Oil well drilling is a process of drilling a hole in the ground for the extraction of natural gas or petroleum. Depending on the soil condition different drill bits are utilized. There are three main categories: soft, medium and hard formation bits. Soft formation rock bits are used in unconsolidated sands, clays, soft lime stones, red beds and shale. Medium formation bits are used in calcites, dolomites, lime stones, and hard shale. Hard formation bits are used in hard shale, calcites, mudstones, cherty lime stones and hard and abrasive formations.