Skip to main content
Top of the Page

3D Look-Ahead Electromagnetic Inversion in Near-Vertical Wells – A Bridge Between Vertical and Horizontal Wells 3D Geolo

One-dimensional (1D) look-ahead inversion for ultradeep azimuthal resistivity (UDAR) tools has been demonstrated in vertical and near-vertical wells, enabling the detection of formation and fluid resistivity ahead of the tool before boundaries are intersected, which helps optimize the placement of casing or coring points. Horizontal look-ahead UDAR inversion is frequently requested; however,this requires three-dimensional (3D) inversion with look-ahead sensitivity to account for variability in resistivity encountered. A bridge between these technologies is look-ahead 3D inversion in a near-vertical well.
UDAR tools acquire data while rotating and measure the full 3D electromagnetic (EM) field. Inversion models are generated and refined by matching predicted to measured data, generating a representation of the subsurface. Inversions often simplify models generated,limiting the number of unknowns; the most common approach treats the subsurface as a layer-cake scenario for 1D inversion. The advent of 3D inversion enables mapping fully 3D geological scenarios. This approach, combined with a tool with look-ahead sensitivity in near-vertical wells, is demonstrated, and the results are verified.
Detection of a high-resistivity salt prior to entry and detection of low-resistivity inclusions within the salt was the ideal environment to test this look-ahead technology. This represents two scenarios: entry into and exit from a high-resistivity unit, both of which are commonly encountered during the setting of casing points. Initial tests with this data set were for a 1D inversion, which has since been verified in other fields and was identified as an ideal data set to test the new 3D look-ahead inversion.
Entry into the salt is a simple boundary from low to high resistivity with the vertical well perpendicular to the target boundary. 3D inversion results using the full resistivity tensor show the boundary at 45 ft below the UDAR transmitter, 36 ft ahead of the bit. The 3D inversion also identified low-resistivity inclusions approximately 70 ft ahead of the transmitter, with a deeper detection depth due to the surrounding high-resistivity environment.
1D look-ahead inversion identifies these boundaries earlier; however, the 3D inversion showed that the inclusions are not simple horizontal beds but have a more complex morphology. The positions of all boundaries were confirmed by the well intersecting the target using shallow logging-while-drilling (LWD) measurements.
Full 3D inversion has proven beneficial in look-ahead applications in horizontal wells. This ability, demonstrated in a near-vertical well, suggests further applications for this technology.
Discounted member price: 1.00
10.00
You could save: 90%
Back to Top
SPWLA Business Office Address
8866 Gulf Freeway, Suite 320
Houston, TX 77017

SPWLA Contact Numbers
Phone: +1 (713) 947-8727
Fax: +1 (713) 947-8747

Copyright 1959 – 2025 SPWLA

Terms of Use  |  Privacy & Cookie Policy

Our vision is to advance the science of formation evaluation through electrical, nuclear, lithological, and other well logging techniques; to promote the proper application of these techniques to exploration for and exploitation of gas, oil and other naturally occurring substances; to maintain high ethical standards and to further the interests of persons professionally engaged in these endeavors. With the support of our Oil and Gas, Service, Software and Educational Institutions we can make a difference in the industry.