Directional drilling technology has been applied widely since the last century. Directional tools and directional drilling technology shall be applicable to the different circumstances.Thus it is necessary to improve directional tools and directional drilling technology according to operation experiences.

In Iran, 146 directional and horizontal wells onshore and 16 directional wells offshore have been drilled by DDDC since 1997. Directional well technology have been applied under different circumstances such as in high weight and saturated salt water drilling fluid system, in the conditions of loss with low flow rate or in 26" or 4 1/8" unconventional hole size.

After contant improving directional drilling technology and tools, drilling hours of the directional drilling tools have been increased from 20 hrs to more than 120 hrs, and the maximum have reached 300 hrs in some wells, the directional tools can keep working in the loss condition, and the unconventional hole of directional wells are completed successful. Improving directional tools and technologY according to the different operation circumstances can lead to increased efficiency of drilling.

This paper presents some practical examples of how to improve directional drilling technology and tools under complicated circumstances, which can contribute to great improvements of directional well service performance.

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