Multi-Gas Ratio Analysis for Deep CO2 Leakage Detection
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Solution Overview
Problem
Current methods for detecting CO2 leakage in the vadose zone above geologic carbon storage sites require extensive background monitoring, which is time-consuming and cannot accurately distinguish between natural CO2 variability and leakage signals, especially due to climatic, land use, and ecosystem changes, and cannot measure CO2 concentrations at all potential small diameter leak points.
Innovation Solution
A process-based approach that measures CO2, O2, CH4, and N2 levels in near-surface geological samples, normalizes the gas mixture to atmospheric pressure, and calculates specific ratios to differentiate between in-situ and exogenous CO2 sources, allowing for the identification of deep gas leakage without the need for background monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CO2 concentration-based monitoring is used to detect leakage in the vadose zone, then leakage detection capability is provided, but the method cannot distinguish between natural CO2 variability and leakage signals, leading to high uncertainty
Solution Approach 1:
The patent changes from monitoring a single parameter (CO2 concentration) to monitoring multiple gas parameters simultaneously (CO2, O2, CH4, N2). By measuring multiple gases and analyzing their interrelationships, the system can distinguish between natural CO2 variability and leakage signals, thereby improving both measurement precision and detection reliability
Solution Approach 2:
The patent uses a composite approach by combining measurements of multiple gas components into an integrated analysis system. The composite gas composition data (CO2, O2, CH4, N2 ratios) provides a more reliable fingerprint for identifying leakage sources compared to single-gas monitoring
2Measurement precision
If extensive background monitoring is conducted to characterize natural CO2 levels, then baseline data is obtained, but the process is time-consuming and delays project implementation
Solution Approach 1:
The patent applies preliminary action by establishing universal reference ranges for multi-gas compositions that represent natural background conditions. These pre-established ranges can be directly applied without requiring site-specific background monitoring, eliminating time delays while maintaining baseline characterization accuracy
Solution Approach 2:
The patent creates a universal monitoring approach where a single set of reference ranges for multi-gas compositions can be applied across multiple sites and conditions. This universal system eliminates the need for extensive site-specific background monitoring while providing accurate baseline characterization
3Reliability
If CO2 concentration measurements are taken at multiple locations to cover all potential leak points, then comprehensive monitoring is achieved, but the cost and complexity of monitoring increases significantly
Solution Approach 1:
The patent reduces system complexity by changing from monitoring multiple locations with single-gas sensors to monitoring fewer locations with multi-gas sensors. The additional gas parameters (O2, CH4, N2) provide enhanced discrimination capability, allowing reliable leakage detection with reduced spatial density of monitoring points
4Measurement precision
If background CO2 measurements are required before injection to establish natural levels, then natural seasonal ranges are documented, but this requirement hinders project progress during the lead time
Solution Approach 1:
The patent performs preliminary action by pre-establishing universal reference ranges for natural gas compositions that can be applied immediately upon project initiation. This eliminates the requirement for time-consuming pre-injection background monitoring while still providing accurate documentation of natural ranges
Solution Approach 2:
The monitoring system serves itself by using the measured gas compositions (CO2, O2, CH4, N2) to automatically determine whether conditions indicate natural background levels or leakage. The system self-distinguishes between natural variability and leakage signals through ratio analysis, eliminating the need for separate background characterization phases
Data Source
AI summary
The present invention includes a method for determining the level of deep gas in a near surface formation that includes: measuring CO2, O2, CH4, and N2 levels in percent by volume from one or more surface or near surface geological samples; adding the water vapor content to the measured CO2, O2, CH4, and N2 levels in percent by volume; normalizing the gas mixture to 100% by volume or 1 atmospheric total pressure; and determining the ratios of: O2 versus CO2 to distinguish in-situ vadose zone CO2 from exogenous deep leakage CO2; CO2 versus N2 to distinguish whether CO2 is being removed from the near surface formation or CO2 is added from an exogenous deep leakage input; or CO2 versus N2/O2 to determine the degree of oxygen influx, consumption, or both; wherein the ratios are indicative of natural in situ CO2 or CO2 from the exogenous deep leakage input.