In the exploration and development of carbonate reservoirs, borehole azimuthal acoustic reflection imaging can be used to survey the near-borehole geological structures such as fractures, faults, or caves in the formation, but the accuracy of azimuth measurement and imaging quality are usually deteriorated due to the amplitudes of event signals being often much weaker than those of borehole mode waves. This study proposes a data processing method for borehole azimuthal acoustic reflection imaging to improve the accuracy of azimuth measurement and imaging quality of the near-borehole geological structures. First, three adjacent receiving sensors in the vertical plane closest to the given azimuth are selected to form a linear phased array receiver subarray, and the elevation angle of the event signals can be obtained by comparing the amplitudes of the stacked waveforms in the vertical plane for different elevation angles. Further, three receiving sensors, closest to the given azimuth, are selected from the arcuate phased array receiver, where the central sensor of the linear phased array receiver subarray is located, to form an arcuate phased array receiver subarray, and the 3D stacked waveforms with the known elevation and azimuth angle can be calculated. In the incident direction of the event signals, the event signals will be significantly enhanced because the event signals in waveforms of each sensor in the subarray satisfy the in-phase stack condition, so as to improve the migration image quality and interpretation accuracy fundamentally. We confirmed this method by processing azimuth reflection acoustic data from a field experiment including two adjacent fluid-filled artificial boreholes. The comparison of the field-data processing results with and without 3D waveform stacking demonstrated that 3D waveform stacking significantly improves the accuracy of azimuth interpretation and imaging quality.
At present, it is difficult to image small-scale abnormal geo-bodies near wells using borehole acoustic imaging, as information from scattered waves is neglected and that from reflected waves is mainly used, thus resulting in low imaging resolution. Imaging methods based on scattered waves can help obtain higher-resolution measurements. Herein, a 3D scattered wave spatial scanning imaging method is proposed to make full use of multi-mode scattered waves for imaging small-scale abnormal geo-bodies near the well. The 3D finite-difference time-domain method was used to simulate the acoustic fields for borehole azimuthal acoustic imaging with a fluid-filled target borehole near a measurement well, and the imaging method was applied for the acoustic detection of nearby wells based on forward modeling and field measurement waveform data. The results show that for the fluid-filled target borehole that is approximately parallel to and distant from the measurement well, the amplitude of the scattered PP-wave is the largest followed by the mode converted PS- and SP-wave; and the amplitude of the scattered SS-wave is the smallest, which is related to the radiation, scattering, and reception of the monopole acoustic field. In this case, the scattered wave from the target borehole can be regarded as a plane-wave. The spatial scanning imaging method based on single-mode scattered acoustic waves and the 3D plane-wave imaging method provide similar imaging results. The comprehensive use of multi-mode scattered acoustic waves can further improve the imaging signal-to-noise ratio and resolution. A field example was used to verify the correctness of the forward analysis and the effectiveness of the imaging method. This study will help improve the imaging resolution for the acoustic detection of nearby wells and the evaluation of downhole hydraulic fracturing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.