Study of Downhole Electromagnetic Boundary-Detection Methods Using Numerical Simulations

Logging-while-drilling (LWD) technology has been used as a real-time aid in directional drilling. In this dissertation, a full investigation is conducted on the use of LWD resistivity tools in geosteering, especially the application in detecting remote bed boundaries. By looking into the electromagnetic field of multiple tool configurations using numerical simulations, an independent evaluation is provided on the downhole boundary detection capability of different resistivity logging tools, as well as their applicability in various drilling environments. In order to explore the potential of predicting formation properties in front of the drill bit, tool responses are first modeled with different downhole electromagnetic transmitters in homogeneous formation, where ahead-of-the-bit field distribution is investigated. Field attenuation rates are compared among different tools, and the influence of borehole conductivity is studied. Next, tool responses are modeled in two-layer formation models to evaluate their boundary detection capabilities. Look-ahead capabilities are compared between tools with axially symmetrical antennas when boundaries are perpendicular to the tool axis. Also, the feasibility of using cross-component measurements to detect horizontal boundaries is studied for tools using orthogonal antennas. After that, the deep-looking capability of a new directional resistivity tool using ultra-long spacings and low frequencies is explored. Tool responses for different configuration parameters and drilling environments are calculated and discussed. At last, an inversion algorithm based on the Gauss-Newton method is developed to recover the boundary distance from the tool response. This dissertation presents a comprehensive summary for the first time on the use of LWD resistivity tools in predicting formation anomalies ahead of or around the drill bit. It is found that the conventional resistivity logging tools using axially symmetrical antennas can only penetrate the formation ahead of the bit by a limited range, which is restricted by the borehole dimension and power supplies, but a deep-looking capability can be acquired by using cross-component measurements in high angle and horizontal wells. The detailed comparisons between tools of different types establish a missing link in the research of deep resistivity logging tools, and provide a natural guide for the future development of downhole boundary detection methods.Electrical and Computer Engineering, Department o