The active substance in crude oil has an important influence on the interfacial tension of chemical flooding formula. After active substance in the crude oil of Block BW in Xinjiang Oilfield was extracted，the interfacial tensions between it and petroleum sulfonate （KPS） and alkali were studied. The results show that the contents of resin and asphaltene in the crude oil are very low，and the interfacial active substance mainly exists in ethyl acetate eluent. Main components of the active substance include phenols，alcohols and carboxylic acids，which fall into two types of C_nH_2n-2O₂ and C_nH_2n-4O₂. With Na₂CO₃ added，the interfacial tension was reduced to 10^-2 mN/m. With KPS added，the interfacial tension was only reduced to 0.5 mN/m，showing a poor effect. After adding both KPS and Na₂CO₃ together，the interfacial tension was quickly reduced to 10^-3 mN/m. This is mainly because that alkali reacts with some components of ethyl acetate eluent，and an activator to enhance the performance of petroleum sulfonate is produced，which greatly reduces the interfacial tension.

The development of most oilfields in China is challenged by such problems as low recovery factor，serious wax formation in wellbore and pipelines，and insufficient gel breaking during stimulation for low-temperature reservoirs. Microbes are widely used in oilfield development due to the properties of their metabolic products. This paper makes an overview of the research of microbial technology and its application in oilfields in respect of enhanced oil recovery （EOR），wax removal and control，and fracturing fluid gel breaking. The paper explains the mechanism of microbial technology in three areas，summarizes the advantages and disadvantages of the application of microbial technology in oilfields，and makes an outlook for the research focus of microbial technology in future oilfield development.

A study on a highly-efficient anti-swelling and salt-resistant slickwater fracturing fluid system was conducted based on the wastewater from fluid preparation in an oilfield. This study was designed to solve the blockage problem of induced fractures and matrix pores and throats due to the hydration expansion and even rock skeleton collapse after fracturing fluid system contacts a readily loose reservoir with high clay content,strong water sensitivity,and weak cementation. The experimental results show that a highly efficient anti-swelling and salt-resistant slick water fracturing fluid system prepared from 0.05% KY-2 （salt-resistant drag reducer ）,0.4% FP-3 （organic amine compound anti-swelling agent）,0.1% ZP-2 （cleanup additive）,and the said waste water with a TDS of 15 548.96 mg/L has an anti-swelling rate （96.2%） equivalent to 4% KCl,which means a satisfactory anti-swelling performance. After washing with tap-water for 10 times,the anti-swelling rate is still as high as 89.87%,which means a satisfactory long-acting anti-swelling performance. Besides,with a drag reduction rate of 78.45%,this system has a satisfactory drag reduction performance. Field test results have validated that the new system can effectively alleviate the problems of high KCl consumption,high cost,and inability to use mixing-free process in strong water-sensitive reservoirs,as well as the decrease in drag reduction rate due to high TDS.