Process-based approach for the detection of deep gas invading the surface
View Patent ↗The present invention includes a method for determining the level of deep gas in a near surface formation that includes: measuring CO 2 , O 2 , CH 4 , and N 2 levels in percent by volume from one or more surface or near surface geological samples; adding the water vapor content to the measured CO 2 , O 2 , CH 4 , and N 2 levels in percent by volume; normalizing the gas mixture to 100% by volume or 1 atmospheric total pressure; and determining the ratios of: O 2 versus CO 2 to distinguish in-situ vadose zone CO 2 from exogenous deep leakage CO 2 ; CO 2 versus N 2 to distinguish whether CO 2 is being removed from the near surface formation or CO 2 is added from an exogenous deep leakage input; or CO 2 versus N 2 /O 2 to determine the degree of oxygen influx, consumption, or both; wherein the ratios are indicative of natural in situ CO 2 or CO 2 from the exogenous deep leakage input.
1. A method of determining a level of deep gas in a near surface formation without a need for background monitoring comprising:
measuring CO 2 , O 2 , CH 4 , and N 2 levels in percent by volume from one or more surface or near surface geological samples;
transforming the measured CO 2 , O 2 , CH 4 , and N 2 levels by adding water vapor content to the measured CO 2 , O 2 , CH 4 , and N 2 levels in percent by volume;
normalizing the CO 2 , O 2 , CH 4 , and N 2 levels to 100% by volume or 1 atmosphere total pressure to generate normalized CO 2 , O 2 , CH 4 , and N 2 levels;
determining the ratios of:
the normalized O 2 level versus the normalized CO 2 level to distinguish in-situ vadose zone CO 2 from exogenous deep leakage CO 2 ; and
the normalized CO 2 level versus the normalized N 2 level to distinguish whether CO 2 is being removed from the near surface formation or CO 2 is added from an exogenous deep leakage input; or the normalized CO 2 level versus the normalized N 2 level divided by the normalized O 2 level to determine a degree of oxygen influx, consumption, or both oxygen influx and consumption; and
evaluating the ratios to determine whether CO 2 present in the surface or near surface geological samples is from natural in-situ CO 2 or CO 2 from exogenous deep leakage without a need for background monitoring, wherein evaluating includes identifying CO 2 from exogenous deep leakage if the normalized N 2 level is less than 78% under dry conditions, wherein evaluating includes identifying CO 2 from natural in-situ CO 2 if the normalized N 2 level is about 78% under dry conditions, or wherein evaluating includes identifying air influx into the near surface formation if the normalized N 2 level divided by the normalized O 2 level is greater than a ratio of O 2 to N 2 in air.
2. The method of claim 1 , wherein an in-situ vadose zone background level of carbon comprises at least one of biologic respiration, methane oxidation, or CO 2 dissolution.
3. The method of claim 1 , wherein a presence of a deep gas source of carbon is indicated if the normalized N 2 level under water saturated conditions is less than 76.4%.
4. The method of claim 1 , wherein if the normalized O 2 level is determined by gas chromatography without separation of O 2 and Argon peaks, the method further comprises subtracting an amount of Argon from the normalized O 2 level to determine an actual O 2 level.
5. The method of claim 4 , wherein the amount of Argon is calculated equal to 1/63× the normalized N 2 level.
6. The method of claim 1 , wherein the water vapor content corresponds to water saturated conditions.
7. The method of claim 1 , wherein an amount of the water vapor content is 2.1 to 2.4%.
8. The method of claim 1 , further comprising installing gas probes into the near surface formation for measuring the CO 2 , O 2 , CH 4 , and N 2 levels.
9. The method of claim 1 , wherein the water vapor content is measured or estimated.
10. The method of claim 1 , wherein the one or more surface or near surface geological samples are collected in a sealed container and later analyzed in a laboratory.
11. A method of determining a level of deep gas in a near surface formation without a need for background monitoring comprising:
measuring CO 2 , O 2 , CH 4 , and N 2 levels in percent by volume from one or more surface or near surface geological samples;
transforming the measured CO 2 , O 2 , CH 4 , and N 2 levels by adding water vapor content to the measured CO 2 , O 2 , CH 4 , and N 2 levels in percent by volume;
normalizing the CO 2 , O 2 , CH 4 and N 2 levels to 100% by volume or 1 atmosphere total pressure to generate normalized CO 2 , O 2 , CH 4 and N 2 levels;
determining the ratios of:
the normalized O 2 level versus the normalized CO 2 level to distinguish in-situ vadose zone CO 2 from exogenous deep leakage CO 2 ;
the normalized CO 2 level versus the normalized N 2 level to distinguish whether CO 2 is being removed from the near surface formation or CO 2 is added from an exogenous deep leakage input; and
the normalized CO 2 level versus the normalized N 2 level divided by the normalized O 2 level to determine a degree of oxygen influx, consumption, or both oxygen influx and consumption; and
evaluating the ratios to determine whether CO 2 present in the surface or near surface geological samples is from natural in-situ CO 2 or CO 2 from exogenous deep leakage without a need for background monitoring, wherein evaluating includes identifying CO 2 from exogenous deep leakage if the normalized N 2 level is less than 78% under dry conditions, wherein evaluating includes identifying CO 2 from natural in-situ CO 2 if the normalized N 2 level is about 78% under dry conditions and wherein evaluating includes identifying air influx into the near surface formation if the normalized N 2 level divided by the normalized O 2 level is greater than a ratio of O 2 to N 2 in air.
12. The method of claim 11 , wherein an in-situ vadose zone background level of carbon comprises at least one of biologic respiration, methane oxidation, or CO 2 dissolution.
13. The method of claim 11 , wherein the presence of a deep gas source of carbon is indicated if the normalized N 2 level under water saturated conditions is less than 76.4%.
14. The method of claim 11 , wherein if the normalized O 2 level is determined by gas chromatography without separation of O 2 and Argon peaks, the method further comprises subtracting an amount of Argon from the normalized O 2 level to determine an actual O 2 level.
15. The method of claim 14 , wherein the amount of Argon is calculated equal to 1/63× the normalized N 2 level.
16. The method of claim 11 , wherein the water vapor content corresponds to water saturated conditions.
17. The method of claim 11 , wherein an amount of the water vapor content is 2.1 to 2.4%.
18. The method of claim 11 , further comprising installing probes into the near surface formation for measuring the CO 2 , O 2 , CH 4 , and N 2 levels.
19. The method of claim 11 , wherein the water vapor content is measured or estimated.
20. The method of claim 11 , wherein the one or more surface or near surface geological samples are collected in a sealed container and later analyzed in a laboratory.