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Understanding Horizontal Well Logs to Improve the Geological Model While Drilling*

By

Arve K. Thorsen¹, Jeremy C. "Jez" Lofts², Trond Gravem³, Knut J. Rønning⁴, and Andrew J. Holden⁴

Search and Discovery Article #40253 (2007)

Posted August 20, 2007

*Adapted from oral presentation at AAPG Annual Convention, Long Beach, California, April 1-4, 2007

¹Baker Hughes INTEQ, 5020 Bergen, Norway ([email protected])

²Baker Hughes INTEQ, Houston, TX

3Baker Hughes INTEQ, 4056 Tananger, Norway

⁴Norsk Hydro ASA, 5020 Bergen, Norway

Abstract 

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 farther 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.

Selected Figures

Summary 

• The flexible logging system delivers the information to update the geological model in real time.

• Horizontal log interpretation gives the answers while drilling to optimize the well trajectory.

• Use all data and expertise available.

• Necessary to have a complete team approach to deliver the optimum horizontal well trajectory.

• The ability to describe the reservoir from the borehole wall and out to 12 meters (35 feet) from the borehole gives the link between well logging and seismic data.

• Continuous updates are a necessity to optimize the well placement in real time.

Reference 

Hagen, Jens, and Benedicte Kvalheim, 1992, Oseberg Field, in Giant Oil and Gas Fields of the Decade 1978-1988: AAPG Memoir 54, p. 417-428.