Method and Device for Discrimination Between Natural Gas and Swamp Gas

Abstract

Method for determining whether a gas sample originates from biological processes or from a gas installation being tested and containing a utility gas is characterized in that an increased concentration of hydrogen in the sample as compared to that present in the utility gas is used as evidence that the sample originates from biological decay processes and not from the gas installation under test.

Claims

1. A method for determining whether a gas sample originates from biological processes or from a gas installation being tested and containing a utility gas, the method comprising the steps of: detecting a concentration of hydrogen in the gas sample; comparing the detected concentration of hydrogen in the gas sample a concentration of hydrogen present in the utility gas; wherein the comparison is used to determine whether the gas sample originates from biological decay processes and not from the gas installation being tested.

2. The method according to claim 1, wherein a hydrogen selective gas sensor is used for detecting the concentration of hydrogen content in the gas sample.

3. The method according to claim 1, wherein a hydrogen selective gas sensor is used to determine whether the concentration of hydrogen in the utility gas contained in the gas installation is below a predetermined level before detecting the hydrogen content in the gas sample.

4. A device for determining whether a gas sample originates from biological decay processes or from a gas installation being tested and containing a utility gas, comprising: a hydrogen selective gas sensor integrated in a field operable detector and used for detecting hydrogen content in the gas sample, wherein said detector can be used simultaneously with a pipeline leak survey gas detector.

5. The device according to claim 4, wherein the hydrogen selective gas sensor is integrated in the pipeline leak survey gas detector.

6. The method of claim 1, wherein the hydrogen comparison is performed simultaneously with a gas leak survey, while the gas installation is being tested.

7. The method of claim 1, wherein unwanted signals originating from biological decay processes are blocked in real time.

8. The method according to claim 1, wherein a hydrogen content above 5 ppm in the gas sample is used as evidence that the gas sample originates from biological decay processes.

9. The method according to claim 1, wherein a hydrogen concentration of at least 100 ppm in the gas sample is used as evidence that the gas sample originates from biological decay processes.

10. The device according to claim 4, wherein the hydrogen content in the gas sample is compared with a hydrogen content in the utility gas of the gas installation being tested simultaneously with a gas leak survey, while the gas installation is being tested.

11. The device according to claim 4, wherein unwanted signals originating from biological decay processes are blocked in real time.

12. The device according to claim 4, wherein a hydrogen content above 5 ppm in the gas sample is used as evidence that the gas sample originates from biological decay processes.

13. The device according to claim 4, wherein a hydrogen concentration of at least 100 ppm in the gas sample is used as evidence that the gas sample originates from biological decay processes.

Description

[0024] The FIGURE shows an embodiment of the invention.

[0025] A gas pipeline 12 is part of a gas installation below the ground surface 14. The tightness of the gas pipeline 12 is to be tested with a leak detector 16. A measurement probe 18 of the leak detector 16 is positioned on the ground surface 14 or into a drilled hole below the ground surface 14 in a region where the gas pipeline 12 and a possible leakage is assumed. A swamp gas producing area 20 is below the ground surface 14 in proximity to the testing probe 18. Therefore, the probe 18 samples either gas leaking from the pipeline 12 or gas originating from biological decay processes within the swamp gas producing area 20.

[0026] The gas analyser 16 detects gas within the gas sample. The utility gas within the gas installation contains methane and/or heavier hydrocarbons while the gas originating from the biological decay process (swamp gas) contains mainly methane. In any case this will be picked up by the sensing mechanism of the detector.

[0027] In order to determine whether the sample originates from the utility gas installation (gas pipeline 12) or from the swamp gas producing area 20 (gas originating from biological decay processes), the hydrogen content of the gas sample is determined with the leak detector 16. The leak detector comprises a hydrogen selective sensor 17 and is therefore sensitive to hydrogen. It is detected whether the hydrogen content is above a certain threshold. The threshold may be based on the previously known hydrogen concentration within the utility gas. The threshold may alternatively be for example 5 ppm or 100 ppm or even larger, depending on the composition of the utility gas and the type of biological decay processes that are assumed in the facility of the gas installation.