Study On Multi-Phase Coupling Dynamic Model And Transport Law Of Fracturing Fluid In Flexible Fiber Suspended Sand

Large-scale hydraulic fracturing technology is the main means of effective development of low porosity and low permeability reservoir.Efficient transportation and long distance placement of proppant are the basic guarantee for the success of hydraulic fracturing.In order to improve the effect of fracturing,in recent years,new fracturing technologies such as fiber temporary plugging to fracturing technology,follow-up fiber sand control fracturing technology,the whole process with fiber sand fracturing technology,and channel fracturing technology continue to emerge.One of the main differences from conventional fracturing technology is the addition of fiber,which changes the flow characteristics of fracturing fluid and the settlement characteristics of proppant.The transport and distribution of proppant is the result of the interaction of fiber,fracturing fluid and proppant.At present,the research on fiber fracturing technology is in the initial stage of exploration,and the mechanism of fiber fracturing fluid suspension sand is not clear.As a result,the construction process design and construction parameters of fiber fracturing can only rely on field practice to debug,and can not achieve quantitative optimization.Therefore,this paper carried out research on the multi-phase coupling dynamics model of flexible fiber suspended sand fracturing fluid and transport rules,studied the multiphase settlement and flow behavior of fracturing fluid,fiber and proppant,quantified the construction parameters of fiber suspended sand,revealed the transport rules of fiber suspended sand fracturing fluid,and provided theoretical support for fiber assisted fracturing fluid suspended sand and reservoir reconstruction technology.To promote the development of large-scale fracturing technology and the efficient exploitation of unconventional oil and gas resources.Research on the settling law of particles in fiber fracturing fluid.Based on the rheological experiment,the influence law of fiber on the apparent viscosity of guar gum fracturing fluid was studied.Based on the single particle sedimentation experiment and multi-particle sedimentation experiment,the influence law of fiber on particle sedimentation velocity was analyzed.The relationship between fiber resistance coefficient and particle Reynolds number was obtained by combining the sedimentation theory with the experimental results,and then the implicit calculation method of particle sedimentation velocity was proposed.The experimental results show that the rheology of Guar fiber fracturing fluid conforms to the characteristics of power law fluid,the average volume fraction of fiber is the main factor affecting the apparent viscosity of fiber fracturing fluid,and the influence of fiber on the apparent viscosity of low viscosity fracturing fluid is more significant than that of high viscosity fracturing fluid.The particle sedimentation process is determined by the comprehensive parameters of proppant,fiber and fracturing fluid.Fracturing fluid viscosity,proppant concentration and fiber concentration all have significant effects on particle sedimentation rate.The experimental results provide experimental verification and theoretical basis for establishing a reliable multi-phase coupling dynamic model of flexible fiber suspended sand fracturing fluid.Fluid-particle coupling theory and calculation method.During the flow process of flexible fiber suspended sand fracturing fluid,there is a large amount of sand and fibers,and frequent collisions between them.There is a contradiction between the calculation accuracy and efficiency of existing particle tracking and collision detection algorithms.In this study,a particle collision pre-search algorithm and a suitable fluid-structure coupling method are proposed,and the particle-fluid coupling calculation time step is automatically adjusted according to the particle collision time step.The accuracy and efficiency of the particle collision pre-search algorithm are verified by two particle uniform and variable speed chasing examples and multi-particle collision examples,and the particle movement in a rectangular channel is demonstrated.The reliability of the particle-fluid coupling calculation method is verified.Dynamic model of multi-phase coupling of fracturing fluid in flexible fiber suspended sand.Considering the typical mechanical characteristics of the flexible fiber,a numerical model of the flexible fiber was established based on the discrete particle bonding model,and the binding parameters and mechanical parameters of the fiber model were given.Considering the interaction between the fiber and the fluid and the energy dissipation during the deformation process,a dynamic model of the flexible fiber was established.The mesoscopic contact parameters between the proppant and the fiber were determined by parameter calibration method.On the basis of fluid and particle coupling,flexible fiber was added,and the interaction between particles,fluid and flexible fiber was considered.Based on the improved CFD-DEM,the multi-phase coupling dynamic model of flexible fiber suspended sand fracturing fluid was established.The accuracy of the fiber-fluid coupling dynamic model was verified by the example of fiber flow in the rectangular channel,the settlement of single particle and multi-particle in the fiber fracturing fluid and the dynamic sand laying in the crack,and the accuracy of the multi-phase coupling dynamic model of the flexible fiber suspended sand fracturing fluid was verified.Study on fracturing fluid transport law of flexible fiber suspended sand.A multi-phase coupling dynamic model of flexible fiber suspended sand fracturing fluid in flat fractures and variable cross section fractures was established to analyze the interaction mechanism of flexible fiber,fracturing fluid and sand,and to study the influence of fracturing fluid injection rate,fracturing fluid viscosity,fiber elongate-diameter ratio,proppant particle size,fiber concentration and other parameters on the transport of proppant in flat fractures and variable cross section fractures.The boundary curve of continuous transport of fracturing fluid in flexible fiber suspended sand in variable section fractures was drawn to provide theoretical basis for realizing continuous transport of proppant.