Understanding
Horizontal Well Logs to Improve the Geological Model While Drilling
Thorsen, Arve K.1, Jeremy C.
"Jez" Lofts2, Trond Gravem3, Knut J. Rønning4,
Andrew J. Holden4 (1) Baker Hughes INTEQ, 5020 Bergen, Norway (2)
Baker Hughes INTEQ, Houston, TX (3) Baker Hughes INTEQ, 4056 Tananger, Norway
(4) Norsk Hydro ASA, 5020 Bergen, Norway
During horizontal drilling it is
important to understand the structural geology of the reservoir, i.e. the 3D
development of the structure drilled.
The geological model plays a significant
role in horizontal drilling as it is the foundation of any horizontal well
placement planning. However, during drilling the geological model has to be
calibrated against the actual formation data recorded, in order to assist in
corrective actions needed to keep the drill bit within the desired reservoir
zones.
To understand the local geological
structures during drilling, image data display and interpretation are done in
real time to better resolve the structural dip and strike attitudes of the
larger structures in the geo-model.
Resistivity logs can be used to reveal
the geology further away from the wellbore. Measurements reading up to 15 m
around the wellbore can be obtained if the environment is favorable. By
combining all the different measurements and use enhanced modeling capabilities
to interpret the horizontal log responses, the well logs can be used to perform
several estimates, like the distance to approaching layers, the true dip and
strike of the formation, warnings prior to exiting the reservoir, distance to
the Oil-Water Contact, etc. By tying the data to the geological model these
estimates can be applied to make plausible predictions of the geology ahead of
the bit and hence significantly aid the geosteering of the well within the
reservoir.
This paper shows two examples from
horizontal wells drilled in distinctly different reservoirs, applying the
techniques described above. The combined use of horizontal well logs and the
specific geological model gives another dimension to the real time wellbore
placement, and hence to the economics of the well.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California