Factors and detection capability of look-ahead logging while drilling (LWD) tools

Abstract

Electromagnetic technology used in logging while drilling (LWD) provides the resistivity distribution around a borehole within a range of several tens of meters. However, a blind zone appears in front of the drill bit when operating in high-angle wells, limiting the ability to detect formations ahead of the drill bit. Look-ahead technology addresses this issue and substantially enhances the proactive capability of geological directional drilling. In this study, we examine the detection capabilities of various component combinations of magnetic dipole antenna. Based on the sensitivity of each component to the axial information, a coaxial component is selected as a boundary indicator. We investigate the impact of various factors, such as frequency and transmitter and receiver (TR) distance, under different geological models. This study proposes 5 and 20 kHz as appropriate frequencies, and 10–14 and 12–17 m as suitable TR distance combinations. The accuracy of the numerical calculation results is verified via air-sea testing, confirming the instrument's detection capability. A test model that eliminated the influence of environmental factors and seawater depth is developed. The results have demonstrated that the tool can recognize the interface between layers up to 21.6 m ahead. It provides a validation idea for the design of new instruments as well as the validation of detection capabilities.