Research On The Supercritical Carbon Dioxide-particle Two Phase Flow In Fracture

Conventional fracturing fluids usually have some problems,like causing formation damage,poor compatibility with formation and unthorough flowback.These problems will be more severe in the development of unconventional resource.Carbon dioxide has several advantages in petroleum engineering,includes inhibiting clay expansion,decreasing oil viscosity,easy to flowback and few pollution,which could better meet the requirement of low damage and less contamination during the exploration of unconventional oil and gas resources.Therefore,the supercritical carbon dioxide fracturing is a potential effective method to exploit the unconventional resource.However,this method still has many deficiencies,such as the flow mechanism of supercritical carbon dioxide-particle two phase flow in fracture is not clear and the particle distribution and transport need to be further studied.This paper proposed a Lagrangian difference method based on the velocity vector and established the fluid-solid interaction model,the fluid flow model with external force term and the particle motion model separately.Then the two,three-dimension particle-fluid model was given by coupling these three parts.Also,the coupling model was verified by comparing the simulation result with the result of references.Through this model,we studied three key flow problems in fracture: the transport of suspended particles,the remigration of deposited particles and the migration of fines in the proppant-filling bed.Researches have found that the established coupling model can be effectively dealt with the particle-fluid two phase flow problems.In the transport process of suspended particles,collisions between particles and the eddy caused by neighboring particles will prompt the particle's vertical settling and hinder the particle's horizontal transport.In the remigration process of deposited particles,particle's motion can be classified into three forms such as saltation,rolling and creep transport.When the fluid velocity is high,the upper particles move as saltation transport and the middle,lower particles transport as rolling transport.When the fluid velocity is low,the upper and middle particles move as rolling transport and the lower particles transport as creep transport.In the migration process of fines in the proppant-filling bed,the motion will be influenced by particle position,particle size and the boundary condition and result in different condition,like deposition,blocking pores and flowing out of the supported fracture.