What Next After a Decade With Significant Advances in the Application of Deep Directional Measurements?

Abstract

Equinor has played an important role the last decade in testing and development of ultra-deep azimuthal resistivity (UDAR) measurements both for Look-Ahead and Look-Around applications. Today, more than 70% of Equinor high angle or horizontal wells are drilled with UDAR-technology. In this paper, the authors will review the use of UDAR in Equinor the last decade and highlight both successful use and real-time challenges related to interpretation of the inversion results. UDAR-technology and inversion algorithms have been very powerful for reservoir mapping to geosteer or geostop according to plan. However, we forget far too often the fact that we need a good understanding of the reservoir to interpret and evaluate the uncertainty in the inversion result. The number one mistake in a real-time setting is to interpret a resistivity contrast as a specific layer in the reservoir (for instance top reservoir) and hold on to that same interpretation even if we drill away from that contrast and may cross multiple layers as distance to the observed contrast increase. Other challenging real-time UDAR-exercises relate to uncertainties in the prediction of resistivity inside the reservoir and reservoir thickness from inversion results when still drilling above the reservoir. A third mistake often seen real-time is detailed interpretation of 1D-inversion results, even when other indicators are pointing towards 2D/3D complexities in the reservoir. Equinor and other operators have pushed for more and more advanced inversion solutions leading to 3D mapping capabilities for more complex reservoirs. The UDAR advances the last few years are important for Equinor’s planned roadmap ahead. However, 1D-3D inversion results can result in wrong decisions if the uncertainty in the inversion result is not managed correctly. We see a need to investigate how to best exploit UDAR-technology and inversion results within its limits, but also ensure assumptions are not extended beyond an acceptable uncertainty level. Better handling of uncertainties in geosteering operations will become increasingly important for the well economy with smaller targets, complex geological settings, and varying sweep efficiencies. How can we best handle the uncertainty in inversion results in real-time operations to avoid wrong decisions that can potentially destroy well economy? This is an important question which will be addressed and should be handled in the future if UDAR-technology is to continue having an important role in many of the wells to be drilled the next decades.