The paper presents drilling progresses and main technical challenges for deep and ultra-deep wells, analyzes deep and ultra-deep drilling-technique actualities worldwide from seven aspects including drilling geological descriptions and evaluations, rapid-vertical drilling techniques, ROP improvement, mud, cementing, drilling information and drilling equipment.

This paper describes the effects of hydraulic energy for deep drilling, discusses some key problems on the study and applications of hydraulic power for deep drilling.

Based on the investigation of various deep drilling techniques in which the depth exceeds 4,500 metes in the recent twenty five years, it is considered that the drilling techniques during US and North Sea of Europe are the advanced in the world and there is a tenyear gap between them and former Soviet Union and China.

Such key deep well drilling problems caused by the complex geology circumstances have been tacklied in Zhongyuan Oilfield; Therefore, a series of supporting teech-niques of casing programming for a deep well, combined drilling with a PDC bit and a downhole motor, vertical drilling, mud, cementing and well control, etc have been developed.