Schlumberger

Technical Paper: Geosteering and/or Reservoir Characterization the Prowess of New-Generation LWD Tools

Society: SPWLA
Paper Number: 2010-93320
Presentation Date: 2010
 

Abstract

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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