Directional wells and cluster wells have become a conventional drilling technique now, which is widely used in various types of oil and gas reservoirs. Each year, more than half of the total drilling are directional wells in China. The main work is not to aim the target area, but to track the reservoirs now. Geosteering drilling is an important technical approach to improve single-well production and recovery ratio, to achieve the "less wells more production" idea.

China Geosteering Drilling System (CGDS), integrated the technology of drilling with logging and reservoir engineering, applies the near-bit geological and engineering parameters as well as controlling method to ensure that the wellhole trajectory can pass through reservoir and get best location while drilling. The wellhole trajectory can be adjusted and controlled timely according to the formation features measured by CGDS. The drilling bit is equipped with "eyes", which can identify oil/gas layer during drilling.

The CGDS is configured with CAIMS(Adjustable Instrumented Motor System), WLRS(Wireless Receiver System), GGMWD(Geosteering MWD System), CFDS(China Formation/Drilling Software System). More than 140 wells in China have demonstrated the system's ability to increase the probability of penetration and recovery rate in complicated formation, to reduce drilling costs and increase production and economic profit.

On the basis of introduction to the system, this paper focuses on the recent achievements as well as the lessons learned from the application in China. Helpful case histories will also be presented.

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