| After decades of development,hydraulic fracturing technology has become the most important way to increase production for oil and gas reservoirs,especially low permeability and ultra-low permeability reservoirs.Conventional hydraulic fracturing technology has promoted the efficient development of oil and gas reservoirs,but there are still problems such as high friction,high pump pressure,high equipment requirements,sand plugging,and reservoirs damage.In order to solve the above problems,a new fracturing technique,changeable phase chemical fracturing technology,is proposed by the acid fracturing Laboratory of Southwest Petroleum University.Its technical principle is to use two kinds of fluid of immiscible phase to create artificial fracture in a certain geometry size.By chemical method,one of the fluids in the fracture forming solid phase to support the fracture by phase transition.The distribution of the flow pattern of the fracturing fluid system determines the distribution characteristics of the self solid solid proppant after the phase changed.It is of great significance to study the distribution of the two-phase flow in the fracturing fluid system,which is of great importance to the improve the effect of the changeable phase chemical fracturingOn the basis of investigating the experimental method of two phase flow,and the numerical method of two phase flow research,the mathematical model of fracture propagation under stress symmetry and stress asymmetry and the two phase flow interface distribution model of the chemical fracturing fluid system is derived in view of the problem of interfacial distribution in the flow process of the changeable phase chemical fracturing.And the fractal dimension,the multifractal spectrum and the placement efficiency are introduced to evaluate the flow morphology of the changeable phase chemical fracturing fluid system,and the calculation program is compiled based on the established model.The flow distribution law of the changeable phase chemical fracturing fluid system is studied under the conditions of different injection rate,viscosity ratio,interfacial tension,density difference,fracture dip angle and injection volume ratio.The research work is as follows:1)The research on two phase flow pattern,two phase flow research method are systematically investigated.On this basis,the shortcomings and advantages of various models and methods are summarized.2)Through the deduction and solution of the geometric model of artificial fracture,the propagation law of the fracture in height,width and length in the process of changeable phase chemical fracturing is recognized,and the fracture geometry is provided for the follow-up of the fluid two-phase flow pattern simulation.3)According to the conservation law,a mathematical model of the flow distribution of the fracturing fluid system is established,which includes the continuity equation,momentum equation and the distribution equation of the two phase interface,and the SLIC method is introduced to reconstruct the interface.4)Based on the finite element method,the flow distribution mathematical model of the chemical fracturing fluid system is discrete processing,the flow distribution numerical model of the fracturing fluid system is set up,and the corresponding Matlab calculation program is compiled.5)Simulate and calculate the flow distribution law of the chemical fracturing fluid system under the conditions of different injection rate,viscosity ratio,interfacial tension,density difference,fracture dip angle and injection volume ratio,and analyze the placement efficiency,fractal dimension,multifractal spectrum width and other parameters under different conditions.The research work and the results obtained in this paper have realized the study of the distribution of the interface of the changeable phase chemical fracturing fluid system,and discussed the distribution of the interface under different parameters,which will provide reference for the design of the changeable phase chemical fracturing parameters design. |
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