Study On Fracture Network Flowback Rule In Tight Sand Gas

Tight sand gas fields need to be developed by reservoir reform technology,such as staged fracturing,because of low porosity and permeability.Reasonable flowback system is helpful to improve fracturing fluid flowback efficiency,control proppant reflux,and enhance fracturing result.To analyze proppant flowback rule in fracture network,design “fracture network flowback simulation experiment”,study fracture network structure,fracturing fluid viscosity and flowback velocity’s influence on flowback procedure.Experiment results show that: with the decrease of distance between fractures and vertical well,and the increase of segment distance and fracture number,proppant flowback ratio become lower;compared to water,low viscosity liner gel can reduce proppant flowback radio a nd unit flowback ratio,as viscosity becomes higher,unit flowback ratio increases;proppant flowback radio and unit flowback ratio increase with flowback velocity.To study pressure changing rule during flowback in staged fracturing,establish staged fracturing flowback numerical model based on equilibrium principle in horizontal well,influence factors analysis results show that: with the increase of flowback time,fracturing fluid leak off velocity and flowback velocity decrease,when they drop to zero,leakoff quantity to flowback quantity is about 4 to1;when noble size increases and fracturing segment number decreases,pressure drops quicker;with the increase of reservoir permeability,porosity and elasticity modulus,pressure drops quicker.To further analyze proppant flowback rule,establish proppant moving model,sediment model and flowback model,the analysis result of proppant flowback model shows that: proppant critical flowback velocity and security nozzle radius increase quickly when fractures close;security nozzle radius increase with fracturing segment number;critical flowback velocity decreases with fracturing fluid viscosity;because of cohesive force,the influence of proppant diameter to critical flowback velocity is opposite before and after fractures closing.According to flowback experiment results,as well as established fracturing fluid model and proppant model,develop optimum design method of staged fracturing in horizontal well,and finish one tight sand gas horizontal well flowback project design.This article’s research contents provide theoretical basis to flowback system optimum design method,which is helpful to the development of tight sand gas.