| In order to solve the problem about fluid of fractured reservoir in low permeable sublayer reservoir's fracture—inject—extract construction,this paper carried out a series of works around oil-displacement fracturing fluid,including micro-analysis,imbibition experiment,filtrate surface acting agent,and optimize fracturing fluid formula,and have completed the following contends including study on imbibition mechanism,configurating a new oil displacement agent and oil-displacement fracturing fluid,evaluating performance of oil displacement fracturing fluid.Analyze the influenced factors of imbibition fluid on imbibition oil recovery,including interfacial tension,surface tension,wettability,water viscosity ratio,pH,and temperature.It is proved that the existence of the best interfacial tension is not in the category of super low interface,and with the increase of the pore radius,the best interfacial tension becomes larger.Wettability and wettability of imbibition medium have great influence on imbibition?The higher hydrophilicity of the rock and the imbibition medium is,the higher the imbibition oil recovery ratio and the faster the imbibition rate is.Acid and alkali can promote imbibition,but the mechanism is different.In a certain range,the smaller the oil-water viscosity ratio is,the higher the imbibition efficiency is.The higher temperature can also improve the displacement efficiency and promote the imbibition effect.It is founded that the Gemini surfactants of carboxylate-twin-sulfonate has excellent synergy with LAS,and determined that the optimum mixture ratio of KL300 and LAS-60 is1:4.The surface tension of the mixed solution of 0.5%combination solution was 27.47mN/m,and the interfacial tension was about 4.56×10-3mN/m under the combination proportion.N-caprylic alcohol has good effect on the activity of system interface of KL300+LAS.The formula“0.4%LAS-60+0.1%KL300+0.1%N-caprylic alcohol“can make the surface tension decrease to 26.02mN/m and the interfacial tension of crude oil reduce to 5.6×0-4mN/m.The results of laboratory tests show that the new oil displacement agent has low cmc value,strong hydrophilicity as well as good temperature and salt resistance.Through the optimization of the main agent of VES fracturing fluid,thickening agent,accelerator,stabilizer and breaking agent,the formula of fracturing fluid is finally obtained.The formula is:0.7%J201+0.4%LAS-60+0.3%NaSal+1.2%KCl+0.01%TF-28+0.1%n-caprylic alcohol,the gel is SR-2.The fracturing fluid is mainly composed of betaine surfactant,Through the experimental evaluation of 189mPa.s;the addition of KCl improved the stability of NaSal and Gemini surfactant thickening;SR-2 can cause flooding.The oil displacement fracturing fluid 170S-1 at 80?under the condition of shear viscosity is still maintained at more than 80mPa.s.At room temperature to measure the elastic modulus and viscous modulus was2.52Pa and 0.79Pa respectively.Static sand suspension measured settlement rate is0.874cm/min;gel breaking liquid interfacial tension as low as 0.037mN/m.Indoor displacement and imbibition experiment showed that the oil displacement fracturing fluid gel breaking system can improve the efficiency of water flooding imbibition by 12.25%and improve the efficiency of 9.60%,proved that the flooding has double effects of fracturing fluid and displacing oil. |
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