Some Problems in Natural Gas-dissolved-in-brine Analyses

• Published in: Journal of the Japanese Association for Petroleum Technology Vol. 48; no. 3; pp. 239 - 246
• Main Authors: TEZUKA, Machiko, NAKAMURA, Morio, OMI, Katsuo
• Format: Journal Article
• Language: Japanese
• Published: The Japanese Association for Petroleum Technology 1983
• ISSN: 0370-9868; 1881-4131
• DOI: 10.3720/japt.48.239

Routine analyses of natural gas-dissolved-in-brine have been performed on the assumption that (1) contents of minor components except CO2 and N2 are negligible, and (2) the gas has no O2. Detected O2 and corresponding N2 are subtracted from the resulting data of analyses, because they are regarded as contaminants from the air. Higher quality of present analytical equipments has made possible even trace components analyses, if necessary, and the other hand, air correction has been considered as not always applicable. So, to determine whether the assumptions were appropriate or not, we conducted precise analyses of the gases from Narutoh field adopting gas-chromatografic methods. Following experimental results were obtained. As to the minor components tested, C2H6 and A were found in all of the samples, C3H8 from 2/3 of the wells, but H2 and He were actually not. And even the detected gases, the amounts were very small. About O22, it was found that O2 had entered into samples through displacing water, so the ratio of O2/N2 which usually adopted for air correction was not that of the air (1/3.55), but that of dissolved air (about 1/2). Therefore, the result of usual air correction had been over-subtraction of N2. However, concerning to calorific values of the gases, existence of the higher calorific C2H6 and the increase of non-calorific N2 offset each other. In conclusion, routine analyses may be performed as before for little influences on calorific values, but it should be noted that the procedure is only for conveniences.