Study On Dynamic Behavior Of Proppant Pillars With Fracture Closing

The channel fracturing alternately pumps the proppant slurry and the clean fluid through pulses to form a discontinuous placement of non-uniform support structures(proppant pillar)in the artificial fractures.A high-speed channel network is formed,and the channel fracture conductivity is several orders of magnitude higher than conventional hydraulic fracture conductivity.However,the understanding of the deformation law of the proppant pillar under the action of the formation closure pressure is unclear,resulting in unknown understanding of the variation rule of the fracture width and difficult calculation of fracture conductivity.In this paper,a large-scale visualized flat plate experimental device is used to simulate the proppant transport process in the channel fracturing,and the proppant pillar placement rules under different experimental parameters are obtained.Statistical analysis of proppant pillar placement patterns and dimensions is conducted.Three typical proppant pillars placement structures are extracted based on the construction displacement and the pulse time of the proppant slurry.Simulate the compression deformation process of the proppant pillars through experiments.The deformation law of the pillar and the Young's modulus of the proppant pillar at different pressure sections are calculated.Then,the proppant pillar is dispersed into particles with actual mass and volume by the smooth particle method(SPH).The normal stress of the particles is calculated using the kernel estimation and the particle similarity within the proppant pillar,and the formation is discreted by finite element method(FEM).Its contact with the proppant pillar is based on the coupling contact method between FEM and SPH.Based on the size of the proppant pillar extracted from the plate experiment,three types of formation fracture-proppant pillar contact models are established to study the closure pressure and rock Young's modulus.Under the proppant pillar and the fracture deformation law,get the shape of the proppant pillar after deformation,normal stress and fracture width.Finally,the shape of the proppant pillar and fractures after deformation stabilization is extracted.Computational fluid dynamics method is used to establish the fracture-proppant pillar flow model,and the fracture conductivity of different construction parameters under different formation closure pressures is calculated.The simulation results show that the fracture widths supported by the three proppant pillars show an accelerated downward trend as the formation closure pressure increases from 14MPa to 41 MPa,and the fracture width under the support of the initial radius of 9 mm proppant pillar is the largest,decreasing from 2.52 mm to 1.72mm,the initial radius of 5mm proppant pillar support the smallest fracture width,from 1.97mm to 1.22mm,the larger the radius of the proppant pillar,the greater the fracture width;three types of proppant pillar particles by the normal stress from 73MPa to 110MPa,and presents a medium-small force distribution law;the elliptical cylinder proppant pillar has the largest fracture conductivity,and its fracture conductivity is reduced from 12500D·cm to 3630D·cm.The fracture conductivity of the initial radius of 9mm proppant pillar decreases from 15500 D·cm to 2580D·cm.The larger the construction displacement and the time of proppant slurry,the greater the fracture conductivity.The model in this paper can calculate the fracture conductivity of different construction parameters under different closure pressures,which lays the foundation for the further study of channel fracturing and production increase mechanism,and has certain guiding significance for the construction parameters of the site.