ABSTRACT

Borehole Reflection Imaging (BRI) stands as an advanced technique meticulously designed to provide comprehensive insights into the subsurface structures surrounding a borehole. Achieving an accurate and high-resolution reflection image necessitates a reliable background velocity model. However, obtaining such a good velocity model in real-world applications, particularly several tens of meters away from the borehole, is typically challenging. As a result, traditional BRI methods rely on velocity models that vary solely with depth, yielding less reliable images and reduced confidence in the final outcomes. To address this challenge, our attention turns to Full Waveform Inversion (FWI), a method renowned for its ability to generate high-resolution velocity models using full waveform information. Despite its merits, several challenges persist in effectively applying FWI to BRI, including (1) a low signal-to-noise ratio in data reflected from distant regions and (2) concerns about the accuracy of source functions. To address these challenges, we introduce an innovative approach—Source-Independent and Total-Variation (SITV) constrained Full-Waveform Inversion (FWI). Leveraging the variable projection method, SITV-FWI can conduct inversion without requiring precise information about the source wavelet. Additionally, the incorporation of TV constrains proves crucial in mitigating artifacts introduced by noisy data and inaccuracies in source functions. Numerical experiments unequivocally demonstrate the resilience of SITV-FWI when faced with inaccuracies in the source wavelet and noisy data, establishing it as a valuable and trustworthy tool for subsurface imaging and characterization.

INTRODUCTION

Borehole Reflection Imaging (BRI) (Hornby, 1989, 1993; Tang et al., 2007) is a geophysical technique widely applied in hydrogeology, petroleum exploration, and subsurface characterization. By examining the travel times and amplitudes of reflection waves originating from geological formations beyond the borehole, researchers can extract significant insights into the composition, porosity, fluid content, and overall geological characteristics of the subsurface. This valuable information extends to regions situated several meters or even tens of meters away from the borehole, achieving a resolution down to centimeters. As a result, BRI bridges the detection or sensing gaps between traditional seismic exploration and acoustic well logging imaging, contributing additional valuable information for the oil and gas industry, aiding in making accurate exploration and production decisions.

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