Study On The Preparation And Performance Of Chemical Tracers For Fracturing

As horizontal well staged fracturing technology is widely used in low-permeability reservoirs and tight reservoirs,how to evaluate the effect of fracturing reformation in different intervals has become an engineering problem that needs to be solved urgently.The tracer fracturing dynamic monitoring technology injects the fracturing fluid containing tracer into the formation,sampling and detecting the concentration of the tracer during flowback to obtain a monitoring response curve,which can analyze the effect of fracturing in different intervals and characterize the shape of fracturing fractures,Optimize fracturing process design and other purposes.However,the current tracers commonly used in oil fields have problems such as poor compatibility with fracturing fluids,low detection accuracy,large adsorption capacity in the formation,and few available types,which restrict the application of tracer technology in fracturing dynamic monitoring.Therefore,it is of great significance to develop a fracturing tracer that meets the requirements of the fracturing process and has excellent performance.In this paper,the water-soluble fracturing chemical tracer 4-trifluoromethyl benzoic acid and the oil-soluble fracturing chemical tracer 4-trifluoromethyl ethyl benzoate were prepared by molecular design and chemical synthesis.The response surface optimization method was used to optimize the synthesis conditions of the tracer,and the optimal synthesis route was determined.The yields of the two tracers reached 89.16%and 87.73%,respectively.Guided by the requirements of fracturing dynamic monitoring on the performance of the tracer,the performance research on the detection method of the tracer and the suitability of the formation is developed.The research results show that a set of more accurate tracer detection methods has been formed by gas chromatography-mass spectrometry.The minimum detection limits of water-soluble tracers and oil-soluble tracers are 0.3μg·L^-1 and 0.5μg·L^-1,respectively.The detection accuracy is All reach the ppb level,which is better than the spectrophotometric detection method of conventional chemical tracers.The two synthetic tracers have good compatibility with fracturing fluids,and have no effect on the fracturing fluid base fluid,the viscosity of the breaker fluid,and the rheological properties of the fracturing fluid.The water-soluble tracer has an oil-water distribution ratio of 0.31.The oil-water distribution ratio of the oil-soluble tracer is 12.14,which is a single-distribution tracer,which reduces the detection error.At 80°C,the tracer concentration basically did not change within 7 days,and the maximum concentration difference was 4.82 mg·L^-1,showing good stability.By comparing the static adsorption and desorption experiments with conventional oilfield tracers,it is proved that the synthetic chemical tracers for fracturing have lower adsorptivity to mixed sand.At 40℃,the adsorption capacity of water-soluble tracer and oil-soluble tracer is 4.52 mg·g^-1 and 3.83 mg·g^-1,which are much lower than the adsorption capacity of conventional oilfield tracers at the same temperature.The designed fracturing fluid flowback simulation experiment shows that the dynamic adsorption of the tracer basically does not affect its flowback law,showing good application potential,and providing a new idea for the design of chemical tracers for fracturing.