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.

With the development of deviated drilling technology in sidetrack well,directional well and horizontal well,the previous structure of landing nipple brings lots of inconvenience and risk to the operation while drilling.

Therefore,research and application in the sidetrack well techniques are carried out and good results are gained.

Study and application of well plugging and its matching technologies for sidetracking well in Xianhe oil area,Shengli Oilfield;

Required by geology or reducing drilling cost by using wells drilled, 3D sidetracking wells are getting more and more, 3D sidetracking wells are increasingly important in oilfield development.

It is considered that particular drilling techniques of horizontal wells, sidetracking wells,extended reach and multi-target directional wells and the other stimulation measures have special functions for enhanced hydrocarbon recovery at the high water-cut stage.