Single-well imaging using full waveform sonic data

The sonic-waveform processing and imaging flow presented in this paper uses fullwaveform data recorded with a conventional acoustic well-logging tool, then adapts known surface-seismic processing steps and optimizes them for the borehole environment. This paper presents improvements brought to our original sonic-waveform processing and imaging flow. These improvements are better geometry assignment, better noise attenuation, better data enhancement, and the application of prestack time migration with improved parameters. The new flow is tested on a portion of a full-waveform sonic dataset, recorded over a section of the 8-8-23-23W4 well, Blackfoot field, Alberta, intersecting three coal seams at an angle. The upper portion of the composite sonic image showed promising indications of dipping interfaces. However, the targeted three coal seams were not very well imaged in the final composite sonic image. This is probably because of the strong attenuation of the sonic energy by the fractured coal. The composite sonic image shows potentially better resolution than the coinciding surface seismic section. More work is planned to improve further on the demonstrated processing flow. INTRODUCTION Acoustic well-logging is presently used for the following applications: formation mechanical property analysis (e.g. elastic moduli), formation evaluation (e.g. lithology), geophysical interpretation (e.g. synthetic seismograms), and more recently, shear-wave anisotropy measurements. All of these applications are generated from the analysis of the full-waveform acquired by the acoustic well-logging tool. The acoustic well-logging tool provides a unique geometry whereby both source and receivers are in the same wellbore, several receivers are located at different offsets along the body of the well-logging tool and, as the well-logging tool is moved uphole, the subsurface surrounding the wellbore is sampled repeatedly. This unique configuration can be analogous to a single-well imaging experiment. Single-well imaging can be considered a subset of the many borehole seismic imaging techniques in use today. Single-well imaging can be defined as the study of the acoustic and elastic wave propagation in and around a borehole where the source and receivers are located in the same borehole. Single-well imaging data can be acquired in different ways: for example, using a borehole seismic source with clamped receivers in the same borehole to image the flank of a salt dome, or using an acoustic well-logging tool to evaluate the elastic properties of geologic formations. The focus of this work is on singlewell imaging using a conventional acoustic well-logging tool. Single-well imaging can contribute to reservoir understanding by bridging the resolution gap between well-logging and seismic data (Figure 1) by extending our understanding of the reservoir characteristics to an intermediate scale. In addition, this technique has the advantage of requiring only one borehole (in contrast to crosswell), one instrument (in contrast to vertical seismic profiling) and the full waveform data is