The Nautical Petroleum appraisal well 9/02b-5Z, located in the North Sea, was recently drilled using a new deep directional resistivity tool which enabled the simultaneous real-time mapping of the upper and lower boundaries of a 100+-ft reservoir, over the length of the 2,000-ft horizontal well. This device was of great benefit in both validating the accuracy of the seismic interpretation and tying the borehole acquisition data to the seismic data.

One of the greatest challenges in geosteering is that horizontal wells are planned using a seismic visualization of the reservoir but are drilled using a borehole visualization of the reservoir. There is a large disparity in the resolutions of these two systems. Often, only a vague structural outline can be trusted from the seismic data, necessitating the geosteering process, while even the deepest reading bed boundary mapping tool currently available can only visualize one boundary in anything other than a relatively thin reservoir for referencing back to the seismic data.

The new generation deep directional resistivity tool, currently in field test, has a greatly enhanced depth of investigation coupled with the ability to detect multiple boundaries in any direction, allowing for the marriage in real time of the seismic and the borehole data and leading to more effective and productive drilling of horizontal wells.

This paper will describe the Nautical Petroleum 9/02b-5Z case study and will detail how this data was used both in the post-well evaluation of the overall reservoir structure and in the real-time application of the data in significantly reducing the risk associated with the placement of the borehole.

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