The last decade has shown a significant development in resistivity measurement technology providing directional resistivity at a larger scale than conventional logging tools. The latest development can identify resistivity contrasts ten's of meters around the wellbore. Statoil has tested deep look-around resistivity on a range of fields during the last 2 years and recorded data in more than 10 wells on the Norwegian Continental Shelf. The look-around images provides information at a scale that bridges the gap between conventional logging and seismic and adds important new pieces to the reservoir characterization puzzle. In good reservoir conditions, resistivity contrast up to 30 m away from the well-bore has been observed. This study will focus on results from the Visund and Åsgard fields, and will demonstrate how the device was used in a range of different applications in the geosteering operation: Detection of the reservoir boundary up to 20m TVD away. Detection of oil bearing reservoir from within underlying shale, through a water zone. Detection of Gas-Oil Contact (GOC). Detection of Oil-Water Contact (OWC) up to 20m TVD away. Detect faulting of the reservoir. These examples will highlight why deep look-around resistivity is a step change related to the possibility for doing pro-active well placement of highly deviated wellbores as well as for gaining a larger reservoir understanding. The imaged variation in resistivity contrasts can be related to geologic zonation and fluid content on the reservoir scale, which opens up a much better cross-disciplinary communication between geophysicists, geologists, petrophysicists and reservoir engineers. Finally, the deep resistivity images contribute in optimization of completion solutions when incorporating information on the reservoir scale.

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.

The process of geosteering, using real-time logging-while-drilling data to actively steer horizontal or highly deviated wellbores, has been in use for more than 20 years. Over this period, the demand for more sophisticated measurements has developed along with the need to access increasingly difficult reservoirs as the simpler drilling scenarios are being exhausted.Such a case is evident in the Yme Gamma development, located offshore south-western Norway, consisting of four horizontal producing wells and two vertical injectors. Abandoned by the original operator because of high water cut, to redevelop the field the current operator needed to drill subsequent wells in a narrow corridor up-dip between the existing producer wells and the bounding fault, in the thin YS 7 (4 to 8 m) inner-estuary sands or the YS 5/4 (2 to 6 m) inner/central-estuary sands.The Yme 9/2-C-2A well was successfully drilled as a replacement for the C-2 well, which had been redrilled because of the reservoir being swept in that area. Since the neighbouring well, C-3T3, showed encouraging results in the YS 5/4 reservoir, which was not targeted in that well, a horizontal well was planned to exploit this reservoir.There were several challenges that needed to be addressed in the geosteering of this well: the need to keep the wellbore within a narrow reservoir (between 2 and 6m in thickness); a very narrow lateral corridor between the main bounding fault and existing wells; observed sub-seismic faulting in neighbouring wells; and the possibility of a coal layer, which would necessitate a sidetrack if intersected.As with any geosteering operation, success is often the result of a combination of inter-department team work and communication as well as the use of appropriate technology. Integrated use of a bed boundary mapping device and real-time density images allowed the 9/2-C-2A well to be geosteered within these tight tolerances, skirting the bounding fault by less than 1 m lateral displacement, and allowing for the drilling of other tight tolerance wells.

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