科研之友
微信
新浪微博
Facebook
分享链接
摘要
This study uses stable noble gases' (He, Ne, Ar, Kr, Xe) volume fractions and isotopic ratios from Antrim Shale natural gas to assess compositional variability and vertical fluid migration within this reservoir, in addition to distinguishing between the presence of thermogenic versus biogenic methane. R/Ra values, where R is the measured He-3/He-4 ratio and Ra is the atmospheric value of 1.384 +/- 0.013 x 10(-6), vary from 0.01 to 0.34 suggesting a largely dominant crustal He-4 component with minor atmospheric and mantle contributions. Crustal Ne-21, Ar-40 and Xe-136 contributions are also present but the atmospheric component is largely dominant for these gases. Crustal contributions for Ne-21, Ar-40 and Xe-136 vary between 1.1% and 12.5%, between 0.7% and 19% and between 0.1% and 2.7%, respectively. A few samples present higher than atmospheric Ne-20/Ne-22 ratios pointing to the presence of a small mantle Ne component. High horizontal and vertical variability of noble gas signatures in the Antrim Shale are observed. These are mainly due to variable noble gas input from deep brines and, to a smaller extent, variable in-situ production within different layers of the Antrim Shale, in particular, the Lachine and Norwood members. Estimated He-4 ages, considering external He-4 input for Antrim Shale water, vary between 0.9 ka and 238.2 ka and match well for most samples with the timing of the major Wisconsin glaciation, suggesting that Antrim Shale water was influenced by glaciation-induced recharge. Consistency between measured and predicted Ar-40/Ar-36 ratios assuming Ar release temperatures >= 250 degrees C supports a thermogenic origin for most of the methane in these samples. This thermogenic methane is likely to originate at greater depths, either from the deeper portion of the Antrim Shale in the central portion of the Michigan Basin or from deeper formations given that the thermal maturity of the Antrim Shale in the study area is rather low.
- 出版日期2015-12-6
