In the development of a reservoir, optimizing the well placement in the desired formations from pre-well modeling techniques is a challenging task. Existing well-planning techniques, such as offset well logs or surface seismic data, do not provide the required level of accuracy and can result in high uncertainty in geosteering decisions. Conversely, conventional logging-while-drilling (LWD) tools determine very fine formation properties, but have a limited detection range into the formation. This limited range can make it difficult to correlate LWD measurements against larger-scale seismic data; consequently, accurate well placement can sometimes be very challenging. Ultra-deep azimuthal electromagnetic LWD logging tools effectively bridge the gap in scale between seismic data and conventional logging data, enabling better correlation between them and, ultimately, more accurate well placement.
A new, multi-antenna, azimuthal electromagnetic LWD tool is now available, which propagates electromagnetic fields in three dimensions around the wellbore with an ultra-deep depth of investigation (DOI). A robust inversion process derives the position and resistivity of formation layers within the range of the tool from measurements induced by the propagated fields. This information provides geologists with a clearer understanding of the surrounding geology, enabling timely geosteering decisions, optimized well placement, and more efficient field development.
Theoretical modeling and field-testing results demonstrate that the new tool is capable of resolving multiple formation layers, with a DOI of more than 200 ft (60 m), depending on the selected operating frequency, antenna spacing, and formation properties. The very high signal-to-noise ratio (SNR) in the tool design yields single-point, unconstrained inversion results that are capable of representing complex geological structures within a very large volume of investigation. The tool also provides ultra-deep, azimuthal geosignals and azimuthal resistivity measurements, providing 360-degree information around the borehole.
With the ultra-deep DOI, it is now possible to identify hydrocarbon reserves and formation boundaries much farther from the wellbore than was previously possible, giving operators the ability to evaluate very large volumes of the reservoir structure from a single well.
