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Appraisal of an Extensive Thin Chalk Reservoir with Long Horizontal Wells: Cyclostratigraphy as Complementary Steering Tool

By
N. W. Petersen
N. W. Petersen
Mersk Olie og Gas AS Copenhagen, Denmark
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J. Toft
J. Toft
Mersk Olie og Gas AS Copenhagen, Denmark
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P. M. Hansen
P. M. Hansen
Mersk Olie og Gas AS Copenhagen, Denmark
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Published:
January 01, 2003

Abstract

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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Contents

AAPG Methods in Exploration Series

Horizontal Wells: Focus on the Reservoir

Timothy R. Carr
Timothy R. Carr
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Erik P. Mason
Erik P. Mason
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Charles T. Feazel
Charles T. Feazel
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American Association of Petroleum Geologists
Volume
14
ISBN electronic:
9781629810553
Publication date:
January 01, 2003

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