Geosteering operations have always had an issue of slow reaction times due to available data being offset from the bit and depth of detection from legacy techniques that can result in sub-optimal reservoir exposure. The introduction and evolution of Geosteering and Reservoir Mapping from shallow borehole measurements to advanced multi-boundary, reservoir scale mapping with ultra-deep detection, has proven to be a game changer in the geosteering operations worldwide. Despite these advancements, minimizing reaction and decision time to formation changes remains a key challenge.

Horizontal look-ahead-of-the-bit inversion capability has always been the goal for decreasing reaction time, reducing the drilling risk and maximizing reservoir exposure. In recent years, we have seen the introduction of innovative Ultra Deep Azimuthal Resistivity (UDAR) technologies, however the type of measurements generated by these platforms lack the required sensitivity, robust low firing frequencies, a broad range of multiple spacings (Shallow, Medium, Deep, UltraDeep) and an array architecture (near to the bit) to provide an accurate mapping of reservoir resistivity changes ahead of the bit.

This paper demonstrates how a breakthrough in sensor engineering enables look-ahead resistivity inversion and an increase in accuracy of reservoir mapping capabilities. The innovation is a new integrated drilling and reservoir mapping platform with a novel array of triaxial co-located antennas that enhance 3D reservoir understanding and allows proactive geosteering decisions with its robust look-ahead capability.

To characterize complex reservoirs with vertical and lateral heterogeneities, multi-spacing azimuthal resistivity arrays (MSAR: combined ultra-deep and deep azimuthal resistivities) have been routinely deployed in tandem. With their measurements coming from multiple tools, they possess calibration challenges, and a non-colocated set of pseudo tri-axial measurements increase the challenge of using such a setup. To overcome the systematic error associated with such tool and antenna architecture, a new drilling and reservoir mapping platform has been successfully developed which combines shallow, medium, deep, ultra-deep and extra-deep measurements (MDAR: multi-depth azimuthal resistivity) with fully triaxial, co-located and calibrated antennas. This new platform provides significantly improved signal-to-noise ratio and complete multidimensional sensitivity to the formation resistivity properties, when compared to the previous MSAR platform architectures.

What makes look-ahead sensitivity ahead of the bit an effective tool for proactive geosteering is the time to inversion. For time to look-ahead inversion, we express the time necessary to receive the logging-while-drilling (LWD) inversion inputs from the downhole tool and their inversion to generate the resistivity map changes ahead of the bit, minus the time (ROP) to drill the interval ahead of the bit before intersecting the already imaged feature.

This new service was run in clastic formations, representing complex channel sands with a strong meandering nature. Such a geological environment often presents features such as pinchouts which are the manifestation of the meandering sand channel in the vertical intersection plane of the wellbore. The look-ahead inversions on the subject successfully captured one of such pinchout features, ranging as far as 70 ft ahead of the bit.

This newly developed, novel multi-depth azimuthal resistivity (MDAR) platform confirmed the benefit of the new triaxial and co-located array configuration providing a robust, look-ahead reservoir mapping while drilling inversion, even within a complex, 3D channelized environment. The look-ahead inversion processing which utilizes high bit-rate mud-pulse telemetry, coupled with cloud computing resources enables inversion processing and interpretation of the results within a real-time context. This unlocks strategic geosteering decisions before features have been intersected by the BHA.