Feasibility of source-free DAS logging for next-generation borehole imaging

Area of Science:

• Geophysics
• Borehole geophysics
• Acoustic sensing

Background:

• Characterizing and monitoring geologic formations is vital for energy and environmental applications.
• Conventional wireline sonic logging faces limitations in high-temperature environments and long-term monitoring.
• Existing methods struggle with tool re-insertion and receiver repeatability for time-lapse monitoring.

Purpose of the Study:

• To introduce and evaluate a novel source-free distributed acoustic sensing (DAS) logging method.
• To assess the feasibility of using borehole DAS ambient noise for subsurface characterization.
• To develop a next-generation borehole imaging tool for harsh environments.

Main Methods:

• Utilized a source-free distributed acoustic sensing (DAS) logging approach.
• Analyzed borehole DAS ambient noise data to derive root-mean-squares (RMS) amplitudes.
• Employed fiber optic cables cemented behind casing as receivers for high-temperature logging.

Main Results:

• Ambient noise RMS amplitudes showed a strong correlation with anomalies in conventional logging data.
• The source-free DAS method enables logging in high-temperature environments.
• The technique overcomes receiver repeatability issues inherent in conventional wireline logging.

Conclusions:

• The source-free DAS logging method offers an efficient and cost-effective way to characterize and monitor subsurface geologic formations.
• This technology is particularly advantageous for high-temperature environments like geothermal reservoirs.
• Further validation is needed to expand the application scope of this innovative logging tool.