A New Compensated Design of Deep-reading Look-ahead Method in Electromagnetic Logging-while-drilling

With the intensifying exploration and development of deep and unconventional oil and gas reservoirs, the advanced prediction of the formations during drilling plays a pivotal role in mitigating drilling risks and optimizing drilling parameters. This technique serves as a crucial foundation for enhancing drilling trajectory accuracy and reducing operational costs. Currently, ultra-long spacing and low-frequency technologies enable the look-ahead, ultra-deep electromagnetic (EM) logging-while-drilling (LWD) tool to detect the top of the target formation more than 30 meters ahead of the bit. However, the measurement signal is predominantly influenced by the stratigraphy surrounding the instrument, resulting in a very low proportion of the spatial contribution in front of the bit. Consequently, the inversion process, which is integral to look-ahead detection, poses challenges for real-time geosteering.

To tackle this challenge, this study introduces a novel multi-spacing interleaved compensating antenna design aimed at augmenting the electromagnetic scattering field signal share at the forward stratigraphic interface. The spatial distribution of the new look-ahead detection signal is characterized using geometric factor theory. Additionally, the response characteristics and look-ahead detection capability of the proposed scheme are simulated and analyzed based on a response fast forwarding algorithm. The integral geometry factor associated with the novel look-ahead measurement effectively excludes contributions from the stratigraphy in the vicinity of the instrument, thereby enhancing the proportion of the look-ahead signal. This advancement is particularly beneficial for look-ahead detection. Simulations based on a single interface model reveal that the response diminishes to zero when the instrument is positioned at a considerable distance from the interface, whereas it attains non-zero values as the tool approaches the interface. In addition, the polarity of the response depends on the difference in resistivity between the two sides of the interface, which offers a more intuitive interpretation compared to existing methodologies. Furthermore, variations in magnetic field attenuation across different spacings leveraged to optimize spacing and signal synthesis combinations, further bolstering the capability of look-ahead detection. Numerical results demonstrate that the new method significantly improves the look-ahead detection capability of phase difference measurements compared to existing methods, with a maximum look-ahead depth of detection (DOD) increased by approximately 50%. The look-ahead DOD of amplitude ratio signal is comparable to that of existing methods.

In summary, the proposed method provides a more intuitive response to resistivity anomalies ahead of the bit, reducing the update time for forward geostructural information and enabling improved look-ahead detection. This innovation will provide a more cost-effective drilling solution for proactive risk avoidance in straight or low-angle wells and optimize casing shoe placement and coring operations.