An associative seawater⁃based fracturing fluids with temperature resistance of 180 ℃ was formed by thermostable and salt⁃resistant thickening agent containing hydrophobic groups, physical crosslinking agent with ionic surfactant, high temperature stabilizer and high efficiency chelating agent. The fracturing fluid forms a high⁃strength network structure through the physical association between the hydrophobic groups on the molecular chain of thickener and cross⁃linker, which enhances its viscoelasticity and takes elasticity as the dominant factor. The viscosity of the fracturing fluid can be maintained above 30 mPa•s for 90 minutes at 180 ℃ and 170 s-1, which has good static sand⁃carrying and wall⁃building properties. The viscosity of gel breaking fluid is 3.3 mPa•s, the residual content is 45 mg/L, and the damage rate of core permeability is less than 10%. The seawater⁃based fracturing fluid meets the requirements of fracturing for offshore ultra⁃high temperature deep reservoirs.

New clean fracturing fluid VES⁃YF was prepared by mixing the betain type amphoteric surfactant YF⁃1 and cosurfactant YF⁃2 with KCl. By measuring the influence of different concentration of YF⁃1, YF⁃2 and KCl on the viscosity of fracturing fluid, the optimized formulation was obtained, which is 2.0%YF⁃1+1.0%YF⁃2+2.0%KCl. The research and evaluation of the system's construction mechanism and its applicable performance were conducted. The results show that VES⁃YF clean fracturing fluid has shear thinning property and good viscoelasticity. The rheological measurement shows that the network structure of worm⁃like micelle exists in the system and can be recovered after shear failure. The apparent viscosity of VES⁃YF clean fracturing fluid is still higher than 80 mPa·s after shearing for 2 h at the temperature of 45 ℃ and the shearing rate of 170 s-1. The system has the advantages of strong sand carrying capacity, good gel breaking property and low core damage rate. VES⁃YF clean fracturing fluid has a broad application prospects in the fracturing operation of low permeability reservoir.

To solve the problem of polymer plugging of polymer injection well area in the bohai sea, a kind of efficient composite depolymerization additive is screened in the paper. Laboratory experiments show that the degradation rate of 5 000 mg/L polymer solution can reach more than 99%, and the polymer scale samples with crude oil from oil well in Bohai can be degraded in 72 h because of the low interfacial tension and good oil washing effecthigh effect of washing oil. Meanwhile, the high chelating ability of this depolymerization additive is good for the depolymerization of the crosslinking polymer, and the degradation progress can be as less as 3 h.The plug removal application in one oil well well shows that the efficient depolymerization additive has remarkable capacity of enhancing liquid and oil.

The graphene oxide (GO) is dispersed in HPAM which is served as the matrix, and GO/HPAM composite system is prepared by physical blending method. The laboratory evaluation experiment shows that: when the amount of GO accounts for 5% of HPAM, the viscosity of GO/HPAM composite system is maximum, and the addition of GO making the viscosity of the composite system increase by nearly 63.82%.GO can be uniformly dispersed in the HPAM solution, and the stability of GO/HPAM composite system is quite good. Stability parameter TSI adds up to about 2.1 and then doesn’t change any more. GO/HPAM composite system and the single HPAM solution are both pseudoplastic fluid, but GO/HPAM composite system is closer to the Newton fluid with better viscosity and shearing resistance. Under the different temperature, the viscosity of composite system of GO/HPAM is higher than that of HPAM solution.

Tetradecyl sulfobetaine（BE14）and hexadecyl sulfobetaine（BE16） were synthesized by onestep reaction, and the reducing oil/water interfacial tension properties of BE14 and BE16 were investigated in high salinity water. It was found that BE14 and BE16 were found to be compatible with high salinity water. oil/water interfacial tension was reduced to 10-2 mN/m magnitude for 0.011%0.182%（mass fraction）BE14 and ultralow interfacial tension was reached for 0.012%0.078% BE16. Furthermore, it also exhibits ultralow interfacial tension for the mixed systems of 0.039% BE16 and 8002 500 mg/L HPAM. 

By the way of initiated polymerization in toluene solution,two tercopolymers were prepared from octadecyl acrylate(acrylamide),maleic anhydride and styrolene in molar ratio 6∶1∶2 as pour point depressant A(B),C(D),akind of pour point depressant,was synthesized by alcoholysis (aminolysis) of A(B) by stearyl alcohol(octadecylamine) in the toluene as solvent at 120 ℃.The drop effect of pour point and viscosity of A,B,C and D for the sample to Daqing crude oil was investigated.The study was tested by adding the pour point depressants A,B,C,D to high pour point crude oil of Daqing at a dosage of 0.5%,respectively.The results suggest that the pour point depressants of C & D are more effective than A & B,meanwhile,the combination C+ D is more effective than C and D.After adding C+D in mass ratio 3∶1 to Daqing crude oil, its pour point is lowered by 15℃ and viscosity could be reduced by 58.38%.