Traditional geosteering with deep resistivity allows us to navigate along a resistivity boundary at a distance of 0 - 5 meters. We have developed an extra deep resistivity service called DeepTrak? to navigate at a distance of up to 12 meters from a resistivity boundary. To accomplish this goal we have added an electromagnetic wave propagation tool which operates at lower frequencies and with longer transmitter-receiver distances to the normal propagation resistivity service.

Combining the measurements at the various frequencies and transmitter-receiver distances allows us to investigate the volume around the wellbore with radii from 1 to 12 meters. Typically, six resistivity curves of different depth of investigation are transmitted in real time. An automated process determines the best fit of this data with a selection of previously calculated forward resistivity models, thus indicating the height above the oil water contact, the top or the bottom of the reservoir.

The well trajectories based on directional surveys and on transmitted resistivities are both calculated and visualized by a web-based data communications system. This improves TVD control and aids detection of approaching bed boundaries.

The service has been run in several wells in the Grane field in the North Sea. The objectives were to stay at a specific distance above the oil water contact, and to detect and possibly avoid shales. Data from offset wells indicates an irregular oil water transition zone in the field which is difficult to see on gamma ray or porosity logs. Consequently, this irregularity necessitates the broad depth of investigation range.

The combined use of Deep Resistivity and Extra Deep Resistivity data provides a stable distance calculation, not possible with standard propagation resistivity data alone. A method for analyzing the sensitivity of the real time distance calculations has been developed, and is adding confidence to the utilization of the data for proactive Reservoir Navigation. The usefulness and limitations of this technique are illustrated with examples of both synthetic and field data.

This content is only available via PDF.
You can access this article if you purchase or spend a download.