Appraisal of an Extensive Thin Chalk Reservoir with Long Horizontal Wells: Cyclostratigraphy as Complementary Steering Tool
N. W. Petersen, J. Toft, P. M. Hansen, 2003. "Appraisal of an Extensive Thin Chalk Reservoir with Long Horizontal Wells: Cyclostratigraphy as Complementary Steering Tool", Horizontal Wells: Focus on the Reservoir, Timothy R. Carr, Erik P. Mason, Charles T. Feazel
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An extensive flank reservoir extension has been appraised and production has been tested by drilling horizontal wells of record length for the North Sea, drilled from the existing Dan field production installation.
The main target reservoir unit with producible hydrocarbons is a thin (<3 m [10 ft]), highly porous zone that forms part of a sequence of cyclic beds in the low-permeable Maastrichtian chalk. The cyclic sequences can be correlated stratigraphically across the field.
It was planned to steer the wells with the help of biostratigraphy and logging while drilling (LWD). Steering proved more problematic than anticipated because the biostratigraphic zones in the target unit changed along the hole.
To prevent jeopardizing well reach and thus the appraised area, severe doglegs and extensive open-hole sidetracking were avoided. This resulted in a gently undulating well trajectory that crossed the target zone several times.
At times, however, it proved difficult to determine whether the well was above or below the highly porous target zone. It was found that the LWD log could be used to determine the position of the well relative to the highly porous zone by means of cyclostratigraphic correlation.
Long-term production testing has been performed in the wells using existing production facilities, with encouraging results.
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Horizontal Wells: Focus on the Reservoir
This book provides an overview of the new technical approaches required for best use of horizontal and extended-reach technology in different reservoir situations. The volume is a selection from more than 50 papers presented at an AAPG/SPWLA Hedberg Research Symposium, “International Horizontal and Extended Reach Well Symposium: Focus on the Reservoir,” held in The Woodlands, Texas, on October 10 14, 1999. The 16 chapters describe horizontal and extended-reach wells and drilling programs in a variety of geologic settings all over the world.