Research On The Law Of Flowback Of Fracturing Fluid Of Low Permeability Reservoir

Hydraulic fracturing is an necessary technology measurement to evaluate and stimulate in low permeability oil and gas reservoir, while the flowback of fracturing fluid after fracturing treatment is an important step in hydraulic fracturing of oil and gas well. At present, empirical methods are mostly adopted to control the flowback of hydraulic fracturing fluid and no reliable and theoretic basis. In this paper, the process of flowback and bottomhole pressure after fracturing are studied in order to offer a theoretic basis for the design of flowback procedures of the fracturing fluid.According to the theory of fluid flow in porous media, mechanism of leakoff of fracturing fluid during fracture closure was analyzed and a 2D dynamic leakoff model of non-Newtonian fracturing fluid was considered. Numerical method was employed to solve this model and the simulation results were compared with that of 1D model. It showed that the 2D model was more applicable to fields because of its consideration of fracturing fluid leakoff in the direction that is parallel to the fracture face and the leakoff rate calculated by 2D model was more reasonable than by traditional 1D model.Based on the study of mechanism of leakoff of fracturing fluid, after the leakoff rate being calculated, mathematical fracture closure model and the flowback model of fracturing fluid was established according to the theory of fluid mechanics and numerical simulations and material equilibrium. Meanwhile, the starting pressure gradient was in consideration and the numerical methods of fracture closure model and the flowback model of fracturing fluid were given. Numerical simulations showed that fractures in low permeability reservoirs should be closed by using aggressive closure procedures in order to diminish damages to reservoir. The result of the numerical solution of the model comparing with practical curve of wellhead pressure drop revealed that this pressure drop model could be used to predict flowback well.Finally, laboratory study on flowback affecting factors were conducted, and core test was done to justify the accuracy of the model, then the model was optimized. Based on those conclusions of the study on the laws of fracturing fluid flowback, the methods and rules used to design flowback procedures in terms of different conditions of reservoirs and parameters of hydraulic fracturing were presented. Moreover, the computer program on forecast of parameters of flowback was developed and its purpose was to provide guidance for flowback controlling by virtue of optimizing those flowback parameters.