■ When sand carrying fluid enters tubing-casing annulus through pack tool, the direction of fluid flow changes, therefore gravel does not erode casing inner wall directly leading to protective effects for the casing
■ The hanging capacity and bearing dynamic load capacity of the flushing tubing has doubled, increasing security
■ The connecting part of central tubing and flushing tubing adopts resistance reduced treatment, which lowers the resistance of breakout and lifting
■ Enlarged channel reduces reverse flushing resistance