Research On The Theoretical Model Of Fracturing Fluid Flowback In Fractured Gas Reservoirs

Low porosity-low permeability fractured gas reservoirs,such as tight gas reservoirs,shale gas reservoirs and coalbed methane gas reservoirs,have gradually become the focus of exploration and development in the oil industry.The mentioned reservoirs are usually characterized with abundant natural fractures.To develop the low-permeability fractured gas reservoirs,multi-staged fractured horizontal well technology becomes the crucial method which can connect the natural fractures and form the fracture networks.The flowback rate and the gas well production are closely related.However,the studies combining the fracture features and flowback are rarely reported.Based on the sufficient overseas and domestic researches,the discrete fractured networks model was established,then the law of fracturing fluid leakoff was analyzed in this paper.Finally,the theoretical model of gas-liquid two-phase backflow considering the clustered natural fractures was established and the effects of influencing factors were analyzed.The main work completed is as follows:(1)Based on fractal theory,the length and the center distribution,the orientation and the aperture of natural fractures were respectively calculated by FDFN,Fisher distribution and corrected SRA methods.The fractal discrete fracture networks model was established considering the clustered center distribution of natural fractures.(2)Rely on permeability tensor theory,the fractured medium was transformed to anisotropic homogeneous reservoir by using superposition principle.The contributions of natural fractures and matrix permeability to the permeability tensor of reservoir grids were studied and analyzed,and the accuracy of transformation method was verified.(3)Based on established fracture networks,the fracturing fluid leakoff model was established considering the clustered nature of fractures,which was solved by finite difference method.The model applies to the simulation of fracturing fluid leakoff in anisotropic reservoir,by which the leakoff process in fractured reservoir has been simulated.The effects of sensitive factors on leakoff were also analyzed by this model.(4)Under the combination of fracture networks and the leakoff result,the gas-liquid two-phase flowback theoretical model was established considering clustered natural fractures.Finally,the contributions of natural fractures to production and flowback rate were studied,and the impacts of geological and engineering factors on flowback were also simulated and analyzed.Throughout the process from reservoir modeling to flowback simulation,a relatively complete flowback research method in fractured gas reservoir was formed.The calculation results have an effective guiding influence on the design of fracturing fluid flowback plan and it can provide the reference for the seepage simulation in fractured medium.