Numerical Simulation Of Proppant Migration And Settlement In Fractures Based On CFD-DEM Coupling

Unconventional reservoir fracturing is easy to communicate with natural fractures to form complex fractures,and the effective placement of proppant particles in fracturing fractures determines the fracture conductivity after fracturing.At present,there are many studies on the settlement and migration of proppant in single straight hydraulic fracture,while the distribution law of proppant in complex fractures is unclear,which needs to be further strengthened.In this study,a CFD-DEM coupling model considering the interaction between particles,particles and wall,particles and fluid is established for different fracture models,including single vertical fracture and complex fractures.The evaluation index system of proppant distribution is constructed,including the equilibrium height,equilibrium time,area ratio,front edge angle,and height variance of sand embankment.The effects of proppant parameters,fracturing fluid parameters,fracture parameters and pump injection process on the migration and settlement of proppant in the fracture are investigated,which improve the understanding of proppant particles transport in the fracture,and provide a reference for improving the construction technology and improving the fracture conductivity to increase oil and gas production.Through the simulation of migration and settlement of proppant in a single vertical crack,the results show that the process of migration and placement of proppant to form sandbank is divided into three stages,namely,the formation stage of sandbank,the increase stage of height,and the increase stage of length.The increase of flow rate and viscosity of fracturing fluid and the decrease of proppant particle size are beneficial to increase the transport distance of proppant and to the remote placement of proppant.The increase of sand ratio is conducive to the rapid filling of proppant,but too high ratio is easy to cause sand up due to excessive accumulation in the wellbore,so that should be appropriately controlled.Through the simulation of proppant migration and settlement in complex fractures,the study shows that: compared with the single main fracture,the complexity of the fracture increases the total effect of diversion,reduces the flow of sand carrying fluid in the main fracture after the branch,increases the height of the main fracture sand embankment,and hinders the further injection of proppant.The closer the branch crack is to the wellbore and the smaller the angle between the branch and the maincrack is,the more conducive the proppant enters the branch crack.The higher the height and area ratio of the sandbank of the branch,the better the filling effect.The outlet of the branch crack is pressure boundary,and the diversion effect is obvious.The influence of the branch position is greater than that of angle.The shape of the secondary crack is mostly parabolic.When the outlet of the branch is a closed boundary,the difficulty of the proppant entering the crack increases.The distribution patterns of sandbank in different secondary cracks are similar,which are triangular,and the tertiary branch joint is not filled.The combination construction parameters of low density proppant and sand carrying fluid with higher flow rate and viscosity can reduce the settling velocity of proppant,improve the transportation distance,form small sandbank into the three-stage cracks,and increase the filling effect of the distal main crack and the secondary crack.The combination of high density proppant,low flow rate and viscosity sand carrying fluid is used as tailrace proppant to fill the near wellbore,ensuring the continuity of fracture conductivity.Using intermediate parameters can improve the filling of the main and branch in the middle of the crack.The research results effectively reveal the law of settlement and migration in different complex fractures,and have certain guiding significance for the optimization of fracturing parameters,fracturing fluid and proppant in unconventional reservoirs.