Abstract:In view of the technical problems of long swelling time and weak water dilution resistance of gel plugging agent in drilling engineering，the pressure sensitive self-healing plugging agent CMC-DAS was prepared from carboxymethyl chitosan （CMC）and dialdehyde starch（DAS）by cyclic freeze-thaw method. The molecular structure and particle size distribution of CMC-DAS were characterized and determined respectively by means of infrared spectroscopy and laser particle size analyzer，and its swelling performance，water dilution resistance performance，pressure-sensitive self-healing performance，nano-micron pore sealing performance，pressure penetration performance and microscopic morphology were investigated. The results showed that after high-temperature aging，CMC-DAS particles were still in nano-micron monodisperse state. The water absorption swelling expansion of CMC-DAS increased first and remained stable，the swelling equilibrium time was 7 h，and the water dilution resistance was controlled within 10% after 72 h. When the pressure increased from 2.5 MPa to 10 MPa，the fracture strength of CMC-DAS increased from 0.1131 MPa to 0.3516 MPa，and the elongation at break increased from 135% to 260% . When the addition amount of CMC-DAS was 0.5%，the reduction rate of core permeability reached more than 80%，exhibiting excellent plugging performance. By comparing the microscopic morphology of CMC-DAS on the core surface before and after aging at 160 ℃ for 16 h，the gel particles could be squeezed and deformed and enter the pores and fractures of the core，and a smooth and flat isolation film was formed on the surface，which played a positive role in improving the stability of wellbore.

Abstract:In response to the economic exploration and development needs of shale oil and gas，a lubricating and plugging agent SMLP-1，suitable for 80 —120 ℃ well sections prone to wellbore instability，was developed using Y # asphalt，petroleum resin， oil-soluble phenolic resin and other compositions as the oil phase matrix material，graphene oxide as the grafting particle，X# white oil as the dispersed phase，and using silicone modifier and organic amine modifier to modify. The lubricating and plugging effect of SMLP-1 in the drilling fluid system and its impact on drilling fluid performance were evaluated through the analysis of drilling fluid performance. The action mechanism of SMLP-1 was demonstrated through characterization methods such as scanning electron microscopy（SEM），infrared spectroscopy，and thermogravimetric analysis，and field tests were conducted. The results showed that SMLP-1 had good dispersibility in the drilling fluid，forming stable oil-in-water droplets in the system. After adding SMLP-1， the API filtration loss of the base fluid did not change significantly，but the high-temperature and high-pressure filtration loss was significantly reduced，indicating that SMLP-1 had a strong effect on reducing high-temperature and high-pressure filtration loss. After adding 1% SMLP-1，the lubrication coefficient decreased by 16% at room temperature，and after 16 hours of hot rolling at 150 ℃，the lubrication coefficient decreased by 43%. SMLP-1 could effectively plug shale pores and had good waterproofing and anti-water invasion effects，with significant inhibition on the hydration and dispersion of bentonite. SMLP-1 had been successfully tested on-site in the Qinye MN03HF well，with a cumulative footage exceeding 1000 m. After the addition of SMLP-1，the high-temperature and high-pressure filtration loss decreased from 13.2 mL to 8.6 mL，and the lubrication coefficient reduction rate was 30%. This not only reduced the intrusion of free water into the formation from the drilling fluid，improved the plugging ability and wellbore stability of the drilling fluid，but also enhanced the lubricity of the drilling fluid，ensuring safe drilling in complex well sections and achieving good application results.

Abstract:Hyperbranched polymers，with their unique three-dimensional topological structures and abundant active terminal groups，have shown significant potential in enhancing the lubricating properties of water-based drilling fluids. However，the structure-activity relationship between their molecular configurations and lubricating performance remains unclear，which hinders the development of new high-performance additives based on spatial configuration design. In this study，based on the boundary lubrication theory，the structural characteristics of multi-generation（G1—G5）PAMAM molecules and their adsorption behavior at the metal iron（Fe）interface were systematically studied by quantum chemistry and molecular dynamics methods. The structural changes of PAMAM molecules at the Fe interface during the shearing process were analyzed. The results indicated that PAMAM hyperbranched macromolecules possessed hierarchically distributed N and O active atoms，with the central N atom exhibiting the strongest electron-donating ability，followed by the terminal N atoms. As the generation increased up to G5，the three-dimensional structural stability of PAMAM molecules improved，with enhanced entanglement of molecular chains at the core and "claw-like" distribution of outer branches，which enhanced multi-point adsorption capabilities. During the adsorption of PAMAM molecules on Fe surfaces，atomic distribution extended along the interface and its normal direction，while shear promoted the aggregation of PAMAM molecules at the Fe interface，forming a transfer film that contributed to the formation of a robust lubricating layer. Finally，a lubrication enhancement model for hyperbranched polymers was proposed，which should provide theoretical support for the design of high-performance hyperbranched polymer additives.

Abstract:In view of the technical bottleneck that the traditional slickwater fracturing fluid is difficult to meet the drag reduction and sand carrying performance at the same time in the middle and high viscosity range，a new hydrophobically associating polymer fracturing fluid was prepared，and its drag reduction and sand carrying performance and rheological properties were tested in the middle and high viscosity range. At the same time，the potential correlation mechanism of polymer structure-rheology-drag reduction and sand carrying was explored. The results indicated that when the concentration of hydrophobically associating polymer exceeded the critical associating concentration（CAC），the drag reduction rate of the fracturing fluid system increased by more than 10%，and the proppant settling rate decreased by 30%. The synergistic optimization of enhanced proppant-carrying performance and maintained drag reduction efficiency could be achieved by increasing the content of hydrophobic monomers. Rheological data revealed the mechanism of key rheological parameters：the sand-suspending performance followed a power-law relationship with the elastic modulus（G'）as v = aG'^b，and the dag reduction efficiency exhibited an exponential relationship with the first normal stress difference（N₁）as DR = a + Ae^{[-0.5(N₁-x/w)]}. Constructing a high-efficiency drag reduction and proppant-carrying system using hydrophobic associating polymers enabled dual improvements in drag reduction and proppant carrying. The established rheological regulation model provides a theoretical basis for the molecular design and performance optimization of associating polymer fracturing fluids.

Abstract:Aiming at the problem of poor effectiveness of reagents when treating high-viscosity fracturing flowback fluid，the degradation experiments using chemical oxidation method，hydrolysis acidification method and enzymatic hydrolysis method were designed. Dynamic parameters such as viscosity，molecular weight，particle size distribution and the concentration of degradation products were measured through viscosity analysis， particle size detection， gel permeation chromatography， and sugar concentration detection. The results showed that when the guar gum was degraded with 10 g/L sodium hypochlorite using chemical oxidation method，the optimal viscosity reduction time was 30 min，and the viscosity was decreased to 4.22 mPa·s，while guar gum degradation remained incomplete，the particle size of the aggregates was greater than 2 μm and the degradation products with molecular weights was around 80×10⁴ Da，predominantly containing saccharide structures. Moreover，the increase of the sodium hypochlorite concentration could not enhance obviously the viscosity reduction effects. When the guar gum was degraded with 10 g/L activated sludge using hydrolysis acidification method，the viscosity reduction rate was slow during the initial stage of hydrolysis acidification but the complete viscosity reduction was achieved within 24 h. The particle size of the aggregates was approximately 0.21 μm and the molecular weights of the degradation product exhibited two-stage decline patterns，demonstrating "long-term effectiveness" characteristics. When the guar gum was degraded with 10 mg/L enzyme using enzymatic hydrolysis method，the viscosity was decreased to 5.43 mPa s within 10 min and the complete viscosity reduction was realized within 15 h. The molecular weight of the guar gum decreased to 160×10⁴ Da within 0—2 h，and the guar gum was completely transformed into small-molecule saccharides after 15 h. At the same time，the aggregates was approximately 0.19 μm. Compared with the control group，enzymatic hydrolysis caused minimal changes in chemical oxygen demand （COD） contributed by saccharides and total solution COD， indicating that the enzymatic hydrolysis reaction had strong selectivity and outstanding viscosity reduction effect on macromolecular guar gum，which was a better choice for the pretreatment process of fracturing flowback fluid.

Abstract:Aiming at the problem of insufficient temperature resistance and retarding performance of conventional acid in acid fracturing of deep-high temperature carbonate reservoirs，S-ANS was prepared by amination and sulfonation of nano-SiO₂ ，and then amphoteric acid-resistant and thickening nano-hybrid polymer S-ANS-HAPAM was obtained using S-ANS，acrylamide（AM）， acrylic acid（AA），sodium 2-acrylamide-2-methylpropanesulfonate（AMPS）and cetyldimethylallylammonium chloride（DMAAC） as main raw materials. The polymer structure was characterized by Infrared spectroscopy，X-ray photoelectron spectroscopy，and other methods. A 20% hydrochloric acid cross-linked acid system was prepared using S-ANS-HAPAM as a thickener. The rheological properties，drag reduction properties and gel breaking properties of the prepared cross-linked acid were evaluated，and the thickening mechanism of the cross-linked acid was analyzed. The results showed that the viscosity of the cross-linked acid-based solution increased with the increase of the dosage of thickener S-ANS-HAPAM at the of temperature of 25 ℃ and at the shear rate of 170 s^-1，and the viscosity of the base solution was 96 mPa s when the S-ANS-HAPAM dosage was 0.7%. The viscosity of the cross-linked gel with 0.7% thickener and 0.7% cross-linking agent was above 37 mPa·s after shearing for 120 min at the temperature of 180 ℃ and at the shear rate of 170 s^-1，indicating that the S-ANS-HAPAM cross-linked acid system had good temperature and shear resistance under strong acidic and high temperature conditions.During the frequency scanning process，the storage modulus G' of the gel was always higher than the loss modulus G''，meaning that the structural stability of the obtained gel was significantly better than that of the conventional polyacrylamide gel. SEM analysis confirmed that the formation of a physical-chemical dual network structure after crosslinking，and the mechanism of good viscoelasticity，temperature resistance and shear resistance of the crosslinked acid gel was also explained. The gel breaking time of the crosslinked acid gel at 120 ℃ and 150 ℃ was only 3 h，and the residue content was as low as 179 and 129 mg/ L，respectively，which was much lower than the standard of SY/T 5107-2016“Water-based Fracturing Fluid Performance Evaluation Method”for residue content（600 mg/L）. The cross-linked acid system achieved stable thickening and slowing performance at 180 ℃ and excellent low residue breaking properties through the synergistic effect of hydrogen bonding physical network introduced by double modified nano SiO₂ and zirconium cross-linked chemical network，providing an efficient and low damage solution for deep acid fracturing of ultra-high temperature carbonate reservoirs.

Abstract:The inorganic scale formed due to the incompatibility between injected water and formation water entangles with crude oil and particles in the pores and deposits，reducing the flowable space of the pore throats. The effect of single acidification is not ideal，restricting the water injection development of the oilfield. In order to improve the effect of the injection measures，it is necessary to clarify the characteristics of scale formation during water injection and the characteristics of scale dissolution during acidification. Taking the Chang X ultra-low permeability reservoir in Changqing oilfield as an example，through the visualization of the reservoir 's own fluid，external fluid and acidification times and the core simulation experiment scheme，combined with the changes of scale and injection pressure in the pore throat，the scale size，distribution change and sedimentary morphology characteristics at different positions were analyzed，and the changes of plug dissolution，migration and deposition during acidification were revealed. The results showed that in water injection development，due to the influence of water-type incompatibility，the inherent oil of the porous medium of the stratum，the migration and adsorption of particles，and the aggregation of secondary and tertiary precipitates during each acidification with the scale at the same location，the blockage gradually transited from a dotted composite scale composed of inorganic and organic matter to block and strip，moreover，the larger the proportion of heavy components in crude oil was，the more severe the scaling was，and the larger the size of the scale body and the scaling area were. The easily soluble scale due to acidification was mainly carbonate scale，which was concentrated in the pore throat channels，and its morphological distribution was layered，dotted and streamlined. Insoluble scale was a complex scale mixed with crude oil and inorganic substances，which was concentrated at the blind end，pore wall and inlet end. It was difficult for ethanol to dissolve it at the reservoir temperature；and petroleum ether，which was prone to dissolve heavy components，was difficult to enter the chip，increasing the difficulty of unblockage. Under the same simulated crude oil composition and the process of non-backflow of residual acid，the more times of acidification，the worse the unblocking effect. The unblocking area at the injection end was larger than that at the extraction end. The unblocking effect of the main flow channel was significantly better than that of the branch channel，and some dissolved and reduced microscopic particles migrated backward. When the well was re-trapped and water was driven to form scale，affected by the cumulative effect of in-situ scale formation，the closer to the inlet end，the more secondary blockages were generated，and at the same time，large holes transformed into medium and small holes. The comparison of different processes showed that the effect of residual acid reflux was much better than that of direct water injection after acidification.

Abstract:Conventional oilfield plugging agent in the deep water plugging of oil wells is prone to degradation and failure，the plugging agent is very easy to be damaged to lose the plugging effect after the absorption of liquid，it is difficult to meet the needs of deep water plugging. Based on the physical crosslinking network of CMC@Fe₃O₄，the physicochemical dual network self-healing hydrogel P（AM/AMPS/NVP）/CMC@Fe₃O₄ was constructed by using acrylamide（AM），2-acrylamido-2-methylpropanesulfonic acid（AMPS） and N-vinylpyrrolidone（NVP） as copolymerization monomers，potassium persulphate （KSP） as the initiator， hydroquinone（HQ）and hexamethylenetetramine（HMTA）as the crosslinking agent. The performance of gel strength，self-healing performance and temperature and salt resistance of the gel system were characterized. The optimum formulation of the self-healing gel system was as follows，91.6% CMC@Fe₃O₄ dispersion，5.6% AM，2.4% AMPS，0.4% NVP，pH= 9，the initiator KSP dosage was 0.8% by mass of the monomer，and the cross-linkers were 0.6% HQ and 0.6% HMTA. The gel strength of the gel was 230.6 Pa. The dehydration rate was only 6.21% after aging for 30 d at a high temperature of 130 ℃ and a high salinity of 2.2×10⁵ mg/L， exhibiting good temperature and salt resistance. The plugging rate of the gel system to the sand-filled pipe with water phase permeability of about 388 μm² was above 99%，and the breakthrough pressure was above 2.12 MPa，which could meet the needs of oilfield plugging. The self-healing of the gel could be achieved after aged at the temperature of 130 ℃ for 1 h，with a gel fracture elongation of 275% and a repair efficiency of 100%. the dual-network self-healing hydrogel demonstrates excellent performance in terms of gel strength，resistance to temperature and salt，sealing effectiveness and self-healing properties，and meets the requirements for deep plugging in oilfields.

Abstract:In order to rapidly degrade and disperse three-dimensional network cross-linked polymer gel causing formation blockage， a non-redox targeted plug remover for polymer gel was developed with polarizing agent（polyether amine 1000），catalyst（vanadium （IV）oxy acetylacetonate），substitution agent（hydroxypropyl tetrahydropyrantriol，diethylenetriamine pentamethylphosphonate） and solubilizing dispersant（18-crown-6，trimethylsilyl ethanol）as the main components. The degradation and dispersion efficiency of polymer gel，core permeability recovery rate and corrosion resistance of the plugging remover were studied. The results indicated that the plug remover had a good degradation and dispersion effect on the polymer gel. At the temperature of 60 ℃，the 10% plug remover could make the degradation rate of the micro-nano gel particles with a particle size of 0.5—100 μm synthesized with acrylamide and acrylic acid as the main monomers more than 92%. The degradation rate of the polymer gel particles increased with the extension of time，reaching more than 90% after 72 h. The recovery rate of plug removal by core displacement was 87%，which could effectively remove the blockage caused by gel particles in the formation. At the temperature of 60 ℃，the corrosion rate of 10% plug remover on tubing and casing was 0.4898 g/（m² h），which was lower than that of conventional plug remover system in oilfield，and could ensure the safe construction on site. The field test results showed that the plug remover had a higher success rate of more than 90%，an average daily injection increase of 16.3 m³ per well，a decrease of 3.2 MPa in injection pressure，an effective period of more than 200 d，and a cumulative injection increase of more than 3920 m³ . The increasing injection effect of the plug remover was good，which was suitable for the application of under-injection wells caused by polymer gel particle profile control and flooding.

Abstract:CO₂ flooding is one of the effective methods to enhanche the oil recovery of low permeability and ultra-low permeability reservoirs. However，due to the lack of CO₂ gas source in some oil fields，its scale application is limited. For oil fields with abundant （ associated ） flue gas resources，it can be considered to use“flue gas + a small amount of CO₂”to form a multi-component gas for oil displacement. In this paper，the feasibility and adaptability of EOR by multiple gas flooding were explored by carrying out high pressure physical property analysis of multiple gas-formation oil and a series of core displacement experiments of enhanced oil recovery by multiple gas flooding. The results showed that the addition of a certain proportion of CO₂ to the flue gas would significantly improve the solubility of the gas and the ability to swell and decrease the viscosity of crude oil. The optimal multi-component gas composed of 48.9 mol% N2+49 mol% CO₂+2.1 mol% CH₄ was determined by combining oil recovery with oil change rate. The multi-component gas had better adaptability in both low permeability and ultra-low permeability cores. Compared with pure N₂ flooding and pure flue gas flooding，multi-component gas flooding could enhanced oil recovery by 4 percentage points—5 percentage points. The use of multi-component gas flooding can not only further enhance oil recovery，but also realize the rational and efficient utilization of flue gas，associated gas and other resources，which has important practical meaning.

Abstract:Aiming at the problems of gas channeling and low sweep efficiency of CO₂ flooding in micro-fractured reservoirs，the effects of anionic，zwitterionic and non-ionic CO₂ foaming agents and water-soluble and gas-soluble nanoparticle foam stabilizers on foam performance were evaluated by laboratory experiments. The nano-composite supercritical CO₂ foam system was optimized as 0.3% foaming agent CAB-35 + 0.5% water-soluble nanoparticle foam stabilizer As30 GA，and the foam performance of the nano-composite supercritical CO₂ foam system under reservoir conditions was studied. At the same time，the core flooding experiment of the nano-composite supercritical CO₂ foam system was carried out in the reservoir environment. The results showed that the foaming volume of the nano-composite supercritical CO₂ foam system was 550 mL，the half-life was 47 min，indicating good foaming and foam stability performance. The viscoelastic modulus of nano-composite supercritical CO₂ foam system was about 90 mN/m higher than that of ordinary foam（0.3% CAB-35）. The foam strength and stability were greatly improved by the synergistic effect of foaming agent and nano-particles. The nano-composite supercritical CO₂ foam system had good temperature resistance and pressure resistance. Under the reservoir conditions（salinity of 10×10¹ mg/L，80 ℃，42 MPa），the foaming volume reached up to 275 mL，and the half-life was 72 min. The plugging and oil displacement performance of nanocomposite supercritical CO₂ foam system in porous media was studied by physical model. In the gas-liquid ratio of 0.5—2.0，the maximum plugging pressure difference of core displacement was 1.6 MPa，the resistance factor was greater than 50，and the recovery degree was 28.8 percentage points higher than that of ordinary foam. The nano-composite supercritical CO₂ foam system had good stability，high sweep efficiency，excellent ability to improve oil recovery，and broad application prospects.

Abstract:Due to good injectivity and high oil-flooding capacity，CO₂ flooding has become a very potential method to enhance oil recovery in low permeability/tight oil reservoir，but due to the reservoir heterogeneity and fractures，gas channeling easily happens during the injection，which affect the development of reservoirs. The CO₂ continuous injection and huff-n-puff experiments were designed and conducted in cores with different permeability contrast，and oil recovery and oil distribution（scanned by CT）was measured as the index to investigate the effect of heterogeneity on CO₂ flooding. The results showed that，during the continuous injection of CO₂，When the permeability of the low-permeability layer was 5.0×10^-3 μm² ，as the permeability contrast increased from 1.0 to 2.2，the oil recovery was significantly reduced from 88.5% to 58.3%；when the permeability contrast further increased from 2.2 to 154.0，the decreasing trend of oil recovery slowed down from 58.3% to 44.8%. The injected CO₂ mainly flowed and displaced the crude oil in the high permeability layer，while the crude oil in the low permeability layer was basically unused，which was the reason why the recovery rate decreases significantly with the increase of heterogeneity. Even if the core heterogeneity was weak，the permeability contrast being of 2.2，which would lead to a significant reduction in oil recover of CO₂ flooding. When the permeability contrast was less than 2.2，the increase of heterogeneity leaded to a more significant decrease in oil recovery. When the permeability contrast was higher than 2.2，the recovery rate continued to decrease with the increase of permeability contrast，but the trend would slow down. After continuous injection of CO₂，the Huff-n-puff was conducted. The oil recovery of heterogeneous core models with permeability contrast of 1.0，2.2，15.5 and 154.0 increased from 58.3%，57.2%，44.8% to 80.4%，75.8%，74.4%， respectively. The oil saturation of low permeability layer decreased significantly，and the crude oil of low permeability layer was effectively utilized. CO₂ huff-n-puff is less affected by reservoir heterogeneity，which is a potential replacement method after continuous injection of CO₂.

Abstract:To address challenges such as uneven permeability，poor crude oil mobility，and high extraction difficulty in tight reservoirs，three kinds of modified nano-SiO₂ particles with amphiphilicity，hydrophobicity and hydrophilicity were prepared by silane coupling agent homogeneous modification method and Pickering emulsion method to modify ordinary nanoparticles with particle size of 20—40 nm，which could adapt to small pores in tight oil reservoirs. Through the analysis of stability，interfacial activity and wettability，the amphiphilic Janus nano-SiO₂ particles were selected，and the subsequent imbibition displacement experiment was carried out. The results showed that the absolute value of Zeta potential of amphiphilic Janus SiO₂ nanoparticles could reach up to 31.01 mV. The transmittance of the dispersion reached 93.3% after standing for 3 days，and the transmittance of the dispersion had the smallest change. Amphiphilic Janus SiO₂ nanoparticles could reduce the oil-water interfacial tension to 0.37 mN / m. The amphiphilic Janus nano-SiO₂ particles could change the wettability of the core，reduce the capillary force in the reservoir pores，increase the fluidity of the oil phase，and achieve the effect of reducing pressure and increasing injection，so as to improve the oil displacement efficiency. The results of core simulation imbibition oil displacement experiment showed that the imbibition recovery rate（19.48%）of amphiphilic Janus nano-SiO₂ particle dispersion with a mass fraction of 0.01% was 12.23 percentage points higher than that of simulated formation water（7.25%），and 8.6 percentage points higher than that of ordinary nano-SiO₂ particle dispersion. With the increase of hydrophilic Janus nano-SiO₂ particle concentration，the imbibition recovery rate increased，and the recovery rate could reach up to 25.71% at a mass fraction of 0.05%. It is feasible to apply Janus amphiphilic nano-SiO₂ particles to enhance oil recovery in tight reservoirs.

Abstract:In response to the problem of the development of micro-nano pore throats in low-permeability reservoirs，the difficulty in the stripping and activation of crude oil，and the difficulty in utilization，the carbon-silicon quantum dot oil displacement agent was synthesized by solvent evaporation and thermal decomposition method. The structure of the synthesized carbon-silicon quantum dots was characterized by transmission electron microscopy（TEM），Fourier transform infrared spectroscopy（FT-IR ）and X-ray diffraction（XRD）. The temperature resistance，salt tolerance，interfacial activity，wettability and oil displacement performance of the carbon-silicon quantum dot oil displacement agent were investigated. The results showed that the quantum dots were spherical with a particle size of about 4 nm and good dispersion. XRD identified the（002）crystal plane of carbon and the（111）crystal plane of silicon of carbon-silicon quantum dots，which were in an amorphous state. FT-IR indicated that the surface of the quantum dots contained hydroxyl，carboxyl and amino groups，which could form hydrogen bonds with water molecules，improving the stability of the fluid. Under the condition of temperature of 135 ℃ and salinity of 300 g/L，the fluorescence spectrum of the quantum dots did not change significantly，exhibiting good temperature and salt tolerance. When the mass fraction of the quantum dots was 0.3%， the carbon-silicon quantum dots could reduce the oil-water interfacial tension to 0.92 mN / m，and could change the wettability of the rock surface to water-wet. The imbibition efficiency of the quantum dot oil displacement agent was 47.4%，being twice as big as that of the simulated formation water. NMR T2 spectra identified that the quantum dots could reach the micro-pores（1—10 ms）. On the basis of water flooding，oil recovery rate being of 63.95%，the injection of 0.5 PV carbon-silicon quantum dot oil displacement agent with mass fraction of 0.3% could enhance the recovery rate by 22 percentage points. The developed carbon-silicon quantum dot oil displacement agent is significant in enhancing oil recovery in low permeability reservoirs，which provides a good reference for efficient development of oil fields.

Abstract:Gemini surfactant is known as "a new generation of surfactants" and has great commercial value. In this paper，Gemini type octylphenol polyoxyethylene ether surfactant was synthesized by one step reaction using maleic anhydride and octylphenol polyoxyethylene ether as the main raw materials. The effects of reaction time，temperature，molar ratio of maleic anhydride to octylphenol polyoxyethylene ether，and catalyst dosage on the esterification rate of the product were investigated to optimize the reaction conditions. Furthermore，the surface tension，interfacial tension，wettability，emulsification，and viscosity reduction performance of the synthesized series of Gemini surfactants were evaluated. The optimal reaction conditions were determined as follows：the molar ratio of octylphenol polyoxyethylene ether to maleic anhydride was 2∶1，the reaction temperature was 200 ℃，the catalyst dosage was 4%，and the reaction time was 6 h. Compared with the conventional surfactant OP-10，the Gemini-type surfactant exhibited a lower critical micelle concentration（c_cmc）and superior oil-washing and viscosity-reduction performance. The gemini-type octylphenol polyoxyethylene ether surfactant（MOP-10）showed a c_cmc value of 0.052 mmol/L，and the interfacial tension between 1% MOP-10 solution and heavy oil reached 8.04×10^-2 mN/m，both one order of magnitude lower than those of OP-10. With the increase of the number of ethoxy groups in the Gemini-type octylphenol polyoxyethylene ether structure，the c_cmc value gradually decreased，while surface tension and interfacial tension increased，leading to a reduction in oil-washing and viscosity-reduction efficiency. This synthetic route is simple，the source of raw materials is wide，and the price is low. It can be used as an intermediate product to synthesize a variety of surfactants or polymers，and provide new raw materials for the development of surfactants and the modification of polymers.

Abstract:In the binary composite flooding technology，the experiment study on the micro-mechanism of the influence of Ca²⁺ on ultra-low interfacial tension can provide reference for surfactant formulation optimization. By measuring the interfacial characteristic parameters of petroleum sulfonate KPS，such as the solubility product constant K_sp，surface tension，interfacial tension，and partition coefficient，the main conditions for KPS to form ultra-low interfacial tension were clarified. The results showed that the influence of Ca²⁺ on the surface tension of the KPS solution was related to the decrease in the polarity of the micellar microenvironment. For the KPS system prepared with de-calcium water，the interfacial tension（IFT）was two-order-of-magnitude higher than that of calcium-containing solutions，with IFT restoration observed upon reintroducing 40 mg/L Ca²⁺ . Partition coefficient analysis in 0.3% KPS/kerosene systems demonstrateed that 40 mg/L Ca²⁺ induced optimal surfactant distribution（K= 0.101）with molecular minimum occupied area（A_min）of 0.58 nm². At this time，the sum of the concentrations of KPS in the two phases was less than the total concentration，and the“excess”KPS molecules were concentrated in the interfacial layer. A novel "interfacial complexation" model was proposed，suggesting that Ca²⁺ bridged two sulfonate groups（—SO₃²）near the oil-water interface，which was further validated through disodium phthalate solution experiments. The“interfacial complexation”model can provide molecular-level insights for understanding the microscopic mechanism of calcium ions affecting the interfacial tension of the oil displacement system.

Abstract:In view of the problem that the production of tight gas wells decreases due to water lock，and the development effect deteriorates，a water lock remover based on metabolites of hydrophobic modified Pseudomonas was prepared，and the surface/interface properties，wettability and spontaneous imbibition ability of the water lock remover were tested，and the effect of water lock removal was evaluated through the core displacement experiment. The results showed that the water lock remover could form a dense superhydrophobic biofilm in the gas reservoir，improve the relative permeability of the gas phase and reduce the relative permeability of the water phase. The 0.6% water lock remover could form a stable adsorption on the surface of the reservoir rock and restore the reservoir permeability of 56%—80%. After chemical treatment，the spontaneous liquid uptake and maximum liquid uptake rate of the treated core（about 60 g）decreased from 0.36 g and 0.05 g/min to 0.16 g and 0.01 g/min，respectively. The simulation experiment of core displacement showed that the water lock remover could effectively reduce the relative permeability of water phase and increase the relative permeability of gas phase，which was mainly reflected in the increase of the water-phase relative permeability shape factor and the decrease of its endpoint value，as well as the decrease of the gas-phase relative permeability shape factor and the increase of its endpoint value. The water lock remover had good adaptability to the water lock damage of the four gas field reservoirs，which could effectively remove the water lock and restore the reservoir permeability.

Abstract:Due to the influence of reservoir porous media shear and other factors，the viscosity-concentration relationship of polymer solution obtained by experimental methods is difficult to directly be applied in numerical simulations. At present，the commonly used empirical or analogical methods have large errors，and there is still a lack of effective numerical simulation methods for determining the viscosity-concentration relationship in polymer flooding. In this paper，the experiment of the influence law of polymer flooding was designed and carried out，and the numerical simulation model of polymer flooding core was established to fit the experimental results. The viscosity-concentration relationship of polymer flooding numerical simulation under different temperature，salinity and permeability conditions was determined. The prediction model of polymer viscosity-concentration relationship adjustment was established，and then the method of determining the viscosity-concentration relationship of polymer flooding numerical simulation was formed. Research results was shown that using the proposed method to determine polymer viscosity concentration relationship data，the fitting error of polymer flooding water content was 1.81%，which was 7.42% lower than that of the existing empirical. The accuracy of polymer flooding numerical simulation was improved，which provided reliable parameters and references for numerical simulation of polymer flooding.

Abstract:Glycine derivative corrosion inhibitor（Gy-D），a imidazole zwitterionic compound，was synthesized using glycine， glyoxal and formaldehyde. The structure of Gy-D was characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy，and the inhibition effect of Gy-D on N80 steel in 1 mol/L hydrochloric acid at 25 ℃ was studied by weight loss method and electrochemical method. The results indicated that the adsorption behavior of the amphoteric corrosion inhibitor Gy-D conformed to the Langmuir adsorption isotherm，with a combination of both physical and chemical adsorption occurring on the steel surface. As the dosage of Gy-d increased，its corrosion inhibition efficiency improved accordingly. Specifically，at the concentration of 50 mg/L，the efficiency was 91.29% ，and it furtherly increased to 93.92% at 200 mg/L. Scanning electron microscopy （SEM） and atomic force microscopy （AFM） results revealed that the inhibitor smoothed the steel surface and diminished corrosion pits. Additionally，X-ray photoelectron spectroscopy（XPS）analysis confirmed that the Fe-N bond was formed on the surface of N80 steel after immersion in hydrochloric acid containing Gy-D，suggesting the presence of an adsorbed protective film on the metal. The amino acid corrosion inhibitor synthesized in this paper provides an effective strategy for corrosion protection of steel under high acid environment.

Abstract:Polyacrylamide polymers are extensively employed in tertiary oil recovery and have demonstrated significant improvements in oil recovery efficiency. However，a large amount of oil recovery wastewater containing high concentration of polyacrylamide will be produced，which pose environmental risks if discharged directly. Photocatalytic degradation offers a promising solution for treating this wastewater. Yet，the current monitoring methods for assessing polymer degradation exist in notable shortcomings in terms of sensitivity，accuracy and reproducibility. In order to solve the above problems，a rapid，simple， accurate and comprehensive method for monitoring the degree of photocatalytic degradation of polymer was established by liquid chromatography combined with mass spectrometry for the photocatalytic degradation process of polyacrylamide gel used in two oilfields. Through liquid chromatography analysis，the changes of transition products with larger molecular weight in the degradation process could be observed，and the photocatalytic degradation degree of polyacrylamide gel at different time points was clarified. Furtherly，through mass spectrometry analysis，the types and changes of small molecular substances generated during the degradation process were clarified. The original structural differences of different types of polyacrylamide gels could be speculated according to the structure and abundance of small molecular products after degradation. This paper provides a new method for rapid，accurate and comprehensive monitoring of the dynamic data of photocatalytic degradation of polyacrylamide gel in the oilfield，which holds significant implications for guiding future research on the processes and mechanisms involved in the photocatalytic degradation of polyacrylamide gel，additionally，it offers a new avenue for investigating the structural variances among different types of polyacrylamide gel.

Abstract:With the development of deep and ultra-deep oil and gas resources，the high-density brine drilling fluids are facing challenges such as salt crystallization blockage，limited solubility of weighting agents and insufficient adaptability to high temperature and high pressure. Salt crystallization inhibitors not only can inhibit the crystallization and scaling of high-concentration brine，but also can promote the dissolution and weight increase of inexpensive soluble salt weighting agents，through multiple mechanisms such as complexation solubilization，micelle dispersion，lattice distortion，and dispersion effects，becoming a key chemical means to ensure the stability of high-density brine systems and wellbore safety. In the article，the action mechanisms and structure-activity relationships of various salt crystallization inhibitors such as copolymers，surfactants，natural organic molecules， and phosphates，were systematically reviewed. Their application status in increasing drilling fluid density and preventing wellbore scaling were summarized. The bottlenecks such as poor biodegradability，poor thermal stability and unclear solubilization mechanisms were revealed. Finally，the development directions of degradable copolymers designed for green and low-carbon and extreme environment requirements，and green-modified salt crystallization inhibitors was put forward.

Abstract:The micro-displacement technology using visual micro-model to simulate real reservoir rock pores has shown extraordinary application value and development potential in recent years. Compared with the traditional macroscopic core flooding experiment，this method shows many advantages，especially the visualization of multiphase flow in pores，which enables researchers to study the microscopic mechanism of oil displacement process. Nano-oil displacement technology has been widely concerned and applied in tertiary oil recovery in recent years. The unique physical and chemical properties brought by the small size of nanoparticles make them play a role in various mechanisms in rock pores. Combing the microscopic nano-oil displacement experiments carried out by many scholars using microfluidic equipment in recent years，the microscopic mechanism of nano-oil displacement mainly includes：wettability change，reduction of interfacial tension（IFT），improvement of mobility ratio，and stabilization of asphaltene. At the same time，the main control parameters affecting the effect of nano-oil displacement were summarized. With the development and improvement of related technologies，the application of microfluidic methods provided a more advantageous platform for the exploration of the microscopic mechanism of nano-oil displacement and optimization of control parameters.

Abstract:The wax in wax-containing and high-wax crude oil is easy to crystallize and precipitate，which affects the flow of crude oil，and easily causes problems such as shaft blockage and pipeline blockage，resulting in serious economic losses. Chemical anti-wax agent has become the main method to prevent or inhibit wax deposition and improve the low temperature fluidity of crude oil. Five types of chemical anti-wax agents，including solvent，high molecular polymers，nano-composite，surfactants，green natural materials/bio-based modified anti-wax agents， were reviewed. The molecular structure， synthesis method， action mechanism，advantages and disadvantages and application effects of different types of anti-wax agents were introduced. The future development trend of chemical anti-wax agents used in oilfield was predicted. It is necessary to deeply study the wax crystal growth process and inhibition mechanism，predict the wellbore or pipeline in advance，clarify the adaptability of different types of anti-wax agents，and strengthen the research and application of compound anti-wax technology.