Thermal estimation of natural source zone depletion rates without background correction

Area of Science:

• Environmental Science
• Geophysics
• Petroleum Engineering

Background:

• Real-time monitoring of subsurface temperature profiles is crucial for understanding natural source zone depletion (NSZD).
• Existing methods for calculating NSZD rates can be complex and require extensive data.
• Shallow petroleum liquids undergo natural degradation, impacting subsurface environments.

Purpose of the Study:

• To introduce and validate a novel "single stick" computational method for determining NSZD rates from temperature data.
• To compare the performance of the new method against established background correction techniques.
• To assess the method's accuracy and reliability in various field conditions.

Main Methods:

• A two-equation, two-unknown system is employed, utilizing subsurface temperature measurements at two distinct points.
• The method models subsurface temperature as a function of surface thermal influences and NSZD-related heat.
• Computational tests and field data from five sites were used for validation.

Main Results:

• The "single stick" method demonstrated near-perfect agreement between predicted and observed temperatures and NSZD heating in validation tests.
• Applied to field data, the method identified significantly lower NSZD rates (0.5-7.5 times less) in areas without petroleum liquids compared to background methods.
• The method showed a coefficient of variation of 6% in triplicate analysis and provided reasonable NSZD estimates in LNAPL-impacted areas.

Conclusions:

• The "single stick" computational method provides a robust and accurate approach for real-time NSZD rate estimation.
• This method offers a more reliable and potentially simpler alternative to existing background correction techniques.
• The findings support the use of subsurface temperature monitoring for effective environmental assessment and remediation strategies.