Junk Slot Area
As part of the drilling process cuttings are generated, which need to be cleared as soon as possible from the bottom. The hydraulic energy is used to aid the drilling and also to circulate the drill cuttings out of the hole. However, if there isn't enough space for the cuttings to get past the drill bit, they may not escape quickly. If the cuttings are not cleared efficiently, they tend to clog the bit and stay at the bottom getting reground, adversely affecting the drilling efficiency. Hence the drill bits are designed with several flow paths, which serve as conduits for cuttings to get past the bit. These flutes are called junk slots.
The Junk Slot Area is measured in square inches and is the total cross-sectional area of these slots when viewing the bit face-on. Junk slots can vary in shape and size. While drilling a soft formation, the rate of penetration is high, which generates cuttings at a faster rate. Hence the bits for drilling softer formations need to be designed with larger junk slot areas to be able to clear the drilled cuttings faster. Junk slots also allow drilling fluid to flow freely and prevent surge and swab while tripping.