Study on the Interaction Mechanism between N2/CO2 and Fracturing Fluid at High Temperature and Pressure
In order to study the influence of gas injection and fracturing on the performance of fracturing fluids,based on the reservoir conditions of tight gas reservoirs in West Sichuan,experiments were conducted to visualize the phase changes and the interaction between pre/companion injection of N2/CO2 and fracturing fluids at high temperature and high pressure in tight gas reservoirs.The results show that:N2 has been in gaseous form after entering the well,with a density of 0.152 g/cm3 under formation conditions;CO2 changes from liquid to gas and then to liquid and supercritical state,with a density of 0.637 g/cm3 under formation conditions;N2 is mainly dissolved in the fracturing fluid in the form of bound gas,but basically has no dissolution with the disappearance of gas bubbles,and there are three kinds of forms of CO2 in the dissolution process:bound gas,dissolved gas,consumed gas,and dissolved gas.There are three forms of CO2 in the dissolution process:bound gas,dissolved gas,and consumed gas,which makes the amount of dissolved gas much larger than that of N2;under different injection modes of the same gas,the magnitude of the effect of N2 accompanied injection on the viscosity of fracturing fluid is 1.16-2.01 times of that of the front,and the magnitude of the effect of CO2 accompanied injection on the viscosity of fracturing fluid is 2.0-2.38 times of that of the front.The effect of CO2 injection on the viscosity of fracturing fluid is larger than that of N2,and the effect of CO2 injection on the viscosity of fracturing fluid is 1.74 times that of N2 2.45 times,so it is recommended to use the front injection method for field application.
tight gas reservoirsgas injection for energy enhancementfracturingfracturing fluid properties
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