Successful Geostopping Using a Recently Developed LWD Look-ahead Ultra-deep EM Resistivity Tool (Karol Riofrio, Halliburton)


Karol Riofrio from Halliburton


Jin Ma, Nigel Clegg, Supriya Sinha, Hsu-Hsiang Wu, (Halliburton), Artur Kotwicki, Torsteirn Skorve, Yngve Bolstad Johansen (Aker BP)


Geostopping is a critical operation due to wellbore-stability, well-control and HSE issues, requiring accuracy of a few meters. Reservoir boundary detection has previously been done with seismic applications and at-bit resistivity or near-bit gamma. However, seismic uncertainty can be up to 20m TVD and at-bit resistivity, and near-bit gamma requires penetrating the target. Early, accurate boundary detection, in vertical or near-vertical wells, requires technology that allows anticipation of boundaries ahead of the bit, enabling geostopping at a safe distance. A recently developed LWD ultra-deep electromagnetic (EM) tool was successfully deployed to geostop a wellbore at a target position. The system successfully predicted the top of the target formation 15m TVD ahead of the transmitter in real time, which was confirmed by gamma ray measurements. A subsequent run that drilled through the formation top confirmed the predicted top and formation resistivity. This is a game-changing technology for well construction, allowing for proactive and efficient wellbore placement.

The look-ahead, ultra-deep, EM LWD tool incorporates a deep-transmitting antenna 2.8m from the bit. To achieve a real-time look-ahead capability in near-vertical wells, anisotropic resistivity measurements are incorporated into the transmitting antenna collar, providing resistivity, anisotropy, and dip around and above the transmitter antenna while drilling. The reconstructed formation profile from the anisotropy measurement is combined with the deep measurement, enabling formation determination ahead of the bit. In a favourable condition, the integrated system can detect a formation boundary 30m or more ahead of the bit.

The EM tool was tested in challenging well conditions. The distance from the existing casing to the reservoir top was short and the tool was in a conductive formation (less than 0.6 Ω·m). This provided a very small depth interval in which to accumulate the necessary real-time EM measurements, and a relatively short depth of detection (DOD).

Despite the suboptimal conditions, the system was able to resolve the target formation top 15m TVD ahead of the EM transmitter while drilling. This was confirmed by gamma measurements after penetrating the formation, which was used as the primary technique to geostop the wellbore. The new EM look-ahead system now offers a more proactive solution to assist operators not only to geostop a wellbore at the planned position, but also to optimize the drilling parameters prior to any unexpected geological variations. This look-ahead EM technique provides more economic and efficient drilling solutions to optimize wellbore placement compared to existing techniques.

This new service makes it possible to proactively identify potential risks in vertical or low-inclination wellbores, helping to avoid drilling hazards and optimize casing shoe placement and coring operations.


Karol Riofrio is a Msc in geology and geophysics of reservoirs graduated from Universitat de Barcelona. Karol Riofrio started her carrer with Landmark Software and Services as consultant geologist and moved to Sperry Drilling Services as geosteering personnel in 2013. Karol Riofrio currently works at Halliburton Norway as geosteering team lead for Aker BP.