Summary
Optimal field development often entails placing the wells in prescribed
locations within the reservoir. An error of a few meters in height above the
oil/water contact or with respect to the roof may result in leaving behind a
significant portion of the producible reserves. Driven by this key requirement,
new technologies continue to emerge to help geologists, drillers, and reservoir
engineers geosteer the wells. In recent years, two types of
logging-while-drilling (LWD) information have been used. On one hand, wellbore
imaging can determine when a well path has left the reservoir and the angle of
exit. On the other hand, traditional axisymmetrical resistivity logs help to
quantify the distance to an approaching boundary through inversion, but fail to
tell its azimuth.
A newly deployed azimuthal deep resistivity instrument recognizes an
approaching geological event before it intersects the well while continually
imaging it at multiple depths of investigation. Of particular interest is the
azimuth of approach with respect to the well path, advising in real time the
most favorable change of direction. In addition, a series of transverse
electromagnetic measurements specific to azimuthal resistivity, called
geosignals, are presented. Geosignals help to quantify the distance and the
rate of approach with great accuracy, before the actual intersection could
occur. With this real-time information, geosteering engineers can remain at
prescribed distances from important boundaries, including oil/water contacts
and overlying shale roofs. Modeling and actual logs demonstrate that the new
LWD instrument performs at its best when the reservoir is overlaid by shale.
Modeling suggests, however, that suboptimal performance occurs in reservoirs
with very resistive caprock, such as anhydrite.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
12 May 2009
- Meeting paper published:
3 December 2008
- Revised manuscript received:
22 May 2009
- Manuscript approved:
22 May 2009
- Published online:
16 February 2010
- Version of record:
20 April 2010
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