The proposed well was planned as a vertical exploratory well, which located in the eastern part of a block in Kingdom of Saudi Arabia. Several wells had been drilled in this area by the same operator. The offset drilling data and information show the targeted formations displayed a wide range of pore pressure and different formation stability from well to well. Therefore, mud systems that were much heavier than pore pressure ECD had been used to drill the reservoir formation in past operations. The concern of the operator was that by doing that the reservoir could be damaged to a point that true characteristic of the reservoir could be disguised, or even worse, the reservoir was hidden.

The primary objective of this well is to characterize Formation A and Formation C and evaluate gas production while drilling. UBD/MPD technology was adopted to achieve the planned objective. One of the major benefits of UBD/MPD technology over conventional drilling technology is that UBD/MPD technology has the capability of a prompt and effciant response to the downhole conditions as they occur by simply adjusting the back pressure. This is critical on an operation like this with uncertain formation characteristics, such as pore pressure and hole stability issues.

This paper describes the planning and implementation of the UBD/MPD technique in the 8 3/8” and 5 7/8” section hole of this well and reviews the results of the drilling operations.

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