We know that underground rock formations, and not all are the same. Some soft, a bit hard. Based on this, we select the crawler drilling rig , and use of drilling methods, time and change. Here a detailed division of underground rock formations to, and the drilling method. Salt formation, is a water-soluble formation, relatively soft. Drilling machine is gummed up with mud, drill out the hole also easily drop mud, or even collapse. Clay liner, shale, is a water-sensitive formations, drills tend to form mud, drill out the hole also oversized. Sand, gravel, loose broken formation, is a loose porous strata, leaks, leakage of sand. High pressure oil and gas wells, underground reserves of oil, gas and other, easy blowout, causing serious consequences. High-temperature formation, geothermal wells and ultra-deep formations encountered, mud treatment failures, unstable formation. Due to the formation of complex situations, so we are in exploratory drilling must be clear. Just to name a few single layer above, some are complex, in a formation, may encounter such situations.