Research On Fracture Condcutivity Of Fiber Pulse Filler Fracturing

The fiber pulse filler fracturing is a fracturing method to achieve the non-uniform placement of the proppant in the fracture by pulsed injection of sand-carrying fracturing fluid and fracturing fluid mixed with fiber,forming a pillar-type structure to sustain the fracture,which leads to a high-speed channel network,thus increasing the artificial fracture conductivity by several orders of magnitude.The non-uniform placement of proppant pillar is the key to maintain the high conductivity of pillar-sustained fractures.However,there is no clear understanding of the law of the proppant placement changing with construction parameters,resulting in the lack of theoretical guidance for drafting fracturing construction parameters.In this paper,the placement pattern of the proppant is investigated via a large scale physical model experiment,and then the trans-scale simulation model is developed.Based on the above work,the conducticity of pillar-sustained type fractures is studied.First,the proppant injection and placement process of fiber pulse filler fracturing is modeled by the large-scale visualization experimental device,in which the effecting parameters on the non-uniform proppant placement structure is investigated.Baesd on the results,four kinds of structure models representing the characteritics of non-uniform proppant placement structure are extracted,including type I three-row cylinder placement structure model,type II two-row cylinder placement structure model,type III two-row cylindroid placement structure model and type IV one-row cylindroid placement structure model.There are simultaneously two kinds of flowing in different dimensions in the pillar-sustained type fractures:the flow in pathway and the porous media seepage in proppant pillar.For the above characteristics,coupling the pathway flowing model based on the standard lattice Boltzmann method and porous media seepage model based on the generalized lattice Boltzmann method,the trans-scale flowing model of pillar-sustained type fractures based on the two-dimensional lattice Boltzmann method is established.The model uses a D2Q9 lattice velocity model.The standard bounce format is used for and the solid boundary,and the inlet boundary and outlet boundary are speed boundary and free boundary respectively.Concerning the structure model extracted by experiment result and trans-scale flowing model of pillar-sustained type fractures,the trans-scale calculation model of the fractures conductivity is established,and the fracture conductivity is solved by programming.According to the condition of the actual proppant pillar,the permeability and porosity of the proppant pillar required in the model are obtained by fracture conductivity experiment using the proppant containing fiber,and the accuracy of the model is verified by the standard example and the fracture conductivity experiment.The calculation of fracture flow field is carried out by trans-scale conductivity calculation model,and the influence rule of the speeage parameters,pillar-fracture ratio(PFR),packing arrangement and placement structure of proppant are discussed.By contrast,under the condition of this paper set,it is found that the conductivity of the fracture support by the type III two-row cylindroid placement structure model is larger than others,and the corresponding optimal laboratory slurry rate is 15L/min and the pulse time is 15-20s.According to the similarity criterion,the optimal parameters of the laboratory can be converted to those of the field condition.In this paper,based on the rules of proppant placement in fiber pulse filler fracturing,the analysis method of the fracture conductivity of the pillar-supported fracture is established,laying the foundation for the further study on the stimulation mechanism of fiber pulse filler fracturing.At the same time,this study is also of a certain guiding significance for establishment of construction parameters on field.