In practice, the eccentric overburden drilling systems (ODEX / Stratex / Tubex / ODS) of three components (mentioned to the guide device, eccentric reamer and pilot bit), symmetric casing drilling systems of two components (ring bit and central pilot bit) and double head casing drilling systems (double drill strings) are the most widely used ones, among them the double head casing drilling systems are mainly used for anchoring. Nowadays, these technologies are very mature and reliable.