Geosteering

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In the process of drilling a borehole, geosteering is the act of adjusting on the fly the borehole position (Inclination and Azimuth angles) to be able to reach correctly one or several geological targets. These changes are based on the interpretation of geological information gathered while drilling.

[edit] Description

From 2D and 3D models of underground substructures, deviated wells (2D and 3D) are planned in advance to achieve specific goals: exploration, fluids production, fluids injection or technical.

A well plan is a continuous succession of straight and curve lines representing the geometrical figure of the expected well path. A well plan is always projected on vertical and horizontal maps.

While drilling the borehole and following the well plan, new geological information are gathered from Mud logging, Measurement While Drilling, chemostratigraphy/chemical Stratigraphy or advanced CheSS or Chemical Sequence Stratigraphy and Logging While Drilling. They show most of the time some differences from what should be expected from the model. By continuously updating the model with the new geological information and the borehole position (Well Deviation Survey), changes can start to appear in the geological substructures and can lead to update the well plan to reach the corrected geological targets.