-healing ability， compatibility with base fluid，and plugging performance were also investigated. Furthermore，the self-healing mechanism and plugging mechanism of the gel were analyzed. The results showed that the gel exhibited a spongy dual-network structure，with multiple non-covalent interactions including hydrogen bonding，electrostatic forces and hydrophobic associations within the network. The gel showed excellent water-swelling properties， which enhanced with increasing temperature. The swelling equilibrium value at 120 ℃ was 37 times higher than that at room temperature. After self-healing at 90 ℃，the gel particles exhibited a high storage modulus（3500 Pa）and a structural recovery rate（83%），while maintainined self-healing properties at 120 ℃. The compatibility between gel particles and base fluid was good. As the concentration of gel particles increased，the apparent viscosity of base fluid rose，while the fluid loss decreased. At a mass-volume ratio of 2%，the gel could meet the plugging requirements during drilling porous loss zones with simulated sand particles greater than 20 mesh（0.85 mm）. The self-healing mechanism of gel primarily relied on non-covalent bonds in its network structure，which broke and re-formed rapidly after damage， restoring the gel’s integrity and functionality. In terms of plugging mechanism，the gel particles migrated，accumulated and compressed within the loss channels，forming tight contact with the formation. The non-covalent interactions enabled self-healing and strong bonding with the formation，creating a durable gel-plugging layer. This self-healing gel showed potential application in enhancing drilling fluid loss control.

Abstract:Sulfonated treatments commonly used in deep-well water-based drilling fluids have significant biotoxicity without exact sources，which lead to the restriction of environmental protection regulations. To solve this problem，the relationship between the physicochemical characteristics of typical sulfonated treatments，such as functional groups，content of heavy metals and organic poisons，particle morphology，and their biotoxicity was analyzed. The results showed that the sulfonic acid groups in agents were not biotoxic，and the traces of heavy metals and organic toxicants were negligible factors. The removal of residue by dialysis through a semi-permeable membrane and the followed separation of water-soluble components using a Soxhlet extractor made the treatments biologically non-toxic，further demonstrating the predominate contribution of residual sulfonating agents （sodium bisulfite and sodium metabisulfite）and the adsorptive inactivation of solid-phase large particles dispersed in water on the Vibrio fischeri to the biotoxicity. Finally，the sulfonated agent was depolymerized using a homemade MOF. When replacing the sulfonated treatment agent in the sulfonated drilling fluid with the biologically non-toxic treated agent，the rheological properties of the drilling fluid were basically unchanged，the API and HTHP filtration loss only increased slightly. The sulfonated drilling fluid system realizes biological non-toxicity，which provide a powerful technical support for the application of sulfonated treatments.

Abstract:With the deepening of oil well drilling，conventional drag reduction can no longer meet the performance and environmental protection requirements of cementing cement under new working conditions. An environmental polycarboxylate oil well cement drag reducer （HZ-1） was synthesized through free radical polymerization reaction using polycarboxylate superplasticizer polyether（TPEG-2400），sodium methacrylate sulfonate（SMAS），acrylic acid and other raw materials. The optimum synthesis conditions were optimized through orthogonal experiments. The structure and thermal stability of HZ-1 were analyzed by infrared spectroscopy， nuclear magnetic resonance hydrogen spectroscopy， thermogravimetric analysis and synchronous thermal analyzer. Indoor evaluation of the drag reduction，temperature resistance and environmental protection of HZ-1 was conducted according to the standards of oil and gas industry. The drag reduction mechanism of HZ-1 was explored through the changes in adsorption capacity，steric hindrance and Zeta potential. The results showed that the optimum preparation conditions for HZ-1 were obtained as follows：10 g SMAS，0.41 g sodium hypophosphite，175 g TPEG-2400，7.6 g hydrogen peroxide，0.91 g ascorbic acid，22.22 g acrylic acid，20 g 20% sodium hydroxide，dropwise addition time of 2.0 h，reaction temperature of 20 ℃，and reaction time of 0.5 h. HZ-1 had good thermal stability and a decomposition temperature of 338 ℃. The cement slurry system prepared by mixing 0.40% HZ-1 with oil well cement at a water cement ratio of 0.44 had good drag reduction performance，the flowability index of 1.033，the consistency coefficient of 0.023 Pa · sⁿ，the compressive strength of 18.413 MPa，and the temperature-resistance capacity up to 170 ℃. HZ-1 had good biodegradability and environmental protection. Its EC₅₀（half effective concentration）was 36 307 mg/L，COD（chemical oxygen demand）was 571 984 mg/L，and BOD₅（biochemical oxygen demand）was 196 330 mg/L. The ratio of BOD₅/COD was 0.3432. So the biological grade of HZ-1 was non-toxic. The greater the steric hindrance of HZ-1，the better the rheological property of cement slurry was. The adsorption curve of HZ-1 on the surface of cement particles met the Langmuir adsorption model，which was the chemisorption of single molecular layer. HZ-1 reduced the Zeta potential on the surface of cement particles and enhanced its electrostatic repulsion，thus enhancing the rheological properties of cement slurry.

Abstract:During the exploitation process of heavy oil reservoirs，the thermal stress generated by the injection of high-temperature steam often leads to the failure of cement. Aiming at this problem，a type of polyaryl ether ketone high-temperature resistant resin powder was selected as elastic material and added to the cement slurry，and the influence of resin powder on the conventional properties，mechanical properties，and high-temperature resistance of the cement was studied. The results showed that when 4%resin powder was added to the cement slurry，the consistency coefficient of the cement slurry was 0.80 Pa · sⁿ，the filtration loss was 34 mL，the thickening time was 225 minutes，and the compressive strength was 17.69 MPa. The conventional performance of the cement slurry met the requirements of in-site operations. The elastic modulus of cement stone could be reduced to below 4 GPa， indicating that the addition of resin powder could improve the elasticity of cement stone. After curing for 28 days at the high-temperature of 320 ℃，the compressive strength of cement stone was 18.68 MPa，the impact strength was 1.97 kJ/m²，and the elastic modulus was 3.67 GPa，which exhibited good high-temperature resistant strength and elasticity. Compared with the cement stone without resin powder，the permeability of the cement stone decreased by 61.3%，the elastic modulus decreased by 39.1%， and the peak strain increased by 119.0% . The addition of resin powder reduced the brittleness of cement stone，increased its elasticity and capability of anti-deformation，and could effectively enhance the ability of cement stone to resist thermal stress damage during steam injection operations in thermal recovery wells.

Abstract:To against the backdrop of volume fracturing in tight oil formations，the study aimed to precisely regulate the degradation reaction of slickwater in distal micron sized or nano-sized fractures using ammonium persulfate（APS）as a breaker. It focused on the influencing factors in the construction and release control of thermal-controlled APS nanocapsule breakers. Using poly（methyl methacrylate）（PMMA），dichloromethane（DCM），Span 80，cyclohexane（CYH），triblock copolymer（Pluronic P-123）and APS as raw materials，APS droplets were encapsulated through the interfacial chemical action of hydrophobic polymer wall materials in a W/O inverse microemulsion，forming nanocapsule breakers. The preparation conditions for the nanocapsule breakers were optimized，and then the mechanism of controlled APS release and partially hydrolyzed polyacrylamide（HPAM）degradation by thermal-controlled nanocapsule breakers was analyzed by measuring the APS release rate at different temperatures and the viscosity retention rate of HPAM in simulated slickwater. The results showed that the optimum preparation condition of nanocapsule breakers was obtained as follows：50 ℃ reaction temperature，1∶1.5 volume ratio of DCM and CYH，100 mg Pluronic P-123，200 mg PMMA，10% mass fraction of APS in the core material，and 1∶1 volume ratio of Span 80 and APS solution. The nanocapsule breakers had an average particle size of 221 nm，good sphericity，and a theoretical shell thickness of 13 nm，with an APS loading rate of 78%. By utilizing the oxidative degradation characteristics of APS on the temperature-sensitive surfactant Pluronic P-123 at specific temperatures（60—80 ℃），a“thermal control switch”for the nanocapsule shell was preset，enabling precise regulation of APS release. The degradation times for HPAM in slickwater at 60 ℃ and 80 ℃ were 24 hours and 12 hours，respectively. The research findings provided a new approach to addressing the bottleneck of degradation and removal of slickwater residue blockages in complex fracture networks，especially in the distal secondary micro-fracture systems of horizontal wells undergoing volume fracturing in tight oil formations.

Abstract:Foam fracturing is a common technical mean in the fracturing and stimulation of coalbed methane reservoir. The selection of foaming agent is particularly important. In order to develop a foaming agent with better foam performance，lower cost and excellent comprehensive performance，the foaming agent（HBS-J）was prepared from tea saponin，alkenyl succinic anhydride and sodium bisulfite by esterification and sulfonation. The structure of HBS-J was characterized by infrared spectrum，and then the foaming property，salt and oil resistance，surface activity，and reservoir protection of HBS-J were evaluated. The results showed that HBS-J had good foaming performance，salt and oil resistance，and surface activity. When the mass fraction of HBS-J was 0.3%，the foaming volume was 590 mL，the half-life of foam was 2562 s，and then the composite index of foam could reach 25 193 mL min，indicating strong foaming ability and foam stability. When the mass concentrations of Na⁺，Ca²⁺ and Mg²⁺ in brine solution were 79 310，5405 and 2021 mg/L respectively or the volume fraction of kerosene reached 25%，HBS-J could still form a relatively stable foam system. Furthermore，its foaming ability and salt and oil resistance were significantly better than those of traditional foaming agents，such as sodium dodecyl sulfate，sodium α-olefin sulfonate，coconut amidopropyl betaine. When the mass fraction of HBS-J was 0.25%—0.35%，the surface tension of solution（about 40 mN/m）was relatively low. The reservoir protection performance of HBS-J was good. The damage rate to the permeability of coalbed matrix was less than 10%. It would not cause serious damage to the coalbed methane reservoir during foam fracturing construction. HBS-J met the requirements of coalbed methane reservoir foam fracturing construction on the comprehensive performance of foaming agent.

Abstract:After long-term water injection and polymer injection development in Bohai L，S and J oilfields，the heterogeneity of reservoir is further enhanced. The polymer is retained in the reservoir，resulting in a significant decrease in liquid absorption capacity of the reservoir. Plugging removal is one of the most effective technical means to alleviate the current situation. In order to meet the needs of chemical flooding plugging removal technology in Bohai Sea，the plugging removal effect of compound plugging removal agent and scale dissolving agent composed of depolymerization agent，acid and chelating agent was evaluated. The influence and mechanism of injection mode，injection pressure and profile control measures on plugging removal effect were explored. The results showed that when the mass fraction of depolymerization agent composed of 1.0% ammonium persulfate and 0.5% inorganic corrosion inhibitor was 1.0% and the slug size was 0.05 PV，the permeability recovery rate of polymer-blocked core could reach 90.31%，indicating good depolymerization effect. When the mass fraction of scale dissolving agent composed of 0.54%citric acid and 5.46% chelating agent was 6.0% and 8.0%，the permeability recovery rate of three kinds of inorganic scale plugging cores was more than 80%，indicating good scale dissolution effect. Improving the injection rate of plugging removal agent could increase the injection pressure and improve the plugging removal effect. When the injection pressure increased to 3.0 times and 3.5 times the water flooding pressure，the recovery rate increased by 0.74 percentage point and 0.88 percentage point. However，after increasing the injection pressure，most of the liquid would still enter the high permeability part of reservoir，and then the increase of liquid absorption in low permeability layer was very limited，which would affect the plugging removal effect. Therefore，the combined operation technology of profile control and plugging removal was put forward. That is，profile control was carried out before plugging removal. Compared with simple plugging removal，when 0.3 PV and 0.6 PV inorganic gel profile control agent were injected，the recovery rate of profile control and plugging removal combined operation increased by 7.7 percentage points and 12.19 percentage points，respectively.

Abstract:Imbibition is a crucial approach for improving oil recovery in tight reservoirs. A shut-in strategy is usually adopted to enhance oil recovery by imbibition after fracturing，and chemical agents such as surfactant and nanomaterials are used to improve imbibition efficiency. However，the enhanced oil recovery（EOR）mechanisms of different types of imbibition agents need be distinguished and explained. In this study，four types of imbibition agent systems were employed to conduct imbibition experiments，including silica nanofluid and pure water with high interfacial tension（IFT）（?30 mN/m），pure surfactant solution with medium IFT（1—10 mN/m）and surfactants compound system with ultra-low IFT（＜10^-3 mN/m）. The results showed that，as for the silica nanofluid and pure surfactant solution，the wettability alteration was the main EOR mechanism to improve the imbibition recovery in oil-wet reservoirs. Furthermore，the pure surfactant system could reduce the IFT and increased the deformability of oil droplets when the droplets passed through the pore throat. Therefore，the Jamin effect was alleviated，and the possibility of the oil droplets being snapped off and retained in the pore space is reduced，thereby improving the utilization degree of unrecovered oil. Nevertheless，the recovery results indicated that IFT reduction had a limited impact on the recovery enhancement，and that wettability improvement was more significant for improving recovery than IFT reduction. However，in the strong oil-wet pores，when the improvement of wettability was not effective and capillary force could not work ，the surfactant compound system exhibited the best imbibition performance. The ultra-low IFT between oil and water favored the spontaneous emulsification of oil，and changed the imbibition pattern from capillary force-driven imbibition to gravity-driven imbibition，and the emulsions formed spontaneously were drained out from the pore under the effect of gravity. The gravity-driven imbibition， which relies on the ultra-low IFT to promote the spontaneous emulsification of crude oil，provides a novel approach for enhancing imbibition recovery.

Abstract:In order to improve the temperature，salt and shear resistance of polymer oil displacement agents，an amphiphilic oil displacement polymer （HAP） was synthesized by free radical aqueous solution polymerization and low temperature induced methods，using acrylamide（AM），acrylic acid（AA），2-acrylamide-2-methylpropanesulfonic acid（AMPS），and independently developed long-chain alkyl polyether amphiphilic functional monomer（POM）as raw materials. The optimum reaction condition was determined by examining the intrinsic viscosity and viscosity enhancement of HAP. The solubility，viscosity enhancement， shear resistance，salt resistance，long-term stability，and oil displacement performance of HAP were studied，and then compared with those of commercially available temperature and salt resistant polyacrylamide. The results showed that the optimum synthesis condition for HAP was obtained as follows：20% total monomer mass fraction，0.4%—0.8% POM dosage of total monomer mass， 8% AMPS，0.1%—0.4% initiator，and 0 ℃ initiation temperature. 0.175% HAP solution was prepared by simulating Bohai Sea seawater. The dissolution time of HAP was 30 minutes at 75 ℃，and then the apparent viscosity was 55.8 mPa s. At 75 ℃，0.175%HAP exhibited good shear resistance，salt resistance，stability and oil displacement effect. The viscosity retention rate of HAP solution was 27.8% when the shear rate increased from 7.34 s^-1 to 100 s^-1. When the salinity of simulated seawater increased to 30 g/L，the viscosity of HAP solution was 75 mPa s. After aging at 75 ℃ for 90 days，the viscosity of HAP solution became 36 mPa s. The core displacement experiment results showed that the final recovery rate of 0.175% HAP solution was 8.8 percentage points higher than that of commercially available polyacrylamide with temperature and salt resistance. The synthesized quaternary copolymer HAP exhibited excellent solubility，viscosity enhancement，shear resistance，salt resistance，long-term temperature stability，and high crude oil recovery rate，with better performance than commercially available temperature and salt resistant polyacrylamide.

Abstract:The Chang 8 ultra-low permeability reservoirs of Honghe Oilfield suffer from high water flooding pressure and low oil-displacement efficiency. Chemical flooding could be a method to enhance the oil recovery in Chang 8 ultra-low permeability reservoirs. However，the adaptability of flooding agents in reservoirs is not clear. Therefore，the interfacial activity，pressure reducing and oil displacement ability of three types flooding agents，including surfactant，nano emulsion，and a silica nanofluid， were comparatively studied and their adaptability in Chang 8 ultra-low permeability reservoirs was analyzed. The results showed that the pressure-reducing rates of the 0.3% surfactant AMS，0.5% nano emulsion LIE，and 0.3% the silica nanofluid were 15.1%， 5.8% and 9.1%，respectively，under single-phase seepage conditions. The surfactant exhibited the highest pressure-reducing rate， which resulted from its superior wettability alteration ability. The wettability of rock changed from intermediate-wet to weak oil-wet under the effect of the surfactant. In contrast，the surfactant could not achieve pressure-reducing under two-phase seepage conditions because the surfactant could not inhibit the formation of oil-in-water emulsions. Meanwhile，the nano emulsion LIE and the silica nanofluid ASN exhibited favorable pressure-reducing performance due to their interfacial tension reducing ability and oil-in-water emulsion inhibition ability. The nano emulsion exhibited the highest pressure-reducing rate，being of 38.6%，because the interfacial tension reducing ability of the nano emulsion was better than that of the silica nanofluid. In nature core flooding experiments，the surfactant，the nano emulsion，and the silica nanofluid achieved enhanced oil recovery of 26.67 percentage point， 23.51 percentage point and 16.35 percentage point，respectively. The surfactant exhibited the best enhanced oil recovery ability. However，considering that the surfactant could not achieve pressure-reducing effect under two-phase seepage conditions，the nano emulsion was the best alternative for chemical flooding in Chang 8 ultra-low permeability reservoirs.

Abstract:The adsorption and retention of nanofluids on the surface of porous media are critical factors influencing the oil recovery enhancement in unconventional oil and gas recovery by nanotechnology. As a kind of amphiphilic sheet nanomaterials，it is necessary to study the dynamic adsorption laws of nanosheet in the cores. Firstly，the standard curve of nanosheet fluid was plotted and then the static adsorption experiment was carried out to clarify the concentration at which it reached adsorption saturation. On this basis，the dynamic adsorption experiments of nanofluids with different influencing factors were carried out. Afterwards，the variation laws of dynamic adsorption capacity were investigated by single-factor analysis and multi-linear regression method，and then the regression equation of dynamic adsorption capacity was established. The results showed that the saturation adsorption concentration of the nanofluid was 75 mg/L，while the maximum static adsorption capacity was 1.83 mg/g. The dynamic adsorption capacity had a negative logarithmic correlation with the permeability of low permeability cores（K），a negative linear correlation with the fluid mineralization ratio（MS），and a positive linear correlation with the injection slug of nanofluid（V₂），as well as the injection rate（v）of the subsequent water flooding. The multiple linear regression equation between the dynamic equilibrium adsorption capacity（ η₂ ）and K，MS，v and V₂ of the nanosheet fluid in the low permeability core was obtained as follows： η₂ = 10^-3(-0.4 - 0.005 K - 0.094 MS + 1.301 v + 3.347 V₂) ，with R²=0.989. Under the condition of 20×10^-3 μm²（K），2（MS），0.3 mL/min（v），and 0.5 PV（V₂），the dynamic adsorption capacity of the nanosheet was 1.328×10^-3 mg/g by regression equation，closing to the experimental result（1.321×10^-3 mg/g）. Maintaining a moderate salinity range（MS＜4），adjusting the slug level of nanofluid （0.5 PV），and reducing the injection rate of water flooding（＜0.45 mL/min），could mitigate the dynamic adsorption capacity， which was beneficial to further improve oil recovery in low-permeability reservoirs.

Abstract:In the environment of high salt and low permeability reservoir，the dispersion stability of molybdenum disulfide（MoS₂） nanosheet is poor，so it is often necessary to play a synergistic effect with surfactant to improve its performance. It is very important to clarify the interaction between MoS₂ and surfactant to improve the application range of MoS₂. By hydrothermal method，MoS₂ nanosheets were synthesized with thioacetamide as sulfur source and molybdenum trioxide as molybdenum source. The effects of five surfactants on the dispersion stability of MoS₂ nanosheets in saline was studied， and then the cationic surfactant hexadecyltrimethyl ammonium bromide （CTAB） was selected. The interfacial performance，emulsification properties and oil recovery effect of CTAB-MoS₂（mass ratio of 10∶1）were investigated. The results showed that MoS₂ nanosheet had layered structure，meanwhile the dispersion stability in deionized water was good. However，the dispersion stability decreased with increasing NaCl mass concentration. CTAB could significantly improve the dispersion stability of MoS₂ nanosheets in 3000 mg/L NaCl solution. When the mass fraction of MoS₂ was 0.1%，the addition of CTAB could increase the stabilization time of MoS₂ from less than 3 h to 12 h. When the mass fraction of MoS₂ was 0.005%，CTAB could reduce the average particle size of MoS₂ from 122.7 nm to 98.1 nm，meanwhile the absolute Zeta potential value increased from 25.0 mV to 33.8 mV. 0.05% CTAB-0.005% MoS₂ could spontaneously form a strong interface membrane and climbing membrane at the n-heptane/water interface. Furthermore，it could not only reduce the interface tension between n-heptane and water to 0.175 mN/m，but also have a good emulsifying effect. Based on its excellent salt tolerance and good interface activity，CTAB-MoS₂ had certain enhanced oil recovery effect in low permeability environment. Under the condition of 60 ℃ and 3000 mg/L NaCl solution，when 0.5 PV 0.05% CTAB-0.005% MoS₂ was injected into a low permeability（48.33 × 10^-3 μm²）core，the oil recovery was enhanced by 9.85 percentage points. The construction of CTAB-MoS₂ with high dispersion stability was expected to provide a solution for the efficient development of low permeability fields，and also provided research ideas for improving the dispersion stability of nanomaterials.

Abstract:Crude oil containing natural active substances，such as resinous and asphaltenes，readily formed a water-in-oil emulsion under throat shear，leading to liquid resistance，formation plugging，and significant reductions in oil well production. This study employed core replacement experiments and microscopic pore flow simulations to examine the flow behavior and liquid resistance of water-in-oil emulsions in complex porous media，focusing on crude oil viscosity，water content，and the size ratio between emulsion droplet and throat. The results showed that increasing water content heightened the liquid resistance effect of water-in-oil emulsions，thereby elevating the threshold pressure gradient. Under the condition of 550 mPa·s crude oil viscosity，20%—50%water content，and 300×10^-3 μm²core permeability，the threshold pressure gradient of water-in-oil emulsion was 12—37 MPa/m. For high-viscosity（550 mPa·s）crude oil，viscosity significantly influenced the emulsion threshold pressure gradient，while for low-viscosity（＜30 mPa·s）crude oil，the droplet-to-throat size ratio had a more pronounced effect. Due to the liquid resistance effect，water droplets accumulated at the throat inlet，leading to agglomeration and the formation of larger droplets within the water-in-oil emulsion. A larger emulsion droplet-to-throat diameter ratio increased the seepage resistance of dispersed phase（water droplets）. A decrease in the capillary number of water-in-oil emulsion increased seepage resistance due to the liquid resistance effect. Calculations showed that when the capillary number was 9.9×10^-4（low-viscosity crude oil）and the ratio of droplet size to throat diameter was 2.5 or 10.0，the liquid resistance effect increased the seepage resistance of water-in-oil emulsion through the throat to 7 or 35 times that of pore flow resistance. The results clarified the liquid resistance effect of water-in-oil emulsion flow in porous media and its influencing factors，providing theoretical guidance for the study of formation crude oil seepage and enhanced oil recovery.

Abstract:In this work，molecular simulation was introduced into the design of molecular structure and the study of mixing mecha-nism of miscible flooding agent，which partly solved the problems of long-time and high-cost of slim tube experiments. First，the structures of five types of functional groups with mixed-phase potential were initially identified，and the affinity of each type of functional group for CO₂ was judged based on quantum mechanics by using the electron transfer in the process of electron density and Fukui function studies as well as the energy change in the process of adsorption reaction energy and frontier orbital studies. The molecular structure design of the amphiphilic miscible flooding agent was carried out based on the full consideration of the number of functional groups and spatial site resistance. Based on molecular dynamics，the interactions and dispersion aggregation of the three miscible flooding agents，simulated oils and CO₂ were investigated，and the mixed-phase ability of the miscible flooding agent，was comprehensively evaluated in combination with the diffusion coefficient. The results showed that increasing the number of CO₂-philic groups synergized with the appropriate spatial site resistance was beneficial to enhance the miscible flooding effect.

Abstract:Research on the mechanism by which surfactants change the wettability of rock surfaces has certain theoretical guiding significance for on-site construction in oilfield. The wettability changing mechanism of oil-wet sandstone surface by anionic surfactant sodium lauryl alcohol polyoxyethylene ether sulfate-1（PES）was studied through the determination of infrared spectrum， morphological scanning imaging，Zeta potential，solid surface oscillation frequency and contact angle. The results showed that compared with the infrared spectrum of oil-wet quartz powder，the infrared spectrum of quartz powder treated with PES had stretching vibration peaks of S—O bond，sulfoxide S=O bond and sulfone —SO₂— bond，indicating that“adsorption”was the wettability changing mechanism of oil-wet sandstone surface by PES. Due to the adsorption of PES on the surface of oil-wet quartz wafer，the surface of quartz wafer was relatively flat and the average roughness was greatly reduced. The Zeta potential of untreated oil-wet quartz particles was -4.2 mV. The Zeta potential value of the sample treated with PES decreased with the increase of PES concentration，and finally tended to equilibrium. The electrostatic repulsion force between PES and negatively charged rock surface made PES adsorb on the sandstone surface with weak intermolecular force. As the concentration of PES increased，the resonance frequency decreasing amplitude of quartz crystal surface became larger and larger，that was，the adsorption amount of PES molecules on the rock surface became larger and larger. In addition，the original contact angle of untreated oil-wet quartz wafer was 140° ，while the corresponding contact angle of oil-wet quartz wafer treated with PES was 109° . With the addition of PES，a double-layer adsorption structure formed between the hydrophobic chain of surfactant and the hydrophobic end of crude oil components. At this time，the hydrophilic head group of surfactant exposed outside，making the contact angle gradually decrease， thus changing the wettability of solid surface.

Abstract:Aiming at the problems of poor flooding effect of water flooding，polymer flooding in high recovery degree and ultra-high water cut stage of high-temperature reservoir，anionic surfactants and cationic surfactants were used in combination，and an in-situ emulsification flooding system composed of 1500 mg/L polymer P5 + 0.3% surfactant S-2 was developed at the temperature of 95 ℃ ，and the phase characterization，reservoir water adaptability，natural core physical simulation oil displacement was carried out，and residual oil start-up mode displaced by microscopic lithography model were evaluated. Further， the heterogeneous core test was carried out to evaluate the displacement effect of the system at different size slug combination. The results showed that the prepared surfactant S-2 had good solubilization ability which can form microemulsion system in low mass fraction 0.1%—0.3% with crude oil in situ，the emulsion particle size were mainly distributed in range of 65—118 nm，forming an aggregate with vesicles，and it had ultra-low interfacial tension，good adsorption resistance and temperature resistance，and the oil washing efficiency was 78%. Considering the strong fluidity of the microemulsion，the optimized temperature resistant polymer had high mobility control capability under the water quality conditions of 0.2—0.4 mg/L oxygen content and 15—20 mg/L sulfur content，the viscosity retention rate achieved more than 100% after aging for 60 days at the temperature of 95 ℃. The experiment of natural core flooding showed that the phase characteristics of the produced liquid and core slice pores in in-situ emulsification flooding were obvious，the heavy components of crude oil were effectively displaced，and all types of remaining oil were well mobilized，which indicated that the system had the ability to form emulsification flooding in the whole process of displacement. The heterogeneous core test showed that the in-situ emulsion flooding system could increase the recovery rate by more than 25.2 percentage point through its variable concentration step injection combined with profile control slug injection. Considering the economic benefits and oil displacement effect，the combination injection mode of 0.1 PV profile control slug + 0.45 PV in-situ emulsification system + 0.05 PV profile control slug was selected. At present，the technology had entered the stage of pre-slug injection in the mine field，0.09 PV had been injected，the injection pressure increased by 5.0 MPa and the digital-analog predicted enhanced recovery rate was 8.06 percentage points.

Abstract:In order to improve the temperature and salt resistance of gas reservoir water intrusion inhibitors and mitigate secondary water intrusion contamination of gas reservoirs，methanol was used as dispersion medium. Through the measurement of surface tension，contact angle，spontaneous imbibition water saturation of cores，and gas-phase permeability in porous media，the surface activity，hydrophobic modification effects，and the ability to prevent and remove water invasion damage of five surfactants were studied. By measuring infrared spectrum，contact angle，Zeta potential and adsorption layer thickness，the mechanism by which the optimal gas reservoir water invasion inhibitor altered the wettability of gas reservoir water-wet sandstone surfaces was analyzed. The results showed that，among the five surfactants，the cationic fluorine-containing bicontinuous surfactant （HB-1） had strong hydrophobic modification ability as well as good high-temperature and high-salt resistance. After aging for 24 h at 180 ℃ and a salinity of 2.0×10⁵ mg/L，the surface tension of formation water could be lowered to 21.0 mN/m at a HB-1 concentration of 0.05%. After the core was treated with HB-1，the contact angle of formation water on the core surface increased from 45.0° before treatment to 110.0°. Injecting HB-1 into the porous medium could effectively prevent water invasion into the core，which could reduce the water saturation of core from 77.4% before treatment to 8.1%. It could effectively relieve the damage of water invasion， and then restore the gas-phase permeability of porous medium from 29.9×10^-3 μm² after water contamination to 52.3×10^-3 μm². The mechanism of HB-1 on the hydrophobic modification of water-wet sandstone surface was“adsorption”. HB-1 molecules could form a monolayer adsorption hydrophobic film with a thickness about 4.3 nm on the surface of water-wet quartz sheet. Furthermore，the thickness of adsorption film increased with increasing dosage of HB-1. When the mass fraction of HB-1 reached 0.1% ，the hydrophobic interaction between adsorption layers gradually formed a tightly oriented bilayer structure，and then the adsorption saturated. At this time，the Zeta potential was stable at 24.30 mV，and the thickness of adsorbed film was finally maintained at 4.3 nm.

Abstract:Wellbore integrity management is one of the key issues to ensure the safe production of oil and gas wells. At present， there is a lack of independent research and development of effective plugging agent materials for offshore oilfield operations. The development of liquid high-strength plugging agent was carried out through the optimization of the main agent and curing agent system. The curing mechanism of the plugging agent was studied by means of scanning electron microscopy and infrared spectroscopy，and the simulated plugging performance was evaluated through the settlement and curing experiments. Th results showed that the developed agent had a low initial viscosity of 90 mPa·s and a high sealing compressive strength，and has good settlement and curing properties，which resulting from the strong cross-linking reaction. it was confirmed that the plugging agent had excellent pressure bearing capacity（＞160 MPa/m）and could settle and cure at a height of 20 m，which has a strong plugging ability. The system had been applied to a horizontal well in A oilfield in the east of the South China Sea，and the leak point plugging operation had been successfully completed. This study provides a new pure liquid plugging agent for well integrity management， and the product has good application potential.

Abstract:A large amount of oily sludge is produced in the process of refining，storage，transportation and use of petroleum， which causes serious petroleum waste and environmental pollution. In order to solve the problem，a collaborative process of biosurfactant-sediment microbial fuel cells（SMFC） was proposed. SMFC was constructed using oily sludge pretreated with biosurfactant as the sediment. The effects of three factors，such as biosurfactant，electrogenic microorganism delivery time and oil recovery，on the electrical production and degradation performance of SMFC were investigated through detecting the daily voltage， total output electricity，power density，apparent internal resistance and oil removal rate. The results showed that the effect of biosurfactant and SMFC combined treatment of oily sludge was better than that of biosurfactant or SMFC. After the oily sludge was pretreated with biological surfactant，the addition of electric-producing microorganisms was more conducive to the degradation of oily sludge and the performance of SMFC. Compared with the treatment that electric-producing microorganisms was added before the pretreatment with biosurfactant，the total output electricity was increased by 1463.63 C and the oil removal rate was increased by 17.09 percentage point. The oil-bearing sludge SMFC constructed after recovering the oil with the biosurfactant agent had better electrical production and degradation performance，the maximum output voltage could reach up to 185.27 mV，and the oil removal rate was as high as 63.65% . The biosurfactant-SMFC could obviously improve the degradation and electricity production performance of the oily sludge，and the electric-producing microorganisms should not be put in early，and the oil recovery could greatly improve the electricity production performance of SMFC and the degradation rate of oily sludge.

Abstract:The composition of Tahe ultra-heavy oil was analyzed by low field nuclear magnetic resonance（LF-NMR）. Based on the composition of Tahe ultra-heavy oil，four oil-soluble viscosity reducers based on aliphatic，aromatic，aromatic + aliphatic，polar compounds were developed；and their viscosity-reducing effect was comprehensively evaluated by LF-NMR，viscosity analysis， and immersion dilution. The analysis results of crude oil group components（SARA）verified the accuracy of LF-NMR technology in analyzing crude oil composition. Except the polar compound viscosity reducer，other viscosity reducers could reduce the viscosity of ultra-heavy oil by more than 90%. The viscosity reducing performance was ranked by aromatic ＞ mixture of aliphatic and aromatic ＞ aliphatic ＞ polar compound. Aromatic viscosity reducer had the best viscosity reducing effect and could reduce the viscosity from 61 000 000 mPa·s（50 ℃）to 14 897 mPa·s. At the same time，it could dissolve asphaltene and prevented asphaltenes from agglomerating. The experimental results proved that LF-NMR could not only be used as a fast and convenient method to analyze the composition of crude oils，but also be used to evaluate the effect of viscosity reducers，as well as to analyze the mechanism of viscosity reduction.

Abstract:Octylphenol polyoxyethylene ether (OP-20) and sodium dodecyl sulfate (SDS) are commonly used surfactants in the later stage of oilfield exploitation. In order to accurately detect the content of each component in OP-20/SDS binary complex system, hydroxypropyl-β-cyclodextrin (HP-β-CD) was used as a masking agent to modify the UV spectroscopy and then detect the content of OP-20 in binary complex system by using its special structure of external hydrophilicity and internal hydrophobicity, as well as the characteristics of spontaneous inclusion of aromatic surfactants. At the same time, the conductivity method was used to quantitatively analyze the SDS in binary complex system, and then the effect of OP-20 on the test results was studied. The results showed that SDS could interfere with the absorbance and critical micelle concentration（c_cmc）of OP-20 when the content of OP-20 in binary complex system was detected by UV spectroscopy. When 0.4 mmol/L SDS was added to 0.2 mmol/L OP-20 aqueous solution, the absorbance of OP-20 at the maximum absorption wavelength of 224 nm increased from 1.727 to 1.751. In 0.4 mmol/L SDS aqueous solution, the c_cmcof OP-20 decreased from 0.223 mmol/L in pure water to 0.198 mmol/L. HP-β-CD had a significant masking effect on the detection of OP-20 in binary complex system by UV spectroscopy. HP-β-CD and OP-20 were encapsulated at a molar ratio of 1∶1, which blocked the mutual interference between OP-20 molecules and SDS molecules. After adding HP-β-CD, the recovery rate of OP-20 in binary complex system changed from 96.42%—106.92% to 99.28%—101.38% . As a result, the accuracy of detecting OP-20 content in complex system by UV spectroscopy was significantly improved. The reason why HP-β-CD eliminated the mutual interference between SDS and OP-20 was that OP-20 molecules entered the HP-β-CD molecular cavity from both wide and narrow aperture directions and then formed an inclusion complex. The conductivity method could accurately detect the content of SDS in binary complex system, while OP-20 would not interfere with SDS. When the concentration of OP-20 in the solution was 0.1—0.3 mmol/L, the recovery rate of SDS in binary complex system was 100.83%—101.92%. HP-β-CD modified UV spectroscopy combined with conductivity method could effectively detect the content of each component in OP-20/SDS binary surfactant system.

Abstract:The nanomaterial technology with rapid development has become a hot research and application topic in the field of oil and gas well cementing engineering. This article discussed the research and application progress of commonly used nanomaterials and polymer nanocomposites in the field of well cementing. Among them，nanoscale functional materials including silicon dioxide， zeolite powder，halloysite nanotubes，calcium carbonate，clay，magnesium oxide，alumina，carbon nanotubes/carbon nanofibers and grapheme had significant effects on improving the mechanical properties of set cement. However，their application was limited due to the dispersion difficulty of nanomaterials. Polymer latex，nanoemulsion and other organic nanoparticles could significantly improve the channeling prevention performance of cement slurry，the oil washing effect and flushing efficiency of preflush，and play an important role in ensuring the safety and quality of cementing. The modification technology of polymer nanocomposites was extensively studied in terms of improving the temperature resistance and comprehensive performance of polymer cementing additives. Its comprehensive performance was greatly improved compared to that of traditional polymers. In view of the major technical difficulties in complex deep and unconventional oil and gas well cementing，the research and development suggestions of polymer nano-composite cementing admixture were put forward from the two aspects，such as nano-surface grafting modification and nano-intercalation composite technology，which played an important guiding role in the research and development of key cementing additives with ultra-high temperature resistance and high performance.

Abstract:The goals of cost reduction and efficiency increase in the oil and gas industry，the demands for environment protection development，and the rapid development of integrated geological engineering technology have posed new challenges and requirements for wellbore working fluids. After working fluids contact with the formation during the fracturing process，a series of physical or chemical reactions occur. It not only affects the effectiveness of hydraulic fracturing，but also closely relates to the process of shut-in and flowback after fracturing，thereby affecting the subsequent production of oil and gas wells. In addition，the different working fluid systems also face some problems such as homogenization waste，functional singularity and physicochemical incompatibility. Therefore，clarifying the required characteristics and research status of the working fluids at each stage is of great significance for the development of integrated working fluids. Based on this，the characteristics that the working fluid needed to meet and current results in various stages such as fracturing，shut-in and flowback were elaborated. The characteristics and research status for polymer，surfactant，foam and gas working fluids were emphatically described. By summarizing the characteristics of working fluids mentioned above，the discussion and outlook on integrated working fluids were conducted around three aspects， such as synergistic effect of fracturing and extraction，improvement of liquid energy efficiency through temporary plugging of fracturing，and low-carbon and green transformation. The integrated working fluid involved a broad range of researches and techniques. It was necessary to strengthen the collaborative studies between multiple processes. The research results could provide a reference for the development and enhancement of integrated working fluids during fracturing，shut-in and flowback.

Abstract:The process of oil extraction，transportation，and paper making generates a large amount of oily wastewater，which brings a great threat to the living environment of human beings. Traditional oil-water separation methods are usually inefficient， costly and cumbersome. Therefore，it is crucial to develop new，green，economical and efficient materials for oil-water separation. Superhydrophobic materials have attracted much attention in the field of oil-water separation due to their extreme hydrophobicity. By combing the superhydrophobic materials used for oil-water separation in recent years，firstly，the wettability and construction methods of superhydrophobic materials were briefly introduced， and then the research progress of two-dimensional and three-dimensional superhydrophobic materials for oil-water separation was reviewed. Among them， two-dimensional superhydrophobic oil-water separation materials included fiber membranes， metal mesh， ceramics and glass， while three-dimensional superhydrophobic oil-water separation materials included rock wool，wood，aerogel，foam and sponge. Finally， some limitations of the current superhydrophobic oil-water separation materials were pointed out. Then the outlook of superhydrophobic oil-water separation materials in terms of sustainability and environmental friendliness was given，such as improving the mechanical strength of superhydrophobic surfaces， investigating the separation effect and applicability of multicomponent mixtures， combining multiple separation technologies， developing good recycling performance and multifunctionality，etc.，which provided some references and inspirations for the research of superhydrophobic materials in the field of oil-water separation.

Abstract:Oilfield Chemistry was founded in 1984. In those 40 years of trials and hardships，Oilfield Chemistry always put the quality of journal in the first place，and insisted on reporting the latest research progress，technological breakthroughs and application cases with high standards，which provided important scientific and technical support for the sustainable development of oil and gas industry. On the occasion of the 40th anniversary of Oilfield Chemistry，this editorial summarized the measures and effects taken to improve the quality and influence of the journal in recent years from the aspects of editing and publishing，digital construction，external communication and publicity，journal influence and awards. Starting at the age of 40，Oilfield Chemistry will keep in mind its original intention，base itself on the new era，keep improving the journal quality，and make greater contribution to the academic prosperity and scientific and technological innovation of oil and gas industry.