Detection Scope Investigation of Logging-While-Drilling Electromagnetic Resistivity Measurement in Vertical and Horizontal Wells

To clarify the detection performance of the logging-while-drilling (LWD) electromagnetic resistivity measurements, this paper systematically investigates the depth of investigation for vertical wells and the depth of detection for horizontal wells. First, a radially layered formation model is constructed, taking into account the factors such as drill collars, insulating rubber, borehole size and mud type, invasion zones, and formations. On this basis, following the definition of induction logging geometric factors, a radial geometric factor for the LWD electromagnetic resistivity logging is established. The calculation of the radial geometric factor comprises two parts: one part is based on the apparent resistivity, while the other part utilizes the original phase shift (PS) and amplitude ratio (Att) signals. Variations are simulated by altering the invasion depth, and the effects of resistivity contrast and frequency on the radial detection depth of the instrument are analyzed in detail. Subsequently, a longitudinal stratified horizontal well model is developed. In this context, the scattered signal is defined. By integrating the detection threshold of the signal, the relationship between the scattered signal and the maximum depth of detection (DOD) of the instrument is established. The finite element calculation method is employed to simulate the DOD of the instrument under different parameters. This research provides important theoretical references and practical guidance for accurately identifying the electrical characteristics of formations and detecting formation interfaces during oil and gas exploration and development.