Geosteering measurements that accurately predict oncoming strata in
high-angle and horizontal wells are the dream of all well operators and an
important responsibility for service companies. To perform this task, service
companies have developed measurements that produce both wellbore images and
petrophysical data. These measurements identify the structural dip of
formations and characterize reservoir properties. The depth of investigation of
these measurements are typically no more than a few centimeters from the
wellbore, and are therefore limited to mapping only the first nearby geological
boundary.
A new deep electromagnetic (EM) logging-while-drilling (LWD) tool
currently in field test extends the depth of investigation to 30-m or more from
the well bore. The depth of investigation provided by the new LWD tool allows
detection of multiple strata over long horizontal distances. The hardware was
tested in three different horizontal wells. Each well had a horizontal reach of
at least 600-m.
The new measurement system allows identification of multiple resistivity
layers that correspond to different geological interfaces. In one of the wells,
an important formation top was identified at a vertical distance of 5-m true
vertical depth (TVD) from the well bore trajectory that had an inclination of
87°. This corresponds to a predicted distance of more than 75-m before the
bit crosses the interface. Individual layers in the horizontal section were
visible for horizontal distances that exceeded 450-m and at radial distances
from the wellbore that varied between 17 and 27-m. This detection capability
gave a high level of confidence in the geosteering process. Not only did the
measurements improve the correlation between geological markers, but they also
attracted the attention of the reservoir geologists who used these observations
to map geological features.
To date, our experience with the new deep EM LWD tool has allowed us to
map a sandstone pinch out, map a region influenced by the washout of water
injection in the field, delineate reservoir continuity, and identify a sub
seismic fault. These types of heterogeneities are important features that
impact fluid flow and our understanding of the reservoir. .
The data delivered by this new LWD tool provides more geological
information than any other technology currently available in the market. This
technology provides valuable information that can be used by geologists and
operational engineers to map and monitor the reservoir.
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