Optimization of detection parameters and ranging verification for LWD acoustic reservoir-boundary detection using an impulsive source

Abstract

Reservoir-boundary identification while drilling is important for geosteering in horizontal wells. Conventional gamma-ray, electromagnetic, and resistivity methods may be limited in oil-based mud or weak electrical-contrast formations, whereas acoustic reflections provide complementary boundary information. In this study, a two-dimensional axisymmetric finite-element model is established to evaluate reservoir-boundary detection with an impulsive logging-while-drilling (LWD) acoustic source, and the COMSOL Multiphysics model is verified against real-axis integral waveforms in a homogeneous formation. Based on reservoir-boundary reflections, the effects of source-receiver spacing, source frequency, mud type, and carbonate-reservoir conditions on reflection identification and ranging are analyzed. The results show that the boundary reflection is sensitive to source spacing and frequency. The 7 kHz source with 5 m spacing gives the highest signal-to-noise ratio of 26.75 dB. For water-based and oil-based muds, the reflection peak arrival time is 4.6 ms in both cases, with a normalized correlation coefficient of 0.93, indicating that mud type mainly affects amplitude and waveform details but has limited influence on arrival-time-based ranging. For the carbonate reservoir model, the interface distance estimated using the theoretical-arrival-time constraint is 3.137 m, with a relative error of 1.13% compared with the true distance of 3.102 m.