Jetting is particularly effective in removing caked drilling mud from the borehole wall. A jetting tool is placed at the bottom of the drill pipe. Horizontal nozzles direct the jetting fluid, which has been pumped down the drill string, at the screen. The jetting tool is rotated as it is moved up and

down over the length of screen. At the same time, the borehole is pumped at a greater flow rate than the jet inflow to remove the displaced particles.