Abstract:In order to improve the lubricity of mud cake in the middle and late drilling of the horizontal well and extended reach well，A solid powder high efficiency polymer mud cake lubricant RHGXJ-3，composed of carboxylate copolymer，fibrillar silicate powder and polypropylene in a mass ratio of 10∶11∶2，was developed，which can effectively reduce the horizontal friction. By measuring the viscosity，temperature sensitivity and drilling fluid compatibility of mud cake lubricant RHGXJ-3，the effect and applicable conditions of the lubricant were studied， and its lubrication mechanism was analyzed by combining micro-characterization technologies such as SEM and XRD. The results showed that when the mud cake lubricant was added to drilling mud with mass fraction of 0.9%，the viscosity coefficient of the mud cake decreased from 0.0966 to 0.0496 within 1 minute，which led to an increase of 48.65% in lubricity. The temperature sensitivity test showed that the suitable temperature of the mud cake lubricant was 30—120 ℃. RHGXJ-3 had good compatibility with drilling fluid，with the addition of 0.9% RHGXJ-3，the funnel viscosity of the well slurry could be reduced from 55 s to 39 s and the flow capacity of the well slurry could be increased by 29.1%. RHGXJ-3 could generate solvated water film and gels substances on the surface and inside of the mud cake，improve the lubricity of the mud cake by filling voids and improving the compressibility，and reduce the frictional resistance of the mud cake. Compared to graphite and spherical solid lubricants，RHGXJ-3 provided better mud cake lubrication，which was 1.6—2.2 times that of other solid lubricants，and reduced the use cost by about 50%.

Abstract:The fracture of granite reservoir in Yongle ultra-deep water block of South China Sea is 1developed，the leakage of drilling fluid is serious，and then the plugging and reservoir protection of fractured reservoir cannot be balanced. Aiming at these difficult problems，a high-efficiency degradation gel plugging system was constructed. The dynamic covalent borate ester bonding cross-linking agent was made from methylboronic acid，methylphosphonic acid and sodium hydroxide，which was cross-linked with polyvinyl alcohol and xanthan gum in a controlled time by dynamic covalent bonding to form a gel plugging system with high strength. The gel formation time，plugging performance，rheology，pollution resistance，degradability and reservoir protection of gel plugging system were studied. Finally，the gel plugging system was applied to the plugging of fractured formation in the field. The results showed that the dynamic covalent borate ester bond cross-linker was prone to bond breakage in low pH environment under the action of peroxide gel-breaker，indicating good degradation performance. The highly efficient degradation gel plugging system had adjustable gel formation time and strong plugging ability. For a simulated core with a fracture width of 3.5 mm，the bearing pressure at 110 ℃ was up to 5.8 MPa. The gel had good flowability and thixotropy before curing. The gel plugging system had a short breakage time of 6.1 h in 6% potassium persulfate solution with pH of 4. The residual viscosity was low after gel breakage，which helped to protect the reservoir during the process of leak prevention and plugging in fractured reservoir drilling， and then achieved the goal of both leak prevention and plugging and reservoir protection in the drilling process of ultra-deep water fractured oil and gas reservoir.

Abstract:The traditional spacer fluid has some problems such as insufficient ability of temperature resistance，calcium resistance， inadequate displacement to oil-based drilling fluid and low flushing efficiency. A solid-free， temperature-resistant and calcium-resistant high-efficiency flushing spacer fluid was prepared by using a temperature-resistant and salt-resistant polymer （HEC）to improve the rheological properties of the flushing spacer fluid，and mixing surfactant to improve the flushing efficiency. The temperature resistance，rheological properties，compatibility and flushing efficiency of the spacer liquid was evaluated and optimized. The optimal recipe of the spacer fluid was as follows，0.5% HEC+ 30% calcium chloride + 2% sodium formate + 0.4% sodium 2-ethylhexyl sulfate，and the density was of 1.3 g/cm³ . The apparent viscosity of the spacer fluid was higher than 35 mPa·s， the plastic viscosity of the spacer fluid was higher than 25 mPa·s，and the dynamic shear force was greater than 10 Pa and the flushing efficiency was greater than 95% after aging at the temperature of 160 ℃ for 6 h. Moreover，the spacer fluid had good compatibility with oil-based drilling fluid and calcium chloride completion fluid.

Abstract:The contradictory nature of gel band pressure sealing technology requiring the required strength of the gel and its gel-breaking properties has limited the development of this technology. In view of the difficulty of external gel breaking，a self-degrading gel was formed by introducing an unstable cross-linker PLG co-polymerized with acrylamide and acrylic acid. the effect of the concentration of formulation components on the gel degradation time was investigated by the univariate method. The gel strength was explored by uniaxial compression experiments，the degradation performance of PLG gel was analyzed by thermogravimetric analysis，which was compared with that of PEGDA gel. Finally，the sealing performance of the gel was explored. The results showed that the optimal recipe of the system was as follows，the acrylic acid dosage was 7%，acrylamide dosage was 7%，unstable cross-linker PLG dosage was 0.4%，ammonium persulfate dosage was 0.3%. The native strength of the gel was 55.1 N. Thermogravimetric analysis showed that PLG gel had excellent degradation performance，PLG gel possessed shorter degradation time compared with PEGDA gel. The gel could achieve degradation at the temperatures of 60—100 ℃，and the higher the temperature the shorter the degradation time. In addition，the gel sealing experiments showed that the gel had good sealing ability at the temperatures of 60—100 ℃ ，and no additional injection of gel breaker was needed after the gel blocking operation. The gel degradation time could be controlled by designing the formulation to achieve rapid gel breakage. This self-degrading gel could be used as a plugging agent for oil and gas well with pressure operation.

Abstract:Conventional acidizing techniques for carbonate reservoirs are prone to water lock，corrosion of tubular columns and wellbore scaling during production，resulting in reservoir damage and reduction of reservoir capacity. Aiming at this problem，the neutral chelating system was made by adding a small amount of Na₂SO₃ with ethylenediaminetetraacetic acid （EDTA） and polyacrylic acid（PAA）as the main components，fused and filtered by deionized water，ground and crushed by dehydration at 120 ℃ ，and activated by roasting at 500 ℃ . The dissolution and corrosion performance of the neutral chelating system was evaluated. The results showed that the system had good corrosion resistance to Ca²⁺ inorganic clogs，with the corrosion rate reaching 95% within 24 h at room temperature. It had good corrosion inhibition to N80 grade steel，with the maximum corrosion rate of 4.45 g/（m²·h）at 90 ℃ after 12 h standing. The average corrosion rate of natural carbonate cores was more than 70%. Based on the inhibition of secondary precipitation of metal ions and improvement of permeability，the neutral chelating system had low corrosion damage to oil casing and could remove inorganic salt scale in the formation without rejection，which would not cause secondary damage to the formation and was suitable for scaling removal of oil wells with mainly carbonate scale.

Abstract:Acidification is an important measure for oil and gas stimulation. However，in high-temperature and strong-acid environment，conventional acidification gelling agents have some deficiencies，such as large dosage，difficult treatment of residual acid，and insufficient temperature resistance，due to the limited function of functional groups. In view of these problems，using acrylamide （AM）， 2-acrylamide-2-methylpropanesulfonic acid （AMPS）， hydrophobic monomer and alkenyl polyhedral oligomeric silsesquioxane nanoparticle monomer as raw materials，meanwhile making full use of hydrophobic association and nanoparticle strengthening，a high-temperature resistant hybrid gelling agent for gelling acid was synthesized by emulsion polymerization. The effects of the dosage of hydrophobic monomer and nanoparticle on the apparent viscosity of gelling agent solution were investigated. The gelling agent was characterized by Fourier transform infrared spectroscopy （FT-IR） and synchronous thermal analyzer（TGA）. The acid dissolution time，high-temperature resistance，retardative property，and residual acid viscosity were also evaluated. The results showed that the optimum synthesis condition was obtained as follows：0.75% the amount of substance fraction of hydrophobic monomer，1.0% the mass fraction of alkenyl polyhedral oligomeric silsesquioxane. This hybrid gelling agent was easily soluble in acid aqueous solution and had a good retardative performance and thickening effect. At a shear rate of 170 s^-1，2.0% gelling agent was dissolved in 20% hydrochloric acid aqueous solution. The apparent viscosity of the acid solution could reach 51 mPa·s at room temperature. At 180 ℃，the apparent viscosity was still higher than 15 mPa·s， exhibiting good temperature resistance. After treatment by combination of hydrogen peroxide and ammonium persulfate，the residual acid viscosity of gelling acid system was only 4.5 mPa·s，which was convenient for flowback. The gelling agent could be applied to the development of high-temperature resistant gelling acid system.

Abstract:During fracturing，the fracturing performance of liquid CO₂ fracturing fluid has changed greatly. In order to improve the effect of CO₂ fracturing and the displacement efficiency of CO₂ to shale crude oil，a new idea of synthesizing silicone CO₂ thickener was put forward. Through ring-opening polymerization and hydrosilylation reaction，CO₂-friendly short chain was introduced into the intermolecular of polymer main chain. As a result，a spatial network structure formed. The effects of CO₂ thickener on fluid viscosity，rheological properties and oil displacement efficiency were studied. The results showed that both the dosage and the relative molecular mass of thickener could significantly improve the rheology of CO₂ fluid. Its consistency coefficient increased with increasing amount of thickener，while the rheological index showed a downward trend. When the system pressure exceeded 12 MPa，the stability of three-dimensional network structure was strengthened and the apparent viscosity increased. Compared with supercritical CO₂ flooding，thickened CO₂ fluid could improve the production efficiency of crude oil in pores above 0.01 μm. Furthermore，the oil displacement efficiency was increased by 12.23 percentage points. The research results provided technical reference for improving CO₂ fracturing technology and molecular design of CO₂ thickener.

Abstract:A large number of metal ions in seawater attach to the surface of guar gum，which inhibits the swelling of guar gum molecules and cannot meet the requirement of continuous mixing on site. The cationic monomer GOA was synthesized by using epichlorohydrin and octadecenoic acid amidopropyl dimethylpropylamine as raw materials. And then the GOA was grafted onto the guar gum molecular chain to obtain the seawater-based fracturing fluid thickener glycidyl surfactant-modified guar gum. The swelling，salt resistance，temperature and shear resistance，sand carrying and gel breaking properties of GOA modified guar gum were studied. The results showed that the coulomb force and electrostatic repulsion on the modified guar gum molecular chain prevented metal ions from attaching to the guar gum molecular chain，ensured the swelling of guar gum molecule，and then improved the salt tolerance of guar gum. The dissolution rate of GOA modified guar gum in seawater was significantly higher than that of ordinary guar gum，while the median particle size in seawater was about 1/5 of that of ordinary guar gum. When the rotation speed was 800 r/min，the viscosity of the gel could reach 80% of the final viscosity after it was swollen for about 5 min. Microscopic analysis showed that the GOA modified guar gum formed a clearly visible random network coil structure. The guar gum molecular chain fully expanded. Meanwhile，the number of cross-linking bonds increased. The viscosity after continuous shearing at 160 ℃ and 170 s^-1 for 120 min was still higher than 50 mPa·s，indicating that the GOA modified guar fracturing fluid had good salt resistance，temperature resistance，shear resistance. The viscosity of breaking fluid was 1.6 mPa·s，the residue content in gel breaking fluid was 297 mg/L at the same time，which could meet the needs of on-site fracturing construction.

Abstract:Viscoelastic surfactant fracturing fluids，also known as clean fracturing fluids，have attracted extensive attention in the field of hydraulic fracturing because of their advantages such as complete gel breaking，no residues and low formation damage. However，the complex synthesis process，high cost and the inability to reuse have limited the practical application of clean fracturing fluids. In this paper，a pH-responsive clean fracturing fluid with pH-regulated apparent phase and rheological behaviors was constructed based on the mechanism of pseudo-tetrameric surfactant and wormlike micelles formed under specific pH conditions by N，N-dimethyl oleoaminde-propylamine and 1，2，3，4-butanetetracarboxylic acid. Then，the pH-responsive behaviors of the clean fracturing fluid，including apparent phase state，viscosity，rheological behavior，pH-responsive cyclicity and microstructure were systematically studied. Finally，the temperature and shear resistance，and gel-breaking performance were evaluated and analyzed. The results showed that the zero-shear viscosity of the fracturing fluid could reach more than 240 Pa·s，and it could switch between high-viscosity gel state and low-viscosity aqueous solution state more than four times by adjusting the pH value. The viscosity of the constructed clean fracturing fluid was still higher than 200 mPa·s after shearing at 90 ℃ and 170 s^-1 for 60 min，indicating that it had good shear resistance. In addition，the fracturing fluid could be completely broken within one hour， and the gel broken fluid had low viscosity and no residues.

Abstract:In order to investigate the effect of different hydrophobic monomers on the salt resistance of polymer drag reducers，the drag reduction performance and aggregation behavior of hydrophobic association polymers formed by copolymerization of three different Hydrophobic monomers with hydrophobic long chain with acrylamide （AM） ， acrylic acid （AA） and 2-acrylamide-2-methyl propane sulfonic acid（AMPS）in salt solution were studied by molecular dynamics simulation. The results showed that all three hydrophobic monomers could improve the interaction between the copolymer and water. Among them，the hydrophobic monomers with long hydrophobic chains composed of hydrophilic alkoxy chains，alkyl chains，and aromatic hydrophobic groups had the best performance. The three hydrophobic monomers could increase the radius of gyration of the copolymer， and the hydrophobic monomers with longer hydrophobic chains and aromatic hydrophobic groups made the hydrodynamic radius of the copolymer larger. In addition，the hydrophobic association of polymer hydrophobic chains was conducive to promoting the intermolecular crosslinking of copolymers through hydrogen bonds，forming the spatial network structure between polymer chains and increasing the rigidity of polymer chains. The drag reduction performance test verified the correctness of the molecular dynamics simulation results.

Abstract:Heavy oil resources are abundant in Bohai region. However，due to the large reservoir thickness and serious heterogeneity，the development effect of water flooding is poor，it is urgent to take technical measures to substantially enhance oil recovery. In view of the actual needs of the field，taking the geological characteristics and fluid properties of LD5-2 reservoir as the simulated object，the experimental research and mechanism analysis of combined profile control and flooding for increasing oil and lowering water were carried out，and an experimental method was proposed to quantitatively study the variation law of the liquid absorption profile of the heterogeneous reservoir in the formation，realizing the simultaneous monitoring of the profile change law from the injection end and the production end. The results indicated that combined profile control and flooding could generate synergistic benefits. Under the condition of injection slug size of 0.3 PV，compared with a single ternary composite system for profile control and flooding，the combined profile control and flooding increased the recovery rate by 18%. Through the core experiment of "separate injection and separate production"，it was found that under the premise of liquid flow diversion，the inlet diversion rate of the high permeability layer was lower than the outlet diversion rate，while the low permeability layer presented an opposite trend. Reasonable control of injection pressure during profile control and flooding could avoid severe pollution of low permeability layers，which was beneficial for improving the effectiveness of profile control and flooding measures.

Abstract:In order to solve the problem of poor application effect of conventional acrylamide polymer microspheres in high temperature and high salinity heterogeneous reservoirs, a polymer microspheres SAM-2 with double crosslinking structure was prepared with acrylamide（AM）, 2-acrylamide-2-methylpropanesulfonic acid（AMPS）and modified cyclic monomer（NW-1）as raw materials, N, N-methylenebisacrylamide and organic zirconium as crosslinking agents. The long-term thermal stability performance, viscoelastic performance, deep migration ability, profile improvement effect, and oil displacement effect of SAM-2 was evaluated, the mechanism of profile control and flooding was analyzed, and SAM-2 had applied successfully on-site. The results showed that the polymer microspheres SAM-2 could still have high viscosity and good expansion performance, good temperature and salt resistance and long-term thermal stability after aging for 180 d at the formation temperature of 110 ℃ and mineralization of 10.2×10⁴ mg/L. SAM-2 had good viscoelastic properties, resulting in strong deep migration ability. After injected into long cores, SAM-2 could produce effective plugging in deep areas and effectively improve the water absorption profile of heterogeneous cores. The profile improvement rate of high and low permeability cores could reach up to 98.7%. Injection of 0.5 PV polymer microsphere SAM-2 into three-layer heterogeneous core after water flooding could continue to enhance oil recovery by 25.34%, exhibiting good profile control and oil displacement effect. The field application results showed that the average daily oil production of M-101 well was increased by 56.8% and the average water cut was reduced by 10.1% after the polymer microsphere SAM-2 deep profile control and flooding measures were taken, achieving a good effect of water production decline and oil production increase.

Abstract:In order to solve the problems of difficult on-site dissolution of traditional gel systems and poor plugging effect for large pore throats，a high-strength gel plugging system with a fast-dissolving water-soluble emulsion polymer as the main agent was studied and the thermal stability and sealing performance of system was evaluated. The experimental results showed that the system，composed of 5000 mg/L HPAM polymer emulsion + 500 mg/L crosslinker + 1500 mg/L acid，could develop a high-strength gel with viscosity above 130 Pa·s at the temperature of 60 ℃. the gel system has good thermal stability and sealing ability，the sealing rate of the system for large pores and cracks was up to 89.36%. In addition，a significant function between the cross-linking agent concentration and the cross-linking reaction process was established by Boltzmann fitting，and a theoretical method to control the viscosity of the gel system by adjusting the cross-linking agent concentration was put forward.

Abstract:With the continuous development of oil field，the number of channeling wells gradually increased due to the change of the reservoir physical properties and the measures for increasing production and injection. The exploration-layer system which is interrupted by the channeling causes serious interlayer interference. The key to achieving effective plugging is to analyze the sealing laws of chemical plugging agent in channeling. In this paper，a set of physical simulation equipment was developed to simulate the sealing process of cement sheath channeling. The sealing laws of cement sheath was analyzed from channeling structure，injection cycle and injection rate，based on the breakthrough pressure，microstructure of channeling model and diversion rate of core. The experimental results showed that，the structure of the channeling model directly affected the channeling sealing effect. The wider the crack width was，the worse the plugging effect was. At worst，the plugging agent could not closely fit the wall of the fracture or plugging agent broke at the upper part of the model. When the channeling crack width was 1.5 mm，the breakthrough pressure was only 11.46 MPa. Most of the plugging agent flowed through the fracture and entered the high permeability layer，which made the diversion rate greater than 80%. Injection cycle was also one of the important parameters that affect the sealing effect of channeling. A complicated channeling required multiple cycles of sealing to ensure the effect. When the injection rounds were increased to three cycles，the breakthrough pressure reached 14.33 MPa. The decrease of injection rate could reduce the pollution of plugging agent to low permeability layer. When the injection rate was 0.25 mL/min，the diversion rate of low permeability core could be reduced to 10.8%. The research on the sealing law of cement sheath channeling had important guiding significance for sealing of channeling well.

Abstract:Polyacrylamide-type hydrogels have been widely used in conformance control，circulation lost control and well workover as plugging agents. However，polyacrylamide suffers from unfavorable temperature resistance，salt resistance and shearing resistance，which makes high strength and stable plugging under high temperature and high salinity extremely difficult. Aiming at these problems，an organic crosslinking chitosan（CTS）gel system was prepared using CTS and N，N'-methylene bisacrylamide （MBA） as raw materials. The effects of chemical dosage，pH value，temperature，salinity and shearing on the gelation performance were studied. The results showed that CTS could be crosslinked with crosslinker MBA through Michael addition reaction. The gel strength increased and gelation time decreased respectively，with increasing dosage of CTS and MBA. The increase of salinity could reduce the activation energy of the cross-linking reaction，promote the gelation process，shorten gelation time，and increase gel strength. The pH value had a significant effect on the protonation degree of CTS. As a result，the gel strength decreased sharply when the pH value was lower than 4.2. The CTS-MBA gel system possessed superior shearing resistance. The gel strength only decreased 2.4% after the gellant being sheard at 6000 r/min for 30 minutes. The gel system composed of 2.0% CTS and 0.6% MBA could remain stable after aging for 90 days under the condition of 120 ℃ and 30 g/L salinity. CTS-MBA gel had better temperature resistance，salt resistance，shearing resistance and thermal stability than polyacrylamide gel. At the same time， the cost of chemicals was reduced.

Abstract:Aiming at the problems of complex great damage to formation permeability of traditional chemical sand consolidation agent，and weak adsorption capacity and short validity of polymer sand control agent，the interaction energy between the polymer of sand control agent and silica was determined through molecular simulation. Quaternary ammonium modified polyamide sand control agent was prepared by using modified monomer 2，3-epoxypropyl trimethylammonium chloride. The structure characterization and performance test of product were completed. The sand control mechanism was determined by studying the intergranular adhesion，the Zeta potential of sand surface and the SEM image of coated sand. The results showed that the introduction of quaternary ammonium groups enhanced the interaction energy between sand control agent（polymer）and silica. Through the simulated downhole sand control experiment，it was determined that the optimum grafting rate of quaternization reaction was 4%. When the flow reached 7 L/h，the sand production was only 32 mg/L. The on-site application effect of electrostatic strengthening film forming sand control agent was significant. The oil and liquid production after sand control construction greatly increased， showing a significant effect on in-situ stabilization of the reservoir.

Abstract:Ionic liquids have great potential to prevent asphaltene precipitation in reservoir development，but the inhibition effect of ionic liquids under high temperature and pressure is not clear. Based on the inhibition effects of two ionic liquids，such as 1-butyl-3-methylimidazole chloride （［bmim］Cl） and 1-butyl-3-methylimidazole bromide （［bmim］Br），and two common commercial inhibitors on asphaltene precipitation in crude oil，the determination experiments of asphaltene precipitation at high temperature and pressure were carried out under the best inhibitor and ratio concentration. The effects of ionic liquids on the initial pressure of asphaltene precipitation（AOP）and the size of asphaltene aggregate in formation crude oil and CO₂ injected formation crude oil were studied. The results showed that the inhibition effect of［bmim］Br on asphaltene precipitation was much higher than that of［bmim］Cl and two other commercial inhibitors. The optimum dosage was 600 mg/L. The AOP of pure formation crude oil was 28.7 MPa. After［bmim］Br was added，the AOP dropped by 21.6%. When isopropanol was added to ionic liquid，the AOP dropped by 29.6%. The AOP of formation crude oil saturated with 30% CO₂ was 31.6 MPa. When isopropanol and ionic liquid mixed solvent was added，the AOP dropped by 44.3%. Isopropanol could produce ternary interaction with［bmim］Br and CO₂， improve the activity of［bmim］Br，greatly reduce the AOP of saturated CO₂ crude oil，slow down the growth rate of asphaltene particle size，reduce the deposition depth and blockage degree of asphaltene in the wellbore，and then introduce asphaltene deposition into more controllable nodes，which had broad application prospects.

Abstract:In order to efficiently develop low permeability and tight reservoirs in Dagang Oilfield，the physicochemical properties of nano oil displacement agent CN-1 were studied through the measurement of particle size distribution，interfacial tension， wettability，and emulsification. Static permeability and conventional displacement experiments were conducted for Dagang tight oilfield，and the mechanism of action of CN-1 was analyzed. The results showed that CN-1 was a heterogeneous oil displacement agent，composed of nano particles and carrier fluid，and the particle size distribution was 10—100 nm. The interfacial tension between CN-1 oil displacement agent（or carrier fluid）and crude oil was higher than 3.69 mN/m，the oil-water contact angle was increased and the hydrophilicity of rock surface was weakened after soaking the core into the CN-1 oil displacement agent or carrier fluid. Compared with injected water，CN-1 oil displacement agent had a higher increase in imbibition recovery rate，indicating that nano oil displacement agent could improve oil washing efficiency. Compared with CN-1 oil displacement agent，although the oil washing efficiency of surfactant BHS solution was higher，and the "Jamin effect" caused by emulsification also had the effect of expanding the swept volume，its injection pressure was significantly lower than that of CN-1 oil displacement agent，the effect of expanding the swept volume was poor，and the enhanced oil recovery was low. The retention of nano particles in the pores of rocks caused the increase of seepage resistance and injection pressure，which in turn caused the increase of liquid suction pressure difference and liquid suction volume in the middle and low permeability parts（pores）. Therefore，expanding the swept volume was the main mechanism of CN-1 oil displacement agent to enhance oil recovery. The earlier the injection time of nano oil displacement agent was，the greater the increase of oil recovery would be.

Abstract:Carbon dioxide（CO₂）flooding is an effective mean to further develop old oilfields with high water cut and improve oil recovery based on tertiary oil recovery. Aiming at the gas channeling problem caused by the large viscosity difference between CO₂ and crude oil，a supercritical carbon dioxide thickener（P）that could be applied to oil flooding was prepared. The preparation conditions of thickener were optimized，and then the solubility，thickening performance and oil displacement effect of thickener were evaluated. The results showed that the amount of initiator had the greatest influence on the molecular weight distribution of the product. The optimum synthesis condition was obtained as follows：72 ℃，4∶1∶1 the molar ratio of reactive monomer（maleic anhydride，styrene，vinyl acetate），22% the dosage of monomer，and 0.16 g the dosage of initiator. Under the condition，the molecular weight distribution of product was 1.12，meanwhile，the yield was 85% . The saturation solubility of thickener in supercritical carbon dioxide was 2.30%. The minimum miscible pressure was 7.77 MPa. The thickener with a dosage of 0.2% increased the viscosity of supercritical carbon dioxide by 19.7 times at 15 MPa and 50 ℃. When the temperature raised to 110 ℃， the viscosity retention rate was 45.26% . Under a simulated formation environment（15 MPa），adding 0.2% thickener could effectively improve the oil displacement effect of supercritical carbon dioxide flooding. Furthermore，the higher the permeability， the more significant the extraction effect was. In the same core，the total recovery degree of supercritical carbon dioxide flooding with thickener was more than ten percentage points higher than that after water flooding.

Abstract:Supercritical carbon dioxide has good oil displacement performance and receives much attention in enhanced oil recovery. In order to investigate the extraction effects of supercritical carbon dioxide on different kinds of Dagang crude oil，the supercritical carbon dioxide extraction apparatus was used as the experimental device，in which crude oil and carbon dioxide reacted sufficiently. The changes of component content，alkane structure and viscosity of crude oil before and after reaction were investigated. The results showed that N-alkane matrix oil was much easier to be extracted than cycloalkane matrix oil；the higher the colloid content of crude oil was，the less the content of extracted oil was，and the amount of extracted oil increased obviously with the increase of temperature and pressure. The extracted oil mainly consisted of alkane and colloid，and the structure of alkane was composed of light components between C₁₂ and C₂₂. On the whole，the extracted oil contents were very small，being of 0.19%— 2.16%，as a result，the property of raffinate oil was similar to that of the original crude oil.

Abstract:CO₂ flooding can improve the development effect of low-permeability reservoirs，and realize CO₂ geological storage by replacing oil and gas. However，due to the existence of oil and gas density difference，the CO₂ gravity segregation affects the oil displacement effect. In order to clarify the effect of gas injection rate on the degree of gravity overlay under the condition of CO₂ miscible flooding in low-permeability and thick oil reservoirs，laboratory physical simulation experiments and numerical simulation methods were used respectively. The research was carried out，and parameters such as injection rate were optimized through the established numerical model and the characterization method of the degree of segregation. The results showed that under miscible flooding conditions，there was still a certain degree of gravity differentiation，and with the increase of gas injection rate，the degree of gravity segregation decreased，and the recovery rate of miscible flooding increased. Compared with immiscible conditions，the degree of segregation was lower，the effect of reducing its influence by optimizing the gas injection rate was more obvious. The simulation calculation results for the given model showed that the influence of the overburden degree was weakened when the injection rate was greater than 10 t/d. Therefore，in order to ensure the CO₂ miscible oil displacement effect in thick oil layers，a relatively large injection rate should be appropriately adopted to reduce the influence of gravity segregation without gas channeling. The research results have certain guiding significance for the design of the CO₂ flooding field test scheme and the optimization of gas injection parameters.

Abstract:In order to study the influence of molecular structure of thermosensitive polymer on the characteristic of its aqueous solution，using the thermosensitive macromonomer poly（acrylamide-co-N，N-diethylacrylamide）［poly（AM-co-DEAM）， PADA］，2-acrylamide-2-methylpropyl sulfonic acid（AMPS），N，N-methylene diacrylamide（MBA）and other monomers as raw materials，thermosensitive polymers（CGPADA）with different grafting rate and molecular weight were prepared by free radical polymerization method. The effects of the molecular structure of CGPADA and the type of added salt on the thermo-thickening properties of CGPADA solution were studied by infrared spectrometer，element analyzer，rheometer and visible spectrophotometer. The results showed that only when the content of DEAM in the thermosensitive macromonomer PADA was within a certain range， CGPADA showed excellent thermo-thickening. In this range，the higher the content of DEAM and the lower the molecular weight， the lower the critical association temperature and turbidity point of CGPADA solution and the more significant the thermo-thickening phenomenon were. Compared with Na⁺ ，Ca²⁺ promoted the hydrophobic association of PADA side chain more strongly，which made the thermo-thickening of polymer solution more significantly. The salt-induced thickening effect was related to the molecular structure of CGPADA，the dosage of salt and the charge number of cations in solution.

Abstract:Accurate prediction of the viscosity of crude oil emulsion is of great significance for the design and operation of oil-water mixed pipeline. Eight kinds of crude oils with different physical properties were used to prepare water-in-oil（W/O）emulsions. The viscosity characteristics of W/O emulsions were measured by rheometer. The effects of temperature，water cut of emulsion and shear rate on the apparent viscosity of W/O emulsions were studied. Based on the experimental data and the quantitative characterization of crude oil physical properties，the viscosity prediction model of W/O emulsion suitable for different crude oils and different shear conditions was established. The results showed that the apparent viscosity of W/O emulsion decreased with increasing temperature，increased with increasing water cut，and decreased with increasing shear rate，showing the property of shear thinning. The power law model could be used to describe the rheological properties of W/O emulsion. With increasing water cut of emulsion，the consistency coefficient K of W/O emulsion increased gradually，while the rheological property index n decreased gradually. With the increase of temperature，K decreased gradually，while n increased gradually. The best applicable condition for the viscosity prediction model of W/O emulsion was obtained as follows：water cut of emulsion ranging from 0.30 to 0.60，temperature ranging from 30 ℃ to 60 ℃，and emulsion viscosity ranging from 10 mPa·s to 2000 mPa·s. The average relative deviation between calculated viscosity value and measured value of the model was 8.1%，showing good prediction effect.

Abstract:Polymer microsphere flooding technology has been widely used in oil production plants in North China oilfield，which achieved good results. Due to the interference of linear polyacrylamide（HPAM）in oilfield produced fluid，it is difficult to accurately determine the content of polymer microsphere. In this paper，the UV spectrophotometer method was used to optimize the best detection wavelength by maximizing the slope of linear fitting curve of samples with different concentrations at a specific wavelength. The influence of HPAM was eliminated by adding masking agent with ammonium group to the reference and the sample by partially masking the UV response. The experiment results showed that the optimum UV detection wavelength of polymer microsphere was 196 nm. When the dosage of masking agent was 2 g/L and the microsphere concentration was 1—200 mg/ L，the linear relationship between absorbance and microsphere concentration was determined. The correlation coefficient of determination was 0.9987. The quantitative detection of polymer microsphere under HPAM interference was realized.

Abstract:Petroleum contaminates soil during refining，storage，transportation and using. Furthermore，it is difficult to treat. Aiming at this problem，a plant microbial fuel cell（PMFC）was constructed using petroleum-contaminated soil as the anode substrate. The output voltage，power density，apparent internal resistance and petroleum removal rate were examined to optimize the cell plants and electrode materials. The applicability and range of petroleum content were explored with the optimized PMFC. The results showed that Epipremnum aureum could not survive in the anaerobic environment of PMFC，while the power production performance and degradation performance of Spathiphyllum kochii-PMFC were better than that of Hydrocotyle vulgaris-PMFC. The power production performance and degradation performance of carbon felt-PMFC were significantly improved than that of carbon sponge-PMFC. The PMFC with the cell plant of Spathiphyllum kochii and the electrode material of carbon felt was suitable for the contaminated soil with the petroleum content of 1—15 g/kg. With the increase of petroleum content，the electricity production performance and degradation performance of PMFC showed the trend of increasing and then decreasing. The best petroleum content range was 5—10 g/kg. PMFC technology provided a new idea for the treatment of petroleum contaminated soil. It could effectively deal with soil contamination and generate electricity at the same time，achieving a win-win situation.

Abstract:Aiming at the research status and challenges of CO₂ in the field of unconventional oil and gas stimulation，the application mechanisms of CO₂ in fracturing，flooding and storage were summarized. Research status and technical demands at home and abroad in CO₂ dry fracturing，CO₂ foam fracturing，CO₂ hybrid fracturing and CO₂ flooding in recent years were analyzed. The future research focus of CO₂ in the field of unconventional oil and gas stimulation was prospected.

Abstract:Water-in-oil emulsion has good mobility control ability，which can expand swept volume and improve oil displacement efficiency. Based on the emulsification mechanism of oil-water system，the effects of crude oil composition，water phase composition and emulsification conditions on the stability of water-in-oil emulsion were reviewed，and the application of water-in-oil emulsion in improving oil recovery was discussed.

Abstract:Biomimetic superhydrophobic materials have important applications in petrochemical industry by the merits of oilphilic and hydrophobic and self-cleaning. In this review，the principles of superhydrophobicity were briefly introduced，and their applications in petrochemical industry were reviewed from four aspects，including oil-water separation，metal protection， condensation heat transfer， and drilling and mining. The future application prospects of superhydrophobic materials in petrochemical industry were also discussed.